Author Topic: 1980 Yamaha RD400g (Canadian Version)  (Read 193 times)

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Offline Tony2T

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1980 Yamaha RD400g (Canadian Version)
« on: May 22, 2019, 04:19:26 PM »
Hello everyone, Ive got a 1980 Yamaha RD400G, running bike but has low compression roughly 80 psi on each cylinder. So I decided to strip down the top end for a rebuild. Measuring the cylinders, it looks like 66mm Bore. According to the manuals, stock bore should have been 64mm. Im a little confused as Im fairly confident that the engine is untouched with about 18,000 kms on it. It is a 2R9 engine. Am I missing something here? or the engine is actually at its final overbore? I was able to find a set of 66.25mm over-sized pistons, so I can probably just fit that and someday re-sleeve the cylinders. But out of curiosity, are the 2r9 engines supposed to be 64mm stock bore? I cannot seem to find a lot of information online about this particular model as it was somewhat of an odd-ball bike but I think 1979 RD400F Daytona had the exact same powerplant? Any information/insight on this from the RD gurus would be greatly appreciated. THanks!

Offline ixe13

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Re: 1980 Yamaha RD400g (Canadian Version)
« Reply #1 on: May 23, 2019, 05:23:45 AM »
64mm is standard bore , if the cylinders are at 66mm , they would be on their 4th overbore , unreal for only 18 000km . Mine has 20 000km and it's on first overbore .
1979 and 1980G are identical save for the decals .