Harmonic Balancer Failure before it was yours- DIY HB keyway fix

Let's say that you bought a Sprinter with rear A/C and two compressors. Let's also say that the rear A/C wasn't working, but you wanted to repair it so it would be working when you took a month long trip with family in tow this summer. For kicks, let's also say that you thought (based on the savvy advice of the forum and Dr. A) that this would be a good time to replace the harmonic balancer as a preventative measure. Sure your not the preventive type, "If it ain't broken don't fix it" you've always said, but a harmonic balancer failure far away from home because you've been running that rear A/C while pulling a trailer doesn't sound like fun.

This is what I thought.

I bought the balancer ($188 plus $45 shipping) from Ebay UK.
Off-brand fly wheel locking tool ($30) worked flawlessly
Bolt, washer, and seal (@$30) Berry Dodge

All was going well until I tried to remove the balancer. The bolt came out, no problem, but the balancer would not budge... not at all. Thankfully, I was with a friend who welds. He made a low-profile puller that would attach around the pulley for the aux. a/c. With a lot of torque and tapping from behind the balancer began to move... slowly. When it came off there was no key. No key on the end of the crankshaft no key in the pulley... No key. When I looked back in the hole I could see that the key had been sheered off at one time. The date stamp on the pulley was 09/09/08. The previous owners must have suffered a failure resulting in a sheered off key. The repairer glued/JB welded the new pulley on!

At this point I was stumped. I did not want to glue the new pulley on. We found some half-moon key stock and began to file. We filed and fitted, and filed some more. Finally our little half-moon fit in the open slot and the new pulley went on. Before torquing to spec I back the bolt out and checked to make sure our home-made key had not moved... it hadn't. Torqued the pulley to spec. 242 ft./lbs. and another 90 degrees, put everything back together and started it up (after a broken fuel line, but that's another frustrating story).

I was expecting a relatively easy job, but the unknown previous failure really messed things up. The end of the crankshaft is not perfect, but not to the point of needing to be replaced. If you find yourself in this situation the new key design part # 05170759AA would fit in the keyway left available by the sheering off of the old design key.

At the end of the day (well, two) I have a new Harmonic Balancer installed, rear SCS frigette A/C working well, and a rebuilt HP pump from Dr. A installed, (oh yeah, a new fuel line that I wish wasn't new as well).



New member
This just happen to
Me as I was driving back home from Boise idaho, and the battery light comes on so I pull over right away I look under oil is leaking I look some more belt is siting all messed up so ya..... I had the Sprinter towed back to SlC Utah ..... At the freightliner dealer. It was there for 2 days they just called me today and told
Me I need a new engine 11k because the keyway is messed up and perfectly good running engine is done!!!! So I am gonna tow it to my house tomorrow and idk if I should try to fix it like u did somehow ...??? Or look for a new Sprinter....

2004 ...3500 .. Grrrrrrr I wonder if I can make it work som how


New member
I been trying to pull out the old key out of the key way for 2 days now it cannot be done .... I am making a new keyway ... On the crank and pulley .... There is no other way .... Does anyone know what's the difference between the old woodruff key and the later version of 06?
I see that you got it figured out... but you cannot pull out the old key because half of it is unaccessible without taking apart the bottom half of the engine. In my situation the original key must have sheared off and then the new balancer was glued on without a key. I made a half moon key out of some key stock and carefully used it in the slot on the front half of the crankshaft. What you did looks great and will probably hold for a long time.


New member
Missouri Blue did you use the flywheel locking tool to hold the crank from spinning when u torque?


Nasko1, does your sprinter have the dual pulley for the rear air conditioner?


Well-known member
Here is what is probably a stupid question, but what the hell. On a hi mileage engine, that is otherwise in good shape, that throws a balancer and messes up the key way, wht would be the problem with simply welding the balancer to the crank. (Asside from the obvious, that you could never replace the seal, and would have to toss the crank if you ever wanted to rebuild the engine.)

I don't suppose you could get a bead in it, and then still insert the torque bolt?



New member
It's possible it would be hard I think because it's a lil tight , but u can go that way2...
Or just J B weld it.. And hope that it will hold....That would be the same and if u ever need to take it apart you could just use high HEAT ... I guess

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