[Half-Inch Stud]

Well, the rattler concept can be applied well to the PMD damper: 9 pockets can house 9 brass cylinder bobs of 3 differing weights. They all fling to the outer pocket wall and bob back and forth in response to accel/decell, and cover many of the frequencies together.

Yea, i designed such for a UAV engine (and did the PMD in parallel ) drafted it, and spec'd out McMASTER Brass for the bobs. Simple machine work, and a cover plate for inspection and a dab of grease. Well, lost interest due to not having a damper problem. Low risk since the "housing" has the diameter and nearly same mass of our PMD damper. A little thicker toward the timing cover.

[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

[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.

[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.

[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".

[Jay S]

When the second dampener failed on the Rbailey example it would sure seem something was up. Did it break the crank in front of the number 2 main on the rod throw?

This is a little fuzzy to me. But for some reason I recall 4” cranks having more of a tendency to fail mag tests from cracks like Probird described? Am I thinking of 421 cranks?


Very interesting on the Ohio crank breaking down at the main thrust. That is about the only example (so far) with a failure there. I think Steve C’s had a crack there, but it was welded there to fit the 455 N crank in a 3” block. Pontiac is in kind of there own strength category there with the larger diameter mains, it isn’t a place you expect to see a crank break. That must have been a bad crank to fail like that, or they welded up to sell it and didn’t get something right on correcting a issue with the thrust. I don’t think it would fail there from bad harmonics, if it did it would be from more torsional harmonics. We have broke cranks there at the thrust on some diesels, for those it was because the chassis frame on was putting a twist on the block. Broke them in 2 pieces.

[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.

[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.

[Jay S]

I follow now….RBailey, The harmonic balancer was bad on that engine. There is more to it than it fitting tight on the crank snout. The inertia ring can look like it is in good shape, and feel tight, but the rubber connecting the hub and inertia ring can get old and let the inertia ring on the outside move just enough that it is bad, making the harmonics on the crankshaft worse. It broke in the exact place I was asking about. Breaking on the rod throw in front on the number 2 main seems to be from a bad STOCK balancer.

We had an engine that no matter what we did we could not keep the belts on in. Everything was perfect on belt alignment. We eventually figured out the harmonic balancer was bad, replaced it, then it was fine. Belts lasted forever after that. There was nothing at all that indicated the balancer was bad on that engine. If your lucky you will have the timing marks shift to indicate it is going bad. Many occasion’s though, it can be bad and the timing marks still line up. Having the belt whip excessively when you rev the engine up can be a sign the harmonic balancer isn’t doing it’s job, so is having issues with the crank pulley’s breaking.

[RBAILEY]

Originally Posted by PAUL K

That's an interesting story. .. Did your crank pulleys have the factory support plate in place when they broke?

Do you recall if the balancer bolt was still tight after the crank failed?

Yes on the support plate; both times it had a support plate.

And all the bolts were tight ... nothing loose at all. It appeared to be a fatigue failure at the point the factory pulley makes the bend/transition from the flat to the start of the dished area. I might be able to find one of the broken pulleys and post a pic, but Im not sure I have it as I've been reading a book titled "How to throw schitt away"

Jays, the damper did not fail in any way...it was only the pulley that broke.

25Steve, I'm not making any statement about fault of the crankshaft failure etc ... only telling of a sequence of events that led to the crankshaft failure and the fact that I experienced a crankshaft breakage where it seems to be the common place to break them when they do break, that is the 1-2 throw.

Hoping to gain insight into how 2 perfectly good used OEM pulleys broke apart in the way that they did and how that may be a warning to others if they experience the pulley breaking apart that it may be a clue that catastrophic failure could be lurking. After the first pulley broke I replaced it with another identical OEM 2 groove crank pulley. Some 6 months later the 2cnd pulley broke in the same exact way, so then I bought a March aluminum billet pulley and 6 months later the crankshaft breaks.

[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.

[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