Compression totally over the top

[randy]

Sure, but listening at the carbs / pipes identifies WHICH valve

[planedick]

Rings

If it's rings the exhaust and noise will come out of the crankcase vent.....

[ClarkGriswald]

Never thought of this one, Cant wait to try it hehe.. thanx .(the leakdown).

[Ivan]

My first reply was from my PDA phone, which is a tad difficult to type on.

The oil in the cylinder will give a better seal on the rings and thus yeild a higher compression reading if they are the culprit. It only works for a few turns, then it starts to bleed away as the oil is pushed past the rings in to the case.

The tool I was talking about is, in fact, called a Leakdown Tester. Clicky!
These regulate the air going into the cylinder and measure the difference between regulated and pressure in the cylinder and give a percentage of pressure lost. Pretty handy tool, and gives an accurate reading of what is happening in the cylinder.

The last trick I spoke about is using the compression gage hose and just hooking shop air on it. This is putting full shop air in the cylinder and will make the engine move if it isnt on TDC. Also, the little schrader valve in the end of the hose must be removed, since it doesn't allow air into the cylinder and keeps the needle up on the gage until the pressure release is hit. While this doesn't give a percentage readout, the air rusing out of the exhaust or intake is a very reliable indicator of what is wrong in the engine.

As for the air rushing out the crank vent, most engines I have worked with have that happen even on a good engine with good rings. Not sure if there is enough space in the ring gap, or if the pressure on the ring while not moving allows more air by, etc. But most engines will blow by the rings with shop air in the cylinder. Don't get alarmed if there is some air escaping into the crankcase, unless it is blowing a full gale force out.

Maybe that helped confuse things up a bit.