skpyle

Hello Gentlemen,

I'd like to think that I have been paying attention. As such, I want to address the 30+ year old, most likely ineffective harmonic balancer on the Red Witch.

There are no new balancers. I don't want an NOS one. Just as old and just as ineffective.

I have seen the ATI Superdamper on 928 Motorsports webpage.

I am awaiting a quote from Mary at Precision Motorwerks on Greg's ATI Superdamper and custom hub.

I have searched through Rennlist 928 and have not found mention of anyone having a stock balancer rebuilt.

Why?

I contacted Damper Doctor and got a quote. $150 to clean, inspect, rering, and balance my balancer. I think that is quite reasonable. I do understand the limitations of the stock balancer, especially how it is a slip fit to the nose of the crankshaft. However, right now, stock is OK for what I am doing.

So...what am I missing? Why would having Damper Doctor rebuild my balancer be a bad idea?

Or, should I go ahead and be the guinea pig?


Thanks for your time, advice, and perspective,

Seth K. Pyle

GregBBRD

My damper, using an ATI outer shell is $695. A new batch of inner hubs should be done, any day, at the machine shop.

skpyle

Oh hell, that's better than I expected.

Thanks!

Seth K. Pyle

jcorenman

Seth, Here's my take: If you have the damper out for any reason (like a TB job), then do something besides just putting it back in. When Greg took our GT engine apart (with 240K miles) we found weird wear (with spots of copper showing) on the #1 main bearing, and fretting between block and girdle that we attributed to damper issues.

The choices depend on budget and your situation. If it is a new build or an engine that you care about, and the budget permits, then go with an ATI damper. If that's not an option then try the Damper Doc, it's got to be better than old/hard stock.

Speedtoys

Greg:

Other than knowing it's there, is there any NVH differences between a 30yr old unit and an ATI?

928S MN

Besides the GB fuel lines, some of the best money I spent on the re-fresh.

dr bob

The damper on the crank nose is there to stop rotational (torsional) vibrations that happen due to the way piston forces are applied to the crank in normal driving. With the uneven torsional load applied and the elasticity of the crank itself, the crank actually "rings" especially at the non-drive end (front of the crank in the car) unless there's something there to dampen the ringing. As Jim and Greg shared from Jim's build, the "ringing" upsets the film of oil in the main bearings, causing what's called a "whorl", a tiny circular spot of no lubrication. When the crank does that little torsional ringing, the surface at the bearing slows or stops momentarily relative to the oil and the bearing surface. The lubrication in the plain bearing depends on motion to maintain a wedge of oil to support the crank off of the bearing. When the rotation stops, even just an instant, that wedge collapses and there's a potential for contact. In Jim's case, it was serious enough to disturb the bearing shells in the girdle, with a little polishing from the movement.

There's no aural evidence available, and no direct contribution to total NVH from a failing damper.

Seth: I'm wide open to you having one rebuilt if you are comfortable doing so. To make this a true validation of the work though, you'd tear down the engine enough to document the current condition of the the main bearings. Then run the car for xxx miles. Then another tear-down and inspection to see if there's any additional wear from torsional vibration. Maybe install new bearings in the forward positions so you have a new clean starting point for the evaluation.

Most think of a damper as "good" if the ring doesn't fall off while driving, but there's a lot more to it than that. Still, new non-hardened rubber in the rebuilt damper stands a much better chance of doing the job. So long as the ring doesn't fall off while driving.

hwyengr

Noting that this isn't necessarily a one-off situation, I had the same markings on the outside of main bearing #1, was showing copper on the inside of #1, and had significantly fewer miles than Jim did (73k shown, but history of broken odo). Just waiting for Greg's machine shop guy to come through with the adapters.

Imo000

I wouldn't hesitate using a NOS unit. 30 years sitting in a box, in a climate controlled environment is not the same as spending the same time under the hood.

GregBBRD

I believe that the "damper problem" is way worse than people are aware....and is only going to get worse, as the stock dampers age further.

I've been rebuilding/repairing 928 engines since they were first introduced, in 1977. I can't even begin to estimate how many engines I've had apart, over the past 40 years....literally hundreds and hundreds of them.

In the "early" years, it was very rare to take apart an engine that had any sort of main bearing wear.....the inspection of the rod bearings was almost always sufficient. And the fact that the main bearings looked almost perfect was irregardless of mileage.

These days....rare to find a good set of main bearings.....even on "low mileage" engines.

I believe that the significant increase in main bearing wear that I've observed, over the years, is the direct result of the dampers no longer "absorbing" the harmonics. These harmonics are being transferred directly to the main bearings and the crankcases. It's the only thing that makes sense, to me.

And the problems I see gradually seem to be getting worse.

I took apart a GTS engine with 240,000 miles on it, this last year. The rod bearing were the absolute best set of rod bearings I've ever seen. They looked like someone had put them in the week before I took the engine apart....virtually no wear anywhere.

The main bearings, conversely, were the worst set of main bearings I've ever seen. The center main had spun a slight amount, presumably from a flexplate issue. The rest of the main bearings were terribly pounded, with copper showing in various spots. The cradle had been "working" on the block. We had to surface the block and alignbore the mains back to standard, to "save" the block.

The Porsche "design damper is a "slide fit" onto the crankshaft. I understand why they did this.....but the compromise of not having the damper fit tightly onto the crankshaft decreases its' ability to absorb harmonics. That's strike one. The age of these dampers has allowed the rubber separating the inner ring from the outer ring to harden, decreasing the ability to absorb harmonics. That's strike two. Now, from my direct observations, main bearing are getting significantly pounded....

This is not a product I actively talk people into buying (except on high performance engines.) I don't try and sell someone a damper, each and every time I work on the front of client's engines.....I do not think that the problem has grown to this point. However, I believe that as time passes, we will see enough engine damage from bad stock dampers, that this could become a possibility.

GregBBRD

What is NVH?

dr bob

Noise - Vibration- Harshness

It's the collective impression that the driver and passenger experience. The term is probably not really applicable in the subject context.

skpyle

Greg: I have a blunt, yet possibly silly question. Is an ATI Superdamper a waste of time and money on a stock 165,*** mile 928 engine?


Thanks,

Seth K. Pyle

SeanR

Greg, put one of these in a box for me to roger please. I want one for my car.

GregBBRD

Truthfully, that's a tough question to answer. I'm about as far from a "hard sell" guy as you will ever find. Except for the small amount of people on Rennlist, other people in the 928 world, have to "find" me. I'm not out there "pushing" my stuff.

I think the fact that the stock dampers are not a tight fit on the crankshaft made them very marginal pieces, from day one. (If you talk to people that specialize in crankshaft harmonics, they flat say that if the damper isn't a press fit onto the crankshaft, you might as well not bother.)

The increase in main bearing wear and the "fretting" of the upper and lower crankcase pieces that I frequently see these days, concerns me, greatly. And I believe that this increase in wear is proof that the stock damper actually did work (before the rubber became hard), to some degree.

What is the long term effect of this? Increased bearing wear, which decreases the amount of oil that can get to the rod bearings? Pounding of the crankcase so far that the crankcases are junk?

Let me give you my perspective to this issue....

There's no question that the original rubber dampers are mostly all bad, at this point in time.
....And there's no downside and lots of potential upside to changing to a more modern design damper, instead of the old rubber version.

$500 better?

I honestly don't know.

But a single set of Porsche main bearings is now over $500.....and an original number crankcase is going to be worth many thousands in the original chassis (if the car is sold)....soon.