My first ever dive into "engine work"... Looking for some advice from the cavalry


XS650 Member
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Fife, Scotland
Good evening, All. First to my first ever thread on this page a few weeks ago, I've got the engine out of the frame and up on to my work bench. I did it solo, and it was up there with some of my dumbest moments. I think I nearly passed out while lifting it from the floor up on to the bench :). Still, got there in the end, and without a hernia, too.

I've got the top end disassembled. I referenced this forum for several little parts along the way and picked up some excellent advice, including using a 6mm bolt in a puller guise to get the rocker arm sleeve from its housing. Now that I've exposed my pistons and the bores, I don't really know what I'm looking for, however my gut tells me what I've found isn't ideal... 1976 XS650 with (allegedly) 28k miles on it. I've owned the bike for approximately six months. The piston skirts look badly scored up to me, and the scoring is enough to catch a finger nail when gently running across the surface. Please see the attached photographs. The bores don't look too bad - there is still some cross-hatching evident, superimposed by some vertical scratches that seem 'surface level' only. Can you tell I don't really know what I'm talking about?

I'd appreciate it if your great collective knowledge could shed some light on the condition of my pistons, and subsequent next steps. Further, if the pistons / rings etc need renewed, what work has to go with it? My engine is standard, as far as I'm aware, and has 477-type con rods.

I'm new to all of this. I've read countless threads on here about top-end stuff, all relevant sections of the Haynes manual etc., but I'm a bit overwhelmed by all the information.

Thanks in advance for any advice you can provide.


Yeah...I think that engine has a lot more then 28000 miles on it, or at least had a lubrication or temperature issue. Lots of burnt oil on the piston crown. You need a rebore at the very least and a thorough going through of the entire engine.
or at least had a lubrication or temperature issue.
Yeah, normally you'll see piston wear at the skirt itself first. Those pistons aren't really worn at all on the skirts. Where they are worn looks like partial seizure either from oil starvation, overheating or (most likely) clearances too close when it was rebuilt. The green Athena base gasket ain't factory, this motor has seen wrenches since new.
Can you clean the carbon off the piston tops and give us a pic? Will tell us about over-sizes
Perhaps pictures of both bores from the other direction
And does both pistons look the same. ?

Thinking out loud Gasket Changed --Newer Cylinder than Pistons ?