13 replies to this topic

[fikasteve]

Done a compression test on my engine today and would like to run the results past some more experienced people for advice please. Engine is a 998cc a+ engine. Compression test was completed when the engine was warm.
The first results are

Cylinder 1 - 150
Cylinder 2 - 130
Cylinder 3 - 130
Cylinder 4 - 160

Then whilst looking into other people's results i realised that i hadn't held the throttle open whilst turning the engine over, so i repeated the test again. Here are the results from the second test;

Cylinder 1 - 160
Cylinder 2 - 120
Cylinder 3 - 150
Cylinder 4 - 170

By this stage i was getting quite confused at what the results were telling me. I know they're meant to be all the same. The compression tester itself is a gunson one which i trust.

The reason i decided to do the compression test was because the mini didn't have any power under load, so this was the first of my trouble shooting. If anybody can offer me advice on what these results mean then i'd be very grateful.

Steve

[booton]

how long or how many turns of the engine did you do the test on each cylinder.

[Harrison541]

Cylinder 2 and 3 both being slightly low indicates that the head gasket might have a small leak between those 2 cylinders, however this dissappeared in your second test. How old is the engine??

[fikasteve]

I think the number of turns was around 4, maybe 5 until the needle settled. The engine is 1991, had frequent oil changes whilst i've owned it the past 3 years but it has niw done around 120,000 miles.

[lrostoke]

could be rings feeling there age, or valve problems.

any smoke ??

[booton]

cylinder 2 is out of tolerances really.

if you repeat the test. put thimble of oil down the bore before you start the test.
if the pressure shoots up then its just ware on the piston rings/ bore. if the pressure does not increase its a bad valve seat etc.


by adding a thimble of oil it should shoot up to over 200 psi

Edited by booton, 12 March 2013 - 07:32 PM.

[fikasteve]

Thanks, i think it is just a tired engine. I put some oil down the bores and re-done the the test

Cylinder 1 - 185 psi
Cylinder 2 - 150
Cylinder 3 - 180
Cylinder 4 - 200

So from this my bores are worn, but also there could be a problem with the valves on cylinder 2?

[jaydee]

Reset tappets clearance paying particular attention at cyl #2 where you could have a worn rocker pad causing incorrect clearance.
By your results i think its just a worn engine, but not an HG fault.

[fikasteve]

Thanks very much

[ACDodd]

I would follow this up with a clylinder leakage test to see where it is leaking from. If it is the valves, a head rebuild would sort it. If it is the block then an engine rebuild is on the cards.

AC

[fikasteve]

I'm expecting the worst and a engine rebuild if im honest. How could i perform a cylinder leakage test? I've not heard of that before

[Cooperman]

A somewhat simplistic test is to run the engine at 1000 to 1200 rpm and take the oil filler cap off. If it is 'chuffing' a bit of smoke out of the oil filler hole, then there is a piston sealing problem, probably bore wear and rings. If it doesn't 'chuff' then it's a top end issue, so remove the head, re-lap the valves, re-cutting the valve seats if this is needed and/or replacing valves if they are in poor condition.

[fikasteve]

Thanks cooperman, i'll try that tomorrow morning and see what happens

[ACDodd]

http://en.wikipedia....eak-down_tester





AC