Signs of the Times

“Tell me where all past years are” requested the poet John Donne, although the prefacing line which urges the reader to “Go and catch a falling star” suggests that no expectations beyond the rhetorical should be made.
I have managed to fill 32 past years working with vintage and classic cars and quite a few more years before that with a very pleasant childhood full of ancient cars.  Classic motoring has changed over those years: Going back to the 1970’s the scarcity of replacement parts made running these cars harder. There were no batches of CNC machined parts made available by spares schemes and expensive “one off” replacements were often the order of the day. Despite this, many enthusiasts persevered with their cars and brought them up to reliable condition and then proceeded to use them extensively – many of my father’s customers in those days did not own a modern car and the vintage car was used for everything from fetching the shopping to motor sport events or continental touring. Buying a vintage or classic usually meant taking on vast amounts of work and expense and auction purchases were for the very brave who could afford all the nasty surprises afterwards.

Strangely those of us who use our old cars extensively now seem to be in the minority among enthusiasts although it has never been easier to keep the cars on the road and I am quite sure that the average condition of these cars is far better than it ever used to be years ago. It has just been my pleasure to fettle a 1935 Austin for a present day “Vintagent” who has taken the spirit of John Donne’s advice to , “Ride ten thousand days and nights” and has returned in the Austin some thousand miles and less than a week later.

The story also rather shows how much better it can be to purchase at auction in modern times: The little Austin was purchased unseen and required only a service. For safety’s sake we decided to fit better lights to the rear with LED bulbs.
AustinJiri Danquah, the proud new owner duly arrived with modern car and trailer to transport the car from the Malvern Hills to Stanstead where the tour was to begin and there the true test of mettle for both driver and car began: The Austin was too narrow to fit the modern transporter trailer and with true vintage spirit the modern car was abandoned and the drive commenced over night by 6 volt headlights to Stanstead airport where the rest of the party was to be collected. The remainder of the tour is best described by Messrs. google who thoughtfully
Mapmapped the whole thing in real time, including a trip to spectate on the London to Brighton rally before another overnight drive back to Worcestershire.
On the right is a clear picture of how reliable old cars should be, the condition one would like to be able to purchase at auction and how true enthusiasts like to drive ancient motor vehicles. Splendid fun for all, although I suspect that the Austin may be due for another service….

Driving Austin

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Subtle Modifications

An ongoing project has been the (hopefully) discrete and (definitely) reversible conversion of an 80 inch Land Rover to take the steering box from a later model. There are plenty of arguments for and against this sort of conversion but two simple facts at the very least make this a worthwhile one: Firstly the later steering assembly of the “recirculating ball” type is lighter and more hard wearing than the original. And secondly this particular Land Rover is missing its original steering box…

This has been quite a popular conversion over the years and the traditional way to do it involves obtaining a left hand drive steering box of the later type and turning it upside down in order to fit it to a right hand drive 80 inch Land Rover. Unfortunately it also traditionally involves welding all sorts of extraneous iron work to the chassis and the bulk head.

Steering BoxThe aim of this particular conversion is to make a steering box which is directly interchangeable with the original and requires no modification to the rest of the vehicle. Here is the casing from a suitable left hand drive steering box which has been machined to reduce its overall height. It has also had the oil filler welded up with an aluminium plug because this will now be at the bottom of the assembly. (A new oil filler has been produced in what is now the top face). After all the welding and machining it has been soda blasted to get everything nice and clean.

Steering BracketA rather hefty bracket is now in the process of being manufactured which will bolt to the steering box and mount (by means of the two smaller holes in the foreground) to the original mounting points on the Land Rover bulkhead. The steering column has already been shortened and fitted with an appropriate spline and this will make it a simple bolt on fit to the otherwise original Land Rover.
Visitors to the workshop may get the impression that – to borrow a line from a well known film – I do both types of welding: Gas and TIG. I have to confess, however that good old fashioned “stick welding”, more technically known as Shielded Metal Arc Welding, is much more appropriate for this job. I used my 30 year old Pickhill arc welder and duly have to confess to being old enough to have bought it new. These simple machines are known in America as “Buzz Boxes” which describes exactly how they sound and exactly what they look like. A good “Buzz Box” combines the harnessed power of a runaway combine harvester with all the finesse and control of a runaway combine harvester. Just the job for neatly joining together two large pieces of 1/4 inch plate!

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Old Fashioned Methods

I have been engaging in a bit of an old fashioned art today: The hand scraping of big end bearings belonging to the Singer Le Mans engine.
I talked about the white metal bearings from this engine in the last post and fitting them correctly calls for a rather different approach compared to the bearings found in most post – war cars and in all modern cars. Perhaps the most important thing to consider first is what constitutes a correctly fitted bearing. Bearings come in various different designs but the ones being discussed here are “plain bearings” meaning that the bearing is simply a round hole which runs on a round shaft with no interspersed rollers or balls. The fact that these bearings operate entirely on a frictional basis with no rolling components gives them some very specific requirements indeed: Firstly they generate much more heat than a bearing which uses a rolling component and secondly they rely much more upon oil pressure. Both of these factors require a certain standard and tolerance of fit: If the plain bearing is a separate component it must have a fit to its housing which is near perfect to ordinary workshop methods of measurement in order for it to conduct this heat away. The plain bearings of the Singer big ends are cast directly into the connecting rods so this is not a consideration for this engine, however the second factor is very much a consideration: The bearing must have the correct fit to the crankshaft and be of a smooth finish which gives a perfectly even clearance for the whole area of the bearing.

The oil pressure upon which these plain bearings rely has very little to do with the pressure read by the car’s oil pressure gauge. The pressure from the engine’s oil pump is only relevant to tell us that a suitable amount of oil is reaching the bearings; after that the bearing and crank pin pump their own much higher pressure which is called “hydro dynamic pressure”.
wedgeThe shaft running in a plain bearing is of course not going to run in the centre of its clearance: It will move to one side of the bearing hole depending on which direction forces (ie: either gravity or other mechanical loads) are acting on it. This will allow the rotating shaft to pump pressure (hydro dynamic pressure) against the oil surrounding it and to form a hydrodynamic wedge of oil as shown in the illustration. This means that as long as the bearing is supplied with oil, the shaft will never actually touch the bearing metal but will instead be supported by the hydrodynamic oil wedge which can be as little as one molecule in thickness.
Imperfections in the fit of the bearing will interfere with the ability to produce a satisfactory hydrodynamic wedge and bearing life will be shortened.

The fit of bearings to shafts is usually measured with a marking compound variously known as “Engineers Blue” or “Prussian Blue”: The shaft is coated with a blue, greasy compound and the bearing then assembled around it and rotated before removing again. In areas where the shaft is a correct fit to the bearing there will be a blue “witness” left on the bearing. In areas where the bearing does not fit closely enough there will be no witness and in areas where the fit is too tight the blue will have been transferred to the bearing and then bear signs of heavy pressure. The ideal situation would be to find an even witness of blue all over the bearing which is referred to colloquially as “100% contact area”. Clearly this is technically erroneous since as we have demonstrated, bearings do not contact shafts but it’s an elegantly simple description and I shall continue using it!
Of course, if you looked at the surface of a bearing under a microscope the “contact area” would be far from ideal but for white metal bearings 100% to the naked eye is the required fit.
Machined White Metal
This is the bit where I am rather happy to be very old fashioned in my methods: These days most people finish white metal bearings by machining them to the required size and then fit them to the engine. Here is a picture of a connecting rod bearing belonging to the Singer after machining to size and obtaining a witness with marking blue. A very poor contact area indeed. There is a very good reason why machines don’t do better than this on ancient designs but that will wait for another post. Since I can’t entertain the thought of assembling a bearing with this sort of fit I have machined a little metal from the “butt faces” where the bearing halves fit together which has closed the bearing up and made it temporarily slightly oval and too tight on the crankshaft.
Scraped BearingThe next stage in the proceeding is rather repetitive: Coat the crankshaft pin with marking blue and assemble the big end bearing to it before rotating it to obtain a witness; remove the bearing from the crank pin and then scrape away white metal from the high spots using a bearing scraper by hand; wash the bearing clean. Then repeat until the desired contact area shown here is obtained. Incidentally, if you “blue” the bearing shells on a modern engine you won’t get contact area this good because they are designed to put up with a lesser standard of fit.
I’ll end this rather long post with picture of two bearing scrapers. These are “half moon” scrapers and are used for removing metal from round surfaces.  The one at the top of the picture is the one used on these Singer big ends and was purchased some time in the 1990s. The cutting edges of these tools must be maintained perfectly sharp using an ordinary oil stone of the type used for sharpening wood chisels. The bearing scraper at the bottom of the picture was the first one owned by my father – he must have purchased it around the time of the Second World War and it would have been identical to the one above it before it became too sharpened away to use any more. These tools which are identical right down to the grooves in the handles are separated by at least 50 years…. thank goodness that they are still available!
Bearing Scrapers

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The Return of the Singer

I started the more formal side of my engineering studies in 1984 and this involved spending one day of each week in a college workshop and four days in the lecture room. Friday was “practical day” and was looked forward to by all the engineering students, most of whom would end up at the stores counter. Those who were not queuing with bits of paper requesting a new bubble for a spirit level, a square drill or a bucket of steam were instead at the side of the queue having been sent down there with a ticket for a “long weight”.
Rear MainI’m not quite sure that victimising 16 year old students is considered acceptable practise any more but I am sure that knowing how to deal with a long wait is an essential skill for any sort of career: The wait for a quality white metalling job has always been a pretty considerable one and at last I have collected the re-metalled bearings and connecting rods for the Singer Le Mans engine rebuild. White metal, properly known as Babbitt Metal now differs a little from the original 1839  alloy developed by Isaac Babbitt in Massachusetts. In the case of the Singer it is cast directly into the steel connecting rods and also into the bronze main bearing shells in order to provide a bearing surface for the crankshaft journals and pins. One of the important duties of the bronze backing shell is to conduct heat away from the babbitt and in to the engine block. (How’s that for precision terminology? According to unspoken convention, the original stuff is Babbitt Metal and the generic term is babbitt.) If the babbitt is overheated it begins a transition from solid to liquid and enters a plastic state. When it cools from this state the macro structure of the material will have been altered and the bearing will ultimately fail.
If the bearing is going to conduct this heat away then the bronze shell has to be a precise fit into the bearing housing with near total contact area. After the shell has been manufactured and fitted to this level of precision it is then heated up and “tinned” with molten metal in order to provide a key for the subsequent white metalling. The Shell is held in a mould and maintained at a suitable temperature for the molten babbitt to be poured into it and when everything has cooled down it will be looking rather lumpy! The excess babbitt is then carefully removed from all areas except the bearing surface and this is done painstakingly both by machine and by hand. The bore of the bearing is then machined with the whole unit assembled into the engine crankcase in order to maintain alignment between front and rear bearings. Finally oil grooves are machined into the bearing surface and the connecting oil holes are drilled. After all this work the near perfect fit to the bearing housing must have been maintained.
This all puts the ease of overhauling a post – war engine with its “thin wall” shell bearings into an interesting perspective and it certainly explains the usual long wait.

There was, incidentally a long standing tale (most likely apocryphal)which maintained that a student had once emptied a bucket of cold water over a lecturer, having apologised that his bucket of steam had condensed on the way up the stairs…….

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Counsel to Maidens

BuckOh damsel fair, beware the car
Where sitting space is wider far
Than any man of reason needs
Except to further his misdeeds;
The steering column change eschew,
No good can come of it for you,
And likewise any motor shun
From which you can’t bale out and run.

Let maidenly modesty decide
To take a summer evening ride
In something of the vintage breed,
For virtue’s friend was ever speed.
No vulpine sibilance can come
From guileless lips of vintage chum,
With passion he is never dizzy
(His motor keeps him far too busy)
And vintage bucket seats preclude
The acrobatic interlude.

Nor can he sit you in the back,
For there a jerry can, a jack,
An inner tube, some oily rags,
A pair of mouldy flannel bags,
A grease gun, several tattered maps,
Dead bottles left by other chaps,
A tow rope and a grimy glove
Leave not a lot of room for love.

Don Juan hands it to his betters
To flirt with triple carburettors,
And modern Casanovas thrive
On ultrahydramatic drive,
But vintage bod of stark appearance
Gives his poppets ample clearance,
He keeps his honour engine bright,
It’s never loose and seldom tight.

And should the half – elliptic ride
Bring bruise to tender underside,
Those precious nylons go to hell
Among the spanners in the well,
And gearbox cast  a blob or two
On tiny white and cherished shoe,
These are but little things to pay
For being out of danger’s way,
The while you blind to kingdom come
And back again, intact, to Mum.

The trouble is the vintage brew
At length may prove too strong for you,
And if with him you ride a lot,
You’ll end by marrying the clot.

So all in all it seems to us
You’re safer riding on a bus.

Anon

Many thanks to Carl for finding it and to Sally Attwood for typing it up from a picture on an iPhone.

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Getting older….

I hope that readers will celebrate with me as I disclose that Cher and I are managing at last to get rid of a habit which has not been helpful to our lives: We are giving up modern cars.
Land Rover 2AThe Series 2A Land Rover was made in 1969 and is a “Suffix G” model, the penultimate example of the range. Having one this late means that you get to have a wider spread of light from the wing – mounted headlights and powerful (well relatively) wipers which operate together and have a park function. Sophisticated stuff! This is to be Cher’s winter car for commuting to work in adverse conditions and it also turns out to be fabulous for exploring out of the way places such as this one near Hay On Wye.
Land Rover V8The long wheel base Land Rover almost counts as modern at a mere 33 years of age this year. The 3.5 litre V8 engine makes it ideal for towing the car transporter trailer loaded here with 1950 AC 2 Litre saloon. After a brief spell last year towing with a more modern Jeep Cherokee petrol the old Rover V8 even seems quite frugal too.

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Further Escapes Curtailed….

Riley Gamecock has its wings clipped:

Gamecock

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Attempted Escape

Chummy

“Tiny old Chummy tries to escape from Thetford Motors by launching into space, but is restrained by the proprietor’s finger and thumb”

Caption courtesy of  Anthony Peake!

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Ergonomics

I have lost count of how many conversations I have had with car enthusiasts about just how hard their cars are to drive.  The owner of a Riley was recently making light of how awkward the pedals are in his car and I had to admit that I keep a special pair of shoes just for driving 12 h.p. Rileys:  My size tens just won’t make the pedals work properly in ordinary shoes so I have found a rather nice slender pair of leather soled ones which actually allow the pedals to be operated one at a time.
The owner of an Aston Martin DB4 recently decided quite wisely that there should be no need to accept this state of affairs:  The accelerator pedal in his car was situated above the level of the brake pedal, so the chances of unleashing the full glory belonging to 3.7 litres of Tadek Marek’s masterpiece of an engine instead of bringing the car to a halt are quite unfavorable.
pedalsThe “organ pedal” type accelerator was the type fitted to the DB4 GT but the original owner of this standard model car had specified the GT pedal from new. It’s the one at the bottom of the picture and the last 53 years of use have worn most of the paint from it. It is rather thick in section and the original idea was to cut it and weld it in order to gain more clearance.  When I took it off I noticed the original gas welds which had been done by a craftsman at Aston Martin.  Who want’s to cut that about? Not me.  The pedal at the top is a reproduction which I made up instead and is over an inch thinner than the original item. The Aston is much nicer to drive and the original pedal makes a nice ornament.          I have included a video of the DB4 on test; eagle – eyed readers might notice that the test route is the same one which features in the clip of the Singer Le Mans in an earlier post and this is no co-incidence:  I often hear the opinion that cars didn’t feature much development until very recently with the advent of electronics, so I think that this clip makes a very clear point:  The Aston Martin and the Singer Le Mans are both quality sports cars; the Singer was designed for 1934 and the DB4 for 1958.  The development between the two videos therefore represents 24 years.

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Field Service 1940s style

Cars At Llanbedr Airfield

I am feeling a little like an imposter already when I choose the title for today’s post:  Mr. Thetford senior did indeed get involved with things mechanical in the 1940’s and in those days of true austerity he did so whilst driving an Austin 7 much like the one in the middle of the picture.  My ‘navigator’, Carl, and I on the other hand have just afforded ourselves the luxury of a drive up to Llanbedr airfield in the Alvis 12/50 special in order to meet up with Elizabeth Halls during the tour of wartime airfields in her Singer Le Mans.
Readers might be forgiven for imagining that the reason for the appearance of the Alvis and the Austin was to give “Chattie” the Singer an excuse to feel youthful at her sprightly 80 years of age.
Maintaining the SingerThe “official” reason for turning up was to give the car a quick check over en-route during the first long trip.
Field service of this kind is to be highly recommended:  Llanbedr airfield lies within some of the most breathtaking scenery which North Wales has to offer and the weather chose to salute the start of Elizabeth’s tour with a cloudless blue sky.

After a spirited drive though the narrow “white roads” which trace over the hills before Llanidloes, through Dolgellau and up to Llanbedr we settled down into a South bound convoy with the Singer for the return journey to England.

Elizabeth’s excellent blog is at www.wheretheyserved.com

 

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Testing Times

AutovacI have recently been working on a vacuum feed fuel system which belongs to a 1929 Delage. These were the first popular type of fuel pump which enabled the fuel tank to be located at the rear of the vehicle instead of the slightly discomforting position for a large quantity of petrol: above the front occupant’s legs.  In Britain one of these is usually called an “Autovac” which was a proprietary name, although they were available from a number of different manufacturers around the world.  They all work on much the same principle:  The engine starts to draw a vacuum through the ‘induction pipe connection’ which lowers the pressure in the ‘inner chamber’.  Because the ‘main petrol supply connection’ is common with the inner chamber fuel is then drawn from the fuel tank and fills the inner chamber.  The reduction in pressure in this area further tightens the ‘drop valve’ onto its seat.  As the inner chamber fills with fuel, the float rises and closes the valve which connects the inlet manifold to the induction pipe connection thereby sealing off the unit from the engine vacuum. At the same time a valve is opened to vent the top of the unit to the atmosphere and the mass of the fuel causes the drop valve to open and drain into the outer chamber. This causes the float to drop and the whole cycle is repeated until the outer chamber is full to the correct level.
It is impossible, of course to guarantee that the vacuum valve will always make an absolutely perfect seal and were this to be the only valve in the system then any tiny leak would mean that the whole unit filled to its brim and then allowed neat fuel to be drawn into the engine. Ingeniously when the vacuum valve is shut, the air vent valve must always be open so this can not happen because as well as allowing the unit to function, this valve also acts as a safety valve.
The one thing that can cause neat fuel to be drawn into the engine is a float which sinks and leaves the unit permanently drawing fuel from the tank.  This is exactly what has happened with the Delage which has been consuming a lot of ethanol – rich petrol during a long spell in France.   The float in the Delage vacuum fuel feed unit is quite small and is made of cork which was coated with shellac – a material which is readily destroyed by ethanol.   The solution has been to manufacture a new float from some ethanol resistant “Nitrophyl” imported from America which has been sealed with fuel – proof “dope” after machining.   The only worry I have had is that the car is still in France so I can’t give it a test run before it drives back home.
So – for anyone who has driven a vintage car with an Autovac and wondered what all that clicking is about, here it is:  The inner chamber on a test rig.  Suction is applied by a brake pump taken from a diesel van and which has been adapted for drive by electric motor.

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A Very Thoroughbred Drive

The Singer Le Mans is all ready to be displayed at Brightwells Leominster next week where I shall be joining her lucky owner Elizabeth Halls on the 3rd March at their viewing day. The most important aspect of the work to “Chattie” is that she should drive properly and reliably and this has meant attending to a number of items on the car to bring engine, brakes and handling up to scratch.  The engine has previously benefited from competent professional attention in the past although clearly some miles have been covered since then.  Attention to a faulty head gasket and to tired valves and seats as well as a good “tune up” have helped no end.
The handling of the car was a little below par and rectifying this has involved not only the replacement of kingpins and bushes as detailed in earlier posts, but also the restoring of the eyes in the axle beam to the correct diameter and the building up of the worn stub axles to restore the fit of the bearings.  A thorough “going through” of the braking system was very well worth the effort for safety’s sake and the subsequent results are rather rewarding.

 

Chattie has been used to compete in VSCC trials in the past and as a result she has a remarkable accumulation of mud and old oil packed in to every considerable area underneath. Some of today has been spent cleaning things up: My most important consideration is to produce a reliable and dependable drive ready for the upcoming tour and there’s no better way to become familiar with every last part of a car than to give everything a through clean!

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Unlikely Stories Mostly

“Chattie”, the Singer Le Mans is due be displayed at Brightwells at the beginning of next month so today’s post features a photo of a pair of her kingpin bushes being line reamed.
Line ReamingIt also features a rather Scottish reference in the title which I have borrowed from Alasdair Gray, and being keen to meet the deadline for the project I shall not tempt fate by making any other Scottish references.
(Angels and ministers of grace defend us).
Expanding reamers are very simple in principle but they do require a certain amount of experience and sympathetic handling in order to produce a good job. I started to learn about these during school holidays – usually in the winter because Mr. Thetford senior (who sadly is no longer with us) used to save jobs like this for the seasonal coal – heated fire in a side room of his old workshop.  Something which has been all but forgotten is the old tradesman’s bit of folklore which maintains that you should only ever use a brush to clean an expanding reamer….. never blow on it or you risk blunting the blades.  Quite untrue of course and with no factual basis, but the legend lives on in as much that I too can not use one of these without thinking of the unlikely story.
Mechanics – or technicians as they are now called – don’t get to use expanding reamers on modern cars but even “back in the day” they were a less common workshop tool.  The biggest danger with their use apart from the propensity of the inexperienced user to remove too much metal, is that they can be allowed to “chatter” and produce a ridged surface finish.  I often think of the story of the garage proprietor who purchased a set of these comparatively expensive tools and , much to the chagrin of his workforce, forbade any one else to use them.  Allegedly he declared on first using them that they were so fine that “only an idiot could make a mistake with them”…. I leave the rather predictable outcome of the story to my readers’ imaginations.

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More Land Rover Repairs

Various work to a 1952 80 inch Land Rover is slowly making progress as the owner tackles much of the restoration to the vehicle and specialist items pass through the workshop.
BulkheadOne of the most interesting jobs is the restoration of the bulkhead: Although most of the Series One Land Rovers were fitted with a bulkhead made from pressed steel, a small number left the factory with an item commonly referred to by enthusiasts as the “aluminium bulkhead”.  This was in fact a fabricated bulkhead featuring a massively strong steel frame which was then “skinned” with riveted and spot welded aluminium panels.  Pictured here is the frame of the aluminium bulkhead which belongs to this vehicle.  It is bolted to the main part of a jig which is being manufactured to facilitate its repair.
The frame itself, although made of some very sizable pieces of steel, has rusted quite badly in places and because it is a comparative rarity it really needs to be restored to look completely “factory original”. The jig will keep all the various mounting points in perfect alignment as metal is cut away and replaced with new sections.
Jig BracketThis is turning out to be one of those jobs where making the tools will take at least as long as the repair itself, and the jig is already starting to feature some substantial bracketry of its own.
It is however, well worth the effort:  Not only can we be sure that the restored item will fit the vehicle properly when  it is finished, the tooling will be left over for the repair or manufacture of any future aluminium bulkhead frames.

It seems as though this type of bulkhead only found its way onto vehicles for the home market which were manufactured in 1952 and 1953. The reason for this has been often attributed either to the tooling for the usual item having broken or else an attempt to save steel during a shortage. I’m not sure that it makes an awful lot of difference to the way the Land Rover behaves but it’s certainly a nice rarity to have.

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A Small Sacrifice

One of the jobs which has been progressing nicely in the workshop is a small single cylinder engine manufactured by The Motor Manufacturing Company of Coventry in 1898 and which comes from a motor tricycle of that date.   This is actually a De Dion Bouton manufactured under another name and is a very significant machine, not only in that it was the most successful European motor vehicle prior to the 20th century but also that the engine itself is often regarded as the inspiration for today’s motor cycle engines.

De-Dion CrankcaseThe crank case of the engine is made from aluminium and is split in two halves which enclose the built – up crank and flywheel assembly. The crank case half on the left is fitted with a newly manufactured brass oil slinger housing which is the main subject of this post.  Engines of this age pre -date modern oil seals by some considerable margin so some other provision was made in attempt to retain the rather sparse amount of lubrication (by modern standards) which they receive.  This was usually done using a “slinger” – a piece of rotating metal which was intended to throw oil back into the bearing area and which often operated in an enclosed housing like this one.  In this case the slinger housing is internally threaded and is screwed on to the aluminium crank case.  I suspect that the original one  had been screwed to the crankcase for most of its 117 years of age because nothing would induce it to unscrew.
Old Brass HousingIt certainly bears the scars of a few attempts at removal in the past and it was this damage which made the only sensible decision into an easy one:  Sacrifice the brass fitting in order to safeguard the beautiful original aluminium crankcase.  With the front cut off the threaded section, the remainder could then be carefully split and removed from the thread on the aluminium, leaving the crankcase unscathed and the brass housing itself beyond further service.

Split Brass Housing
The Coventry engine features a seemingly arbitrary mix of metric and imperial measurements and the thread inside this fitting measures 46mm with a 1.5 mm pitch.  All my machines are imperial ones so I chose to make it on my much loved South Bend lathe which was manufactured in 1943 and comes with a set of metric “change wheels” in addition to the standard imperial ones.  The South Bend is a delightful lathe to use and was manufactured in South Bend, Indiana at a factory which had been purchased from the Studebaker car company. New HousingI recently used the South Bend to manufacture a set of kingpin bushes for a 1920’s Erskine car which was a brand name belonging to Studebaker. This rather  neatly forges a common link between that particular car and the lathe which had probably each been made in the same building well over 70 years ago and 4000 miles away. What a pleasantly small world these ancient machines seem to inhabit.

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Strange Measurements

One of today’s jobs has involved attending to the king pin bushes of the Singer.  I have some new king pins and bushes in my possession with which to complete the job, and thankfully the new hardened and ground kingpins (which are deceptively expensive to manufacture in small quantities) have been made to perfection.  I’m afraid to note, however that I shall not be using the new bushes which is something I had entirely expected and which I was able to decide upon within seconds of unpacking the new components when they arrived.

The tell tale clue lies in the fact that the new bushes were an easy fit over the new kingpins.   The kingpins themselves are made of hardened steel; manufacturing them is quite involved because it neccessitates machining the metal stock to an oversize, cutting the grooves in them to allow passage of grease, drilling and threading them for grease nipples and cutting the locating flats for the taper cotters which prevent them from turning in the axle beam. After this they are hardened and then surface ground to an accurate final size.  Axle Assembly The Kingpins are shown here in the illustration – they fit into the  bushes which in turn are fitted to the stub axle assemblies, and this is where the wheels pivot in order to steer the car. Even the very smallest amount of wear between the kingpins and bushes is magnified many times at the wheel rim and leads to excessive tyre wear and to poor handling of the car. Providing a precise and correct fit between kingpins and bushes will result in no discernible “play” at the wheel rims and (if greased regularly) will last for an astonishingly long time before replacement is needed.

This point is where we stray into the realms of the eponymous “strange measurements”:  Machinists in the 1930s measured in thousandths of an inch, known universally as “thou”.  I too measure in “thou”, not because I was about in the 1930s but because I am an automotive dinosaur and very proud of the fact.   As it happens most of us choose inevitably to ignore that “a thou” is 1/1000 inch and we regard it colloquially as a unit of measure in itself; therefore it is quite acceptable to us when we refer to “a tenth of a thou”. And so it is that the tolerance for fitting a kingpin to a kingpin bush is “two tenths of a thou”. Yes, we all know that really means 0.0002″ or  1/5000 of an inch but calling it “two tenths” is traditional and tradition is strangely pleasant in this context.

Many people are surprised that the tolerance is this close, and although it is quite possible to measure and to manufacture to sizes this accurate it is only meaningful if it is done in a temperature controlled room.  In practice this is done by trial and error:  The kingpin bushes are fitted to the stub axle assemblies and they are then progressively enlarged using an expanding reamer and a pilot.  The pilot ensures that the two bushes (one at each end of the kingpin) are kept in perfect alignment, and the reamer is progressively expanded by tiny amounts until the kingpin is the perfect fit. For this reason I recently commented to another engineer that we know the tolerance is “2 tenths” but no one knows precisely which “2 tenths”.

The important part of all this is that the bushes should be manufactured to an internal diameter which is too small to pass over the kingpin.  They are .002″ (two thou) larger than the bore in the stub axle assembly and when they are pressed in we can then be certain that they will no longer be perfectly round or of perfectly predictable internal size; neither will they be in perfect alignment with each other.  The line reaming will correct all these faults and will leave a superior surface finish to that which could be obtained by machining in a lathe.

The new bushes which I have manufactured today have been made from Phosphor Bronze.  This material would have been considered a luxury in 1935 and was seldom used for this sort of application.  Certainly the replacement bushes which are currently available are made from “bearing quality brass” which theoretically is the correct specification.  Sadly “bearing quality brass” is not what it used to be – presumably because there is no longer any call for it in modern automotive engineering and the use of Phosphor Bronze ensures a job which will give a decent length of service. How long is a decent length of service? The kingpins in my 1930 Alvis need to be re-bushed some 100,000 miles since my father replaced them; when I mentioned this to him he looked disappointed and wondered whether he had fallen in some way short or whether I had neglected to grease them properly.

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Another year… another blog post

Singer Le Mans

Another year has passed and I find that I rather miss writing on the blog – a feeling which coincides with a few recent words of encouragement from readers and which occasions another belated post.

Although the past year has featured quite some time away from old cars while waiting for a broken leg to heal, I am now back in the workshop playing “catch up” with a number of interesting projects.

One of these is the fettling of a Singer Le Mans to prepare it for some extensive use.   These pre-war Singers were charming cars of well above average performance in respect of both engine and brakes and which are very much up to the cut and thrust even of today’s town driving.  This particular Singer is affectionately known as “Chattie” and features on the blog of its intrepid and capable owner, Elizabeth Halls:
The “Where They Served Blog” can be seen here

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Why do so many cars have uneven front tyre wear?

I have been to look at a rather nice Mercedes Benz which was offered for sale today and I subsequently pronounced it to be in very nice condition too. One of the comments I had made about the vehicle was that the front tyres are wearing unevenly – something I see on the vast majority of vehicles which I inspect for purchase.  The key to looking at front tyre wear in these circumstances is deciding whether the cause is maladjustment (which is of course easily corrected) or distortion in the body shell / chassis (which nearly always means that you should run away. Quickly.)  There is rather more to this judgement than can easily be explained in a blog article but here are the rough and ready guidelines:

If a tyre is worn more on one edge and that wear is completely smooth to the look and to the touch, then there is probably a fault with the camber angle.
If a tyre is worn more on one edge and that wear is rough to the look and to the touch then the there is probably a fault with the wheel alignment (and possibly with the camber angle as well)
The critical thing about wear which indicates an alignment problem is in deciding whether it has been caused by maladjustment (ie: the “tracking is out”) or distortion (ie: the body shell or suspension components have been distorted in an accident) Generally speaking, if only one tyre is showing evidence of misalignment, or if both tyres are showing different evidence of misalignment then it’s more than likely a distortion related problem and will often be impractical to repair economically.  If both tyres are showing evidence of misalignment and look mostly like mirror images of each other then it is most likely an adjustment problem and is easily sorted by the right person…. if you can find that person…

Please remember: This is a generalisation and there is a bit more than this in practise when it comes to making the correct judgement!

But why do the vast majority of used cars seem to have so many tyre wear problems? Well a lot of them have been involved in accidents, and that is why they are now for sale.  As to the remainder, let’s take a look at how the front wheels have to align:

Wheel Alignment

The picture on the left shows how the front wheels can align with the steering in the straight ahead position.  Nearly all modern cars are adjusted to have the front wheels with “toe in” so that they are ever so slightly steering towards each other.  It is also usual for modern cars to have “negative camber” where the wheels are inclined inwards at the top. Cars built in the 1960s and earlier often had “positive camber”.  All these angles are so slight in practise that it is hard to tell them with the naked eye of course.

Ackermann Geometry

 

When the vehicle starts to turn a corner however, different things need to happen:  The wheel on the inside of the turn has to describe a tighter arc than the wheel on the outside of the turn as can be seen in the image to right.  This was first described by Rudolph Ackermann in 1818 and the theory bears his name to this day.

All cars for road use have their steering linkages arranged in order to provide for this geometry.

Steering in Action

 

This animation of a vehicle steering system probably shows how it works infinitely better than I can describe things! (With the sole exception that the wheels are turning backwards!!)

 

 

Tie Rods

 

Here lies the key to where it all goes wrong: The point at which a garage or tyre specialist adjusts the front wheel alignment or in popular terminology, “does the tracking”.  The adjustment occurs at the tie rods which are coloured red on the right hand picture.  The crucial thing is that the tie rods are exactly the same length as each other or the geometry shown in the animation above won’t work.  (The “Center Link” labelled on this picture directly corresponds to the red bit of the animated picture.)

The trouble with vehicle alignment gauges is that nearly all of them measure with the steering in the straight ahead position. This means that if a technician is lazy or lacks knowledge he can adjust either one of the steering tie rods in order to obtain a correct reading on the alignment gauge.  However, if as a result the tie rods are now not exactly the same length then the Ackermann geometry will have been destroyed and the vehicle will wear tyres unevenly.  Not only this but the steering wheel will no longer be in the straight ahead position on a straight road – as was the case with today’s Mercedes.  Some modern equipment holds the steering wheel in the centre position in order to ensure that the technician adjusts things correctly, which all works well unless someone has previously re-fitted the steering wheel to a maladjusted system……

The solution when this happens is to remove the steering rack bellows and to set the distance between the inner and outer ball joints so that they are exactly the same for each side of the car.  And I do mean exactly. I use a large vernier caliper in preference to a ruler for this.  Having equalised the length of the tie rods the wheel alignment is then set (often in the case of Mercedes Benz a spreader bar needs to be used first, which pre loads the steering) and any adjustments are made identically on each tie rod. Once the Ackermann geometry has been restored and the wheel alignment set correctly the steering wheel can be re-fitted in the correct position if it has been previously disturbed.

Lastly – a quick footnote:  I am used to working with steering and suspension but I am not at all used to producing nice drawings and animations, so I have taken the pragmatic solution and um… “borrowed them” to illustrate my point.  If I have used one which is copyrighted then please feel free to contact me via the blog!

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The Land Rover TDi finally leaves

The fitting of the 200 TDi engine to the Series 1 Land Rover has finally been completed and the owner has now taken delivery after much engineering (on my part) and much patience (on his part)!

20130606_006The original objective was to produce a conversion which performs well and looks unobtrusive and in keeping with the vehicle. The owner of this Land Rover had some splendid ideas which have produced a very pleasant vehicle indeed:  The 200 TDi Discovery engine produces more than enough power and yields very soothing fuel economy into the bargain. Other features include heated windscreens, and a detachable relay board to provide an electrical sub – loom for auxilliary equipment.

Thetford Plaque

It is not my habit to provide many links to other sites on this blog, but special mention should really go to Gavin Martin who provided bespoke metal CNC machined badges for the conversion which are of lovely quality and very modest cost. Gavin’s blog is at http://artmincnc.blogspot.co.uk

The only thing which remains on the Land Rover is the addition of plenty of miles – a task which (sadly for me) falls to its happy owner!

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The Prince Of Darkness Strikes Again

The latest return to blogging is precipitated by a recent annoying mishap: A rather ironic breakdown.  The Bristol 403 has been a recent visitor to the workshop for a thorough check over and service. Since this car is in regular enthusiastic usage  I had been becoming increasingly aware that the ignition coil must have covered considerable mileage by now and in the interests of continued reliability I recommended replacing it as a matter of course. An equivalent to the original coil for this vehicle is still manufactured but I have had trouble with recent ones which began to leak oil from the H.T. tower so I decided to fit a “Sports Coil” since it is at the top of the range.  The car went very well indeed when set up with this coil and because I am an individual who is probably bordering on Obsessive Compulsive Disorder I can vouch for the fact that the vehicle was driving superbly the night before the owner collected it.  Following said collection I received a phone call to say that the car had been missing on the way home and shortly afterwards it transpired  that the car would no longer start.  The reason?  It turns out that said “Sports Coil” now produces no spark whatsoever and has a rather excessive primary current draw. A quick trawl of google suggests that this is by no means an exceptional circumstance these days.  There follows in the next posts an extensive consideration of the requirements of ignition coils and some ideas of which ones would be the best to fit to a classic car.  I realise of course that since I write in a professional capacity, any mention of the brand of coil which has been causing such problems would be inappropriate. Should the reader wish to use the title of this post to make speculations as to the brand in question then I’d imagine this to be entirely appropriate.

All of this leaves me both with a paradox and a problem to solve:  Paradoxically the person who has a kind understanding of the problem following a breakdown is the nicest person to deal with and also the very last person one would want to experience said breakdown.  Problematically there remains the issue of finding a future supply of suitable alternative coils which have the reliability and the performance for the job.

Conventional current – day wisdom suggests that this has quite an easy solution: There are a variety of ignition coils available with impressive claims for the power which they produce and I’m sure that some of these coils are well made items.  If power output is the only consideration of a coil then the choice is simple and this post will conclude very shortly. I suspect that the reader will have guessed already that I do not consider power output to be the only consideration of coil design, and for many classic cars it is not even the most important consideration.

Of the many experiences I have come across regarding older coil ignition systems, two in particular illustrate perfectly why I am inclined to consider things a little more deeply:  Some years ago I used to drive around 10000 miles a year in a 12/50 Alvis with coil ignition and I prided myself in keeping it running as well as I could.  I discovered that when the car was fitted with an original 1930s coil of the correct type, it would pull without labouring in 3rd gear to the top of the hill where I live. With any recently made replacement coil (and I tried many) it needed a change down into second gear at the top of the hill although in every other way the car sounded well and drove nicely. Clearly a standard 1930s coil doesn’t produce the impressive spark voltage which we have come to associate with later items but something was making a measurable difference.  The second experience came from a meeting with “Steady” Barker at a VSCC meeting at Madresfield some years ago. He had brought a recently restored V16 Cadillac which was running so perfectly that the single tail pipe was producing an almost silent waft of gas with no discernable pulses from the cylinders. My compliments to him on such a beautifully turned out car lead to an interesting discussion during which he told me that the only way he could find to make the car run that smoothly without ever missing a beat was to fit a pair of new old stock Cadillac coils obtained from a dealer in the U.S.  Once again, there must have been some quality of these items other than high output voltage which made them so suitable for the car.

I intend to use the following posts to examine the requirements placed on ignition coils and how these have been met in the past and present.

The Bristol is now running as it should once again courtesy of an elderly but serviceable secondhand coil which, unlike the currently available ones still continues to provide good service…..

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