What cylinder mods are required to fit the more readily available RS125 pistons into an NSR250? Why is this a good or bad idea? Your expertise is appreciated.
Thank you _________________ Two-strokes and its all over!
The barrel itself needs very little modfication. The RS/F3 piston is alittle shorter than the NSR one so the barrel needs to have its base and head gasket faces mechined to bring squish, port timing and head volume back into check.
There is also the trouble with what RS piston to use, the later pistons having a longer skirt that will foul a MC21/28 crank. The earlyer type using a shorter skirt but with a off set pin.
The RS piston normaly also uses a 14mm pin, the NSR is 15mm. This means finding a new little end bearing.
Then there is the matter of rings. The RS/F3 ones being just a little over 0.8mm wide if i remember right meaning I'm replacing mine every 150 miles. _________________ If I have to take the carbs off once more...
I have a set of 15mm pin A kit pistons which will fit the NSR stock crank. I haven't fitted them yet (had them 2 years!), but the cylinder will need shortening to get the timing and head volumes correct.
NX5 pistons may work, but you'll need to check ring end position to make sure it doesn't fall in the port.
VHM have flat top RS125/250 pistons that weigh nothing, use a 15mm pin and are horribly expensive! They also run a super low friction 0.7mm ring. They (VHM) also have dome top RS125/250 15mm pin pistons & 0.8 ring, but are out of stock. Again they weigh nothing. I'm trying to negotiate a decent price.
Well, that's right Brother Steve. Looks like a 28 piston...has two rings like a 28 piston...even has the coated crown like a 28 piston, but it sure ain't no 28 piston!
They are a secret Andy. Maybe we're just making this all up. Maybe the wall thickness of the HRC pistons aren't 0.5mm thinner than the stock ones. Who would know? Who would ever have had the chance to see one? Maybe it's all a big wind up A bit like those cheater cranks eh Steve?
I think we should have a special room for Steven, Matt and Andy where they can post all their mysterious maybe/maybe not F3 stuff.
It should be closed to everyone else as they don't want to tell us anything anyway
As if it isn't enough to make everybody envious, they don't even do the only mitigating thing: give us details.
Nobody even understands them any longer. I think they have formed a boys club with secret language, handshakes and pistons _________________ Poul
"If Life Gets Boring, Risk It!"
MC21SE, KISS box
MC21SP, HRC box, racing loom
Wait till they tell you about the bing bang ignition unit that HRC never made... _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
Well I know that Steve has made (or will make) tooling to rephase the crank at XXX degrees. I know the project outline, but obviously Steve's not gonna give me the full story Maybe be needing a couple more of those RS/Dash rotors eh mate?
Going back to unobtainable HRC stuff, there's an HRC MC28 swingarm in my shed that Paul stuck his name on as soon as it turned up. He's desperate for me to fit it, but I'll keep him sweating
The HRC swingarm is neither here nor there in my boof as it's 28 stuff and doesn't really strum my banjo, but what does annoy me is Steve's MC18' four bolt factory clutch I hope it breaks
Oh, and Andy's full on factory MC16. There's simply no emoticon available for feelings on this one.
I can take two bolts out of my clutch too, what's so special? _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
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A bit like those cheater cranks eh Steve?
Maybe be needing a couple more of those RS/Dash rotors eh mate?
I hope it breaks