Pistons & Rings

[srq68]

I have low compression readings (95 psi) in all cylinders, but all consistents. I isolated it to the rings by squirting some oil in the cyls and getting much higher readings after that (125 psi). My question is: will the compression return to specs if I replace the rings with standard size rings and nothing else, or do I need 1st size over, in which case, what else needs done, i.e. oversized pistons and honing?
I had to replace one piston due to damage by a broken valve, this new piston with standard rings has the same reading as the other ones. That leads me to believe that standard sized rings won't cure the low compressions, right?
THX

[Geezer]

That test isn't all that reliable. Pull the head off and check the valves and measure the cylinders. Until you do that, it’s all guesswork.

Geezer

[TopCatGr58]

Hey there SRQ68,

Even if/when you do pull the heads off and measure the innards, the wear on the cylinders, piston to cylinder clearance, out of round wear etc., if you do find that it's out of spec, and you have lots of miles on the engine which is probably true, you really only have one option.

You'll have to do a Big Bore kit, cause Yamaha doesn't support the XS anymore with regards to pistons and rings in ANY oversize, you just can't get any. So you'll have to have the cylinders bored, and get new pistons and rings, and you have two flavors: 1179cc and 1196cc, both bore the cylinders a considerably more thinner than the book specs state is allowed, but many have done it and have not seen any excessive heat/warping issues so far!!!

The Bore Kits are around $400.00, include pistons-rings, head gasket, wrist pins and keepers. Then you'll need to find a machine shop, usually $40.00 a hole for boring, plus other gaskets and work to recondition the head...lapping valves, replacing valve seals, etc.! So anywhere from $750.00 on up for the rebuild total costs.

So....now you have to ask yourself one question....do you feel lucky?! Whether the performance is so bad in your XS that you want to put that $$ into it, or if it's still very drivable, then continue driving it and save your $$ for later!! Hope this helps.

[tony7914]

just out of curriosity has anyone looked into having the cylinders sleeved?? not sure what this might cost or even if it can be done on these cylinders, but i thought it might be worth asking about!
thanks!
tony

[Snow]

I am pretty sure these cylinders can be resleeved, but then you still have the problem of finding replacement rings and wristpins. Not sure how much resleeving would cost though, could get as expensive as big boring.

[sixtysix]

We just had a thread about this, do a search for compression and see what comes up. Make sure you are doing the test correctly (engine warm, WOT, etc)

[srq68]

Well I took your advice and did a new test with engine warm and WOT, the reading came up to the 120's, so I am not going to touch anything on the engine at this point. Thanks for the info and advice.