Checking engine compression/leakdown

[jlevie]

Yes, all plugs out, throttle locked open and a 30-50a charger on the battery for compression tests, and injectors disabled if using the key to spin the engine. If using the starter pins in the diag connector or jumping the starter solenoid, there is no need to disable the injectors since the DME won't be running.

[Vspec]

So I finally got around to get a new battery and run a compression test, throttle fully open following the Haynes manual instructions.

Round One - Engine lukewarm bordering cold:
1 - 178
2 - 180
3 - 90 /180
4 - 100 / 180
5 - 90 /180
6 - 110 / 180

I was expecting much lower numbers for a 280,000+km engine.

Since I was having doubts about the numbers, I put everything back together and warmed up again for 10min to 1/4 temp gauge and run the test again.

Round 2 - Engine warm, must wear gloves to keep skin un-burnt taking plugs out:
1 - 90 /178
2 - 100 / 180
3 - 100 / 180
4 - 90 / 180
5 - 100 / 180
6 - 100 / 180

First number is the first reading, second number is the final reading, 7-8 strokes for each cylinder.

At this point, I should mention that the engine is running rich and plugs are covered with soot. I am suspecting heavy carbon deposits. I will need to go through fuel, air intake and exhaust at some point but what I am trying to determine is if I can leave the bottom end alone for the moment. I do plan on taking the engine out to fit a new clutch, steering rack, shifter overhaul and cleaning up of the rusty engine bay so head will most likely come off, I'd be dumb not to peak in there.

What should I take from those numbers? The low variation between each cylinders and both test is a positive but I do find those numbers quite high for sure a high mileage engine.

Should I proceed with a leakdown test?

[jlevie]

The compression numbers are very good. Carbon in the head could being bumping the numbers up sightly. A leakdown test will tell something about the condition of the valves. But with 280Km on the engine there's little doubt that there is valve wear. And probably enough to justify a valve job.

[Vspec]

Will a leakdown test tell something about the rings?

As I said, head is coming off so head refresh will be done.

[jlevie]

It can tell you something about the condition of the rings. But with those compression numbers and the mileage on the engine, the leaks past the valves will probably dominate the results.