Small Engines (Lawn Mowers, etc.): leak down test, compression stroke, leak down tester

Question
Hi Eric
I recently got a new leak down tester and I experimented with it a little
today on a new tecumseh 9hp engine. I got the piston at TDC and
aired it up to 100psi. I had a drop to 85psi. I’m not sure I was at
the exact tdc, but the piston would stay up without holding the pto
or flywheel. I put low pressure in the cylinder at first and moved the piston
up and down a little till it would stay up without holding it. Piston was
on the compression stroke.
I could hear air coming out the muffler. Is it normal for some air to escape
through the exhaust valve. The engine starts and runs fine. Help will be appreciated
Does the compression release have anything to do with the exhaust valve leak.


Answer
It could be on the compression release or you may have the piston at TDC with the valve overlap.

The leak down tester I have tells you to perform the test at TDC on the compression stroke.  There should ber very little if any valve overlap on the compression stroke.  Do you havn an OHV engine or L head engine?

Check out the following link on compression:
http://www.cpdonline.com/692509.pdf
Let me know if this helps.
Eric