Last week the crank snout broke on my Procharged 1991 Trans Am while cruising on the freeway (no boost).

I am aware that this has happened to several other list members, but would like to learn of the specifics of these crank failures.

Willie had a failure on his forged crank, but from what I understand it was due to a defect from a specific manufacturer.

I am considering rebuilding the engine and replacing the original cast crank with a forged steel crank. However, I may not go this route if I see that others have had similar problems with even forged cranks.

Please list your experiences, both good and bad, as related to the effects of your supercharger on the crank.

Thanks!

 

the cast crank is definitely a likely culprit there.....although crank snouts do break off forged cranks too.....generally it's caused by having the belt too tight, with a serp belt its tough cause if its not tight enough it will slip, and if its too tight, well you can snap the crank snout lol.

if you're super concerned about it happening again, ASC racing makes a crank snout support with ball bearings in it for procharger setups......not sure how street friendly it would be, as it bolts to the 4 lower holes on the front of the block.....but it would definitely work, its pricey though around 1,000 bucks i believe.
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PS......what blower do you have? how much boost? and how long has it been on there?

 

Willie had a failure on his forged crank, but from what I understand it was due to a defect from a specific manufacturer.

Here's the entire story. With the original factory crank and a SuperDampr, the crank snout did not shear off. Rather, the balancer cut the keyway (see pic). I replaced the crank with a 4340 Scat piece, a ATI balancer with ASSC's inner hub. It's much thicker, stronger and has two keyways. No change in the supercharger stuff. With under 1800 miles, the crank snout broke. Upon inspection by several mechanical engineers, I was told the fracture occurred over time and the breakage occurred along the weakest plane, just at the base of the chamfer. Coincidentally, the end of the bolt hole stopped on the same plane. This may or may not have contributed to weakening the weakest part of any crank. In any case, I believe this crank was NOT spec'd to U.S. 4340 grade steel specifications as the forging originates from Taiwan. I currently have a class action lawsuit against this company, claiming they cannot advertise their stuff as "Made in U.S.A." After this suit was filed, they immediately modified all their advertisements. However, the lawsuit continues and hopefully, I and many others will be compensated for the time and money.

When my engine was disassembled after the last failure, we found zero evidence for the cause. This leads us to believe the crank was at fault, simply because I did not put additional stress on the engine during it's initial 1800 miles -- no boost.... Having found nothing obvious, nor anything that may have caused this failure, we can only surmise the crank was defective. In as much, I still didn't feel comfortable rebuilding the engine and doing the exact same thing. This is THE primary reason why I decided to go the turbo route. (I think my wife would make me sell my car if this were to happen again, so I didn't want to take any chances!)

 

Mine broke on a stock crankshaft but held up fine with a 4340 and a cog system. I know I overtightened mine and it was my fault it snapped.

 

Thanks for all of the quick replies.

383backinblack, I am running a D-1SC Procharger with an 8 rib belt. I can get 10 lb boost with the pulley set up, but rarely push it.

I have been driving the car as a daily driver with the Procharger since Janurary 2003.

I never felt that the belt was excessively tight.
I still have to investigate the actual failure. As willie noted, his ballancer cut the keyway on his original crank. I will post some photos to show what actually failed on my crank once I start tearing things down.

CRZYTRN-92Z28, does using the cog system help eliminate an over tight belt?

Willie, I am with you on the feeling of not wanting to go through this again. If I am going to spend $$$ on forged internals, I would like to see from others that forged steel has a good track record with a supercharger.

 

your scaring me mypontiac, that suck your crank broke, i'm running the d1sc on my 305 with 10lbs but i had to tighten the belt a lot for my liking to get there, i'm using an 8 rib 7.625 crank and a 4.13" to get 10lbs. i need a cog setup

 

86Z, how long have you been running with the Procharger?

I figured I would end up blowing the engine from taking it to the track. Never made it there though.

Keep us posted on your experiences and maybe you can get some good information from this thread.

383backinblack, can you post a link to information on that crank support?

Thanks!

 

Well Sean, I'm still driving the ticking timebomb...but it's not my daily driver.

sorry about your breakage, it just means you have to build it stronger and faster!!!

Later
Larry

 

im making 22psi right now on an f1r with a cog belt......the cog belt doesnt have to be quite as tight as a serp belt does for obvious reasons lol.......but its still easy to overtighten one.

 

poke around on RCD Engineering Inc. Home

 

383backinblack, I went to the web site and this is definitely the way to go.

I emailed sales and asked if a support was available for the 305.

I am betting that the issue will be with fitting the Progharger pulley along with the accessory pulley.

Hopefully, they can provide the support for our application.

I will update once I get some information.

 

Eww your scaring me... Should I check with my machinist about my crank before I do a Weiand 142?

 

My Stock 305 crank snout snapped ideling in my driveway. It belive it was a combination of things.

1) Vortech belt tightened to tight.
2) Accy. belt routed incorrectly. Instead of the belt routed on the crank pullies right side, it was routed on the left, the same as the Vortech belt. Both belts were pulling in the same direction.
3) Poor tune with cold start. At idle, it would shake like crazy until closed loop.

Iwill make a spring loade tensioer for the Vortech pullies and up grade to an 8 rib belt. This should prevent excesssive pressure on the crank.

BTW for my rebuild I used a Scat cast Nodular Iron crank. I'm betting it was more my errors that caused the failure and not the material as much.