Low Compression In One Cylinder

[anxious]

I had noticed a slight vibration in my car when my 325 was in D or P stationary. The exhaust also had a very slight rattle. Me being the fuss port I am asked my mechanic to do anor modic test. The test showed vanos solenoid but I had already changed that. Then he did a compresseion test which revealed that one of the cylinder has low compression ...about 70psi. The others all are about 140-150. He then told me the only way to find out what is wrong with the engine is by opening it up and checking whether:- i) the head gasket is goneii I have a bad valveiii) cylinder head crack(wrost case scenario) Apart from the minor vibration, probably due to the said cylinder I had no other problems. No overheating and no oil in the water and no loss of coolant. I guess the previous owner lack of maintainance has reared its ugly head. My mech suspects some overheating with the previous owner based on the condition of the radiator tank when i got the car.(I had changed the cooling system parts when servicing my car after getting it) This just goes to prove that low mileage means nothing if the owner neglects the car. Had I know about the compression test thing I would had got my mech to do it b4 buying the car. It only took 15mins. Why did my mech do it earlier when he serviced my car and changed all the wear and tear parts? I am so dissapointed and am hoping its nothing serious. Should I do a top overhaul if it turns out to be a valve or a gasket? What does that entaill and how much does that cost? Thanks guys.

 

[LCP]

Check the E36 maintenance thread to see whether someone has done a top overhaul, there should be... I also replied to your posting on this on your E36 Experience thread...

Btw, the modic test should not show the Vanos solenoid error message if you have already changed that... you might wanna check with them again.

 

[LCP]

Low Compression - advise from Haynes Service Manual

Okay, looked through my Haynes manual... healthy compression readings should be around 10-11 bars, that's 145-160psi. And I summarises the following tips:

If the pressure is low, squirt a teaspoon of oil into that cylinder, if the compression figures improved, you have bore or piston wear. If there's no improvement, it suggested leaking/burnt valves, or blown head gasket.

If there's low reading from two adjacent cylinders, it means the head gasket is blown between them, should have coolant in engine oil also in this case.

If a cylinder is 20% lower than the others, and slight rough idle, a worn camshaft lobe is the like cause.

Low compression on 1st stroke, but gradually/slowly increasing on succesive strokes, it means a worn piston ring.

Low compression on 1st stroke, but does not build up indicates leaky valves, blown head gasket or cracked cylinder head. Deposits on the underside of valve heads can also cause low compression...

 

[anxious]

Could carbon deposits be the cause?

Could decarbonising help?

What about a blast on the highway?

 

[viewfinder]

If it's due to worn piston ring and/or valvue guide, I suppose there should be blue smoke from the tail pipe.

 

[anxious]

No white blue or black smoke

 

[LCP]

On further thoughts, it may not be carbon deposits... all your other cylinders have normal compression. If some of them have abnormally high compression, that is a sign of excessive carbon deposits.

 

[LCP]

Be careful though, the catalytic converter is capable of "suppressing" some oil smoke, so a smokeless exhaust doesn't mean all's well.

Here's a suggestion:

Really monitor your oil consumption... take a note of the engine oil level on your dipstick and your mileage. Then continue driving, check the oil level every 1000km, do it for maybe 3000-5000km. Make sure the condition when checking the oil level is always the same, eg. when the engine's perfectly cold, etc. Note also that if your engine oil level is above the max mark, drain it a bit first (or your measurement will not be accurate), if it is above the max mark, there's a likelihood that oil will get blown somewhere.

 

[elwine30]

Anxious, it's not magic science for your compression is low. The only way is to open engine and be prepared for some $$$.

As for LCP's idea, it's a way to identify the source of the problem if it's piston ring, valve guide. Since your cooling system is alright, then it can be just the valve guide.

Top overhaul on M50 not cheap or. Can you imagine how many valve guide required.

I had the same problem as yours and I did the top overhaul on my LA 332, E36 318i M40. It was the valve guide based on the oil test. Cost me about less 1K plus.

 

[anxious]

If you have been following My E36 Experience thread, you would have realised that i have solved the problem. It was a cracked cylinder head and cracked valve at Cylinder No.3 that caused my problem.

A second hand head costed me RM3700. On top of that I also did a top overhaul and replaced my radiator, termostat and piping to solve the overheating problem. (i hope its ok now)...bill came up to RM7k.

Compression test today revealed all cylinder b/w 150-155psi. Cylinder No. 3 up from 70- to 150 after clinder head replacement.

 

[anxious]

Should this thread be also moved to ur close section?????????????????

 

[anxious]

B4 u accuse me of "spamming", in my defence I am just pointing out my threads that u have missed out.