MC21 Cylinders

**Thu Jun 02, 2005 7:29 am » Post: #1 » Download Post**

What is the difference between MC21 wet clutch cylinder and dry clutch cylinder? Why aren't they interchangable? Either, I got the same cyclinders on both motors and the one with wet clutch are the wrong ones. Vice Versa?

**Thu Jun 02, 2005 11:11 am » Post: #2 » Download Post**

I assume you mean the barrels, and not some other cylinder related to the clutch?

If so, the SP bikes had dry clutches, and the SP cylinders are slightly taller than normal. All wet clutch bikes came with shorter cylinders, which have a higher compression ratio. Don't mix the two on the same bike, but you can run both of either.

It does get a bit more complicated as the SP heads were different too...
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MC21SP Plaything
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Triumph 9551 Daytona Big boys toy
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GTS1000 oddball

**Thu Jun 02, 2005 12:22 pm » Post: #3 » Download Post**

Dave - Do you know why the sp would come with lower compression than an R?

**Thu Jun 02, 2005 1:06 pm » Post: #4 » Download Post**

I dont, no. Several possibilities:

Reduce power for the restriction.
Remedy reports of blow ups with poorer quality fuel.
Race homologation.
It was friday in the design shop and they forgot a decimal place. Laughing

_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

**Thu Jun 02, 2005 11:56 pm » Post: #5 » Download Post**

my understanding si the compression on an r or an sp is the same , but an r has short barrells and long heads and a sp has long barrells and short heads , so probs only arise when barrells and heads don;t match

**Fri Jun 03, 2005 12:19 am » Post: #6 » Download Post**

I read that the R cylinders are .2mm shorter, and the SP heads are .2mm shorter. Don't quote me on that though...
What it meant is, with production or SP racing, you could put R barrels and SP heads on, for better compression, and still be inside the rules...
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The Chopster

**Fri Jun 03, 2005 7:32 am » Post: #7 » Download Post**

I measure the R pair with a Dial caliper and they are .010" shorter than my other SP pair. Maybe the previous owners of both motors put wrong set of barrels. Hey at least they were matching set meaning same height barrels. As for the heads, who knows. Can you tell which one is for what base on the numbers at the top of the heads? Also HRC Part #s- What is meant by 06122-kv3-680 or 830. What does the last 3 digit represent?