harmonic balancer question

ken_79-fj40

 
 
 
Joined
Jul 2, 2002
Messages
1,373
Location
New Hampshire
I searched around a bit, but didn't exactly find my answer. A few years ago, My balancer nut loosened up and I had a terrible (duh) vibration in the motor. I luckily discovered what it was and tightened it up. All was fine, but the pulley/balancer was a bit wobbly from that point forward. So this weekend I heard/felt the same thing again. So I drove home and got out the 1 13/16 socket again. I put it on the nut, and it just turned the crank, but the balancer was loose. So I got out my impact wrench and tighted it up. Now it's tight, and the pulley doesn't wobble. But now i'm a bit concerned I might have buggered up the threads in the end of the crank. Is it common for these nuts to come loose? Am I worried about nothing? I plan on rebuilding this motor next winter, but I want to reuse the crank and balancer.
 

Mark W

 
Joined
Jan 7, 2005
Messages
6,381
Location
The Greatland
It sounds like your balancer, crankshaft and locating key are all damaged. The only thing holding the balancer in place is the friction of the crank nut. Normally (when the nut is kept tight) all of the rotational positioning is acomplished by the key. When the nut comes loose the keyway in the crank and the balancer fractures pretty quickly as does the key.

Repair requires a new balancer, a new key and some careful brazing and grinding/sanding of the cratered area around the keyway in the crankshaft.


Mark...
 

ken_79-fj40

 
 
 
Joined
Jul 2, 2002
Messages
1,373
Location
New Hampshire
Mark W said:
It sounds like your balancer, crankshaft and locating key are all damaged. The only thing holding the balancer in place is the friction of the crank nut. Normally (when the nut is kept tight) all of the rotational positioning is acomplished by the key. When the nut comes loose the keyway in the crank and the balancer fractures pretty quickly as does the key.

Repair requires a new balancer, a new key and some careful brazing and grinding/sanding of the cratered area around the keyway in the crankshaft.


Mark...

Hmmm. Not cool. Replacing a balancer I can do, but theres no way i'm messing with a crankshaft. Perhaps I'll keep my fingers crossed it stays tight until it's rebuild time and let the machine shop deal with the crank when the time comes. Stayed tight for 10k miles last time. And yes #4 is there, not sure if it's still keyed though, The nut wouldn't come off this time. I wasn't about to remove it in fear of it not going back on. So I just used the impact to tighten it. It only went about a 1/4 turn before it was tight. It's funny the first time I went through this it seemed like these things coming loose was really common. That tbi 350 sitting in the corner of my garage is tempting me.
 
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