Compression test

[chard]

I've just run a compression test on a buddy's Sunbeam Rapier 1725 and astonished by the results. It was a cheap ebay screw in jobbie so calibration may be less than perfect. We carried this out with throttle jammed open. When cranking the gauge went up in 25psi jumps.



1) Dry 75 psi Wet 85psi Plug nice colour
2) Dry 100 Wet 110 Plug looked a little rich
3) Dry 75 Wet 100 Plug looked oily
4) Dry 75 Wet 85 Plug sooty

We ran the test because the car is using a little more oil than desirable (1tr per 6-700 miles)and fouled a plug when idling in traffic + a little oil in the coolant. No blue smoke from the exhaust and no excessive crankcase pressure. The car runs well pulls strongly, has an even tick over and tops out at an indicated 100 mph achieving 30 mpg in day to day use.

The results would indicate worn rings, worn valves and maybe a small blow in the HG (tiny bit of oil in coolant, alloy head on this one) We're tempted to leave well alone whilst it's running well.

But 75 psi?? that can't be right can it?

What does the collective think?

Edited by chard on Thursday 16th September 11:26

Edited by chard on Thursday 16th September 11:28

[Justin S]

Depends how long the pipe to the compression tester is. Longer hose means more area to compress outside the cylinder.
If you want a proper test, then you will need a leak down test done.

[chard]

Justin S said:

Depends how long the pipe to the compression tester is. Longer hose means more area to compress outside the cylinder.
If you want a proper test, then you will need a leak down test done.

The pipe could be it about 21" + the engine was only tepid not hot.

Edited by chard on Friday 17th September 06:36