Need advice leaking cylinders

I did a cylinder leakage test on my 525 last week. These were the results by cylinder.

1. 50%
2. 5%
3. 50%
4. 8%
5. 40%
6. 50%

For all the cylinders with bad readings, I could hear the sound of air escaping clearly. On two of them, the air escaped on the intake. Opening the throttle body made the hiss louder. On one it was through the exhaust I guess. It had a different note I could not hear it through the tb but was loud. The 4th one the sound was like the intake hiss on the other two but couldn't hear extra through the throttle body.

The car is running fine. Pulls well, didn't know I had an engine problem. Ran better after cleaning the plugs following the test. Slightly rough idle have had that for years. Cleaning the icv, changing hose and change the vcg did not help that but I left it wasn't a big deal. Motor is old, at least 150k.

What should I do ? Lap the valves ? Leave it alone ? Will it get worse? Am I looking at valve damage here ? Am only hearing ticking while at idle.

Can I clean the valves without taking off the head ? With mmo, piston kleen or berryman's chem dip after filling up the chambers with it, or maybe pouring it down the fuel injector slots and covering the intake valves for a few hours ? Steam cleaning with water mist through the intake ? I've read about all kinds. Don't want to spend if I can avoid it or its not a big deal, or there's a good workaround. Any advice would be great. Thanks.


Charles

And can I say that if not for the valves, all the chambers would be reading under 10% ? Which is supposed to mean that my piston rings are in good shape.

How did you do the test? I guess you are talking about a leak down test or a compression test

Do the leak down test again... Take a spark plug out, and put a long stick in there, when it reaches the top point, do the pressure test on that cylinder.

If you did this already... You will be pulling the head of the engine... New valves are cheap, like $15 each.. Change them all with the stem seals... And rebuild the vanos while you are at it...

Originally Posted by cutter67

How did you do the test? I guess you are talking about a leak down test or a compression test

No, it was a cylinder leak down test, not a compression test. It was done like this and in fact with the exact same testor :



And yes Rahulk that is exactly how i determined tdc. Thanks. If i leave it alone, will this get worse? Is there an easier way to loosen and blow off the carbon on the valves ?

My engine actually feels normal. Am i losing anything important by keeping it going ?

When you do that test make sure the engine does not rotate and give a false reading. If those were reading with a 100% stationary engine - remove and service the head.

Are you saying that the air pressure from the gauge might rotate the engine ?

Originally Posted by samsonnyc

Are you saying that the air pressure from the gauge might rotate the engine ?

yes the pressure can rotate the engine it just takes a little. the readings you are posting and with what you say your hearing. i really think you are getting a false reading. plus that is a Harbor Frieght gage right i never trusted them either. do another test and check for rotation

There is not a chemical you can use on the car that will fix, or even help a head that needs a valve job. It is not carbon build up on the valves that keeps them from closing, it is inconsistensies in the head and the valve where they interface that causes the leaks. The valves and head will need machining off the car to repair the problem.

IF you did the test correctly and you have that much leakage in the cylinders, yes, it will get worse and worse until it starts fouling plugs and losing power big time.

or just dropping a cylinder or 2

Originally Posted by snowsled7

There is not a chemical you can use on the car that will fix, or even help a head that needs a valve job. It is not carbon build up on the valves that keeps them from closing, it is inconsistensies in the head and the valve where they interface that causes the leaks. The valves and head will need machining off the car to repair the problem.

IF you did the test correctly and you have that much leakage in the cylinders, yes, it will get worse and worse until it starts fouling plugs and losing power big time.

Holy cow. Thats bad news.

I'm pretty sure i did the test correctly. The air pressure was not high at all around 12 psi. But i can do it again.

Will probably just get differently bad results.

You are doing the tests. How well - only you know. Here I use 80psi as a test pressure. Keep us up to date.

Originally Posted by BMWFatherFigure

You are doing the tests. How well - only you know. Here I use 80psi as a test pressure. Keep us up to date.

Thank you, i will. Will get in a compression test too if i can find the gauge.

Originally Posted by snowsled7

There is not a chemical you can use on the car that will fix, or even help a head that needs a valve job. It is not carbon build up on the valves that keeps them from closing, it is inconsistensies in the head and the valve where they interface that causes the leaks. The valves and head will need machining off the car to repair the problem.

IF you did the test correctly and you have that much leakage in the cylinders, yes, it will get worse and worse until it starts fouling plugs and losing power big time.

I always thought it was carbon buildup that ****ed it up and machining the head was only to correct warpness. Can you explain how those inconsistencies in the head and valve occur? And they re drill the valve seats ?

Thanks man.

Hey one more question. Two of my chambers had beautiful low leakage. The valves must be closed perfectly, the leakage must only be through the rings.

Can we say that the rings for all would be equally good? Because if they are bad they should be uniformly bad?

The one cylinder with the hiss i couldnt pinpoint, the hiss did not come out the crankcase. I listened through the dipstick tube.

Originally Posted by snowsled7

There is not a chemical you can use on the car that will fix, or even help a head that needs a valve job. It is not carbon build up on the valves that keeps them from closing, it is inconsistensies in the head and the valve where they interface that causes the leaks. The valves and head will need machining off the car to repair the problem.

IF you did the test correctly and you have that much leakage in the cylinders, yes, it will get worse and worse until it starts fouling plugs and losing power big time.

^ +1

Sent from my Desire HD using Bimmer App

Should a compression test be done on a hot or cold engine. Is there a difference ? Is the difference important if there is one?

Maybe try lubro-moly valve cleaner, try a full bottle with half a tank of gas a couple of times and see if that cleans the valves out... It's cheap like $7 a pop... Napa has it I think

Originally Posted by samsonnyc

Should a compression test be done on a hot or cold engine. Is there a difference ? Is the difference important if there is one?

i have been wrenching on cars for 40years now and i was always taught to do it on a cold engine. if you think its rings or a bent valve you do a compression test. if you think its a headgasket, cracked head you do a leak down test and you use 80psi plus. you simulate the engine under compression running. a lot of time a head gasket can be bad or a crack in the head wont show up under a normal compression check. it just sounds funny you are hearing air hissing if you hear that then the compression has to be super low and the car would not run like you say it does. i really think you did the test wrong. just do compression check with a high grade gage not a HF gage you can rent them cheap at autozone and other parts store

Originally Posted by cutter67

i have been wrenching on cars for 40years now and i was always taught to do it on a cold engine. If you think its rings or a bent valve you do a compression test. If you think its a headgasket, cracked head you do a leak down test and you use 80psi plus. You simulate the engine under compression running. A lot of time a head gasket can be bad or a crack in the head wont show up under a normal compression check. it just sounds funny you are hearing air hissing if you hear that then the compression has to be super low and the car would not run like you say it does. i really think you did the test wrong. Just do compression check with a high grade gage not a hf gage you can rent them cheap at autozone and other parts store

+1

Originally Posted by samsonnyc

I always thought it was carbon buildup that ****ed it up and machining the head was only to correct warpness. Can you explain how those inconsistencies in the head and valve occur? And they re drill the valve seats ?

Thanks man.

The poor little valves are slammed shut by a 200 lb spring several thousand times a second. Heat and metal fatigue set in and, the tolerances change, less so on well built engines like in your BMW.

There are several procedures you go through rebuilding a head. One is resurfacing but this pertains to the head and block surface not the valves. As mentioned valves are relatively cheap considering the rest of the work it takes to get to them. They can be re-ground though, same with the valve seat on the head. When you do a three angle valve job you cut a 15* angle, a 30 and 45, the valve sits on the 30, the other two cuts smooth the airflow and provide just a bit more volume.

When I did a full valve job, it was 25 years ago in high school. We had a small stone grinder jigged to grind valves and a set of angled gringing stones for doing seats. Since then, I have paid to have it done. Today it wouldn't surprise me to see machine tools used to cut valves and seats depending on the shop.

Hey one more question. Two of my chambers had beautiful low leakage. The valves must be closed perfectly, the leakage must only be through the rings.

Yes, two of them are good numbers. There will be some leakage 5-8% is very good. I can't believe it runs with four cylinders at 50%.

Can we say that the rings for all would be equally good? Because if they are bad they should be uniformly bad?

Stop trying to hurry and cheat it The compression test will tell you more about the rings but if the leakdown is really as bad as posted, those numbers will be low on those four as well.

At that point, the engine needs serious repair or replacement. There are thousands of used engines that fit in these cars for sale cheap, less than a good head repair.

The one cylinder with the hiss i couldnt pinpoint, the hiss did not come out the crankcase. I listened through the dipstick tube.

Sounds like there are some issues, especially if 12 psi is hissing through.

Which engine is this, M20 or M50. If it is the M20, is the belt service current? Jumping a tooth or two on a worn belt would give you numbers like that but I also think it would be VERY sluggish to drive... that is the stumper.

snowsled - These days the repair shop tool picks up on the valve guide. If it is worn they replace it or you get oval valve seats. Sealing is checked by vacuum. I hang around and listen to the bloke at my head shop.

OP - you can get one broken ring gouging the bore, so test everything correctly on each cylinder.

I must have messed something up. Let me do the tests again. Will hold the crank with a socket wrench while doing the test. I will try to increase the air pressure too. Will post results over the weekend.

What is the difference between doing the compression test cold and hot ? Isnt compression the same cold or hot ?

Thank you the three wise men. I have learned alot about this here. Cutter, that car is yours ? It is stunning.

Originally Posted by Rahulk

Maybe try lubro-moly valve cleaner, try a full bottle with half a tank of gas a couple of times and see if that cleans the valves out... It's cheap like $7 a pop... Napa has it I think

I run fuel cleaners regularly. I don't think it helped. This is an old spare motor, it has been like this from day one. I didn't think too much of it until I did the leakdown.

If its baked on carbon, I doubt that liqui moly will be able to help. It will have to be a hard carbon stuff that the valves and pistons can soak themselves in overnight. It looks like only Piston Kleen and Berryman's has a good record there.

The cheap cleaners in the tank will probably keep a clean valve clean I guess. I think mine was bad from the beginning. I've always had a slightly rough idle. Checked everything, nothing helped, then I did the leakdown.