hi all seized my mc21 up again but this time don't no why (bottom cylinder same one) she had been running really well then first ride out in the sun this year and nipped up two miles down the road all warmed up didn't even get on to main jet?

ok then don't really no a lot about nsr250s but im ok with 2strokes my question is, my top barrel and piston are fine its a B barrel but i have a spear A barrel with the correct head for it.

can i run the B top and A bottom together ?

also david silver guy on the phone said i need to run B pistons with an A barrel !!! is that right sounds mad to me what is the differents between A and B

thanks

Maybe it was a bit colder than you thought - what were the temps last time you ran it?

Temp was up to were I ride it normally is and I didn't get on to main jet can you buy bigger slow jets? There was quite a bit of rusty tank crap in the floats? I did take the head off ones and I didn't put a new head gasket on but that was in the summer last year

Any idea about the barrels

Yep, you run B pistons in A barrel, no mark pistons in a B barrel, and D pistons in a C barrel, sounds weird, but thats how it is.
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Proud Father of , 05 ktm 400exc supermoto 2018 honda crf rx supermoto

I would be checking ring gap and piston clearances rather than relying on a A, B, C or no marking.

Without knowing the full history of the cylinder, it may have been replated with a different tolerance.

Hello, Marcus asked what is the differences of these barrels ?, it does sound weird and makes it more complicated, is it just about bore size as in a 4 stroke where you have plus sizes of pistons.

Like some other forum members I know nothing about 2 strokes, so all the info the better.

D.

I think you first need to identify why it has seized. Where on the piston has the seizure occurred? There is no point replacing a top end if you don't pin point what the cause of the seizure was first.

Yes I agree I've now put clear oil line pipes on maybe it wasn't up to temperature, it munched most of the piston opposing the exhaust port, the little end bearing and goodwin pin have only done 800miles can I use them again or not because of the seizure

Thanks for the info guys

I was asking about the air temp, rather than the engine temp.

If it was cold then the engine would have run lean and that could have caused the siezure as well as causing it to take longer to get up to temperature.

Not sure I understand "didn't even get onto the main jet" statement?

Check your pistons failure against this

http://www.thetuningworks.co.uk/assets/Piston%20Diagnosis.pdf

HTH

It's impossible to advise on reusing any parts without physically inspecting them, however we would personally advise against reusing anything following a top-end failure.

For the sake of around £20 for a gudgeon pin and small-end bearing, why risk it?

As nxrsr20 has already advised, given the NSR's age now, unless you can confidently identify OEM Honda plating vs. aftermarket plating, you are better off matching a piston to the barrel with the correct clearance, rather than with the "correct" ID for it.
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Andy.
NSR-WORLD.COM

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