prepping for new rings

[Greg Carberry]

Going to be putting some new rings in an old saw. Bore is very good no scuffs or gouges. Anything I need to do besides just putting it back together? Like light honing or don't these chrome cylinders need that?

 

[bwalker]

If the saw has a nicasil bore I always lightly ball hone it with a hone 10% undersized and lots of two cycle oil for lube. This helps the rings seat faster.

 

[Greg Carberry]

I'm pretty sure its just chrome, do the same for it? Where can I get a ball hone at?

 

[Crofter]

Be very careful not to oval shape the cylinder. Unless you use a rigid hone you will be likely to remove extra material around the edges of the ports and the rings wont seal well. Also the cylinder liner material can be quite thin. Sometimes the word is "if it ain't broke, don't fix it" My experience is more on 4 strokes, so get some opinions from the 2 stroke whizzes.

Frank

 

[Fish]

I don't hone, just polish off any pasted on metal. If the
cylinder wall looks fine, just put it together, the more material
you remove, it is just like wear. Oil rings/seating does not
apply here.

 

[Greg Carberry]

Originally posted by Fish
I don't hone, just polish off any pasted on metal. If the
cylinder wall looks fine, just put it together, the more material
you remove, it is just like wear. Oil rings/seating does not
apply here.

Alright sounds good to me Fish.

 

[stihltech]

hone

I use a spring loaded glaze breaker, just to scuff up the bore a bit. I have also just installed rings in a nice, clean bore. No problems either way. If it is a good cylinder, it will work just fine.

 

[bwalker]

A ball hone of the right grit and size will not remove material or snag the ports as some suggest. The hones that are hard on the ports are the spring loaded type Stihltech mentioned. IMO Its always a good thing when reringing to hone the cylinder in the manner I described. It ensures good ring seal and reduces the likelyhood of glazed cylinder that never seats the rings.
BTW Crofter in a two cycle most cylinders are slightly oval by design, same with pistons. The reasson for this is that with the port windows cut out expansion favors one side of the cylinder. If they where perfectly round you would have clearance problems on the exhaust side.

 

[Tzed250]

Round bores

Sorry bwalker, but 2-stroke bores are not intentionally oval. The highest performance 2-stroke cylinders are the ones that go on GP roadrace bikes and they are very near perfectly cylindrical when they are new. Many 2-stroke pistons are cam ground so that they will be round when they expand. A round piston in a round bore keeps the piston from rocking and beating the skirt of of it. Also the cylinders that are hard coated (nikasil, electrofusion, chrome, do not need to be honed at all. A piece of scotchbrite is all you need to make sure that the ridge at the top of the bore is smooth.

 

[Crofter]

BWALKER I agree that the cylinders are oval to allow for the greater expansion at the exhaust side. This would be by design and accomplished by controlled conditions such as laterally preloading the cylinder before honing etc. With a spring loaded or centrifugal flexible hone I feel more material might be removed in the port areas because the higher stone pressure per unit area there. I don't know if that cylinder has open transfers or not..that could be a problem. Don't know which would be the greater risk; rings not seating after, or possible greater wear or damage from a honing. It would be interesting to see what kind of ring end gap clearance he has.

Frank

 

[Tzed250]

Hones

If you run a hone in a coated cylinder you run the risk of causing the coating to peel near the ports. If this happens the cylinder is ruined.

 

[bwalker]

TZ, I am sorry , but your info is wrong. I have afreind who works with USchrome and has tuned GP bikes. The info I pased on is straight from his mouth including the ball honeing.

 

[Tzed250]

Difference

Sorry bwalker, it you who is mistaken. A Kawasaki factory technician, one who tuned Jeff Ward's bikes, instructed me NOT to use a hone inside the bore. Scotchbrite only. By the way, how many 2-stroke top ends have you worked on, and did your life, or anyone else's, depend on the quality of your work?

 

[bwalker]

You wouldnt be reffering to Tom Morgan would you? BY the why the guy I know tuned for some of the big names as well as worked for a plateing vendor thst built formula 1 stuff. I have done many two stroke topends and I have always ball honed them. BTW I hope your factory guy isnt the same one that told you cylinders are round. Besides not being round they are also taper bored.

 

[Tzed250]

No, it was not tom morgan. Nobody "told me" cylinders are "round", I have measured plenty of brand new ones myself. They were NOT tapered,or oval shaped. I KNOW what a round cyclinder is. I am a Production Engineer at a corporation that produces over 50,000 hydraulic cylinders every year. You "hone" your cylinders if you want, and i'll do mine how I want. By the way, the tool with the abrasive balls mounted to a shaft is known as a glazebreaker.

 

[Crofter]

Cylinders when measured at room temperature and unbolted from their working counterparts CAN have tapers and out of round conditions but this is designed so that when heads, manifolds. exhaust flanges etc. are bolted and torqued and at operating temperatures the bore will be as close as possible to round and taper free. Piston rings that have to work in and out and change shape to follow a crooked surface wear out themselves and the sides of the ring lands. At certain rpms this motion will match the resonant frequency of the ring. Ring flutter and washboard on the cyl. results. Ring breakage also.

Hey this is fun!

Frank

 

[Tzed250]

True

That is all very true. The main reason that 2-stroke motorcycles became water cooled was to make more power. They could make more power because they kept the piston crown cooler. The way they did that was to control water flow around the bore in a way that kept the bore round, which let the ring or rings transfer more heat from the crown to the bore. To paraphrase Pontiac, "Rounder is Better".

 

[Crofter]

Have read in another post somewher about using acid that will selectively remove any aluminum galling and perhaps slightly etch any glaze on the chrome - nikasil of the cyl. Don't do it on your lap though.

Frank

 

[bwalker]

Crofter, Muiritic is the acid that removes seized on aluminum. I have used and it works pretty good you just have to make sure you clean it properly when your are finished.
TZ, I work in engineering also. I know for a fact I am correct on this and I will try a dig up some sae papers on what I have described.

 

[Tzed250]

Papers

The inside of my YZ250 cylinder can't read SAE papers. It is not tapered, and it is not oval. Thanks anyway.