Harmonic Balancer

[Pat Bush]

Re: Harmonic Balancer

Bob -

I am an engine machinist. As others have said, yes it can be drilled and tapped in the car, but if I were you, I wouldn't try it yourself. Even I would not do it in the car freehand -- it is way too easy to get the drill slightly cocked given the position and location of the nose in the car. Screw up, and you are done.

I would pull the motor and have the crank drilled and tapped by a machinist if you have slop on the nose. First though, try a new woodruff key in the crank. Often times they get buggered if someone improperly tries to seat the balancer on the nose or if you lose one. As long as the keyway is not rounded or will not hold the key, this is your best bet at an "in the car" fix. This you can do on the car without too much aggravation.

I did do this a couple of times (to install a helicoil) on a 69 Chevelle and a 71 Monte Carlo with the crank in the car and fabricated what I needed. It was essentially a 3" round X 1/2" wide steel doughnut with a 7/16 hole drilled dead center in the middle as a guide. Three posts were gas-welded to the doughnut and then tapped on the outer ends to grip the nose. I wrapped the nose in thin copper to not bugger up the finish. These were loosely attached with a pilot down the center of the nose, fastened with the pilot in place to lock center, and then drilled and tapped without removing the guide. I also had the car up on a lift so I could appropriately support the drill. It worked fine but I had all the equipment to make what I needed to get the job done.

Good luck with your solution. If you need help, email me and I can send you plans for the tooling.... I just have to find the thing in my toolbox.... It's there somewhere but it's been 15 years since I did it!

Hope this helps --

Pat

[Joe L.]

Re: Harmonic Balancer

Bob-----

The GM #3896904 balancer remains available from GM. It's a bit expensive with a list price of $163.42. However, you should be able to buy it for at least 25% off that price.

Also, keep in mind that the configuration of this balancer is not exactly like the original used for your car (for that matter, the replacement that you have on there now is likely not like the original unit, either). The original balancer is of a "stepped" design. The 3896904 balancer is of uniform thickness. In my opinion, it's a better balancer from a functional perspective. Also, it WILL SERVICE your application perfectly.

[Robert D.]

Re: Harmonic Balancer

Thanks guys for all the information. I will order the new balancer and try that
with a new keyway and some type of compound.

Bob

[Joe L.]

Re: Harmonic Balancer

Bob------

If you have the instruments to do it, when you get the new balancer measure the ID of the crankshaft hole. You can do this with an inside micrometer, snap-gauges/outside micrometer, or, even, a good vernier caliper. I'd be interested in knowing what the ID of this balancer is. You might also want to measure the ID of the balancer that you're taking off. If there's a difference, that will tell a lot about the reason for your problems and whether or not you really need to do the staking mod I described and/or use Locktite. If the new balancer actually has a slightly smaller hole producing a tighter interference fit with the crankshaft snout and you do either of the foregoing, then you're going to have a hell of a time ever removing this piece when and if you need to.

This is going to have to be a very precise measurement, though, since there will likely be only a few thousandths difference. Those few thousanths can make a BIG difference here, however. If you can't do it or don't have the instruments, perhaps a local machine shop that you do business with would do it for you. It would only take them less than a minute.

[Robert D.]

Re: Harmonic Balancer

Joe,
I will try to measure the ID of both balancers and let you know.If the new one is smaller I will not use anything but a new keyway.

Bob