A heads up on loose pan bolts.

[sheepdog]

While repairing my engine (update below), I found many bolts inside the engine to be awefully loose. This led me to question if maybe the engine internals may have vibrated loose over the years as well as question what could be causing this problem as rpm and vibration could be the culprit.

I almost did not check, but curiosity got the better of me and I gave a rod bolt or 2 a twist to see if it was tight (not enough to move it if it was tight). Things were good. Far as I can tell the only things loose appear to be the items attached to the pans. Timing case (just the case, not the covers), upper pan, and lower pan were all semi-loose. Other items seemed to be in good shape (tight).  


Basically it seems that the pans are taking a beating. Anything connected directly to them, mostly directly above the lower pan) is also being knocked loose. As I suspected, it does not appear to be rpm related, which is good to know, since I am sure at least a few of you are driving them like you stole em', just like myself. The investment in some sort of pan protection is looking better all the time.
 
Keep the revs up.
(Maybe that should be the m42 slogan)

[silverblades181]

Well I know for a fact that the S14 is an engine that vibrates a lot...and it seems the little M42 vibrates too...maybe it's a caracteristic of BMW's 4 bangers..Anyway it's good to know the important things (rods) are all tight lol.  Thats not something I want on my mind at 6500 rpm on the track. Btw, I rly like that slogan! Let's make a poster!

[D. Clay]

Four cylinders vibrate.
Most are smooth because they have balance shafts. This is added weight but smooths it out.
M42's have none of that. Just a heavy flywheel.
Adding to the mix is that aluminum and like materials have a different coefficient of expansion and are softer than cast iron. The covers and pans are expanding more than the steel bolts and block. The aluminum gradually squishes a little as it expands more than the bolts. It's also vibrating as it gets less torque on the bolts. Then you do it for 15 years and 150,000 miles. They need re-torquing every five years or so. Loc-tite doesn't help as the problem isn't the bolts backing out.
If that's true, something similar should be happening to aluminum heads on iron blocks. Maybe someone else knows how they deal with that or maybe I'm writing fiction.

[FL318is]

 Timing case (just the case, not the covers), upper pan, and lower pan were all semi-loose. Other items seemed to be in good shape (tight).  
 
Keep the revs up.
(Maybe that should be the m42 slogan)

For those of us mechanically challenged could you post a Timing case visual?  I just replaced pan gaskets and tightened things.  Hope I didn't miss something.

Thanks again!

[bmwman91]

I am with Clay on this one.  Makes perfect sense to me.  I always figured that was why the valve cover bolts had the rubber grommets on them, to prevent something like this.

[sheepdog]

Four cylinders vibrate.
Most are smooth because they have balance shafts. This is added weight but smooths it out.
M42's have none of that. Just a heavy flywheel.
Adding to the mix is that aluminum and like materials have a different coefficient of expansion and are softer than cast iron. The covers and pans are expanding more than the steel bolts and block. The aluminum gradually squishes a little as it expands more than the bolts. It's also vibrating as it gets less torque on the bolts. Then you do it for 15 years and 150,000 miles. They need re-torquing every five years or so. Loc-tite doesn't help as the problem isn't the bolts backing out.
If that's true, something similar should be happening to aluminum heads on iron blocks. Maybe someone else knows how they deal with that or maybe I'm writing fiction.

Good point and very likely at least some of the cause.

It does not explain why as you move further from the sump though that things are tighter.

[Choking Hazard]

I have a couple of quesstions-
- what does the flywheel weigh?
- how do balance shafts work?

[Berlin]

a balance shaft is just an unbalanced shaft that spins in such a way to cause vibrations that negate those of the crank, not entirely, but reduce the overall vibration of the motor... just comfort-tech as i call it.
the flywheel weighs a buttload


i thnk things are tighter up there cause its closer to the center of the vibration so the amplitude is smaller ?

[Vladi]

If i remember well, BMW used to put some sort of "grease" on the bolts to prevent them from unscrewing due to vibration. Our screws being taken out at least once in the engine's lifetime that "grease" is gone.:rolleyes: