Low Compression, what does it mean? M52B28

[jbabin87]

I have white smoke coming out of crank case vent, and I thought this could mean a blown head gasket. I was messing around with my newly boosted motor and I definitely broke something, question is, what?

Here are the results of compression testing (cold, dry):

1. 165
2. 180
3. 160
4. 170
5. 180
6. 75 ****

Does this mean one thing or another? Or do I still not know if it's a valve, piston seal, or head gasket? Or could my head gasket having blown caused the smoke, which caused me to compression test it and to realize I have had a problem all along? It's been slightly rough.

I'm going to leak down test it tomorrow, but I wanted to see what these compression results might mean, or if I should be looking for anything very specific when doing the leak down test.

[bmwdirtracer]

When you say you have white smoke coming out of the crankcase vent, where exactly do you mean? After all, the stock crankcase vent system isn't designed for a pressurized intake. Did you accommodate this?

Did you repeat the compression test, unscrewing the gauge, screwing it back in, and also trying it again on another cylinder you'd already tested? After all, maybe you lost the o-ring that seals it, or maybe it wasn't correctly screwed in. Doublecheck.

After that, well, you've got a bent valve, or bad rings, or a hole developing in the piston. Hopefully, you used a well-designed boost system, which provides correct air fuel ratios and mapping, and had tuning pros set it up on a dyno. Otherwise, you probably have a boat anchor.

[WadiM3]

It doesnt take a genius to figure it out but cylinder 6 is down and your running on 5 lol, what was you doing when you noticed this problem... Downshifted? I reckon you have a bent valve or even a blown head gasket, what have you used in your build? Lower compression forged pistons or mls .140 gasket or a ces cutring gasket?? Also what power are you running ? More details will help

[jbabin87]

I'm fully aware that I was destined to blow up the engine, but I just didn't think it would be after just a full pulls.

bmwdirtracer - Smoke was coming out of the vent that's part of the valve cover near the vanos. I removed it from the stock PCV and used an oil catch can so that it wouldn't become pressured. I didn't get far enough to actually hook it up to vacuum (pre-turbo). I did repeat the compression test. I actually tested 130 on Cyl 1 the first time around and the second time yielded a better result. I repeated the test 3 times on Cyl 6 (the bad one).

The boost system is fairly well designed although the quality of the actual turbo is so so. I'm swapped the ECU for a standalone MS3. I really like it.

WadiM3 - I understand I'm only running on 5 Cyl.. I might have been for a while, I'm not really sure. Never felt 100%. It's all stock internals. I planned to go to 15 psi until I wrecked the motor and actually build a new one while I played with the old one. The new one will be designed for much more, but I knew the risks. What was I doing? Well, I ripped down a strip with incorrectly set boost controller and got to 255 kpa absolute pressure. Not smart, I know, but yolo.

My question was more about determining where the actual problem lies before I rip the motor apart. Primarily because if it's piston/piston seals then I'm not even bother going to try and fix it, I'm just going to get a new engine and the rebuild the old one over time. If it's a head gasket, I'll just throw a new one in over a couple days, it won't be that bad. DIY head resurfacing, etc, just something to last me until I can find an S52 to build as my baby.

Leak down test is tomorrow, I'm going to post my results and hopefully someone can say "Yeah that's definitely your head gasket" or "sorry bud, definitely piston seal related."

[WadiM3]

Good luck! Ill lean more towards a headgasket.. Try the people in the F/I Sub forum! Im personally going to do a m52b28 build soon after some more research and reassurance lol because my steering rack gets in the way of the headers. Well i dont know what boost you was running but i wouldnt go over 9-12psi on standard internals not smart to make more then 450-500bhp

- - - Updated - - -

Good luck! Ill lean more towards a headgasket.. Try the people in the F/I Sub forum! Im personally going to do a m52b28 build soon after some more research and reassurance lol because my steering rack gets in the way of the headers. Well i dont know what boost you was running but i wouldnt go over 9-12psi on standard internals not smart to make more then 450-500bhp.

from the sound of things and your reply you didnt really answer my question about what headgasket your using but im assuming you havent put in a spacer gasket ?

[jbabin87]

I'm asking about head gaskets and what I should be using in the FI forum. I'm not sure what gasket is in it because I only got it a few months ago. Good luck on your build! Haha, knowing what I know now I would have done things differently in terms of some parts.

OK, here's my leak down test results:

Cylinder 1 - 7%
Cylinder 2 - 4%
Cylinder 3 - 3%
Cylinder 4 - 8%
Cylinder 5 - 3%
Cylinder 6 - 87%

It seems that the air from cylinder 6 is coming straight out the crank case vent.

Is this for sure a blow piston seal, or is it still possible that it's a head gasket?

[WadiM3]

Did you build the turbo kit and bolt it on or did you buy the car already converted? What this sounds like to me is that you have a blown headgasket but hey im no mechanic im just a bmw enthusiast who just tends to read alot and linger in this forum!

[bmwdirtracer]

If the air is coming out of the crankcase, you have a hole in the piston or badly broken rings and ring lands, which still means, almost certainly, new pistons, rings, boring. You might get away without the boring, but why? If you really want a good FI engine, you should invest in forged pistons, and other appropriate mods to suit.

I'm betting you've got a burned/holed piston.

[jbabin87]

I installed the turbo kit after I bought the car... lots of fun, I had a good time doing it. This is my 3rd E36 and I've always wanted to turbo it, and really it's even better than I thought it would be!

bmwdirtracer - this is what I've read, so to hear you say the same thing is some sort of affirmation.

I found a new engine on Craigslist today. Going to leak test it on Friday, if it checks out I'm going to take it home. Will be rebuilding the m52b28 that I already blew up over the next few months. I'll want to know more about the suggested forged pistons!! I see lots of sets but I don't really know which are best. I'll probably be starting a thread for it next month.

Thanks for the help and the responses.