Cylinder Head Compression Tester

[GraemeSmith]

This shows the head testing jig I made for the AeroVee. You can do similar for other engines with separate heads from the cylinders.

When the compressions head south. Is it the valves or is it the rings? Or both? And did you lap those valves properly last time you lapped them?

Time for the Cylinder head compression tester. (Click on each picture to see as intended)

I used 3/4" birch ply for the base, circles of ply that were a very snug fit in the cylinder head, high enough to allow the head to bolt down tight and 1/8" plumber's rubber to give the heads a "gasket" to sit and seal on.

Threaded rod bolted to the base with big load spreading washers underneath represented the cylinder studs. Torque the head down using the normal torque sequence in the manual.

Fit plugs to the "bottom" plugs. Apply compression tester at the top plugs.

If you have a leak - like here - you can cup your hands over the exhaust or inlet ports to figure which is leaking - it is USUALLY the exhaust.

If you can service the head, getting the valves properly lapped - it is pretty easy to get a test result of 80/80. With a known tight head - when fitted to the engine - the next compression test will tell you the state of the rings.

[daleandee]

I used to check my VW heads for leaks by blocking the head level and pouring in a little 100LL mixed with MMO. It was easy to see the leaking valve as the thin fuel would seep out of the port for the offending valve.

Dale
N319WF

[Area 51%]

A similar device might be handy to check the cylinders before going through the cost of a set of head gaskets and trouble of re-installing the heads only to discover the rings are bad.