What happened in my cylinder?

on my right cylinder CB378 with maybe 500 miles on the rebuild.
Took the engine apart do to a broken cam guide from a bad "sticky" cam chain.
Found this! I can feel the horizontal lines across the cylinder wall with a fingernail, but not the vertical ones.

Looks like previous damage.


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Yup, looks like they were honed and hatched, needs to be over sized... Not too bad, but should have been done for you on the "rebuild"... did you buy pistons or just rings and gaskets for that job?

Did you just buy that bike ?

Thankfully, Ive had this bike for a few years.
I found an GS850 Overbore Kit on eBay for cheap, and rebuilt the top end with it. I don't remember these markings being in the cylinder when I installed them, and am fairly certain they're within recent miles. My cam chain and guide were both damaged as well, I believe. Just going to hone and go with it.

raptormeat said:

Just going to hone and go with it.

Click to expand...

Bad idea.

The only thing I can think of is it got some moisture on that side and the ring rusted just enough to score the cylinder wall and the corrosion on the ring caused the vertical lines, inspection of the rings should show some pitting if that is the case.

Maybe not so bad as you mention on those vertical lines but the deeper horizontal marks that look like corrosion to me may need some attention if honing doesn't clean it up, do you use a bead hone or stones? bead hone is the best method, stones are worthless (IMO) and can get you in deeper than you are. I would get a set of rings to go back in with and gap them as close as allowable.

The cam chain and guide may just have been because of the chain adjustment, it's important to have the slack at the adjuster side when adjusting it and can be done before you put the valve cover on to assure the tension
is correct. Too tight or too loose can cause adjuster failure resulting in chain stretch/rubbing and damage.

Section 17 page 45 of the manual (GS1000 but samesame) very detailed and maybe you already have it, but here it is anyway. Good detail for chain adjustment on your motor if it's the right generation.

Link: http://www.mtsac.edu/~cliff/storage/gs/GS1000_C-E-S-L_Manual.pdf

could this be the culprit? on the right side as well, it was cracked and I have removed excess metal out. is this ok to run?
i didnt see any marks on the piston, so i think this was just stress heat and time affecting the case...but idk.

I would investigate what caused the chip, the location suggests that the crank bearing underneath has or is failing... some serious pressure cased that chip.

Tune-A-Fish said:

I would investigate what caused the chip, the location suggests that the crank bearing underneath has or is failing... some serious pressure cased that chip.

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it looks big enough to be called a 'chunk' I'd certainly split the cases.

You can take this to the bank.What you see there is the ring carving into the cylinder.Either stuck in the groove or the end gap wasnt wide enough...It mite be now though.

thanks guys, i am rebuilding the cases, just waiting on an aftermarket cam chain to arrive.

i have them rebuilt now as a mock up and there is a clicking noise when i turn the crank over ccw, and it wont spin at all clockwise either, which i believe it is supposed to do. its in neutral as far as i know. any explanations??

https://www.youtube.com/watch?v=ZJFs7Dj2F4A

wrap all 4) connecting rod small ends w/ cotton & tape and see where the noise is then.

those liners look like a broken ring, but what's with the colors? Top pic looks like detonation and second looks like a PO tried to cover it up with something, but that's probably an optical illusion.

It's much lower than the top ring, so was the oil ring assembled incorrectly or was it a one piece ring that broke?

Crankcases look like a bearing locating pin pressed up into the crankcase moth where it was machined for larger liners.

You need someone else to hold and guide the rods while you turn it over.Do them one at a time to eliminate rod noise.