To Replace or Not to Replace….

It has been a while since I wrote a blog on a Sunday so here’s a post to make up for it. Actually the fact that the Sunday roast hasn’t yet quite cooked although I have finished sweeping the workshop floor and servicing the machinery is the major factor inspiring this post, not my wish to redress any perceived imbalances of posting frequency.

I picked up a few spares for the MK2 Jag yesterday, at the same time that I collected some Triumph spares from an adjacent premises. This morning I took a moment to unpack them and inspect.  I have been working recently on a Moss gearbox which will end up in the MK2. It’s a box which I have known since the 1970s when it was fitted to a 3.8 litre car belonging to a family friend; when the overdrive packed up he continued to drive it as a 4 speed Jaguar, but when he forgot about antifreeze in the winter and the core plugs blew out, the car (at that time without much value) was forgotten about. Some considerable time later the remains were purchased by a customer and many spares were used in the rebuild of another 3.8 litre car. Further years down the line I obtained what parts were left and have kept them until now.  It’s amazing how much changes with the passage of time: What was regarded, in my childhood as valueless must have been an ailing but low mileage MK2 Jaguar which has yielded an almost unworn gearbox.

It was once suggested to me that part of the skill in overhauling old machinery is knowing what to replace.  I’d extend that suggestion as far as knowing what not to replace:  The gearbox in question is fitted with nearly new Hoffman “two spot” bearings. This dates from the time when ball bearing races were available in three tolerances and had one, two or three little circles etched on the outer race to indicate which one a particular bearing conformed to: One, two, or three spot.  two spot was normal for a gearbox: closer tolerance than a “bog standard” bearing but not so tight that it risked siezing as the case expanded and contracted and the shafts bent and twisted.  These days, a bearing is a bearing – and the tolerance is roughly equivalent to the old “one spot”.  Modern machinery is designed to work at this looser tolerance (despite all the popular myths about the greater accuracy of modern  production). Old machinery has to put up with this sort of tolerance in the absence of anything else. Not this particular Moss gearbox though; that will be assembled with it’s orginal bearings and will give 100,000 miles or so of further pleasant and quiet service before I have to give in and fit new bearings to it.

The other new parts which won’t be fitted to the gearbox are the end gaskets which I picked up yesterday: The holes for the bearings are the wrong size to clear the retaining circlips and the rear bearing oil feed hole is non existant. This of course could be rectified, but what can’t be rectified is the fact that they are four times thicker than the original gasket. This last fault will ensure that the bearings aren’t retained properly in the case, restulting initially in excessive main shaft endfloat and secondly in the case being worn away by live bearings.

This may be sounding a little like a lament of the current situation, but it is far from that; these times are excellent: I regularly turn up unannounced on the doorstep of my favourite parts supplier and collect parts off the shelf for Jaguar, Triumph, MG, Morris and others. That’s certainly far better than you can expect of parts supply for any modern car!

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