Machining the head/ Boosting compression

RLorange

New Member
Jun 21, 2008
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Australia
I am considering machining the top of the cylinder (the head) down by a millimeter or two on a lathe to boost compression. Has anybody tried this? There is a bloke from Australia who has apparently with success.

Shouldn't be too difficult and should work fine... bit of a risk tho! Hmmmmm
 

RLorange

New Member
Jun 21, 2008
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Australia
Shouldn't be too hard Just take the cylinder to a metal turner. I think it would be a good idea to tread cautiously. The extra compression might rip a head bolt right out of the engine block! I stripped the engine block thread just by over tightening a while back, luckily I had it heli-coiled back in place
 

Ilikeabikea

Moderator
Staff member
Jan 27, 2008
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Norman has a piece of glass with sandpaper glued to it that he uses. It removes metal real nice and slow. He keeps it wet and soapy...................
 

Easy Rider

Santa Cruz Scooter Works
Jan 15, 2008
2,144
4
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Nor*Cal
We done a few and the best one we did was around 70 thousand of an inch. We even redomed one and it works for a little bit but we found out the the head bolts (which are made of cheap metal) stretches. Then leaks and blown head gaskets occur.
 

Norman

LORD VADER Moderator
Staff member
Jan 16, 2008
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pampa texas
going to a thinner head gasket will up the compression and a thinner base gasket will up the compression and change the port timing a little so with out taking metal off anything you can play with it until you find a combo that you like. when going to a thinner gasket make sure you don't ram the piston into the head when the piston is a DTC, Modeling clay put in the piston will tell you how close your getting to smacking the piston into the head and it will smack at the pistons edges and not in the center. So start playing and see if you can make a mild nice riding and easy to start 2 stroke into a nasty chain snapping clutch burning monster.(^)
 

RLorange

New Member
Jun 21, 2008
127
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Australia
I ordered a new cylinder which was taller than my old one so what I am trying to do is get it back to normal and maybe a little bit meaner. Hence the 1mm or 2 cos right now my new cylinder is weak as and compression is less than normal by a lot.

Just removed the lower gasket and replaced with silicone and did some wet n dry shaving of both the head and cylinder. I am now back to normal and a bit extra.

I agree with the head bolts being weak. My engine supplier has his engines fitted with high tension steel ones and has them lock-tighted into the engine block. I have heard that putting a tuned pipe on can blow engine bolts as well I am hoping this wont happen with my tuned pipe which I am hoping to get going real soon now :)
 

nogoodnic

New Member
Jan 29, 2008
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Shelby MI
forum1.freakbikenation.com
There was a guy on Motokruisers about three yeard ago who milled a head and at first he reported alot more power but within I think a month he cooked his piston. I don't have any details and the article has been lost with the forum so this info is from my falty memory and thats how I remember it...Kelly