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Semi-retired, as of Feb 1, 2023.
The days of free technical advice are over.
Free consultations will no longer be available.
Will still be in the shop, isolated and exclusively working on project cars, developmental work and products, engines and transmissions.
Have fun with your 928's people!
There are specialty crank welding machines to weld on cranks. And once you have the machine, it's an art to use it properly.
You also need to use the correct welding rod to match the induction hardness of the current material.
And it has to be straightened perfectly, after it is welded, before it is ground.
And there's about a dozen other details that I'm not smart enough to know....
You need to find the right person, to do this, or you will turn this piece of gold to junk.
Yes, you are correct. According to my guy, Gary Grimes of Grimes Machine Shop here in Alpharetta, GA, the submerged arc welding(SAW) in use here was developed by two women engineers. It's all computer controlled and allows the welding of crankshafts immersed in an anaerobic fluid so no oxygen can affect the weld. It is different from other SAW processes that use probes in flux. It's a $60k machine and it's south of Atlanta.
I am looking forward to the repair, additional cross-drilling and maybe lighter.
Snapped a picture of one of the engines because I recognized the harmonic balancer.
Yes, you are correct. According to my guy, Gary Grimes of Grimes Machine Shop here in Alpharetta, GA, the submerged arc welding(SAW) in use here was developed by two women engineers. It's all computer controlled and allows the welding of crankshafts immersed in an anaerobic fluid so no oxygen can affect the weld. It is different from other SAW processes that use probes in flux. It's a $60k machine and it's south of Atlanta.
I am looking forward to the repair, additional cross-drilling and maybe lighter.
Snapped a picture of one of the engines because I recognized the harmonic balancer.
Good that you have it figured out and under control!
Edit:
Kevin: As I sure you are aware, these crankshafts are made from a steel that responds quite well to induction hardening, which is how they make the journals hard enough to not wear, while keeping the surrounding material soft enough to not be prone to cracking.
As a data point, can you ask how they approach this problem after they are done welding and machining?
The crankshaft is due to be ready this week. They welded and straightened it. Mains will be .25 undersized and rod and bearings will be .50 undersized.
While they have it I've asked them to cross drill it.
Your post leaves me wondering whether my original TBF'd GTS crankshaft can be recovered by weld build up on the ground out thrust face.
Will your crank have to be nitrided again to recover the original mechanical properties? Either way, best wishes for a successful outcome
Had to do some research to understand the question. For folks following along at home... Nitriding is a heat treating process that diffuses nitrogen into the surface of a metal to create a case-hardened surface. These processes are most commonly used on low-carbon, low-alloy steels. They are also used on medium and high-carbon steels, titanium, aluminium and molybdenum.
nitriding is extremely common for most crank work and gives a satisfactory hard finish on the journal surface, a few thousandths thick..
the OEM Porsche crank MFR used induction hardening, which is kind of like a super-microwave wrapped around each journal (magnets really) and hardens the material to a much greater depth (1mm is easy) than nitriding would.
like Greg said, that's how the journals can be so hard and wear-resistant under normal circumstances with the rest of the crank being "soft" enough to be very durable overall.
Why not turn it down to a common size like 2" and get lighter stronger rods and not have to pay a fortune for those 0.5 mm rod bearings. The bearings used by Porsche on the rods are rubbish as they are way too soft.
10-12-2018, 01:50 PM
Can this GTS Crank be saved? Yes!
