Clutch operating mechanisim

[David Morris]

Hi all,

John Airey, Nigel Woodford and I were involved in a Javelin engine change on Monday. We discovered what would have been a 'show stopper' had we not had a spare clutch pivot pin to hand of the right size. Between the two engines, we found the clutch pivot pins had different diameter shanks. The engine coming out had a 5/8" diameter pivot pin shank and the engine going in needed a 1/2" diameter shank. There were also corresponding size differences in the bronze Clutch shaft Cover, and the aluminium Clutch Housing. The Jowett reference number for the Pivot pin is 50837, the Shaft Cover is 50007 and the Clutch Housing is 50836.

Interestingly, Jowetts seem to retained these same reference numbers throughout the production run for all three components, although they are clearly not interchangeable.

With the engine separated from the gearbox, the Pivot Pins and bronze Clutch Shaft Covers will easily slip out, so our advice is to keep them with the engine they came from, as you might need them again and your spare pins or bronze shaft covers, tucked away in your spares tray, might not be the right size!

Jowetts are usually pretty good at keeping track of design changes by part reference number changes, but not in this instance!

I believe that the Clutch Housings were line bored with the crankcase set, and given a reference serial number to identify them with a particular engine crankcase set. This was to help align the rear crankshaft lip seal, which sits in the Clutch Housing.

The Clutch Housing which needs the 5/8" diameter pin carries a stamped reference number of 1488 which bears no relation to the engine number or the casting numbers on the crankcase set. Also, the hole in the Clutch Housing for the 5/8" pin is in both the RHD and the LHD positions. Normally, the Clutch Housings have the Jowett part number cast just above where the central inspection hole is for observing the flywheel marks. This Clutch Housing has no such number, which suggests it is non-standard.

My suspicions here are that the 5/8" pivot pin we found was a factory 'mod' to reclaim the situation where the original 1/2" holes were worn or out of tolerance, perhaps during production? It may be unique, but who knows, after all it is a Jowett!

Any ideas?

All the best,

David