Hello. I'm finally getting around to rebuilding the engine of my 1967 C25 which I stripped down 15 years ago. Engine and frame No C25-317, these early bikes had no provision to monitor oil pressure. I would like to keep an eye on oil pressure in future. Amongst the many used spares that I have is a later inner timing cover with oil pressure switch. This later cover will bolt straight onto the crankcase, and I also have the matching outer cover.
The later inner cover has the wider cast web that includes an O ring to seal the oil supply from the pump. The matching web on the crankcase half is however much narrower and will not provide a surface for the O ring to seal on. Does anyone know if the gasket for the inner cover as made for the earlier engines will seal against the later inner cover. This gasket is missing from the set that I bought all those years ago. I have the excellent RR book, and this suggests maybe machining an O ring groove around the oil outlet in the crankcase half. I don't think that this will work if I use the later inner cover due to there being insufficient space between the inner cover O ring groove and its port to allow an O ring around the crankcase port to seal.
Apart from the above issue, is anyone aware of other reasons why I could not use the later inner cover? I see that the machined slot for the gearbox cam plate is longer in the later cover. If I cannot use the later cover, has anyone come up with another method to monitor oil pressure?
Thanks in advance.
I am surprised that there is insufficient metal around the crankcase oil outlet for the inner cover O-ring to bear against. Looking at another inner cover (albeit from a B44), it looks as though the O-ring is only ~7 mm in diameter. In terms of a gasket, there wasn't one fitted between the inner cover and the crankcase because it would then not have been possible to set the end float on the gearbox shafts.
Thanks for the response. The O ring is indeed approximately 7mm ID. The section of the O ring that protrudes the furthest from its groove is approximately 9mm ID and this is pretty much exactly the same as the narrowest part of the mating web around the oil outlet in the crankcase. I'm not confident that it would produce a reliable seal.
Thanks for the info ref the gasket, at least now I understand why it and one for the outer cover are not in the kit!!
Measuring my (B44) inner cover a bit more accurately, the O-ring slot is actually 8 mm OD. If the web around the output hole is 9 mm then that would be ok for my inner cover seal. Bear in mind that, up to 1969, there was no O-ring fitted and so, provided most of the O-ring can press against the crankcase web, it's going to be an improvement on the original scheme!
Fitting an O ring to an earlier bike was a suggested mod by this BSA USA service sheet.
The 5/16" end mill produced hole recommended in the Service Sheet in the inner timing cover is the same size as the 8 mm OD I measured on my B44 cover! As said, if the later B25 cover is the same then a 9 mm web on the crankcase side should be ok?