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650SS Conn Rod - which way round? (Oilway)


Hi Guys, Preparing to rebuild my 1967 650SS engine.  My trusty Haynes manual shows a nice picture of the conn rod and states 'oilway MUST face outwards - late 650 and 750  engines after engine number 116372.' However, when I stripped the engine the oilways were facing inwards on my engine number 18SS/117285 - obviously a later engine.

Can anyone confirm the Haynes data, the correct fitting direction or give me a reason why this would've changed for later engines?

Cheers, Len


Hello Len - I do suspect that your engine has been assembled incorrectly or perhaps if it had been seizing pistons on the inside surfaces perhaps the con-rod spray holes were reversed deliberately.  In any event I shall quote from an article in our technical data-base from a gentleman J.B Nicholson as follows :- In 1966 when the oil pump speed was increased and other lubrication modifications were introduced on the 750 and 650 motors a 1/16 inch diameter spray hole through the big-end was provided to give additional piston and cylinder lubrication. These rods should be installed with the oil spray hole to the outside of the engine, i.e. away from the flywheel on each side. This rod big-end spray hole is not recommended on the 1965 and earlier motors with the slower speed oil pump and if a later rod is being fitted to one of the earlier motors the spray hole can simply be peened shut from the outside.

Personally I would not peen the rod but instead I would simply fit the shell without the hole at the top and the one with the hole at the bottom if I wished to stop the spray facility.  Cheers, Howard

Thanks Howard - that makes a bit more sense. I assumed that there was always a spray hole and the position had just been changed for some reason. If there was a known need for improved cylinder lubrication and the oil pump speed/supply was increased to provide this (and perhaps other requirements?) then I think it makes sense to leave it open and fit it outwards, as suggested. I agree that the engine may have been incorrectly assembled...but it also worries me that it had been apart at all as the bike has been laid up since before 1976 - ie since before it was 9 years old. I did discover a broken exhaust valve guide which had resulted in valve/head damage, which is, presumably why it was laid up in the first place (?). The pistons and bores were in reasonable condition (standard bore), however I have had a rebore and new pistons as they were reaching top limit of wear. I don't know how many miles the bike has done  as the  clocks  were not original. Thanks again for your help.


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