Harmonic balancer breakage...Does the main bolt break first?

phils89sc

Registered User
So what exactly is the reason why the HB's break on our cars? Does the bolt break and allow the HB to walk itself off the crank, or the the balance come apart and the cause the bolt to break? Is it a good idea to just go ahead and replace the bolt now before the HB has any problems?
 
I want the steel balancer but got no $$ for it , so I'm getting a new bolt and going from there. the old bolt is good for mockup and thats it.
 
So what exactly is the reason why the HB's break on our cars? Does the bolt break and allow the HB to walk itself off the crank, or the the balance come apart and the cause the bolt to break? Is it a good idea to just go ahead and replace the bolt now before the HB has any problems?

.more often than not the rubber seperates on the stock balancer and breaks the bolt.........get a solid balancer,check the for sale forum or go to "spinning wheels",one of the prefered vendors......
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it has been said on here that the balancer does not sit flush with crank snout. so....

is it possible to hvae a flat steel washer machined to "fill" the gap from the snout to the washer on the bolt. i mean wouldnt that "stiffen" the whole assembly.

balancers are a terrible design anyway i wish the american auto builders would have taken some advise from germans.
 
my theory

a thought came to me last night -- the key on the crankshaft does not protrude to the end of the crankshaft it stops with about an inch or so to the end which is right where the shear occurs.. with all the weight at the pully and balancer end theres no key to aid the support of the balancer itself and with the aluminum used inside causes a twisting to the heaviest part hence a clean shear leaving snout / sleeve intact due to the keyway in place. as im in the middle of a second balancer job with the same break right where key ends. i feel if key went the length of crank shaft this wouldnt be such a popular issue.. the key way is cut the entire length of i.d. on balancer.
just a thought to ponder would any one else like to agree with this senario ?
 
I had wondered the same thing about the key... mine just broke and I feel that it probably has something to do with it.
 
The stock balancers fail because the center hub is made of aluminum. Either the balancer is removed and reinstalled, or the elastomer breaks down and the otuer ring causes an imbalance in the balancer. This leads to stresses on the hub which cause the aluminum to stretch. This causes the balancer to loose its interference fit on the crankshaft and vibrates against the bolt at the end of the crank, breaking both the bolt and usually part of the balancer.

If a new balancer fails, it is almost exclusively due to the fact that it did not fit properly on the crankshaft. The bolt is not a primary retention device. The key way is to prevent the hub from turning due to the excess horsepower the blower pulls off the crank pulley. The main retention device for the balancer on the crank is the use of a interference fit. The balancer should be .001 -.0015 undersized for the crank so that it needs to be pressed onto the crank snout.

If that interference fit isn't present, the bolt will never be able to hold that balancer on the end of the crank.
 
If a new balancer fails, it is almost exclusively due to the fact that it did not fit properly on the crankshaft. The bolt is not a primary retention device. The key way is to prevent the hub from turning due to the excess horsepower the blower pulls off the crank pulley. The main retention device for the balancer on the crank is the use of a interference fit. The balancer should be .001 -.0015 undersized for the crank so that it needs to be pressed onto the crank snout.

If that interference fit isn't present, the bolt will never be able to hold that balancer on the end of the crank.

Well, in my case I think Dorman gave me a bad one, and I didn't know that they never neutral balance them very well. They told me it'd be replaced under warranty, but its still quite aggravating to go through it. I replaced my old one before it fell apart, the elastomer had failed, but the balancer center bolt was not broken, and the balancer did not wobble.
 
I have no clue what dorman is doing. The manufacturing tolerances of the forged crankshaft are not consistent so if the center hub on the dorman is steel, it will need to be made undersize and finish honed to fit. If it's made out of aluminum, it should still be slightly undersize, and I assume they engineered it to stretch to fit.
 
Just read all this and am wondering....Would it be alright to have a longer key put into the keyway. Makes sense that with the torque it would need the extra length to keep it from breaking. Would getting a longer key be a viable option when replacing the balancer?
 
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