URQ quirqiness Compression testing

[Henry A Harper III]

> Won't just testing all 4, 5, 6 or 8 cylinders as the motor sits
> leave some
> valves open?
>
> Don't you have to turn the engine over to TDC or some position where the
> cylinder being checked has both valves closed?  Hence screwing in
> the compression
> tester in the last hole:  the spark plug?
> -Scott by BOSTON

A typical compression test involves inserting the compression measuring
device (pressure gauge) into each spark plug hole in turn and while the
gauge is in each hole, cranking the engine briefly with the starter while
the coil lead is removed to prevent actually starting up the engine. Thus,
valves opening and closing is pretty much taken into account. If the
crankshaft is not moving and you're measuring a cylinder's retained pressure
(usually supplied with compressed air not by cranking the engine) with a
gauge that is a leakdown test.