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orkboss View Drop Down
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Points: 135 		Direct Link To This Post Topic: Compression test woe
    Posted: 02-February-2005 at 08:42

The results of a compression test on my M40 engine were as follows;

Cylinder 4 : 160 Psi Spark plug Light Brown. OK

Cylinder 3 : 158 Psi Spark Plug Light Brown. OK

Cylinder 2 : 100 Psi checked twice Spark plug Red light Brown

Tested with little oil poured into spark plug 150 PSI. Oh dear

Cylinder 1 : 195 Psi Spark plug Light Brown. Trouble

 

My head is very noisey which could be worn cam or valve. This would coincide with the high reading of cylinder 1. Cylinder two had no oil on the spark plug it was clear and there is no blue smoke from the exhuast. Do you think the low reading which improves with oil could be accounted for by something else?
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Madrab View Drop Down
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Points: 569 		Direct Link To This Post Posted: 02-February-2005 at 10:20

Doing a compression test is proving that the compression rings are ok and that the valves are seating correctly. In my experience, and I hate to say it, if ur no2 cylinder is down on compression and adding oil then raises the compression then it may point towards a bad, siezed or broken ring/s or worst case, worn cylinder (hope it's not this - rebore and new rings). If it didn't rise with the oil added, then it would normally point to a valve/valve train issue.

Though with an M40 stock average of 145 - 160 psi then your no 1 cylinder does sound like a valve train issue. Hope it's not too bad. Have you taken off the rocker cover and checked the cam and followers for visual wear as you may just have a goosed/siezed hydraulic lifter on number 1?

Rob 



Edited by Madrab
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orkboss View Drop Down
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Points: 135 		Direct Link To This Post Posted: 05-February-2005 at 03:50
If I ignore it will it go away.
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orkboss View Drop Down
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Points: 135 		Direct Link To This Post Posted: 15-February-2005 at 17:35
I checked the cam and there was no wear.
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Peter Fenwick View Drop Down
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Points: 6484 		Direct Link To This Post Posted: 16-February-2005 at 04:33

Originally posted by orkboss orkboss wrote:

If I ignore it will it go away.

LOL...It would be nice if life was like that wouldn't it Big Smile
Entering an age of Austerity and now driving a Focus Diesel.
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Madrab View Drop Down
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Points: 569 		Direct Link To This Post Posted: 16-February-2005 at 07:42

It sure would.

All the information unfortunately points towards a cylinder based problem with no 2, pants!!

No1 sounds like it may be able to be fixed by replacement of the lifter but it could also be a sticky or problem valve/guide if the cam is clean. Sometimes they free themselves up but if not it could cause big problems if it sticks open. With No2 being the way it is it sounds like a strip and investigate unfortunately, if you want to go there.

Rob
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Doive View Drop Down
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Points: 1212 		Direct Link To This Post Posted: 16-February-2005 at 07:47

That definitely sounds like piston rings to me on number two. Could number one be a seriously gummed up combustion chamber? It may be more economical in the long run to pull the engine and put in a second hand unit, depends what the diagnosis is of course.

Mine is in having the compression checked at the moment, hoping for a low reading on two cylinders to prove it is the head gasket that has blown and not anything more sinister!!
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orkboss View Drop Down
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Points: 135 		Direct Link To This Post Posted: 18-February-2005 at 16:15

There is a tapping noise especialy on cold start but it doesnot sound like the usual worn valve cam noise (I know because of my other BMW and every other m40 BMW that you see or rather hear. It seems the tapping varies in cycles going quiet for 4 second then building up in volume for 7 seconds before going quiet again.

 
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