So I parked my 2004 WRX up over a year ago and haven’t started it since. It was running fine when I parked it up. I have just changed the oil pump, water pump, cambelt and idlers. However, I still haven’t run the engine yet.

I have just done a compression check with all the plugs out and the throttle body fully open. I did this because my next plan is for mods and a remap and I wanted to check the engine health before throwing more money at it. Also I was worried if there was any damage from incorrectly rotating the N/S cams during cambelt change.

Cylinders 2,3,4 are all showing between 145-150psi. Cylinder 1 though was only showing 55psi. I couldn’t understand this. I tried a few more times, and some longer cranking. Then adding some oil to the cylinder. Eventually cylinder 1 has gone up to 75, 85, 90, 110, 145, and finally 150.

Can anybody suggest what caused this and if I need to investigate further and how? In between trying to sort cylinder 1 I have been reading lots of threads and trying to work out what is going on. I saw on a thread that a very rare occurrence of both piston ring gaps lining up could cause one cylinder to have very low compression?

 

I just went back out to the car and put a bit of oil down each cylinder, including cylinder 1 that has ready had some. I then did a compression test again on each cylinder. The results are between 160-170psi for all cylinders.

 

sticky compression rings on no.1

 

What does that mean? And do I have to do anything or was it just a temporary problem from not being turned over in so long?

 

Correct

 

This.

First thought as I was reading this or a valve not seating fully.

If the car is stood it's probably corrosion; Especially if parked in a damp environment (UK in general outside or garage with no damp proof membrane in the concrete), or worse over grass/gravel where dew hangs. Cone filters and open oil breathers won't help here.

Same can happen if engine is ran for short periods before laying up...moisture from combustion and fuel washing the bores from cold running.

Also an engine with excess carbon/varnish deposits on the ring grooves or on valve stems will cause the rings or valves to stick as the deposits harden from lack of use.

What I'd do when re-commissioning an engine is before turning it over, squirt a few table spoons of thin machine oil (some use ATF or WD40, or engine oil, it probably doesn't matter too much), down the bores and hand turn the engine, leave a while, add more oil and turn again and leave 180degrees from previous. Then crank on starter (no plugs, and crank/cam sensors disconnected, with rags to catch the oil ( ) that'll spray everywhere. Until there is oil pressure. Add plugs connect sensors. Prime fuel system by cycling ignition in/off three or four times and purge crappy fuel in the lines/rail (won't work on newer cars with single feed fuel rail with no fuel return pipe, you'll need to disconnect a hose or bleed via a schrader test point into a suitable container and check fuel colour/smell for ethanol separation/water/rust etc.).

Then fire it up.

Sticky valves and rings can self heal, but be aware this engine won't be in its prime. As either rust or deposits will have caused it to stick and it may happen again. Or it may not; After it's been given a run another compression check and cylinder leakage test may give a idea if it's a ongoing issue.

 

Thanks for all the replies and the full explanation of it all. I was mega concerned when I first saw the very low compression on that cylinder, especially as it was the first cylinder that I compression tested.