How many inches of intake manifold vacuum is considered normal for this engine running at idle?
Thanks, John ANSWER: COMPRESSION AND VACUUM Hi John – As far as compression – the key thing you are looking for is even readings. While it is certainly likely that a worn engine will give lower reading than a fresh engine, if they are even, you can assume your valves and rings are doing a decent job. When valves begin to leak it will be far worse in one or two cylinders – so you will see a large variance in compression readings. I think 65-70psi is probably absolute max for a Series 11. If you get much below 50, you would want to investigate further. I tend to use cylinder leakage tests far more than compression tests. This involves introducing compressed air into the cylinder and measure the quantity of air leaking out versus going it. There are differential pressure gauges that measure this. Or simply silver soldering an air line coupler fitting into and old spark plug body and pressurizing a cylinder while it is at TDC will tell you a great deal. The air will leak out. Usually it le
