12 replies to this topic

[Jeansie]

Model:Rover Cooper MPI
Year:1997
Description of problem (please be as in depth as possible):

Just got a compression test done on the mini (spark plugs out, throttle open), this was just routine I have not been experiencing any issues results were

1: 165
2: 125
3: 165
4: 150

Not so concerned about 4 being slightly down, but 2 is way down. There is no smoke out the back, the engine is running fine (not lumpy) and I don't seem to be down on power. The guy who did the check suggested that the valve may not be sitting properly (slightly bent or a loose seal) and if I want to get the problem examined further I should get the head examined, I agree with this assesment but just wondered what other possible causes there may be?

Any non-standard parts that might be involved with the problem?

Edited by Jeansie, 18 November 2008 - 03:52 PM.

[icklemini]

quite poss the valve seat...

could be compression rings gone but less likely

need to do a leakdown test: that will indicate the area that needs looking at..

[Bungle]

the next test is to do the same compression test again but with a squirt of oil into the bores

if the results improve then its rings if no change the yes look at the valves

have you been running unleaded petrol on a unconverted engine ?

[icklemini]

squirting oil in the bores can lead to false readings.. yes the oil *will* improve the seal (no matter what), and trying to get the oil onto the bore... rather than the dish in the piston.. is awkward.

[Jeansie]

have you been running unleaded petrol on a unconverted engine ?

No it's an unleaded engine. Rover Cooper MPI.

[Bungle]

ahh yes i missed that bit

[Jeansie]

squirting oil in the bores can lead to false readings.. yes the oil *will* improve the seal (no matter what), and trying to get the oil onto the bore... rather than the dish in the piston.. is awkward.

Does that mean squirting oil in the spark plug hole will not tell me if it's valve seating or piston ring?

Is oil in the hole only for testing, presumably it will not improve the compression for more than a very short time?

[ANON]

why would they do a comp test and not follow it with a leakdown test ??

also seems a bit odd to suggest pulling the head before a leakdown test, i would say try a different garage

[Jeansie]

He's a mate in the club who has his own garage, he said he'd get the head off first to check it is not something serious, cracked etc, and to see if the valves are seated correctly that the valve is not slightly bent etc. Also to check the head gasket. He said we'd know more once we get the head off and we could take it from there. Everything he seemed to say makes sense I thought. I've known him a while he's an honest bloke and he knows his way very well round mini engines.

[icklemini]

why would they do a comp test and not follow it with a leakdown test ??

sadly very very few garages know what a leakdown test is - let alone how to do one..

Jeansie - i can do a leakdown test if you want to drive up to northampton...

Does that mean squirting oil in the spark plug hole will not tell me if it's valve seating or piston ring?

It will boost your compression figures - as the bore is now wet.. it will seal better and up the compression figures across the board

Is oil in the hole only for testing, presumably it will not improve the compression for more than a very short time?

Correct - it will burn off when you start the engine (or get pumped straight out to the cat and start to degrade that!)

Cheers,
Dave

[ANON]

Everything he seemed to say makes sense I thought...

appart from not doing a leakdown test.

ask him to do one, it will pretty much tell you what's wrong before you even start to strip the engine

[Jeansie]

Thanks for your help today Dave, least we know what the problem is now (head gasket), my mate is going to get this sorted in a couple of weeks time.

In the meantime I'll keep watching the engine temp

[icklemini]

Good stuff