M30 Crankshaft Keyway Repair

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Courtesy of Aaron Sterry (with contributions from Peter Florance, Mike W, Frank Fahey Motorsports)

After going to get a roadworthy test done on the E12, the Mechanic doing it discovered after taking it for a test drive that there was funny noise coming from the front harmonic balancer and pulleys, after putting it on the hoist he discovered that the whole unit was loose and spinning freely on the crank shaft...not a good thing, not only that the crank-nut was missing too; that’s even worse.

So loaded with the Knowledge of what had to be done to get a roadworthy we towed it home.

After removing the radiator, fan, and belts, the harmonic balancer just slid off.

The reason why is because the woodruff key or key-way was completely missing from the slot that it sits in on the Crankshaft, when it finally went it took a bit off the side of the slot the key fits into too, as well as splitting the Harmonic balancer hub that slides on to the Key.


Peter's note: Frank Fahey Motorsports offers a hub, primarily offered for M5 S38 motors, It is made from much harder steel which is supposed to prevent this problem. Renee from Fahey states:

"The crank hubs are the same and you should definitely be running our improved crank hub if you do any sort or racing or track events.The M30 motors have a tendency to vibrate the crank hub nut loose when run in higher RPM for extended periods. This is actually caused by the soft stock crank hub. I'm sure you read all about it before, so I won't go into detail. Just make sure your crank nose is in good condition and that the keyway is still tight (your woodruff key should be tapped with no slop what so ever). Our replacement hubs will fix the problem, but they won't make up for an already hurt crank."

The complete article can be found at - Peter

Key way slot on hub split

The operation isn’t all that hard, but figuring out how to fix a new woodruff key in to position was the problem. I asked the guys at the first fives site and had several suggestions.

1/Just bolt it all together with the new key and Hub, and should be fine.

2/use Red Loctite, pour it in too the Slot and sit key back in let dry.

3/Make a new Woodruff key to fit it out of key steel.

4/ Use JB-Weld to hold the key in place.

5/Swap out engine to a 3.5 litre form a 7 series...Yikes

I hadn’t heard of JB weld before so i went down to the shops to find some, and low and behold they did, I read the pamphlet that comes with it and it is meant for Crankshaft pulleys and Keyways; so I was convinced.

JB weld is like Araldite, it has 2 parts, Steel and Hardener and you mix the 2 together in equal parts.

I put the Woodruff key in position and dab the JB weld around the edge were it had torn away from the crank.

Let dry over night.

JB weld

Here’s a Photo of the crank after i put the new Woodruff key in and Oil seal (should do this while down there)

The photo is not the best, a little fuzzy, but you can see that gray looking stuff on the left next to the key, that’s the JB weld, after it had dried I used a razor blade to cut off the excess JB and then a bit of wet and dry to clean up the excess JB around the key, you can also use a file. (Peter's note: note the smart-looking new seal. This is a great time to fit a new crankshaft seal. See specs below)

left, next to the key you can see were the key pulled out, and now JB weld helds it there. (the light grey stuff)

After doing all this, it was now time to put the harmonic balancer back on. I got the new Harmonic balancer hub from my Spare e28 M30 I have hanging around that saved me $350, as well as the crankshaft nut too.

I placed the hub on, and it slid on for the first bit then just wouldn’t go any further, I figured excess JB weld in the way as it is difficult to get rid of all the excess after it dried, so as it was lined up with the key way i pulled it on by doing up the Crankshaft nut to push on the Hub and balancer, this worked a treat.

There is a special tool you can buy from BMW to lock the flywheel while doing up the Crank bolt, I didn’t have it, but got my father to hold the Flywheel from timing whole with a larger screwdriver.

New Hub fitted to harmonic balancer


Crank nut: 36mm socket

Crank nut torque: 440 newton-meters (My torque wrench doesn’t go that far only 220NM, so I jut did it up as tight as I could ....well until the screw driver slipped of the flywheel)

Harmonic balancer to Harmonic balancer Hub 8x13mm bolts tightened to 22NM each.

Oil seal dimensions outside 62mm inside 42mm width 12mm (don’t have part number)

Woodruff key, there are 2 one for the Harmonic balancer and the other for the timing chain both are identical, only one is needed. Part Number: 07 11 9 951 485

And that is it, Crankshaft nut is difficult to remove, you will need 3/4 drive with a 36mm socket and a extra piece of pipe for leverage, some mechanics even put the socket on with the bar and quickly crank the engine, the bar hits the ground and loosens the nut.

I just had my father hold the flywheel with a couple of screwdrivers took a couple of attempts, but we got it.

I have since driven the car about 200klms, checked the balancer, nut, etc, and they seem to be fine; no oil leaks either.



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