mc 18 fuel, and piston clearences

**Fri Apr 10, 2009 7:36 pm » Post: #1 » Download Post**

hi was woundering what fuel you guys use in your bikes is 95ron ok ,and does any one know whats an acceptable piston clearence, ive been told o.5 to 0.6 between piston skirt and bore does this sound right,
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**Fri Apr 10, 2009 7:39 pm » Post: #2 » Download Post**

0.5mm is somewhat excessive!

It really depends what the bike is being used for but something like 0.040/5mm is middle ground.
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**Fri Apr 10, 2009 7:54 pm » Post: #3 » Download Post**

it will be road use only i wat to run bike on spare pistons to make sure its all ok befor i put new in,as am still not 100% sure what caused seazure,but not sure what clearence should be every body has differnt opinions on it ,so you say 0.4 to 0.5 ,
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**Fri Apr 10, 2009 7:56 pm » Post: #4 » Download Post**

No I say 0.04-0.045mm
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**Fri Apr 10, 2009 8:42 pm » Post: #5 » Download Post**

StephenRC45 wrote:5mm is middle ground.

shake rattle and roll.
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**Fri Apr 10, 2009 8:44 pm » Post: #6 » Download Post**

Am I the only one that read your first post 0.04~0.045 Steve? Rolling Eyes

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Andy.
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**Fri Apr 10, 2009 8:52 pm » Post: #7 » Download Post**

It's what I've come to expect Rolling Eyes

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**Fri Apr 10, 2009 8:58 pm » Post: #8 » Download Post**

About time we start reinforcing the old "strongly technically biased" direction of the forum again before it slips into something more akin to 400 Gay Bike or other forums I think! Confused

Permission to quivver bottom lip sir? Wink

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Andy.
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**Fri Apr 10, 2009 9:24 pm » Post: #9 » Download Post**

Someone is asking is 0.5mm is OK for piston clearance, how's that not technical?
OK, it's not a good technical question and the real answer is the upper limit of the service data (max undersized piston to max oversized bore) is 0.1mm.
Min clearance that should ever occur (upper limit on piston size, lower limit on bore size) is 0.039mm.
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**Fri Apr 10, 2009 9:30 pm » Post: #10 » Download Post**

Someone's been reading his English manual!

Still interpreted "0.040/5mm is middle ground" as "0.5mm is middle ground" though, didn't you?! Wink

Standards are slipping.
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**Sat Apr 11, 2009 9:16 am » Post: #11 » Download Post**

Actually I interpreted it as 5mm (i.e. half a centimeter), which is what it says. But even I know thats a bit much.
Hence my comment.

And of course I've read the book, that's what I bought it for.
All this service info is pretty much unknown, people stress about A, B and C pistons yet if you put the smallest D piston (the smallest piston of the 3) ever made in the largest A cylinder (the largest of the 3) ever made the clearance would be 0.053mm. That's a bit sloppy but it'll work and it's got another 0.047 to go to reach service limit.
It's the other way round you'd get problems, biggest piston in smallest cylinder results in a clearance of 0.031 which is a bit tight.
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**Sat Apr 11, 2009 9:20 am » Post: #12 » Download Post**

No, it says 0.040/5mm Thats 0.040 to 0.045mm.

If it was 0.040 to 5mm it would be shown as 0.040-5mm.

Very Happy

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**Sat Apr 11, 2009 3:49 pm » Post: #13 » Download Post**

fontyyy wrote:Actually I interpreted it as 5mm (i.e. half a centimeter)

WTF? That's a joke, right? Shocked

**Mon Sep 17, 2012 11:12 am » Post: #14 » Download Post**

Read with interest tks. I have low comp and will be stripping down top end. From what you say if piston barrel clearance is within spec I can just replace rings or is it wise to always put new pistons in tks.

**Mon Sep 17, 2012 10:37 pm » Post: #15 » Download Post**

For stock pistons, 0.04/5mm as already proposed.
0.05mm for pistons with low silicon content like Vertex, Wossner etc

I would only feel comfortable with 0.08mm clearance as the service limit.
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