Piston rings and cylinder walls

1981 xj650. So after getting the bike running well last summer I noticed I was having to refill the oil with another quart every 300 miles or so. Not terrible but not ideal either. After checking compression in the cylinders, 1,2, and 4 were good, all in the 120-130 range. 3 was very low and in the 60 range, not good. Decided I was going to take it apart this winter and replace the piston rings to see if that would help solve the problem, and to check it out. Definitely found something way worse than just piston rings. There is a gouge and scrapes on the sides of the cylinder walls in cylinder 3. You can see it in the picture about an inch down from the edge of the cylinder. The horizontal gouge is at least 1mm deep if not more, and the vertical scrapes are not quite as bad, but still not good. Guess I know where that oil was escaping to.

Question now is what to do with it and how to get it running again. Do I try to get it bored larger and get a new piston? And if I do that do I have to re-jet? Is it ok to only enlarge one cylinder/piston? Would it be better to buy a replacement cylinder and get it swapped out? If I did that could I keep the same piston? Or should I scrap this cylinder bank and get another one on ebay? The cylinder walls in 1,2, and 4 have no defects or even rust. Any advice and help would be awesome!

 

your least expensive option would be to just buy a decent running engine and swap them out. the cost of rebuilding an engine can get up there fast. if you do decide to rebuild it, just get a good used cylinder bank and piston set. the cylinder bank pictured above is a boat anchor.

FU

 

I wouldn't call it a boat anchor. I would save it for a later date when a rebore is a more economical option. I would not bother with a whole engine unless you can get it locally and hear it running befor the sale. Look for a set of good, used cylinders that can be rehoned, along with a set of rings (after you have the bores checked). Sometimes you get lucky and cas score a set of jugs with the pistons and rings.

That gouge was likely caused by a broken ring.

 

I found a set of cylinders that looked pretty good from the pictures, guess I will get those and rehone them, check bores, and get some new rings. Unfortunately they do have some chipped cooling fins that mine didn't have

 

A machine shop can build up the cooling fins with weld for a lot less than having your other cylnders rebored would cost. If you have a college or high school in your area with a welding program, you might be able to get the work done for free.

 

I remember seeing a post a long time back where someone was baking their cylinder bank for whatever reason (might have been powdercoating or prepping for paint)... and the sleeves worked their way out of the bore holes. The user pushed them back in, and said all was good.

Just as a purely academic exercise, I wonder... would it be possible to just re-sleeve the cylinder in question? (Or all four for the sake of completeness.)

 

Sleeves run about $80-$90/each, a replacement cylinder bank can be had on ebay for $35. Either way you have to remove the top end which means new gaskets, may as well just replace the bank entirely. Do not overbore if you can help it, rings, if they are even available, are very expensive.

 

Also one-up rings require a one-up piston...yes?

Gary H.

 

I don't know what the measurement of that gouge is, but on MY screen it looks like it's waaaaay deep. If it's really as deep as it looks, there's no way that you're gonna be able to bore that one out and get past the damage that is GONE.

I'd just look for a replacement cylinder block.

Dave F

 

Kinda going along with what these guys said.... That looks DEEP....

FWIW.... just buy a good complete motor or parts bike. Do a motor swap and keep the original for parts. You'll come out ahead

 

Waaaaay ahead

 

Ya it is deep in a bad way. New cylinder bank arrived yesterday, looks good so far, just need to check bore and hone. Gaskets for the rebuild are already on the way as well. I thought about a replacement motor but this seemed just slightly more cost effective, plus half of the reason is the fun of putting it all back together again.

 

You got a point there dude.... Just be careful... i nearly junked mine by bending unobtainium piston rings...

 

Well thats your fault for buying the unobtanium ones, should bought the cheaper ones made of obtainium.