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…..