M50TU Valve/Piston interference?

[David Shealey]

I have a '94 E34 with the M50TU engine, 160,000 miles on it. This morning it started then immediately shut down. When I tried re-starting it spins with no compression, like the spark plugs are out. I am only guessing at this point that a timing chain has failed.

Question: Does anyone know if this engine is an interference or non-interference one? Have I likely crashed valves or not? If just replacing timing chains it is not such a big deal, but if valves/pistons are likely damaged, this is going to be a very expensive fix. Love the car, but don't know if it will survive that kind of cost, even though I do all my own work.

[Bill R.]

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I have a '94 E34 with the M50TU engine, 160,000 miles on it. This morning it started then immediately shut down. When I tried re-starting it spins with no compression, like the spark plugs are out. I am only guessing at this point that a timing chain has failed.

Question: Does anyone know if this engine is an interference or non-interference one? Have I likely crashed valves or not? If just replacing timing chains it is not such a big deal, but if valves/pistons are likely damaged, this is going to be a very expensive fix. Love the car, but don't know if it will survive that kind of cost, even though I do all my own work.

[David Shealey]

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I was afraid of that.

[NovceGuru]

Open her up and take a look, doesn't take but maybe an hour to get down to the valves. Good luck, I did my cam chain at 189k and didn't have the special little tool to hold the 2 cams in place...rigged something up with a couple oddlots channel locks. Good so far, knock on wood.

NovceGuru

[bjl4776]

You might of goten lucky if it was startup. I did something similar, and I was almost lucky as all of the cyllinders but one had good leak down. My suggestion to find out if you messed up the valves is to get a leakdown tester to tell if the valves are bent. I had 10% on 5 cylinders, but 90% on one, but when i took the valves out I measured them with a dial indicator and they were all only 20-30 thousandths off.

[David Shealey]

I have a '94 E34 with the M50TU engine, 160,000 miles on it. This morning it started then immediately shut down. When I tried re-starting it spins with no compression, like the spark plugs are out. I am only guessing at this point that a timing chain has failed.

Question: Does anyone know if this engine is an interference or non-interference one? Have I likely crashed valves or not? If just replacing timing chains it is not such a big deal, but if valves/pistons are likely damaged, this is going to be a very expensive fix. Love the car, but don't know if it will survive that kind of cost, even though I do all my own work.

Well, came home early today, pulled the valve cover, and the timing chains are fine. Cam timing seems to be right on. Made a air line connector and checked the Vanos unit, it seems to be fine also. Checked compression, and found cylinders 3,5 and 6 at 100-120, 1,2 and 4 between 70-85.

Would like to do a blow down test, but no idea how to lock each cylinder at TDC for the test. Not to difficult with a manual, but more difficult with an automatic.

No clue what could have happened so sudden other than valve timing, but that seems to be exactly as it is supposed to be.

Going to check fuel pressure tomorrow to see if there is another reason it stopped and won't start, but the low compression is a problem in any event. Looks like a teardown is in my future. Sure was not ready for that! All the plugs look good, no evidence of a problem from looking at them.

[winfred]

i see this compression issue all of the time, it's not your problem it's just a byproduct of whatever the real problem is, the modern double overhead cam bmw motors can and do loose compression after certain running problems, it will pump up after you get the problem figured out, make sure you have spark and injector pulse and fuel pump, if those are good look at the temp sensor's resistance and compare to the chart that's in most repair manuals, then theres stuff like airflow meter tests (hard to do with diy tools) fuel pressure test, and it can always be more then one problem, car is living with one problem like a air leak and then something else fails killing it. when you figure out what's wrong make sure you have a fully charged battery and clean good dry spark plugs, crank it in 30 or so second shots and let the starter cool and battery recover a couple minutes and try again, no joy after 4-5 of these there may still be a overfueling problem, double check for spark and non dripping wet with fuel spark plugs. i've had to screw with m42/44 318 motors (hands down the worst for this but m50/52/60/62 have all done it to me) for over a day to get them to pump up and start, once you get it started it may or may not blow oil smoke ether way block the throttle open to around 2k rpm for 10-20 minutes to let it reseat the rings and keep a eye on things

[David Shealey]

Thanks for the reply!

I plan on doing some testing to see if there is an external problem before pulling the head.

If it was just the two adjacent cylinders with low compression, I would expect the head gasket blown between them. Have seen that a few times over the years. But the fact that I also have one lone cylinder low between two relatively good ones is more disconcerting.