Question about 1991 kawasaki KR-1S

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Cylinder head skim

Hi folks, head was warped. My machinist has skim the head around 0,5mm. After this there was no edge round the combustion chamber an the squish was to less (~0,6mm). i am told him that the squish band must recessed into the head by 0.4mm and angled at 15 degrees. I thought a squish clearance around 1mm is safe. today he has finished the work. ok at home i measure the diameter from the combustion chamber (edge to edge). The diameter is exactly 56mm. Shocked the piston has 55,6mm. my old destroyed head has an combustion camber diameter from ~57,5mm !! ok my questions. why is the diameter from the standard head combustion chamber much bigger then the cylinder bore diameter? can i use the head with 56mm? the head skim was 0,5mm. to much compression now? ok i know... many questions and perhaps some stupid questions. I have a new crank, new coated cylinders and new pistons. i have no interest to destroy the engine with a bad cylinder head.... Pray thanks

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From my understanding, the combustion area of the head should have a diameter that is the same as the cylinder i.e. 56mm. If you took 0.5mm from a standard head, your squish would PROBABLY be Ok, however, you need to measure this. Its quite easy, poke a piece of solder wire in to the cylinder via the spark plug hole and trap it between the piston and the head by gently turning the engine over with the kickstarter by hand. Remove the squashed solder wire and measure with a set of vernier calipers. 0.8mm is about right and as Elf said, anything below this is getting a bit close. Do this for the front, back and left and right of each cylinder. Reducing the squish only has only a moderate effect on the compression ratio and does not require higher octane fule. I did this for mine and it was fine - so you 'should' be Ok.

Posted on Nov 20, 2008

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