Cylinder Markings

**Wed Apr 01, 2009 9:43 pm » Post: #1 » Download Post**

I'm attempting to identify the cylinder configuration of my 1991 MC21 SE. I could clearly see a 'B' on the base of the right cylinder, but could not find a marking on the left cylinder. Or at least couldn't see it.

If the right is a 'B' should I assume the left is a 'B' also.

Thanks.

Skunkbait

**Wed Apr 01, 2009 10:04 pm » Post: #2 » Download Post**

Assumption is the mother of all cock ups!
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**Wed Apr 01, 2009 10:15 pm » Post: #3 » Download Post**

Maybe this will answer your question!

http://www.nsr250.net/forums/viewtopic.php?p=56129#56129
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Andy.
NSR-WORLD.COM

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**Thu Apr 02, 2009 1:48 am » Post: #4 » Download Post**

It helps.

Once again, I appreciate all the advice.

Skunkbait

**Thu Apr 02, 2009 5:59 am » Post: #5 » Download Post**

fontyyy wrote:Assumption is the mother of all cock ups!

Very True.

If you ASS/U/ME, an Ass (Arse) will be made of You or Me Wink

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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

**Fri Apr 03, 2009 3:57 am » Post: #6 » Download Post**

I assumed, and it cost me a piston, thankfully not a cylinder.
Actually I'm still a bit confused check out these pics.
Here's the cylinder, it has two hard to read stamps.
I think that if the B piston scrapes, it must be an A.

What do you guys think?

**Fri Apr 03, 2009 8:03 am » Post: #7 » Download Post**

You've really got to measure the clearance. You don't know that the barrel hasn't been replated, if it has the letter means nothing.
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**Fri Apr 03, 2009 8:15 am » Post: #8 » Download Post**

B cylinder. Heed fontyyy's advice, on bikes this old you cannot really rely on factory specified marks that may well have no bearing on the cylinders current state.

edit: spelling

**Fri Apr 03, 2009 10:46 pm » Post: #9 » Download Post**

I agree fontyy, how do I measure the clearance as I believe the pistons are not round, and what should the clearance be?
Cheers
Blair

**Sat Apr 04, 2009 1:49 am » Post: #10 » Download Post**

o o

Last edited by DifferentStrokes on Mon Sep 28, 2009 6:31 pm; edited 1 time in total

**Sat Apr 04, 2009 3:56 am » Post: #11 » Download Post**

Ha ha, I'll have to borrow the telescopic gauges and micrometer from work.
Does anyone have an idea on what the tolerances are?
Cheers

**Sun Apr 05, 2009 7:24 pm » Post: #12 » Download Post**

Youre quite right pistons are not round nor are they turned parallel.

You need a micrometer to measure the piston (a vernier will never be good enough, it would be like measuring barrel hights with a plastic rule!) and a bore guage to measure the internal dia of the bore.

The amont of piston taper as well as bore clearance and taper needed will depend on what type of work the engine is required to do.
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If I have to take the carbs off once more...

**Sun Apr 05, 2009 9:05 pm » Post: #13 » Download Post**

o o