BHJ Damper Update

gldiii

SCCoA Lifetime Member
In the next post is the promised email letter I received from Brian Clarke (President of BHJ Products) containing their company response to the issue posted earlier on their SC/XR7 dampers.

For those of you that are unfamiliar with previous posts on the subject, here are a few links for reference:

http://www.sccoa.com/forums/showthread.php?t=46828

http://www.sccoa.com/forums/showthread.php?t=50482


SCCoA FAQ:
(This will be updated with the new BHJ damper installation document and also the wording on the brightly colored tag that will now be attached to each damper. Brian is forwarding that new information to me.)

http://www.sccoa.com/forums/showthread.php?t=18410

There were a total of 11 late model dampers (94-95) that were sold by BHJ that had a stock center bore depth. These were serial numbers 31548 – 31558 (10 to Super Coupe Performance and 1 to Blue Tongue).

All early style dampers and all other late model dampers have the raised center bore. This will remain unchanged on all dampers manufactured in the future.

While there have been no reported issues with using the stock or Mustang damper bolt, an M14 x 1.5 in a 50mm bolt length will give about the same thread engagement as the stock bolt. The BHJ dampers are .425" thicker (approximately 11mm) in the center bore area. The stock bolt was approximately 40mm in length. Replacement bolt should be of the same strength as the stock one, 10.8. Also, use the thick washer like was used on the stock damper.

Big thanks to Brian for taking the time to address this issue that has been a concern of many damper purchasers and potential purchasers. Also, thanks to the posters who brought this to everyone's attention and worked on sources for the longer bolts.

Brian does not frequent the boards very often, but I have offered to forward any outstanding questions to him via email.
 
From: Brian Clarke, President of BHJ Products, Inc.

TO: George Davenport, SCCoA Co-Administrator

George,

I would like to clarify the confusion that has been created regarding the BHJ V6 Super Coupe Harmonic Damper.

When this project began, the design goal was to eliminate the common failure pattern of the “early” model O.E. damper. The common failure occurred when the hub broke off just past the end of the crankshaft snout.

During our recent design review, our notes and calculations proved that one of the solutions to the hub break / failure was to reduce the depth of the hub counter-bore. The counter-bore depth reduction increased the cross-sectional thickness of the hub at the transitional area of the seal, counter-bore and spokes. No other option was available due to the “trigger-wheel” and other fixed design features. Therefore our design correction was actually a “goal achievement” rather than a “missed” dimension as suggested by one of the respondents to your web site.

BHJ’s original verified design was also implemented on the “late model” damper. Our engineering department decided to maintain design consistency in both models by leaving the additional material in the hub counter bore area, even though the larger diameter “trigger wheel” location was moved back toward the engine block on the late model.

The issue of bolt engagement for both models of the dampers has also been raised. We were initially under the impression that the engagement dilemma was related to the “late model” dampers only. Since BHJ has always been and always will be a “customer satisfaction” driven company, we moved to resolve the problem expeditiously. Do to the “late model” having a larger rear diameter, we increased the counter-bore to the O.E. factory depth.

Further investigation has shown that the same bolt engagement situation exists in the early as well as the late model damper. Our design decisions are based on mathematical, mechanical, and empirical data. We have NEVER been informed of ANY type of failure with these dampers. Therefore, BHJ’s position is to maintain our original and proven design concept of additional material in the hub. Both of our dampers will remain consistent in the raised counter-bore area.

Unfortunately, in our haste to correct a “perceived problem” some dampers were shipped. Apologetically to you George and contrary to our previous conversation, a total of 11 of the “late model” dampers with the O.E. factory counter-bore depth, have made their way to market. With the “late model” having the larger rear diameter, we feel there is no issue with the integrity of these 11 units.

To facilitate better communication, we will include with each damper instruction sheet, a brightly colored note informing the end user or installer that a .425-inch difference in dimensions exists between the BHJ damper and the O.E. unit. Additionally, we will note and recommend checking the bolt hole depth in the crank snout, amount of snout engagement in the damper hub, and the remaining distance to the washer face. This will allow the engine builder to make the appropriate fastener decision based on application.

We feel it is necessary to address one other issue, press-fit of the damper to the crankshaft snout. The BHJ specification for steel hub dampers requires .001 - .0015-inch interference fit with the crank snout. Our design sources show the crank snout diameter as 1.377-inch. Subtract the interference amount and a .0005 manufacturing tolerance, and you arrive at our specification of 1.375 / 1.3755-inch.

In most cases our damper will fit right out of the box, but occasionally with tolerance stacking, our damper might require honing. If our instruction sheet is followed using an anti-seize compound and a quality installation tool (such as BHJ Part No. HB-1) this damper will provide many years of trouble free service.

Once again I apologize for my miscommunication on the shipping of the retrofitted units. Thank you for your concern and efforts in clarifying this issue.

Brian Clarke
President
BHJ Products Inc.
 
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