luigi524td

Brought my car in for service and a broken motor mount bolt was discovered - when then lowered the plastic flap to do the oil service the broken bolt fell out :-( I didn't take a picture but the bolt looked like it was made of a cast alloy "metal" ... not anything like hardened steel ?? SA said these are issues rare and it's probably NJ roads - broke from road "shock"!

Car details - '07 530xi / 61K miles

For the past 6 months or so I have been hearing something like a 'metallic rattle' coming from the middle of the car and kept rearranging things in the center console because the noise seemed to be "inside" the car - guess that proves sounds car really travel. There was hardly a hint of drivetrain looseness that a broken motor mount might cause ... hope everything else is bolted in OK.

Has anyone had a similar motor mount issue?

korrosive

I just recently got this repaired on my vehicle. I bought the bolts from the dealership and took it to an Indy. 2 hours labor and he had the thing fixed. He did not need to drop the entire engine, but instead lifted it and removed the remaining parts of the bolts. Mine was all 4 bolts that needed to be replaced, but I bought it with that issue, so not sure what caused it.

Update: The bolts are aluminum screws Real OEM

ssmokn

Anyone know why BMW uses aluminum bots? I read it was to avoid galvanic corrosion but every other engine in the world uses steel bolts with aluminum blocks and heads. Put a little anti-seize on the bolts and they are fine.

I wonder why BMW sees this as necessary. Seems to me, the lack of strength of an aluminum bolt vs. steel isn't worth the tradeoff.

What's the scoop with BMW and aluminum hardware? Anyone know?

pcy

Aluminum hardware weighs much less than steel. Less weight ==> better fuel efficiency.

luigi524td

I wish I had taken a picture of the aluminum screw/bolt that fractured. That said, all is put back together and I had to admit that annoying metallic rattle I've been hearing for 5-6 months is gone! BMW shop time to remove the mount and the part of the screw that was inside the mount and replace them and button everything up was 3 hrs. Not an inexpensive repair given the usual shop time but they gave me a courtesy loaner for the day (a new 328 "Modern line" with only 100 miles on it) and a 10% discount on the total repair order.

luigi524td

UPDATE: Why motor mount screws and "aluminum" and not a stronger (stainless steel, etc) metal.

The design of the engine drive train mounting system is designed to meet crash and safety standards. In the "OLD DAYS" a severe frontal crash could cause the engine to intrude into the passenger compartment. If you've ever seen pictures of a head-on crash often the engine would be pushed into the car 'cabin' with deadly results.

Today's automobiles are designed so that the engine and drivetrain 'break away' and are pushed under the car and NOT transfer energy (or the motor) into the passenger compartment.
Makes sense to me but I guess it doesn't take too much force to cause these aluminum fasteners to snap under other "normal" driving conditions.

AchtungE60

Sorry to hear about this. I would flame you for 1) not servicing the car for 6 months 2) not doing your own service lol!
You're one of the guys doing things yourself so when i know you're going to the $tealer it's for a reason so maybe you had a courtesy or a discount or have no time. I know you're always taking care of your stuff so good thing you did take it in there. I'm sure you would have found it anyway when doing some of your own service. I have the underguard off my car so I can cool components a bit better while driving and also so I can be proactive on leaks. Can you imagine if a bolt broke off and i never knew? Or imagine it lodged its way into my tire at high speeds
Glad you're all doctored up

luigi524td

You're right there ... it's always best t to catch things "before they break" .. .. this one was a bit tricky because there were no tell-tale signs that a motor mount bolt was at fault. I checked for stuff from the top down to the bottom up (even when my car was on the lift at my Indy for the tire replacements a few weeks ago. .. but saw nothing "unusual". And it seemed that every time I rearranged the stuff in the console cubbie the "rattle" stopped. ?!?!? I suppose it was a coincidence that when my dealer did the oil service (my car is covered by the BMW service warranty for 'scheduled service' for 6 yrs / 100k miles) the broken bolt made it's way to the front of the car!

Even at that, since the repair required removing the mount, drilling and tapping the old bolt piece out etc ... it's not the sort of repair I'm taking on my own at this stage ... my time is invested in (TOO) many other personal and business priorities at this time (I have to stop my spouse from adding to and updating my appointment calendar one of these days !!! )

twh

Could also be that the bracket is not Al, and may be Magnesium or Al-Mg alloy. Mg has a very high Anodic index.

AchtungE60

hahaha....I'm in the same boat. TOOOOOOOOO many things to do. This here is my escape I guess.