Attention Crank Vendors...

[mgmshar]

I mentioned this idea on another board, but didn't hear anything back. Just curious...

I've discussed this with some "experts" (automotive engineers) at work, and they seem to think that the following would be possible, and economical. Thoughts?

1. Procure a NA 3.8L crank (they're everywhere!).
2. Fixture the crank, and fillet roll all of the journals (like a turbo crank).
3. Cut the crank to .010/.010 (or whatever) to take out any blemishes and to re-straighten the crank.
4. Presto! You now have a used "turbo" crank!

The thought would be that this would be much less expensive than buying a new billet crank. As long as the original NA crank was in good shape, I would think that one of these would be just as good as a used turbo crank.

[KendallF]

I mentioned this idea on another board, but didn't hear anything back. Just curious...

I've discussed this with some "experts" (automotive engineers) at work, and they seem to think that the following would be possible, and economical. Thoughts?

1. Procure a NA 3.8L crank (they're everywhere!).
2. Fixture the crank, and fillet roll all of the journals (like a turbo crank).
3. Cut the crank to .010/.010 (or whatever) to take out any blemishes and to re-straighten the crank.
4. Presto! You now have a used "turbo" crank!

The thought would be that this would be much less expensive than buying a new billet crank. As long as the original NA crank was in good shape, I would think that one of these would be just as good as a used turbo crank.

The fillets are rolled hydraulically, using special tooling. I don't think anyone other than the OEMs will be equipped to do this. An idea I've had is to grind a NA crank to SBC journals, using a large radius at the journal edges. The radius is what prevents stress risers from forming. You might also be able to widen the rod journals to wide journal rod specs while turning it undersize, and get a radius on the journal while doing that..

[Mike Licht]

Kendall is right on. We looked into this years ago and the equipment to do the rollling is just not accessable. Your other idea is interesting but I think we would have a few hundred plus a core whenit was all done not sure how much we would save.

Mike

[V6DVette]

I know a lot of guys are scared away from N/A cranks but with less and less turbo cranks avalible wouldn't the N/A cranks be OK in a car that only sees the street and very little full boost passes? As time passes and fewer cranks are around the price will only go up. How many guys loose their cranks on the street? :confused:

[GNX Guy]

For those that may not know.

Eagle will be offering a replacement crank for our cars in the VERY near future. I confirmed this with them as SEMA last month.

Joe

[mgmshar]

...an interesting footnote. I found a copy of an SAE (Society of Automotive Engineers) paper that was written by GM in 1978. The paper gives an overview of the technical development of the 1978 carbed turbo V-6. It was interesting to see some of the engineering and thinking that went into that first attempt at a turbo-V6. For example, they mounted the turbocharger after the carb and right on the top of the intake manifold "to minimize undesirable 'lag'". Hmmm...

In the paper, they mentioned that crankshaft failures were a problem during the development of the 1978 turbo 3.8L engine. Here is an interesting quote from the paper:

"Crankshaft failures were exposed primarily on dynamometer durability. These failures consisted of cracks or fractures in the fillets of the crossover area between No. 1 and No. 2 rod journals or between No. 2 rod and No. 2 main journal. The fatigue failures were caused by increased loads creating excessive tensile stress in these fillet areas.

A manufacturing process that induces static compressive stress in the fillet area to help offset the dynamic tensile stress was incorporated. The 'rolled fillet' process (Figure 28) provided an increase of crankshaft bench fatigue life in excess of 5 times that of the conventional crankshaft."

When you look at the photo of the crank (from 1978, with the rolled fillets), it looks darn near identical to the LC2 turbo crank. Funny how that design work done in the 1970's carried-over.

I wonder what would have more fatigue life - a cast crank with rolled fillets, or a steel crank without rolled fillets? :fragez:

Here's the required funny smiley icon that must appear in every post on this board...

:wc: