Rover V8 compression test

[WLAcopilote]

Hello,
results from compression test of a 3.9 litre 9.35:1 compression ratio Rover V8. Any advice gratefully received!

results (PSI)
1 180
2 175
3 175
4 190 second try 190 oily
5 180
6 175
7 175
8 190 second try 175 oily

The figures obtained for 1 to 3 and 5-6 are from memory but the range is correct (i.e. 175 to 180 ish). Why would 4 and 8 be higher? It was suggested that there is an oil control ring problem which may explain the oil (although I did not check the end of the tester for oil on the other cylinders I am pretty confident it came from number 8 and possibly number 4.

Is it possible that the ticking noise I hear on the overrun (i.e. descending a steep slope in low ratio) is a broken piston ring?

I haven't checked what the expected pressure should be for a healthy V8 high-compression engine but they seem to be about what we got with the 4.6 V8

regards
Matt

[trooperiziz]

WLAcopilote said:

Is it possible that the ticking noise I hear on the overrun (i.e. descending a steep slope in low ratio) is a broken piston ring?

Is it only on the overrun? I had an occasional tick at idle which turned out to be a broken valve spring, which also explained oil burning as the spring had scored the valve seal.

[Boosted LS1]

Got any smoke on lift off?

[GreenV8S]

There seems to be a bit of a knack to compression testing, if you simply take the plugs out and do each cylinder in turn you might find the cylinders you do last read lower because they have dried out while you were doing the other cylinders. You can prevent this by putting a couple of drops of oil into the cylinder you are about to test. What order did you test the cylinders in?

For what it's worth, the figures you've got seem pretty consistent to me, and are slightly higher than the figures I got from my 4.6 (all in the region of 165 - 175). My laymans interpretation of those figures is that they don't show any problem.

[HarryW]

Agree with Peter the actual figures seem fine, so long as they are within 10% of each other. For a 9.35:1 compression they are on the high side but that could just be the gauge. Seem to recall anything north of 150 and equal across all cylinders is OK, dependant on age, mileage etc.
One point also is the amount of time you crank, as you can 'pump up' the gauge for a duff cylinder by letting it turn over longer. Each cylinder should be subjected to (approimately) the same cranking time for it to mean anything too.

HArry

[WLAcopilote]

Thanks for your contributions. I did the odd bank then the even bank. Each cyclinder had six compression strokes before stopping to take the reading. The engine was cool enough to work on. All valve springs are OK,I had a look when I replaced the rocker cover gaskets.

The engine has nominal compression ratio of 9.35:1 with the heads skimmed .006" and using tin head gaskets with the outer four bolts only torqued to 30 lb.ft

It does use oil, I haven't noticed puffs on the overrun, I'll have a look tonight,
thanks again...
Matt