Piston Rings

[5v3d3b0]

A question:
What is the difference between having 1, 2 or even 3 piston rings? The more the merrier? More compression?

[Ichy]

Different rings can do different jobs. Generally the top ones control compression and the lower oil supply.
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[Ben.]

top compression bottom oil/ lubricate the bore, middle is a bit of both...
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Race bike - R6
Road bike - sv650

[5v3d3b0]

So single ring pistons are shite?

[twotakt]

Apparently with a single ring has less friction and as such they can rev easier. Higher revs=more power (to an extent), so the easier that these high revs are 'accessed' the more power is available.

But apparently the single ring is under more 'force' and exposed to wear and therefore need to be replaced more often than twin or triple ringed pistons.

This is what I've read and I'm not 100% sure these statements are fact.

Ta,
Jack
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R.I.P. Tareree Shiimi, 1985-2008

[quacker_boy]

Generally most four stroke engines will have three sets of piston rings, the top two rings are compression rings and the bottom ring is the oil control ring which prevents oil getting into the combustion chamber.

Most two stroke engines have got two rings for compression as the fuel and oil is mixed and the big end, small end etc are all lubricated by splash lubrication.

You only really need two compression rings as the rings have gaps to allow them to be taken on and off, the bottom one is just used to stop the motor loosing compression trough the gap in the top ring. So no, you don't really need any more.

Why'd you ask?

I'm yet to see an engine with more than three rings, although some of the older members might have seen them like Stink, Sickpup, Kickstart etc...

HTH
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[.Chris.]

Certainly some pistons for the A-Series (car) engine use up to 5 rings, 3 for compression and 2 for oil control. Not sure if any bike engines use that many but I wouldn't be surprised if some of the old British stuff did.
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Chris
1985 Kawasaki Z550F

[5v3d3b0]

Not really asking for any particular reason. It just came to my head that I've seen single double and triple ring pistons, and I remember hearing single ring are best for performance. I guess I heard right. I'm guessing that more frequent top end rebuilds or at the very least ring changes will be required, so not really an option for an already delicate bike like the Rs 125...

[5v3d3b0]

Now that we're on the subject, What is the advantage of a flat top piston and head?

[quacker_boy]

[5v3d3b0]

Which means more power right?

[Rockhopper]

From years ago when i last built an A series engine i think it has three compression rings and then a three piece oil control ring.

As to flat top pistons and heads - well that depends on if that particualr engine is suited to that kind of mod - you need to speak to someone who is familiar with tuning your engine.

I'm not a 2 smoke expert i'm afraid.

[Wafer_Thin_Ham]