ProMod, TA/D, TA/FC Crankshaft question

I among several others have experienced crankshaft failures (broken in two) at the front rod throw in our blown BBC's.

These cranks have been 4340 cranks. After my 4340 broke I put a Bryant in it along with a crank support, figured I cured that problem. Well after about 45 1/8th mile passes upon freshen up I had the Bryant crank mag'ed as a precaution, sure enough there was a surface crack in the same spot. Shaftech repaired it. These cranks are breaking at the front of the front throw through the lightening hole.

My question is this, do the cranks for PM, TA/D and TA/FC have a lightening hole in the rod throws? Without the holes it would be much stronger in that area, and of course much heavier too.

 

Shaftech welded and re-nitrided it. They said it was a very shallow crack and very repairable...……………...

 

I’ve used and know the people at shaft tech. They are excellent quality and service. I’ve seen some crank supports actually pull in the snout creating a issue.

 

I noticed less galling between the hub and the snout when we moved away from the crankshaft support on our 481x. The alky guys use some sort of special bolt and tapered deal that goes behind the bolt with a ring and (6) really good quality bolts for the pulley. They claim it helps with the flex in the front of the crank.

AI think that the two step is pretty hard on the front of the crankshaft. If your bang it off the rev limiter or use some time of slew rate traction control that rev limits, that is hard on it as well. If your tune up is off slightly and you run into detonation (kicks the belt on occasion, belt looks terrible after a couple passes) that a can be hard on the snout as well. We ran a bbc forged crank in that 481x and went 5.40’s with it at 260 and it was old and run real hard when we got it. We abused it pretty good but never broke a crank. For what it’s worth, I feel that the forged cranks have a better grain structure than the billets.

 

rb, did you have a crank support on that engine? What crank was it?

I did go to a grade 9 3/4" bolt in the Bryant crank after it was repaired, torqued it to 280#...…

I did have to cut the hub off the crank because it was microwelded, that's why I sent it to Shaftech, they found the crack

 

We started with a crank support but the front cover was the original style and wasn’t able to support a crank trigger. After speaking to Terry at AJPE we went with the non crank support model. Around that time we also switched to the hemi rods/flange as we had a hemi clutch and the rod bearings were easier to source than the bbc ones. On the torque, I was told a long time ago from a top fuel guy that 300 lbs was the sweet spot. I had to cut one off also and ever since then we’ve been at 300 ft. Lbs.

 

So what is the consensus, is the crank support worth the investment? For a RCD support, by the time you buy the support, new hub, crank trigger ring and mount etc its about $1500 from RBS

 

Rob are you meaning aa front crank support with a bearing and a brace up front, or a bearing behind the pulley and no brace?

 

We started with the Outboard RCD style. We did not have a roller bearing in the cover behind the pulley when we switched, just the regular #1 main. The whole roller bearing in the front cover was just starting to become “a thing” when we switched.