LegendsRacer - Legends & Bandolero Racing Forum
LEGENDS => Engine Care & Tuning => Topic started by: Legend732 on January 11, 2018, 01:05:14 pm
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First time leaking one of these engines and here is my question and appreciate any help:
I am turning the engine and at TDC/compression stroke with the cam lobes away from each other and the piston at the very top. Using 100psi into the gauge, I put air into the cylinder and it is moving the cam lobes almost a 1/8 of a turn thus opening the valves and is not allowing an accurate reading because it is pushing the piston back down. Is there a way to stop this??? My valves are adjusted correctly and the engine is at a warm temperature.
Also I am attempting to do a compression test on the cylinders and have the plugs in all the cylinders except the one I am testing. The engine is also warm as well. I am finding a low reading of 120psi-130psi across the board. Is there anything I need to do besides have the throttle wide open when testing?
Really appreciate the help and any response given.
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If air is pushing the piston down, it is not on TDC.
If on TDC, the air cannot force it down. It can be very difficult to get to TDC on these engines as the are very short stroke compared to automotive engines.
Randy - RPM
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I would assume it is pushing the piston down as it is turning the cams?
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I would also suggest removing all spark plugs when doing compression test as that will allow starter to turn engine over at a maximum speed for longer duration. Also, make sure compression tool hose seal ring is in good condition and not cracked. Sometime a little silicone grease will do the trick if seal is on the dry side. I can only assume that choke is not applied either when performing compression test. A little more history in regards to your engine would be helpful as well. How old? How may races? Seal or unsealed?
Good luck!
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Here is my experience:
Compression Test -- Remove all of the spark plugs. Either remove the carbs or have the butterflies 100% open. Put a battery charger on the battery so the starter turns the same RPM throughout the test. Check compression on each cylinder.
Leakdown Test -- Remove the spark plug for the cylinder you are testing. Use a wire, stick, or ideally a dial indicator to find top dead center. Run the leakdown test. I own a cheap leakdown tester. I've heard some people say that you need a very expensive one for this test to work properly. My tester always shows every cylinder in the "green" zone of the gauge.....even with an old motor.....
Hope this helps.
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Thanks all for the responses and great feedback.