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D piston in larger barrel - what rings do I use?


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craigsutton

 
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D piston in larger barrel - what rings do I use?

Sat Mar 20, 2010 6:27 pm » Post: #1 » Download Post

Matt @ Tyga (or was it Paul?) told me he used to run D pistons in larger cylinders for extra clearance. Since I had a piston nip up on me last year I decided to do that even though it was more my fault than the bike's. However, I forgot to ask what rings to use - do I use the ones for the D piston or the appropriate cylinder, or doesn't it matter? Thinking about which would work better makes my head hurt. I'm putting the engine together now and have the D rings on the D piston so please help!

Thanks for any advice.
Craig
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Dave Ett
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Sat Mar 20, 2010 6:34 pm » Post: #2 » Download Post

The right ring is the one which when fitted gives the right ring-end clearance...
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cgallant
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Sat Mar 20, 2010 6:48 pm » Post: #3 » Download Post

In other words, you will want to size different rings, and make sure your ring end clearance is proper. You can use a small file to take some off to make it just right.

That and the NSR250 only has once set of rings (rings are not matched to pistons/cylinders).
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craigsutton

 
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Sat Mar 20, 2010 6:49 pm » Post: #4 » Download Post

Of course I typed this out as fast as I could so it was posted while I checked the online engine rebuild section. And naturally it had my answer - all the rings have the same part number Embarassed So now all I have to do is fit them up and I should be good to go! Yay, don't have to wait for another order to finish the engine.
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cgallant
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Sat Mar 20, 2010 7:03 pm » Post: #5 » Download Post

You got to watch our for those tyga boys, they tried to sell me a set of power bands and some muffler bearings...

At least I think that's what they said, I couldn't really understand their typing, it was all in that british language or something.
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craigsutton

 
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Sat Mar 20, 2010 7:10 pm » Post: #6 » Download Post

Tyga has bower bands??!! I'll put 2 on each cylinder!!
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Neal

 
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Sat Mar 20, 2010 7:46 pm » Post: #7 » Download Post

What ring end gap are you working to ?
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craigsutton

 
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Sat Mar 20, 2010 8:09 pm » Post: #8 » Download Post

The online rebuild section says .30-.45mm so as long as I'm somewhere in there I won't touch them. (I'd rather have a factory end than one I've carved myself.) Any suggestions for a "race" setting? The tracks I'll be at are for the most part short (1/4 mile straights) but I'm hoping to visit some longer ones this summer, namely Road Atlanta. Whether or not Charles will admit to knowing me when I get there is another question...
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Neal

 
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Sat Mar 20, 2010 8:21 pm » Post: #9 » Download Post

I work towards 0.24mm and change rings when i get to 0.35mm . I notice a difference of 6bhp on the dyno with fresh rings only .
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craigsutton

 
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Sat Mar 20, 2010 8:23 pm » Post: #10 » Download Post

Wow....ok thanks. Maybe someone will chime in with power vs reliability (while flogging like I plan to).

The engine is in and I'm connecting everything up now.
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Neal

 
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Sat Mar 20, 2010 8:38 pm » Post: #11 » Download Post

You don't want the piston too loose as it will rattle in the bore and break the piston skirts . Make sure the bike is at running temp before you speed off . I have never measured the piston to bore clearance of a worn piston to compare results .
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Matt@TYGA
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Tue Mar 23, 2010 12:33 pm » Post: #12 » Download Post

My method was:

Short twisty circuit with no long straights = tight piston/bore, advanced timing, high comp.

Long fast circuit, flat out forever = loose piston/bore, retarded timing, low comp.

Reasoning:

On a short circuit with only short bursts of acceleration there's little chance of excessive heat build up/piston growth, so you can run a tighter clearance. The high comp and advanced timing is relative of course, but this gives good punch out of corners, but little over rev.

On a fast flat out forever track the opposite of above is true.


As for ring end gap, affecting the power. I'd say not a lot, if you're talking the difference between 0.24mm and 0.35mm on a new ring. The power loss comes from the loss of pressure of the ring against the bore when the ring is worn. A keystone ring does help here of course, as it is mechanically forced against the bore wall by design.
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Neal

 
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Tue Mar 23, 2010 4:45 pm » Post: #13 » Download Post

We use the same advice here in darkest africa ! Very Happy
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Andy
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Tue Mar 23, 2010 7:13 pm » Post: #14 » Download Post

Matt@TYGA wrote:
Long fast circuit, flat out forever = loose piston/bore, retarded timing, low comp.

I never knew you could fit a Seizuki ignition to an NSR! Very Happy
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Kieran

 
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Fri Mar 26, 2010 8:47 pm » Post: #15 » Download Post

ROTFLMAO
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