The MC18 I purchased was rebuilt with single ring pistons, and according to the mechanic (a pretty well known nsr expert), it's no good at all. So I got him to order a complete top end kit from japan. He said I was pretty lucky because he mentioned something about it should have damaged the barrels over time but it must have seized before any real damage was done. I'm not sure if that was due to the single ring, or possibly a poor rebuild or maybe shabby replating. Anyway he didn't recommend the single ring at all.
do single ring pistons give higher compression ? because i was thinking that on a 2 stroke this will course pre ignition im i right about that or am i barking up the wrong tree
The single ring has less friction, but it wears out quicker. Shouldn't cause any damage as long as it's set up correctly. Which is key on any 2 stroke. Hope that helps. _________________ To much HP is barely adequate!
Theorizing here, but a single ring piston of the same dimensions will cause a slight drop in compression since there's only one ring to contain the gasses. Two rings means twice the seal.
I guess it's not much, and the reduced friction makes up for any loss of power.
Anyhow, so long as the piston is the same height from little end to piston crown I can't see how it'll have any effect on compression. _________________ MC21SP Plaything
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You get more life from a double ring piston. The compression is what seals the ring to the cylinder wall, causing it to wear. When the top ring wears too much, the compression bypasses it and seals the second ring.
I have Wiseco single ring pistons in my overbore, and they work great. Use a top-notch oil in good quantity, and that can greatly enhance your ring and cylinder life. _________________ Paul Herr
'88 FZR4/GSXR/YZF Frankenbike
MY BIKE PICS
I have no idea what application his single ring piston was originally for, but mine is actually an early 90's RM125 piston (but 2mm overbore). And yes, the piston crown is about 1mm closer to the wrist pin than the stock NSR piston. The cylinders will have to be turned down on a lathe to accomodate this.
I dont think there is any single-ring piston on the market that perfectly matches the NSR piston specs. So if your engine has single-ring pistons, you really should take some measurements on the piston and cylinder and match them to the stock NSR specs to see where you are at. Then, you will have to figure out what application the single-ring piston was for in the first place. _________________ Paul Herr
'88 FZR4/GSXR/YZF Frankenbike
MY BIKE PICS
Just had a barrell off my MC21...it too has a single ring piston! Was this a trend in racing or something? I have a good idea my 21 has been used for racing in the passed but I could be wrong.
Fenton, did you leave yours or replace with standard top end?
Best you (a) measure that barrel, and (b) pull the other one off to check that too!
If those pistons are indeed RM items, you run the risk of massive detonation if you replace them with NSR pistons and the barrels have already been machined to compensate for the single ring items. _________________ Andy.
NSR-WORLD.COM
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I was hoping someone was going to say...you lucky git, you probably have an eric gorr over bore .
I will get it all measured up and see how it compared to standard. Why is nothing simple, all this cos of a dodgy powervalve....guess its best I know for sure rather than an expensive rebuild!
Dave Ett wrote:Theorizing here, but a single ring piston of the same dimensions will cause a slight drop in compression since there's only one ring to contain the gasses. Two rings means twice the seal.
I guess it's not much, and the reduced friction makes up for any loss of power.
Anyhow, so long as the piston is the same height from little end to piston crown I can't see how it'll have any effect on compression.
Best to think of things in perspective here..
A single ring has the benefit of less friction so you theoretically get more performance but to be honest, the road going rider probably wouldn't notice anything great except a nasty bit of piston slap after a few thousand miles.
Running plated bores you would expect the ring to wear long before the barrel creating problems when the piston starts to rock about a bit - no bottom ring to support it any more and all the accellerated wear etc... - problems, problems...
They are designed to go into higher performance engines i.e. something like a TZ or RS and you would re-ring it regularly, even if they look good.
You can't really do this to a road bike with any sense of economic justification but sayng that, I've tried a set of Wiseco pro-lite single rings in the YPVS and it gave about the same top end power but the torque was up as was the mid range grunt and the compression has settled in at 145 - 140. Even after a 500 mile maintenance strip down there is virtually no blowby and the compression is steady but it runs a steel bore, not nickle silicon c.
I'd keep the single ringers if you can affort to maintain it - just coz it's different but if you want reliability and originlity (vanity) then use the blueprint item.
Bikes are there to be fun and we are all part time / wanna be race technicians, well I am at least and finding something off the wall in your bike is (I think) something very pleasant.
Any chance of some images chap ? _________________ These aren't the droids you're looking for.
Last edited by Binka on Fri Mar 17, 2006 5:42 pm; edited 1 time in total
Well you have to remember that not only detonation, but even just a "simple" seizure could completely destroy a motor! It's just lucky that the majority of the time it doesn't.
Remember too, that if bits end up in the crankcases and get into the bearings, then it's bye-bye crank as well! _________________ Andy.
NSR-WORLD.COM
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Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.
Its going to be mainly a track bike, with just the odd run on the road for testing, by the time my 28 is finsihed I wont want to ride an old fashioned 21 anyway!!
Will get it measured up then decide what to do with it.
Here is the pic (quite clear considering it was taken in a dark garage with a mobile !):-
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