Harmonic balancer bolt sheared off

[Georgia306]

Ok so I was driving home from the waffle house and suddenly noticed a strange vibration coming from the front of the motor. As soon as I got home I started checking timing and it was way off. Looking around in the engine bay and found a big broken bolt on the ground under the car. After some investigation I found that it was the bolt from the harmonic balancer to the crank, it had sheared off. I think I know why the bolt broke… due to a bad tail shaft bushing in the trans. My question is how can the timing be so far off when the balancer was still very tight on the crank? Car is a 92 GT.

 

[jrichker]

The inner hub is kept from rotating on the crankshaft by a woodruff key. As long as the key does not shear, the inner hub will not rotate. That does not mean that the outer hub won't shear the connecting rubber and allow the outer hub to rotate This would throw the engine out of balance and move the timing marks.

 

[rd]

Been there, done that. Bolt broke deep enough in the crank to stop buy a parts store and get a short one to put in by hand and drive home, without the balancer coming off...

Most likely the outer ring slipped, causing the vibration, and that fatigued the bolt, and then it broke.

When you replace the balancer, inspect the crank key, and the keyway carefully. If the key is damaged, replace it. Hope the crank slot/keyway is not hurt.

I lost two balancers in 92, including the new Ford one I installed without really checking the key. New key, and the next balancer was the stock 78 unit that came with the crank from the junkyard. It is still on the engine and goes to 6k regularly.