1972 Yamaha XS650 project

Okay as I measure the allen bolts they are far larger than 20 mm. See attached pics. That however does not explain why it didn't leak when I bought the bike last fall. In the meantime I have ordered replacement bolts; just in case, from Partzilla. It will be telling when I receive them and compare them to the bolts I removed from the bike. Thoughts?

scanney said:

Okay as I measure the allen bolts they are far larger than 20 mm. See attached pics. That however does not explain why it didn't leak when I bought the bike last fall. In the meantime I have ordered replacement bolts; just in case, from Partzilla. It will be telling when I receive them and compare them to the bolts I removed from the bike. Thoughts?

Click to expand...

While waiting for new bolts to show up I think I would clean all the blue stuff off of everything. If you happen to have a new gasket I would use it. I would then stack some washers on the bolts to shorten them up. Put it back together and see what happens. Worst it can do is leak.
I have no idea why it didn't leak before. Yamaha does call for a 20mm bolt. It's possible the longer ones are bottoming out before clamping the cover.


I have a spare cover. I tried a 25mm bolt in each hole. On the left hole the cover tightened up just fine. In the right hole the cover was loose (movable) when the 25mm bolt felt tight.

The ones you have are correct, stock length is 25mm as noted in my post #87. Well, at least that's what's called for on the later models. Maybe your early cover is different?

5twins said:

The ones you have are correct, stock length is 25mm as noted in my post #87.

Click to expand...

5twins am I reading the part number wrong. Isn't #9 a 6x20 mm bolt?

Yes, it is. Looking at diagrams from different years, it appears the 25mm screws were used from '74 on. I guess the covers changed somehow? Interesting, I never knew this before.

Looks like the long 75mm screws were also shorter on the '73 and older covers, only 70mm long.

All very strange. I really appreciate everyone's insights. I couldn't believe the effer was leaking oil. Looking forward to the fix and happier trails.

Mebbie worth a mention; the nearby tach drive is a notorious leaker.....

OK, I "fixed" my drawing in post 87, lol.

Ordered new gasket and bolts (yes they are shorter than what was on the bike). Installed and no more oil leak!

However, today I discover a significant fuel leak from the left petcock. I'm certain it's coming from the lever mechanism - on off reserve. See schematic. I did previously purchase and install petcock rebuild kits (MikesXS) on both petcocks. The right petcock does not leak. Today I drained the fuel and disassembled this mechanism - I left the petcock body attached to the tank. The rubber gasket is good and the spring washer, lever, and plate looked clean and smooth. For good measure I cleaned all parts and reassembled. Still leaks! I noticed on the spring washer there is a subtle difference between each side - one is smoother than the other. I re-installed smooth side in and then smooth side out. It leaked both ways!!! I checked my patience and found it to be way low! Can anyone provide some insight into how this can be remedied? Thanks