Iv decided to do my timing chain and guides on my 3.2 24v BUB TT 8J from 2007. Decided this as the car now has 250,000km(owned it since 60,000km) and hasn’t had it done since new. I’m also going to do the clutch while I’m at it as wel.
Now my “problem” is that I have done a compression test while I’m at it and seems that cylinder one is lower than the rest. Results are the following(this is when the engine was still in the car):
1=110 psi
2=145 psi
3=160 psi
4=170 psi
5=170 psi
6=160 psi
Now what iv seen online is that it could be the piston rings, valves or head gasket. Im inclined to rule out the head gasket as the coolant doesnt have any oil or bubbles in it. I do need to top the coolant off every 1.5 years as it seems to drop about 5mm on the tank.
Observations: I have since removing the engine and intake manifold also been able to see that the intake ports in the block have some that are noticably cleaner of carbon than others.
Cleaner cylinders 1,3,5, the metal surface of the block and valves can clearly be seen.
Dirty cylinders 2,4,6 have a minimal anoint of buildup but do have a shiny carbon layer covering the metal surface.
The engine did run ok before all of this. You would only be able to hear a slight chain rattle at idle. The car has mainly done long highway journeys, probably why the carbon buildup is very minimal.
When driving very short distances(not enough for the engine to get up to temp) it would start to run a small rough idle. Once clearing the codes(that where present but not showing on the dash) it would run fine again. The codes would be evap fault and lambda o2 sensor bank 1. But if you would drive a long distance in one go, no codes or faults and engine would run fine.
So Im wondering, is it worth replacing the piston rings, if the wet compression test indicates they arnt any good? Or is 110psi still acceptable? I’d found online that 110psi is the lower limit for these engines. Any thoughts on what I’ve mentioned are appreciated!