piston rings

buying piston rings online for xj650, have option of .25 or .75 oversize. what do you suggest, first time changing them, whats the difference, thanks Lou

 

When I was looking for new piston rings for my XJ900 the Yamaha people said that I should use the original standard size rings.

Using oversize rings may mean that the gap may be to small when compressed thereby restricting oil flow on the barrels.

I replaced my old rings (150,000kms - around 100,000 miles) on the engine at the time. My 900 was drinking oil, had a smoking problem on start-up, and kept fouling plugs. Put in the new Yamaha standard size rings and it's as good as new.

The advice given to me was standard rings for standard pistons - oversized rings for oversized pistons, usually as a result of rebore or aggressive honing of the barrels.

I think Rick may have done something with oversize rings from memory which involved fitting and filing the gap of the compressed rings.

Check out the details before committing yourself on the purchase.

 

You have to Measure the gap in the ring.

You place the new ring in the Cylinder and Push it down the Bore with the Piston so its not cocked or out of horizontal position.

Then, ... you take a feeler gauge and measure the gap in the ring.
You select the ring that has the closest gap to specs.

You need to have it close to specs because if its too tight you will risk cracking the rings once the engine is fired up and the heat expands the ring.

An insufficient gap will cause the ring to become too tight and it will overheat and crack.

 

Ditto what Rick said. Most air-cooled engines run "choked" cylinders.....smaller at the bottom of the bore and larger on top. (After the cylinder reaches operating temp, the bore stabilizes). When measuring your cylinder, take your readings with a tee-gauge or cylinder bore dial indicator at the BOTTOM of the choke. This will give you your tightest ring gap reading. Once you determine which rings to buy, you'll need to hand-check each one by pushing it to the BOTTOM of the choke to measure your ring gap. If it's too tight, you'll need to file the ends of the gap to open up the clearance. I've done this by hand with a small flat file, but it's a much wiser idea to buy a ring gap filer fro Summit Racing or a similar company-it does a much neater and far more accurate job. Not to mention faster! It would also be in your best interest to run a Flex Hone down the bore PRIOR to fitting the rings......give those new rings a nice cross-hatch pattern bore with which to seat.

 

Very good thing to remember! It would be a waste to put in new rings without honing the cylinders. When the cross hatching wears out the cylinder can't hold oil as well, that is when the rings wear out quickly. If you don’t hone the cylinders the new rings will wear out faster.

Ring sizes match the piston, standard pistons require standard rings. If your cylinder is worn out of spec. then you not only need bigger rings but bigger pistons (and a bore job) to match. You can use oversized rings and file them as mentioned, I now some who insist on buying the next size rings and gaping them themselves. I buy the same size as the piston and double check them in the cylinder, I haven't had any problems.

 

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Anyone have a recommendation on where to purchase a new set of rings affordably?

Nothing turns up on ebay search for "xj550 piston rings". I also checked Bikebandit.com and a new set of standard rings for my 82 XJ550R Seca is $53/per piston. ouch.

A friend of mine suggested Hastings Piston Rings, http://www.hastingsmfg.com/ but I'm a little bewildered as to how I would locate and price out a complete matching set.

 

chacal carries them for $39 per piston/set.

 

ChaCal is the parts guy!!!!

 

Does Chacal have a phone number or a web site? I dug up a Chacal username on the forums along with an email address, but that's it.

 

Send him a PM or email. He is usually pretty quick to respond. He is a good guy and a big help. He has a parts list in the Supporting Vendor forum.

I have a post in the Vendor Review section titled "Who is Chacal" that gives more info. He is not your 'typical' parts guy which is a good thing when working with these bikes.