182 engine compression

[Tookers]

Just done a compression test, to put my OCD at ease, and the results arent as bad as i was expecting. The dry results pose a bit of a question mark though...
dry
cylinder 1 = 187
cylinder 2 = 172
cylinder 3 = 179
cylinder 4 = 180
wet
cylinder 1 = 183
cylinder 2 = 180
cylinder 3 = 180
cylinder 4 = 182

I ran the dry test about 3 times and got roughly the same result. The wet seems fairly consistent so im happy with that.
Any ideas on the dry though, esp cylinder 2 which is way off the other 3.

 

[masekwm]

Looks fine, less than 10% difference

 

[bloke]

you certainly have ocd if those figures are worrying you:wink:

 

[Tookers]

Phew! Given my luck with the car so far i expect the worst, pleasant surprise. Now i know i just need to get 182 across all cylinders ;-)

 

[Rone]

Phew! Given my luck with the car so far i expect the worst, pleasant surprise. Now i know i just need to get 182 across all cylinders ;-)

Getting better compression readings when wetting the cylinder can mean that either the piston rings or valves are not sealing properly. But with your readings everything is in order. Does it feel it has all the oomph it used to?

 

[Tookers]

Getting better compression readings when wetting the cylinder can mean that either the piston rings or valves are not sealing properly. But with your readings everything is in order. Does it feel it has all the oomph it used to?

@Rone only had the car since july and its spent most of its time in the garage. Been doing the odd job here and there on it, and havent touched the engine. Wanted to make sure it was all in order before getting cambelt done next week. It seems to pull pretty well and still kicks at 5k

 

[STEVE.M]

Getting better compression readings when wetting the cylinder can mean that either the piston rings or valves are not sealing properly.

Just the rings I`m afraid.


piston rings / cylinder walls: After running the dry. first test, squirt 2 oz. of oil into the cylinder and rotate the crankshaft three more turns per cylinder. If the compression increases, the piston rings are at fault.

Burned valves: If results remain the same after injecting oil, one of the valves are bad or not seating correctly or bent.. Low compression in only one cylinder typically indicates a bad valve. Exhaust valves burn due to hot gases passing through. Intake valves have the advantage of being cooled by the incoming fuel.

 

[Rone]

Just the rings I`m afraid.


piston rings / cylinder walls: After running the dry. first test, squirt 2 oz. of oil into the cylinder and rotate the crankshaft three more turns per cylinder. If the compression increases, the piston rings are at fault.

Burned valves: If results remain the same after injecting oil, one of the valves are bad or not seating correctly or bent.. Low compression in only one cylinder typically indicates a bad valve. Exhaust valves burn due to hot gases passing through. Intake valves have the advantage of being cooled by the incoming fuel.

I had on over-revved engine and as a consequence it had developed a knocking sound. I measured the compression wet and dry. The compression leveled out when wet, so I thought it must be a broken piston ring. Ahead I went and pulled out the pistons and replaced the rings.

Upon reassembly leak tested the head by pouring gasoline on an upside-down turned cylinder head and noticed that two valves were actually bent and not sealing properly when closed. Gasoline was pouring out through the valves. So I wasted hours taking the pistons out and changing the rings because I also thought that the wet & dry compression would only show rings when the oil increased readings. But for me, it sealed the valves also. At least to the point that I saw an imrovement on the compression tester. Dunno how then, as apparently this is not possible as per you say?

P.S. And yeah, didn't see any problems with the piston rings upon removal... so they were totally okay. Although, it is possible that I mistook the results of the compression readings and the tester never even showed the affect of the two broken valves... But then again???

 

[bloke]

That's why it's always worth doing a leakdown test to confirm the problem. Or at least point you in the right direction.

 

[STEVE.M]

Although, it is possible that I mistook the results of the compression readings and the tester never even showed the affect of the two broken valves... But then again???

If you use too much oil you are effectively reducing the size of the combustion chamber,so will achieve a higher reading despite leaking valves.

Maybe this is what you did?

 

[Rone]

If you use too much oil you are effectively reducing the size of the combustion chamber,so will achieve a higher reading despite leaking valves.

Maybe this is what you did?

Yeah, must've been something like that.