22 replies to this topic

[Noodles]

Hi again all, as you may know I'm having lots of problems with my engine burning excessive amounts oil. I have just done a compression test and got these results:

1 - 8 bar
2 - 5 bar
3 - 6.5 bar
4 - 7 bar

To me these seem way to varied, I just want to know if there is any possibility this could be down to the head?? Or is it worn bores/rings??

Thanks in advance,

Dale

[wassupcrew]

sounds like its the rings or bores if youre burning oil and the compression is that far out

[Steve D]

Lack of compression

1. Faulty valve seat, excessive wear in stem or guide. 1. Recut seat and valve, fit new guide and valve.
2. Faulty head gasket. 2. Fit new gasket or reface head.
3. Worn pistons, rings and bores. 3. Either fit new rings, pistons and rings and rebore. If engine badly worn then recon. engine.

As you seem to be down compression on cylinders 2 and 3 it may be a head gasket problem, it may have gone between the 2 and 3.




8bar = 116.0304
5bar = 72.519
6.5bar = 94.2747
7bar = 101.5266

You could do with doing a wet test, to see if it is head or rings.

[Min E]

If you haven't already done so, it might just be worth adjusting your tappets.

A tight tappet wil prevent the valve making a good seal.

[Asphalt]

Anyway; did you do the test wiht cold or warm engine? Are all valves adjusted?
Did you hold the throttle fully open?

And as said - try to put a little oil in the cylinders and repeat the test.
But make another 'dry' test first with the engine warmed up to have comparable conditions
If the pressure rises with oil in the bores, it's likely to be the rings.

New rings & hone alone will not work if the cylinders are worn...

[Sprocket]

That is a typical result of poor valve seal. One way to check is to read the manifold vacuum at idle, if the vacuum is low, its valve seal

[bmcecosse]

They are ALL low - some desperately so. Looks like knackered engine I'm afraid.

[Noodles]

Thanks for the replies guys. Just swapped the head for my old (71000 miles old) standard 12g940 and got a compression of just above 5 bar on all cylinders. What should the compression be? Do you think it could just be the valves?

Edited by Noodles, 05 December 2009 - 05:45 PM.

[Ouster]

People will say different things, but I'd be looking for around 10-12 bar.

[Ethel]

The pressure is also be effected by the static compression ratio, cam & starter performance. As long as they are about the same and it pulls ok without burning oil I wouldn't worry about the numbers.

[Sprocket]

below 10bar on anything other than a balls out turbo motor is a worry

[Ouster]

Would you not say though that 5 bar is too low even taking into account that?

[Ethel]

I dunno if the plugs were out, if the tester was leak free or how rapidly the starter span it. If the cylinders were leaking that much I think you'd notice something was amiss without needing to test the compression.

[Sprocket]

Would you not say though that 5 bar is too low even taking into account that?

Yes

[Noodles]

OK, when I did my compression test I removed only the plug I was testing, screwed the compression tester in and opened the throttle. Then turned the engine over 6 times and it turned over very quickly as it was nice and warm. Is this the correct method or am I doing something wrong?

Also it does seem to be a little down on power but nothing major.

I think I will do a wet compression test tomorrow. Do i just put a bit of oil into the cylinders and then re-test? If so how much oil?

Edited by Noodles, 05 December 2009 - 07:56 PM.