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92 745 Turbo - 'thud', loss of power, now crank doesn't turn- 'is it dead Jim'?

N

NoVA Dad

New member
Joined
Jan 11, 2014
Hi All,

Its been while, but I've got a doozy for the group.

My son was driving our 92 745 Turbo (~200K miles) on the highway. The car was at normal operating temperatures when he accelerated to pass a car. The car surged as expected but as he passed he heard a "thud" followed by a loss of power, but no warning lights-that he recalls. He pulled to the shoulder and killed the car.

After a quick visual inspect of fluids etc, he tried to restart the car but only got the usual start sequence lights. There was also the audible sound of the starter "thunking" as it made contact with the flywheel- but no start.

After additional road side diagnosis, we towed the car home.

We've removed and tested the starter- it was fine.
Removed and inspected under the valve cover- nothing out of the norm.
Upon attempting to turn the crank via the retention bolt we discovered that it wouldn't budge.
Removed cover and inspected the timing belt- it was intact and well within mileage as it had been changed along with water pump etc less than 30k miles before.
Removed the timing belt and discovered the cam would turn just fine with no noticeable issues, but also discovered the crank could now be turned just a bit more than before.

I'm afraid the grand old lady has passed her last beemer but I'm not ready to call her out just yet and am open to any suggestions.

Anyone else ever dealt with these symptoms before? Is this a bottom end rebuild? or am I missing something simple?

Thanks!

NoVA Dad
 
It sounds like an intake pipe might have popped. At first glance you don't notice but it's a silent killer.

Check all the intake pipes for leaks and any that popped off.

Was the car in gear when you tried to turn the engine manually? Stupid question but it might be

When you turn the key, does the engine crank or not?
 
Have you removed any spark plugs to look at what was happening in the chambers? You can remove all the plugs and see if the crankshaft will turn without compression. Maybe you detonated and a chunk of spark plug is in the chamber? Definitely want to look at the plugs.
 
Can you rotate the engine at all, using the center bolt in the balancer (27mm maybe, or is it a 32mm?)

With plugs out she should spin easily unless "in a mechanical bind". If the oil still looks good, and you can confirm the cam timing is correct, it could be a bottom end failure or perhaps even the aux. shaft. You must determine if you can rotate the crank with no plugs.... report back.
 
Yeah if the motor doesn't turn all the way around something broke. Can you turn it one way then it stops cause it hits something and then turn it back the other way around till it hits again?
 
NoVA Dad said:
Anyone else ever dealt with these symptoms before? Is this a bottom end rebuild? or am I missing something simple?
Click to expand...

Jack and support the entire rear-end on stands (make sure the parking brake is off).

Attempt to turn the crank by hand again. See if the rear wheels turn with the crank.
 
LeedomtoFreedom said:
Was the car in gear when you tried to turn the engine manually? Stupid question but it might be
Click to expand...

Not a stupid question at all. Exactly what I was thinking.

When a clutch disk comes apart, it sounds like a thud (in my experience). If the transmission was in gear when the disk broke, the engine will not turn (unless the wheels are off the ground).
 
Thanks for the questions all. Really appreciate the support.

I should have mentioned the car is an automatic.
I’ll confirm the car was in neutral and update the thread.
I did pull number four plug and all was fine but will pull all four and update as well.

Can a dislodged intake or exhaust pipe be seen with the valve cover off?
 
2oodff.jpg
 
NoVA Dad said:
Thanks for the questions all. Really appreciate the support.

I should have mentioned the car is an automatic.
I’ll confirm the car was in neutral and update the thread.
I did pull number four plug and all was fine but will pull all four and update as well.

Can a dislodged intake or exhaust pipe be seen with the valve cover off?
Click to expand...

Intake pipe connects air cleaner to turbo, and turbo to intake, all visible when hood is opened, but this sounds fairly serious. Let us know what you see with all plugs out
 
Afternoon All,

So I should have written "flex plate" vs flywheel- my apologies for the confusion.

The car was in Park, the first time we tried to turn the crank by hand, but we've since put it in neutral and the movement is the same.

I'll pull the plugs and update on their condition.

Hard to believe the lady may have dropped a rod that didn't crack the case.

Guess a valve could have also dropped... looking more and more like its time to pull the head...

So glad its winter.
 
Is there any oil in the engine?

Number 1 killer of these old bricks. My car eats a quart almost every 500 miles.
 
Check for a bolt that backed out on the flex plate. Only a few bolts to pull the cover and break it loose.
Also pull the valve cover, see if any followers are sitting away from the cam, indicative of a dropped valve.
 
Hi all,

Thanks again for the feedback and input.

I've pulled the plugs and the crank still only rotates about 30-40 degrees before stopping. The same is true if rotated in the opposite (from where it stops). So total free movement is 30-40 degrees. Anyone know how many times a cylinder fires before the crank makes a full 360?

Visual inspection of the plugs shows they should be cleaned/replaced, but only because of carbon buildup. Nothing else looks out of the norm- none have oil on them or missing pieces nor terrible discoloration.

All fluids are full and no (more than usual) leaks/seeps can be found.

Under the valve cover- everything looks normal for a car with near 200k miles. All of the lobes and discs are in place and free of defect or out of spec movement. I haven't pulled the cam-yet.

If the weather holds out, I'll get under the car to remove the bell housing and inspect for a loose/backed out bolt.

More to come.

Thanks again!
 
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