Pre BMW TIS:

(min.): 10 to 11 bar (145 to 160 psi)

Above would represent a 'new' motor; if I recall, as motors age and the top of the pistons (and valves) become coated w/carbon buildup the compression pressure tends to increase; however that may be somewhat offset by the fact that the rings & valves do wear, and don't seal as well as with new motor.

Just FYI, here's compression and leak down data for my M52 motor at 212K miles:

(spec compresion for M52 same as your M54)

Compression: Leakage:
Cylinder #1 193 psi 30%
Cylinder #2 199 psi 28%
Cylinder #3 200 psi 30%
Cylinder #4 197 psi 30%
Cylinder #5 203 psi 25%
Cylinder #6 192 psi 31%

Good luck / Bill

 

Pre BMW TIS:

(min.): 10 to 11 bar (145 to 160 psi)

Above would represent a 'new' motor; if I recall, as motors age and the top of the pistons (and valves) become coated w/carbon buildup the compression pressure tends to increase. Just FYI, here's compression and leakdown data for my M52 motor at 212K miles:

(spec compresion for M52 same as your M54)

Compression: Leakage:
Cylinder #1 193 psi 30%
Cylinder #2 199 psi 28%
Cylinder #3 200 psi 30%
Cylinder #4 197 psi 30%
Cylinder #5 203 psi 25%
Cylinder #6 192 psi 31%

Good luck / Bill

I wonder if the increased pressure is what causes leaks.

 

I believe the absolute readings can vary, depending on whether the throttle is held wide open, the compression gauge accuracy, and the ambient atmospheric pressure, among other things. Just FYI, the m54 compression ratio is 10.2:1. If you multiply that by the atmospheric pressure at sea level (14.7 lbs./sq.in.), you get about 150 lbs./sq.in., equivalent to the Bentley specs for a new engine.

 

Also, make sure when testing that all plugs are removed.

 

I performed test as per Bentley:
DME relay removed.
All plugs removed.
Gas peddle depressed...full open throttle.
Grounding strap removed.
4-6 strokes of engine.

I also read that the first stroke should get up to about 90+.

It is odd that Bentley does not distinguish the different engine but just says 142-156 is OK in all 6-cylinder engines.
The M54B22 has a compression ratio of 10.8:1 so that is 159
The M54B25 10.5:1 154
The M54B30 10.2:1 150
The S54B32 has a compression ratio of 11.5:1 so that is 169

http://www.ask.com/youtube?q=What+is+engine+compression?&v=uPYlNR16q3k&qsrc=472
http://www.ask.com/youtube?q=What+is+engine+compression?&v=nveqCMNTth0&qsrc=472
If this second video is a correct explanation of compression ratios:
Carbon build up would Decrease the volume of the cylinder.so 10.2 would become,say 10.
The second half of the ratio 1, may also decrease slightly.
I do not see how carbon build up would dramatically change the compression.

 

...If this second video is a correct explanation of compression ratios:
Carbon build up would Decrease the volume of the cylinder.so 10.2 would become,say 10.
The second half of the ratio 1, may also decrease slightly.
I do not see how carbon build up would dramatically change the compression.

Carbon buildup reduces the volume of the combustion chamber with the piston at the top of its stroke. A given volume of carbon buildup will reduce this volume more on a percentage basis than it will reduce the percentage of the total volume of the cylinder with the piston at the bottom of its stroke. In other words, if you reduce the volume of the combustion chamber by 1 cc, this will result in a proportionately greater reduction in combustion chamber volume than the reduction in the total cylinder volume. That's why carbon buildup increases the compression ratio.

 

Wikipedia lists the different M52 engines and according to the ratio X 14.7 formula:
The range of compression is a low of 150 and a high of 163.
The numbers that Barracuz shows are extremely high if Wikipedia is to be believed.
Where did you get your number?

 

Larrick: those compression figures for my M52 came from mechanics test. Range I quoted jibes with Bentley, info came from BMW's "technical information system"; BMW technician reference service/repair documentation.
As best I recall excessive carbon buildup can raise compression pressure, potentially cause pre-ignition, knock and such....again, Excessive, abnormal buildup situation.
Bill

 

What do you think of an AC Delco Piston soak.
Are they safe for the Cat?

 

No personal experience with soak; seems others here have had some success. Can't help on that one.
Bill

 

You arent going to ruin cats with a piston soak. Blow the excess cleaner out before starting the car.

 

There are thread out there that warn against blowing out AC Delco soaking cylinders with intake valve open: possible head gasket damage.
The poster was dealing with oil consumption, something he said is inherent in m54.
The reason is low tension oil control rings.
To work on these, get piston to bottom with intake closed and exhaust open , pour in AC Delco, cover tail pipe and apply compressed air to distribute cleaner.
Repeat for all cylinders.
Then, with pistons slightly down pour in more AC Delco and let sit for 24 hours. Does not blow anything out and runs engine the next day.
Change oil.

I do not want to cause any new problems and am a bit worried by some of the warnings>

 

Forgot to add.
How would you hand crank the engine into the intake valve closed position?

 

I guess I'd take the valve cover off and watch the intake cam lobe for each cylinder.

 

These are some pretty high numbers, but all cars when manufactured, are going to vary a bit from one to another; there's no way they'll all be the same from car to car. How they got ~15-20 pounds over, is a mystery. Does the car run poorly, or knock? What made you think to do a comp test to begin with, unless I missed it? I don't suggest trying to fix a problem that may not be there.

If they were low, or all varied greatly, that's a problem. The piston soak deal may be a bit extreme. IDK? But sometimes those methods of cleaning can dislodge large enough particles of carbon to cause cylinder scoring and valve damage. I'll admit I've never done the piston soak method, but that seems to have the potential to hurt more than help, just IMO. That would take A LOT of carbon build up, I would think, to raise the numbers that high. Seek out a reputable BMW mechanic for some suggestions first.

 

How would have the intake valve open when using a solvent ruin the headmaster? Whatever the valves position the solvent can always have contact with the head gasket?

What you DO NOT WANT TO DO is crank the engine over with piston soak or any other solvent/liquid and crank it over with the spark plugs reinstalled as you would risk hydrolocking the engine.

The process is simple. You remove the spark plugs and drop in enough piston soak to submerge the piston. Remember the engine sits at an angle so too little will solvent will only work on a part of the piston. Then you use some clean rags to cover up the holes and either crank the engine by hand or give it a few clicks with the key. Go back into the bay and clean up any fluid that might have escaped. Then let it sit for 24 hours.

When you come back turn the engine once more and use a turkey baster to remove excess fluid. Reinstall plugs and start engine. Keep your eyes on the rpms as the engine might stall. Once the smoke start to clear out go for a spirited drive and your done.

 

I thought that the head gasket damage warning did not make sense either.
I just had to make sure that there was not something which I was missing.
I do like the piston soak idea and do not see a problem if most of the liquid is removed before firing up the engine.
I am going to rig a small hose to a Craftsman wet/dry vacuum at insure most liquid is out.
My only worry is the catalytic converter being damaged.

I under stand the piston head being decarbonized by soaking because it is in contact with the liquid.
How are the valves and upper chamber cleaned if they are not being soaked?
Is the cleaning strictly for the piston?

Is an oil change necessary after the soak?
Will solvent have gotten into the oil pan?

I am going to replace the oil separator and the associated hoses.
What Brand is recommended and what source is best?
I have been looking and can find nothing which claims OEM or mention Brand name for the "kits".