Hitchcocks Forum

I have recently acquired an Interceptor which is registered as 1966 although there are a few questions around that date. Crankcases are a matching pair of replacements as they have the same number stamped behind the cylinders but no engine numbers on the side. The engine is fitted with head gaskets and looks to have been modified with the original sealing ring replaced with a compression ring to seal against the gasket. I have included some images and wondered whether anyone has come across this conversion before or even knows of this bike, it seems to have lived in South Somerset since returning to the UK in the mid 90s.

More than one owner has given up on cross-ring seals. Some use the cross-ring in conjunction with a head gasket. In your case they appear to have engineered a solution to exclude the cross-rings. Maybe the availability of oversize cross-rings had a bearing on their decision? They have not always been readily available. If it seals OK then the conversion is a success, no problem. However the compression ratio will be lowered by a significant amount. This is not such a terrible thing for a historic motor, which being a bit long in the tooth, might actually benefit from detuning. One could always revert to the original set up with replacement barrels. Photos of the matching crankcase numbers & the blank engine number area would be appreciated. I have the correct size & font of number & letter stamps if you wish to restamp the engine with the original number, which as it is a replacement motor, would be entirely in order. You not not mention if the gearbox number is stamped on the front of the crankcase. This would also be absent on replacement cases & can also be restamped without fear of any wrongdoing.

This will help - its all on our hosts website:

https://www.hitchcocksmotorcycles.com/p ... osition-41

Its had our hosts cylinders fitted

Thanks for the replies,
Here are some more photos, I have been advised that the number on the front of the right crankcase is possibly a frame number for another frame in which the engine may have been installed previously.

Crankcase matching numbers behind cylinders - W951
Front of right crankcase number - 62815
Gearbox Number - AGZ 1151

The front crankcase looks as though it has had the original "AGZ****" number erased. Would need a closer photo of that front area, but it certainly looks that way. The matching crankcase numbers look fine (I have seen bodged/erased ones), although all that blue hylomar frightens me. Your alternator wiring looks a bit stressed too. Cannot detect any erasure of an engine number, looks OK. Perhaps the RE records (Graham Scarth) could provide the original engine number for that frame?

I remember selling a set of NOS crankcases with the Cam caps 30 years ago with no engine numbers stamped.

And I bought a pair of NOS IA crankcases without cam caps & numbers (except for matching crankcase numbers) 7 years ago.