compression numbers, how bad are these Options

[mobymutt]

Just did a compression check, here's what I measured:

108, 120, 96, 85

I've got a stock 1.8L, but would like to build a 1911 or 2056 in the relatively near future. Hopefully I'll be ok for another year or so with the current setup.

[DM_2000]

I don't do the often repeated "add oil to the cylinder to check ring sealing" Also see below about rings being matched to cylinders.

Oil or any other non compressible liquid added to a cylinder will raise compression ratio because cylinder / head volume has been reduced.

As rings wear, oil will naturally be in the cylinders so adding more 'aint gonna make things seal better.

For a leak down test you don't need a fancy gauge setup. Many compression gauges have the same quick connect fitting as a air compressor hose. Remove the check valve from the tip of the compression gauge hose with a tire valve tool. ( don't lose the check valve, it has a way lighter spring than a tire valve. )

Thread the hose into a cylinder, turn the engine to piston at top , both valves closed. Apply air ( 100PSI is an good even number but anything from 75 to 125 would be fine ) in a quick burst while watching the crank pulley / flywheel. If it turns, rotate in the opposite direction and try again.

When you are able to keep air applied without the engine turning on it's own, listen for air leaking out.

Slight exhaust valve leakage is common on mid mile motors.

Ring leakage is always present and gets worse at the engine ages.

Leaking out the intake will really reduce power.

Leaking between the head and cylinder needs to be addressed.
~~~

As for rings being matched to cylinders, it is possible to remove pistons from cylinders and reinstall without fear of leakage.

Piston rings slowly rotate as the engine it running so the perfect gap stagger of a new engine is soon lost. I've worked on countless engines across most brands and none retain the factory gap stagger.

The only rings that don't spin are 2 stroke piston port engines as if the gap made it's way to a port it would snag.

I'm pretty sure Chrysler did tests in the 50's / 60's with a radioactive pellet in a piston ring to determine ring rotation.