Thread: 300Tdi crank keyway damage

Ouch.. JB Weld? Or, Loctite 660 was recommended to me once before.

Originally Posted by TonyC

I guess the proper fix is crank out and cut a new keyway... Refit the key with more epoxy metal, and reassemble...and loctite...Which Loctite?

Two D1 TDi's acquired second hand have had damage done in this area.

The key did not shear cleanly in the first vehicle, but instead what remain protruding acted as a reaming tool widening the diameter of the hole running through the harmonic balancer...ugghh!!! The otherwise good harmonic balancer has sat for years on the shelf waiting for me to sleeve it and re-cut the key way. Thankfully the key way on the crank was not damaged.

The second D1 had near identical levels of damage per your photo but in this case the key completely sheared. And the damage is on the same side, as expected, given the direction of rotation.

When I repaired the 2nd vehicle the engine and crank remained in place. I removed the radiator for extra work room.

I'm not keen on using pure resin to fill large gaps when mostly metal replacement is possible. I like the key way to be regular in shape and not off kilter for lack of some remedial work.

I used a tiny grinding stone mounted in a hand held Dremel style drive unit to repair the damaged side. The grind stone was slightly smaller in diameter than the key slot, allowing me to work up to the required shape, rather than have the size dictated to me by an over sized stone.

I stopping grinding once the ground out portion matched the half moon shape of the undamaged part of the key way. Don't touch the undamaged reference side. Basically you are aiming for a fatter key way with both sides of the slot at right angles to the long axis of the crank. Don't extend the length of the slot otherwise the new key will have a sloppy fit.

I put a new key against the undamaged reference side and proceeded to shape scrap steel to occupy the extra space - or you might shape a spare key to fill the extra space. Make sure the shaped scrap piece is flush with the crank surface and not proud like the new key, and that the piece touches both the new key and the opposing side wall of the expanded key slot. New keys from CBC or independents like MR Automotive Brisbane.

With the new key in place against the reference side, but the shaped scrap steel on the bench, I filled the new space with resin. I then forced the scrap steel next to the new key and into the resin with as much force as possible to seat it. You have very limited time to do this before the resin cures. The objective was to have as much space as possible occupied by metal while the resin's role was just to fill in the micro gaps. I used A&B 'Liquid Metal' - this is not a recommendation as I'm sure there are other equally good products out there - it's just what I could get at the time.

The repair has been good for two belt changes so far.
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The toothed drive in the picture butts up hard against a collar machined into the crank. Trouble is that there is a rubber o-ring seal between the collar and the toothed drive. It is expected when the toothed drive is tightened against the collar that the rubber o-ring will self locate into a recess at the back of the toothed gear. I find the rubber ring refuses to self locate and instead gets squashed between the collar and the toothed gear. Having the rubber squashed this way will make it impossible to torque the nose bolt correctly - you will get the torque wrench firing off correctly for the first stage - then the degrees of rotation will seem fine in the second stage - job seemingly done except for the fact you do not have metal-to-metal contact but rather metal-to-rubber-to-metal, and flex undetectable to your self. This failure of the o-ring to seat is easily missed under the torque pressures applied.

The seal in the clam cover (not to be confused with the seal behind the toothed gear) wears a witness mark into the male part of the harmonic balancer - if the o-ring has failed to seat and is being squashed you will notice if reusing the harmonic balancer that the witness mark may be sitting one or two mil proud of the clam cover seal - in other words the harmonic balancer is sitting further out than it should.

I install the o-ring into the recess at the back of the toothed gear before installing the gear itself. The tricky bit in this case is getting the ring over the 2 keys. At this point I use a probe to pull out just the right amount of o-ring to get past each key, then just after the 2nd key I push the ring back in with the probe. It is tricky because space is limited at the second key. If all goes well you get a nice metal to metal clang as the collar and gear meet. If it's a dull thud then likely that rubber has come out to some extent and is being pinched by the collar and the toothed gear.

I have 4xD1 TDi's and the rubber o-ring has been a pain to reinstall in all cases - some say they have never had problems with the o-ring self seating - discrepancies in the service item between manufacturers maybe? It does seem logical that the o-ring should seat itself but I've never had that experience.

I don't loctite although I suspect the manual has the procedure starred for it. I have not had harmonics come lose provided the the nose bolt is torqued correctly. If I had to, I'd use the loctite that breaks with hand tools.

I would suspect who ever tightened the crank nose bolt (in your and my case) did not achieve required torque because they lacked the tools and or did not appreciate the method of torquing, and or missed the rubber o-ring issue. If the o-ring looks OK on your disassembly of the parts then they got the installation of the o-ring bit right. If there is no o-ring then its probably been mashed and flung away.

We have put it all back together.

We cleaned out the keyway slot, fitted the key, and refilled the void with JB Weld metal putty, let that harden, refitted the harmonic balancer with medium strength retaining compound Loctite 641 and the bolt with 222.

This should be easier to get apart than what was on it.

I marked the bolt head, washer and balancer with a paint pen so we could see if it moves.

It has done 350km home and ran well.

I'll update if we see any problems.

Tony

I had a 300 belt change that went sideways quickly when I realised that Mr Crank had been introduced to Mrs HB with a liberal dosing of TIG

One thing for sure - that was never going to just wobble off

Originally Posted by roverrescue

I had a 300 belt change that went sideways quickly when I realised that Mr Crank had been introduced to Mrs HB with a liberal dosing of TIG

One thing for sure - that was never going to just wobble off

How did you fix that one 🥺