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Oil leak from behind Advancer

Thuban

Horse scratcher
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Paris, Texas
1978 CB750K. I have an oil leak from behind the Advance unit. It looks like there is only a 6 X 2.3 O-ring behind there on the Spark Advancer Shaft. It looks like it may be easy to change? Any cautions I should know about or pointers?

Thanks
 
That o-ring only seals the advance shaft and maybe a drop or two of oil behind it. Getting more than that says the main crankshaft seal behind all there is leaking and you likely split the cases to get to that.
 
I would try the o ring first, they get hard and can seep. If the main seal is leaking then the case has to be split.
 
Thanks guys. I'm just getting back to this. Yep, I saw the big seal and ordered one to have a close look at it. It has a small raised lip on the inside. I'm not going to split the case for just this seal. I'll try the little O-ring first and cross my fingers. It will be a while before I get to it.

This bike only had a bit over 8K on it when I got it. I'm the third owner. The other two were old farts like me. It's spent most of it's life just sitting. It had a vetters faring and a box on back. Took that off. If you don't watch your shifting you will get a false neutral every once and a while. I checked the shift mech. That looked ok. The shifter mod would have been incorporated on this one. Pulled the sump and looked around. No metal bits anywhere. Doesn't jump out of gear but when hot it clunks pretty hard in the up shifts. Down shifts are smooth. I had the engine out last year. Compression was good so I just retorqued the heads and generally checked it over. clutch feels fine so maybe it's just me and switching back and forth between the Honda and Yam XS? ( That second gear dog breaking crap scared me! ) One things for sure. If something is going wrong, it will get worse. :)

Thanks again Guys
 
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