18 replies to this topic

[cian]

Ok guys here are my dry figures didn't a perform wet test but the dry figures speak for themselves, opinions please, car has an awful misfire on half throttle and loss of power only way to get the car remotely driveable is to advance the timing, no adjustment of the fuel made a difference

1 - 115
2 - 115
3 - 125
4 - 130

[Dusky]

Was this hot?
to be honest, theyre all equal(within 10%). Not too bad, Just a tad low.

Edited by Dusky, 09 September 2017 - 04:01 PM.

[nicklouse]

what are they done in the other order.

[slidehammer]

I wouldn't thought they would account for the mis-fire, even though they do seem a bit low (I assume the throttle was wide open when you took the readings?. I would start checking the ignition system as you have already checked the mixture isn't out.

[dyshipfakta]

If advancing it helps is the vac advance working properly

[cian]

Engine was cold, throttle was closed, checked over the ignition system and all is correct points gaps etc, vac advance seems to be working blown down the vacuum pipe and weights popped out

Edited by cian, 09 September 2017 - 05:05 PM.

[sledgehammer]

When doing compression tests (all plugs out) , remember starter motor will draw a bit of change out of battery ,

 

so sometimes the results can be skewed , with the later results being slightly lower

 

as nick said , do them the other way around (full throttle) you may find the average of the two figures more even

 

although the figures seem close enough

[cian]

I thought they where very low

[carbon]

Engine was cold, throttle was closed, checked over the ignition system and all is correct points gaps etc, vac advance seems to be working blown down the vacuum pipe and weights popped out

Compression testing should always be carried out with throttle fully open. Also take all sparking plugs out, so engine can spin freely.

 

Your results are very low, would typically expect 180psi or more if the engine's compression ratio is about 9:1

[cian]

Was on a 1275 was rebuilt by an autotest competitor but totally unaware of what was carried out

[Cooperman]

Take the plugs out, spray a good quantity of WD40 into each bore, open the throttle fully, then carry out the compression test.

 

If this is not done the test is a bit meaningless.

[cian]

Should the test not initially be done dry cooperman?

[Cooperman]

Not necessarily. You want an indication of the operating condition with the bores having oil on them.

A dry check will not give the information you require.

[carbon]

Only time I have seen compression results as low as 115-125psi was on a 1293 which had been used for club rallying. This was running a 643 cam and compression ratio was about 10:1. The main reason for low results was all of the top compression rings were in several pieces.

 

This motor was from a time before electronic ignition and rev limiters...

[Rorf]

Do a leak down test - I would suspect poor valve seats or rings. Compression test with oil should be over 165 psi.