[Jay S]

Originally Posted by Dragncar

Do you know what the construction of a BHJ balancer is all about. ?

I looked up the construction of the BHJ and what they did was use an aluminum hub bonded to a steel inertia ring. By decreasing the hubs mass they increase the ability to control more harmonics. This style dampener controls a torsional dimension (stock does also) where an ATI or a Fluid dampener would not, and are 2 dimensional. For a big HP nodular crank drag racing combo I think I would still prefer the other style like the ATI with the 3 inertia disks to take out the tougher harmonics. They may say other wise though. That BHJ looks like a heck of a nice harmonic balancer. For a higher hp street and strip combo I would take a hard look at that one.

[PAUL K]

Another nice feature of the BHJ it is more of a "bolt on" balancer. It will use the factory bolt pattern pulley's and not require modification to the timing cover. Fluidamper needs the bolt pattern modified. The ATI requires both. This needs to be considered more for a street build than a race engine.

[Dragncar]

I bought my last BHJ from Nightmare Performance. He paid a bunch to get WD or whatever you call that.
His balancers have a modification to allow for factory AC and sells them for 535 $
He has a big lot of them so what you do is get a exact measurement of your snout and he picks one out that is the correct press fit.
But I had to buy a not so cheap Moroso puller-installer to take it on and off.

Thanks Jay S for explaining all that for me and everyone else.

http://nitemareperformance.com/bhjbalancers.html

[mchell]

Cast crank?

Broke it….

[Tom Vaught]

OUCH!!!!!!!!!!!

Tom V.

[25stevem]

Someone please kick me in the Head here if I am wrong with what I will post up, but I do not see any advantage to a balancer that is such a tight fit on the Crank snout that it needs to be pressed on and off.

The keyway to Crank slot should be a nice tight fit and the keyway into the balancer slot should be a tight fit in terms of degreeing accuracy,
The proper keyway fit should call for the balancer to be lightly taped on with the wood end of a hammer.

With a Pontiac set up and that large 160 psi torque on the balancer bolt its so high that it compresses that main steel section of the balancer a few thousands and holds it in place.

So like I posted, I see no plus side to a pressed on Pontiac balancer, only a negative with the extra work and steps involved in getting it on and off.

[Half-Inch Stud]

The big stress to rework on my engine is the press-fit damper is too brutal to remove or install. Factory Slip fit is sufficient.

[PAUL K]

The press fit of the balancer helps transfer harmonics to the damper and the transfer of the dampened harmonics back through the crank. According to damper experts they say increasing the torque of the balancer bolt will not increase the performance of the damper at all.

[Skip Fix]

The old BHJs would slip the outer ring then they had a fix. I think Steve Coombs had one do that. When I sent mine back to have the new udate they also beveled the outer ring for an A/C pulley.

[PAUL K]

Originally Posted by Skip Fix

The old BHJs would slip the outer ring then they had a fix. I think Steve Coombs had one do that. When I sent mine back to have the new udate they also beveled the outer ring for an A/C pulley.

That was a common issue. We had that happen several times while we were on the dyno. They initially blamed the heat generated on the dyno and told us it was excessive because we were spraying the engines.

[25stevem]

All the pictures in this string ( especially post 84 )with broken cast cranks and even a few I have looked at on line I think show a common failure point.
I see the cracks starting internally at the intersection of the main and rod oil passages where there are a lot of sharp edges that naturally can not be got to and rolled over to help lessen the chances of a crack starting.

These sharp edges must look just like what’s found in the main journals of the block where the oil feed holes meet up.

[Dragncar]

Originally Posted by PAUL K

The press fit of the balancer helps transfer harmonics to the damper and the transfer of the dampened harmonics back through the crank. According to damper experts they say increasing the torque of the balancer bolt will not increase the performance of the damper at all.

Thats how I understand it. Stock slip fit balancers worked with low RPM Pontiacs.
I can not imagine a 9000 RPM engine not having a problem with a loose slip fit balancer.

[Dragncar]

Originally Posted by Half-Inch Stud

The big stress to rework on my engine is the press-fit damper is too brutal to remove or install. Factory Slip fit is sufficient.

The Moroso tool is a nice piece and actually is pretty easy to take a balancer on and with it.
Building up a little bit of engine building tools. The LSM shaft rocker spring compressor is another nice thing to have if you are building engines.
Kind of fun and nerve racking at the same time.

[Jack Gifford]

Originally Posted by Dragncar

... I can not imagine a 9000 RPM engine not having a problem with a loose slip fit balancer...

I routinely ran my hemi V8 to 9,000 on pulling tracks. I've never used a press fit on a Pontiac crank snout (damper or blower pulley hub). However, the hemi hub is not a "loose slip fit"- it's a precise "snug fit", requiring a puller to remove it. Admittedly it's a smaller engine than most of you run- only 370 c.i. and 900 HP.

[mgarblik]

Originally Posted by PAUL K

The press fit of the balancer helps transfer harmonics to the damper and the transfer of the dampened harmonics back through the crank. According to damper experts they say increasing the torque of the balancer bolt will not increase the performance of the damper at all.

This has been the information I have gleaned from reading about torsional vibration, crankshaft balancing, and talking to the folks at ATI, BHJ and others. The ATI balancers are a "light press fit", about .0005"-.0075" press. We always "overtightened" the large bolt to 200 Ft. Lbs. with a balancer and 235 ft. Lbs. with just a hub on the blower engines. Used a very thick hardened washer, a L9 bolt, locktite on the threads and ARP lube under the bolt head between the washer. I know this sounds like overkill and may not add any additional benefit. But I have seen what happens when a balancer bolt backs off or the fit is just a slip fit in a race application. Engine doesn't have to be high performance to break a crank nose. When I worked at the Pontiac dealer we had a campaign for balancer failure on the "T Grand". (Pontiac Chevette" The bolt would come loose, sometimes break in the crankshaft, sometimes break the nose off, sometimes just beat up the keyway. Those engines probably made 70-80 HP. Had to repair a bunch of therm. Replaced a few crankshafts.

[Jack Gifford]

Mike obviously meant .0005"-.00075".

[mgarblik]

Good catch Jack. Anyone that can install a balancer with .0075" press I will address as "sir".

[25stevem]

Address as Sir, and complement the thrust bearing main cap if it was cast iron for not cracking in half, lol!

[Elarson]

Here's a few bits of info about the balancer fit and how it affects the crank nose. As usual, there are no black and white answers. It's all about managing your own set of risks.

When you tighten the balancer bolt, the balancer hub is in compression and the crank nose is in tension.

When you apply side loads from belts (either accessories or a blower) they try to create a bending moment. If the balancer hub is still in full contact with the crank face, the hub face reacts all of the bending load and the crank nose does not have any bending stress. But if the side load exceeds the preload on the balancer hub and the hub starts to lift off, then all of the bending is taken by the crank nose. Since the crank is spinning, the bending stress continuously orbits around and the nose quickly fatigues.

The fit of the balancer on the crank nose is especially important if there are side loads from belts. If there is radial clearance, the belt loads can cause the balancer hub to slide around, fretting the face against the crank and resulting in a loss of the bolt preload. Although there is considerable friction on this face due to bolt preload, friction becomes less reliable in the presence of vibration and heat.

So boiling all this down to a few rules of thumb:
The joint is more reliable if there is no clearance on the radial fit.
Belt side loads aggravate the problems with this joint.
Bolt preload needs to be higher if there are belt side loads. I suspect the factory engineers were worried about people tightening accessories with a 4 foot bar.

So if your race engine doesn't have belt driven accessories, you've reduced the abuse on the crank nose. But....belt driven stuff helps to dampen harmonics. That's how blower drives can work without a "balancer".

So manage your risks and go racing!

Eric

[Jay S]

That last post is also a lot of the reason why modern drives look like this. With the serpentine drive pulley integrated into the outer ring instead of the center hub.