m42 timing/blownup/wtf/issues

[e30lov]

I'll try the best to describe what happened today..

I was cruising around 40mph, 5th gear when all of a sudden I hear this bzzzzzzzzz (kinda grinding noise) randomly for about 3 seconds and then the motor died. I figured immediately that I broke a timing gear/chain/guide etc. I tried to start it back up and it cranks normally. No signs of loss of compression. However the motor does not fire back up. I got it towed to my shop and I pulled my valve cover and the timing gears are pointing up at TDC like they should. the three chain guides that you can see from the top are intact. The chain has no slack whatsoever and the gears look ok. (looks like the timing has been messed with before, several marks on the cam gears from a previous tech working on it.)

I didn't really look too far into this yet, but does anyone have any experience with something like this? If something happened to the timing wouldn't i have slack in the chain, broken plastic guides? cam gears not at tdc... etc

any input would be greatly appreciated, I kinda don't want to go through the trouble of swapping a 24v into this thing if I don't need to

[Asbradley21]

Checked the timing chain idler sprocket?

[bmwm42]

Tensioner took a shit

[e30lov]

I haven't taken a look at the tensioner yet, but wouldn't abnormal "diesel" motor sounds be the cause of a failing tensioner? My motor had no abnormal sounds at all. It ran absolutely perfect. When I pull the tensioner out today how can I tell if it's shot?

I'm more leaning twords the idler sproket as asbradley said. Either way, if this idler sproket or tensioner took a shit while the motor was running I likely have valve damage and this motor is junk right?

[bmwman91]

Yeah, you need to pop the lower cover. It sucks, but that's the only way to be sure. I have experienced both flavors of idler sprocket failure...shit sucks bad. I can tell you from experience that the motor should still run, but who knows.

Summmer 2011

http://www.m42club.com/forums/showthread.php?t=13574

Spring 2012

http://www.m42club.com/forums/showthread.php?t=14748

Maybe if you are super lucky it is just this, although the motor would run fine probably.
Winter 2011

http://www.m42club.com/forums/showthread.php?t=13720

Have you ever pulled the lower oil pan to check for bolts? Sometimes the bolts in the upper oil pan, around the oil sump inlet, fall out and the gasket implodes, making the oil pump suck air. It sounds like you didn't seize the motor, which is good. My oil pump once ate a chunk of metal and the car immediately stalled with the loss of oil pressure (I think that the Motronic shuts it down if it is running and the pressure sender turns off). It made some funky noises for a couple of seconds too.

[e30lov]

I haven't really had time to look at anything yet.. Can you tell just by looking at the tensioner if it has failed?

But what really gets me is that the motor made a zzzzzgrrr noise and shut off. It cranks but does not fire up. It never made diesel sounds. The cam gears look fine and are at TDC. If that idler sprocket failed wouldn't I have slack in the chain and likely the chain would of skipped a couple teeth?

[Ryann]

If your vibration damper separated you may not be getting a good crank sensor signal to the DME.

[Dj Buttchug]

If your vibration damper separated you may not be getting a good crank sensor signal to the DME.

Im banking on something along these lines. Deflection wheels fail, but It doesn't sound like that is the case here.

[Ryann]

Are your accessory drive belts intact? If your compressor clutch failed it or the drive belt could've also taken out the crank sensor wire.

[Massimo]

It is easy to check if the idle sprocket is still working romove the valve cover and turn the engine, if the chain turns in time with the engine then it is all good.

I would suspect something else. Was the sound defernetly from the front? I am maybe thinking the fuel pump shat its pants.

Do a compression test.

[Dj Buttchug]

op you may be back to basics on this. You need all of these and youre missing one.
Fire
Air ( you for sure have this)
Fuel
Time (which you most likely still have)

[e30lov]

I think you guys are on to something. I appreciate all the input. I should have some time tonight to really dig into this. A couple days before this all happened my fuel pump was making a really loud noise btw. It went away shortly after though.

[TobyB]

It went away shortly after though.

t