I have realised that I'm terrible at searching for things on the web! cause I'm sure this topic has been discussed.

What I'd like to know is what parts are not interchangeable in a MC28 R and SE/SP engine? also what parts are not interchangeable between the MC21 and MC28?

Really what I'm trying to achieve is rebuild a MC28 engine, but have more choice in replacement used parts, as Australia has not got much in the nsr department. I also have a mc21 that i have some spare parts for that i was thinking of using.


Ill list the ones i can think of.

Clutch and clutch side engine casing.
Cylinders


Thanks heaps Guys,
Markus

Really, all the parts between the 21-28 are about the same except things the frame, swingarm and electricle system. But if you want to change from mc21r forks to mc 28sp forks, then you will need the brakes as well. The clutchs should change from and R to SP with no problem, as long as you have all the parts.

Your questions should be more specific.
_________________
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

j911brick wrote:Really, all the parts between the 21-28 are about the same except things the frame, swingarm and electricle system. But if you want to change from mc21r forks to mc 28sp forks, then you will need the brakes as well. The clutchs should change from and R to SP with no problem, as long as you have all the parts.

Your questions should be more specific.

I thought my Question was specific enuff but maybe not? , firstly the question revolves around the engine! not the frame, swingarm, electrical system or Forks.
I know for a fact that the cylinders are not the same for a mc21 and mc28. I also know that the cylinders from a MC2x R engine not the same as a SE/SP engine. what id really like to figure out is what parts are not interchangeable between the mc21 R and SE/SP and the mc28 R and SE/SP.

Thanks,
Markus

You couldcross referance the parts numbers from the parts manual.
_________________
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

Bottom end wise almost everything is interchangeable. About the only thing that got altered was the oil pump from early to late '21's. The late '21's being the same the the '28.

Barrel and head wise the two are pretty much the same though the porting on the '28 cylinders is just a little less peaky compaired to the stock 21. However the difference is almost nothing. The '28's do seem to make alittle more in the middle over a 21 of the same spec though.

I can never remember which way around it works, but R cylinders I think are shorter than SP cylinder so while they can be swaped you must use the right head with the right cylinder. Best way though is to measure them up and replace with the same hight. Just because some says the cylinder is off an SP or R doesnt mean it is lol
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If I have to take the carbs off once more...

SP barrel, SP head normal compression
R barrel, R head normal compression (both the same in fact)
R barrel, SP head higher compression.
SP barrel, R head lower compression.

R barrels are marked H and 86.3mm tall. R Heads are also marked H
SP barrels are marked L and 86.5mm tall. SP heads are also marked L

You can get .4 and .6 HRC base gaskets as well as the std Honda .5 ones.

To illustrate Steve's point I have a L barrel here (should be 86.5mm tall) and it measures way under 86mm.
It also has a cracking score mark down it where it seized at around 100mph!
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Please do not PM me technical questions, if you can't find it on the Forum start a thread

That one was mod'ed to run with an SP head though

But thats why you shouldn't take for granted what they say on the side.
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If I have to take the carbs off once more...

Regarding cylinder height, there have been cases where the plater polished the ends of the cylinder thereby decreasing the height, so it pays to check the height no matter what the cylinder is marked.

There have been a thread with the exact measurements and markings on this site.
_________________
Poul
"If Life Gets Boring, Risk It!"
MC21SE, KISS box
MC21SP, HRC box, racing loom

Hey guys thanks for your help in this, this will allow me to buy another engine and strip some parts from it. im only a 'weekend mechanic' and really appreaciate your help. ill keep you updated and im sure ill need some more help soon.

Cheers Markus