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Compression

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Hello, I just bought a 912H and I tested the compression in it and it was 35psi. Then I went and did it to my 716H and it was 30psi. I then went to my B-112 and tested it, it came to 100psi. What should be the right compression for the Kohlers? What might be the problem? Would it be the rings? Thanks for the help! William Jordan

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Guest
Hi William, Not sure your getting an accurate reading as I think the those engines have compression release valves on them. But I do think abou 100 is good but I just can't remember to be sure hopefully someone can advise you more. >>->happyjack<-<<

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Sandy_Lake_Imp
Happyjack is correct, the Kohlers hav a comp release built into the camshaft. Kohler has a tool to measure leakdown of air as it is hooked to an air compressor. This indicates engine condition. You can also remove the cam gear cover & temporarily disengage the comp release & strap it down with a zip tie to check compression.I believe the intent was for app 40 to 45 psi with an active release. We had to "adjust" many when the tractors were uncrated but that is another story. Bill

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Al
William, Both Briggs and kohler use a compression release. Briggs is a little bump ground on the cam lob that lifts the valve off of the seat slightly on the compression stroke. The Kohlers use a mechanical release built in the cam lobe with a lock and a bar in a recess in the lobe. We expect to see about 50 to 75 lbs. It will be lower is the compression release is a little high and higher if it is worn off. If you see cranking compresion of 100 lbs or more in a Kohler the compression relief arm needs to be bent up a little. [We do these through the timing gear cover] With this much compression the strater will have a hard time turning it over and it will act like it has a weak battery or a weak starter. Compresison is one of the first things you should check if you go to start the tractor and the starter has a hard time turning it over, or you have to hit the starter a couple of times to get it over compression the first time. Compresson release is often the culprit. On a Briggs this is caused by excessive valve clearance on the intake valve. The little bump then never lifts the valve off the seat. One other thing. When checking the compresison do not use a guage with a hose. Use a guage with a short stem that pushes or screws in the plug hole. The guages with the hoses will read up to 50 pounds low, depending on the volume of the cylinder and how long the hose is. The problem is the check valve is up at the guage and when you screw the hose on all of the air in the hose acts like additional air in the chamber when the piston is clear up, reducing the apparent compresison ratio and lowering the readings. If you use one of these automotive guages with a hose on a small 2 cycle string trimmer engine and engine with 140 lbs may only read 80 lbs on a guage with a hose. Good luck, Al

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Al
Thanks for the help guys. It really helps me out alot! Al, I used a gauge with a hose when I did my testing. I will see if I can get one with out the hose and retest them all. Thanks, William Jordan

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Guest
i know older b&s eng have 110 to 80 psi to be good to go

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