I've got a potential line on a couple of mc21 bikes, with around 25,000km on them. Providing that they are currently in reasonable running condition right now, and assuming they have not recently been rebuilt or anything, what kind of parts should I expect to need to replace?
I see a lot of talk of crank bearings, what's life expectancy on those? Is that the only real area of concern in the bottom end?

thanks!
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n00b

Honda say pistons and rings last 10,000kms, cranks 30,000kms.
At 25000kms you'd be surprised if it'd never been apart for something.
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chris_s wrote:Is that the only real area of concern in the bottom end?

It's a 2 stroke, the whoe thing is a concern

But yes youre right, its only really the crank you need to worry about. barrels can be replated, pistons can be replaced as can most other running parts.

The new crank however is an exspensive bit of kit and finding a good second hand one is very hard.
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If I have to take the carbs off once more...

Is it the crank, or crank bearings that typically need replacing on a schedule? I see new bearings in the classified section.
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n00b

I don't know of anyone who would do crank bearings just as they were scheduled.

Be very wary of anyone else who says they can locate bearings and rebuild your crank, the parts they are using are almost certainly wrong as the real Koyo parts are not available to retail, as detailed here you'll either get bearings without the locating pin and /or ones not rated to a high enough rev limit.
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I see

so is it possible that when this "limited supply" of bearings runs out, everyone will be out of luck as far as rebuilds? Or are they still available from honda aswell?
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n00b

They're not available from Honda and never were, Honda say the crank cannot be rebuilt and should be replaced as a unit.
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I'm glad fonty pointed this out. Acording to Honda the cranks cannot be rebuilt and no parts are available. But there are people who do rebuild them (such as NSR-World). About all that can be done is to replace the bearings. If the journals are worn or the rods are bad, then you can't do anything. When I faced this decision last year I calculated that it cost almost as much to rebuild a crank as it did just to buy a new one. In the end my crank wasn't even rebuildable since the journals had rust and both rods were bad. So I bought a new crank and sent it off to Falicon (in Florida) to be balanced and blueprinted. Now I have a $1,400 crankshaft; but the bike idles as smooth as a I4 motor, if not better.
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james
Its not how fast you go...Its how you go fast.
MC21 Rothmans
RS250
RC31
CRF250X
748R
Porsche (many)
http://members.rennlist.com/j911brick/rennlist3_002.htm

My NSR hasn't run for 7 years and the crank is a huge concern.

Who sells new cranks?

tyga has them listed for like 300#
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n00b

apexxn wrote:My NSR hasn't run for 7 years and the crank is a huge concern.

Who sells new cranks?

Honda, only.

I paid about $750 for mine. Contact www.redline-ci.com
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james
Its not how fast you go...Its how you go fast.
MC21 Rothmans
RS250
RC31
CRF250X
748R
Porsche (many)
http://members.rennlist.com/j911brick/rennlist3_002.htm

chris_s wrote:I see

so is it possible that when this "limited supply" of bearings runs out, everyone will be out of luck as far as rebuilds? Or are they still available from honda aswell?

Thats about it, once Honda stop producing cranks (they already have for the MC16 and MC18) and the bearinsg run out, which they will once the cranks stop then its doesnt look good.

We (Andy and myself) are stock pileing them and I'm sure Matts got a few tucked away for when it happens.

This goes for the RS250 as well, no more NF5 cranks from Mr Honda.
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If I have to take the carbs off once more...

is there not enough market for an aftermarket fabricator to pick up the slack? I come from a honda touring car racing background, and you can pretty much build an entire motor using aftermarket parts, including the entire block!

Maybe after honda stops selling the crank kits, koyo will play ball as far as releasing the proper bearings to consumers.
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n00b

I have seen cases where a manufacture reproduces a part if demand is high enough, but for the most part they want you to buy their new products. Don't count on Honda reproducing a crank for the NSR. 21/28 cranks should be available for several more years though.

The cranks can be fixed, or even made from scratch, but currently the cost is about twice that of a new crank, if not more.
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james
Its not how fast you go...Its how you go fast.
MC21 Rothmans
RS250
RC31
CRF250X
748R
Porsche (many)
http://members.rennlist.com/j911brick/rennlist3_002.htm

Cranks wont be around much longer... the '21 crank now is the '28 crank and '28 parts starting this year have started to be discontinued.
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If I have to take the carbs off once more...