mrbill3

Over here from the Jeep forum as I also have a Bimmer. Tonight on the way home from work, my timing belt broke on my 1986 325e while I was driving. The belt was only about 4 years old (12K miles). I'm guessing my engine is screwed now, but was wondering if there was a chance that it's not. Any body ever have a belt break while in motion and not have other damage?

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89XJ Laredo, 2 door, 4.0L, Automatic. Rusty's 3" Full-Spring Pack Lift, Steering Stabilizer, Bumpstops, Steering Brace, and Adjusatable Track Bar. ProComp 31X10.5X15 AT's on 8" Steelies. Dynomax Super-Turbo Cat Back.

pada

Ooooh, bummer Mr Bill,

4 years isn't really uncommon, but 12k???? That's bizarre. Anyway, there's no question that the BMW M20 is an "Interference" engine, so there will be damage. I was a Service Advisor at a franchise BMW dealer for 8 years "back in the day". I've seen plenty of belts break and never one without some measure of damage. Question is: How much damage? It all depends on the engine rpms and level of acceleration at the moment it broke.

The ONLY way to determine is to disassemble, i.e. remove the Cylinder Head. The least amount of damage you can expect to have will be a few bent Intake Valves. I say Intake, as opposed to Exhaust, because the Intakes are a larger diameter, thus have less clearance than the Exhaust Valves from the pistons.

The next level will be lots of bent valves, Intake and Exhaust, and maybe damage to the tops of the pistons.

Also, check the Head casting at the lower end of the Valve Guide, they can break from the force.

Worst case scenario is when the Head casting breaks at the Camshaft bridges and/or Rocker towers. If there's any Head casting damage at all, trash it. You may be able to find a good used one at a reputable dismantler or perhaps a reconditioned one. Or, there's always a used replacement motor ...

Problem is with old cars like ours is that it will often cost more to repair when big stuff like this happens than the car could ever be worth ... but then there's that emotional attachment. Dr. Phil, where are you when we need you?!?

Good luck, keep us posted...

Paul (pada)
89 325iA
204k and still looks new!

mrbill3

Fourtunately (maybe) I was just pulling out of a parking lot on to the street when it happened so I was barely moving(low RPM's). I hope this may lessen the damage. I am going to have it towed home today and then tear it appart tomorrow to access the damage.

Funny part is I was going to replace the belt again soon as my water pump was starting to have a small leak and I figured since I had to take it off anyway, I might as well......

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89XJ Laredo, 2 door, 4.0L, Automatic. Rusty's 3" Full-Spring Pack Lift, Steering Stabilizer, Bumpstops, Steering Brace, and Adjusatable Track Bar. ProComp 31X10.5X15 AT's on 8" Steelies. Dynomax Super-Turbo Cat Back.

pada

Yeah, isn't that just the way it goes ... ?

Hopefully your damage has been kept to a minimum. I would recommend that, even if the head doesn't look like it's damaged, still it would be smart to have a machine shop pressure test it.

Also, remember to replace the T/Belt Tensioner when you reassemble.

Good luck and keep us posted...

Paul (pada)