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Old 10-08-2011, 05:29 PM   #33
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Joined: Jul 2008
Oddometer: 703
I have never measured compression just by turning the engine by hand, so not sure if you would get a reading or not. That said, 70 psi WOT cranking is not good. I have not measured compression on my ninja motor, but I have on similar displacement liquid cooled twin cylinder DOHC 11:1 ish CR engines and 200 psi not uncommon. Heck, old air cooled 2 valve 8.5:1 CR engines will crank out 130-140 psi.

One more thing on the compression, what altitude are u at? If you are 12,000 ft you might get a reading of 70 psi.

You could possibly make a temporary leakage check tool from your compression gauge or from an old spark plug, I have done both. Remove the gauge and check valve from the hose of the compression tool. Find some fittings and hoses to connect regulated compressed air to the gauge end of the hose. Now you can apply compressed air (100 psi is good) to the combustion chamber. Set piston at TDC and apply the air pressure. Listen and feel for air escaping through the intake, exhaust and oil fill. There should be only a very small amount of air coming from any of theses openings. This will not give you a leak % value, but will identify gross leaks. If your compression reading of 70 psi is correct, this will find your problem.

Using an old spark plug is similar. Break off the top of the plug and gut the hex and threaded part. Weld or braze a 1/8" pipe coupling to hex section (of course the weld has to hold air) and you have an adapter to get compressed air into the engine.
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