Soft crankshaft?

Reply Subscribe

Thread Tools

Search this Thread

Nov 25, 2007 | 04:44 PM

noah1504

Thread Starter

Teching In

Joined: Nov 2007

Posts: 2

Likes: 0

Soft crankshaft?

I just got donw putting back together a 1997 5.7 vortec in a Chevy 1500 truck It had a pretty bad spun rod bearing and I had to get a reman crank and new bearings and 4 of the rods got reconditioned. Started it up and it ran good except a little miss but got that taken care of it ran for about 30 mins then we took it for a drive. It throw a rod and head no evidence of a spun bearing.... do cranks ever have soft journals like cams have soft lobes not to mention the machine shop gave us the wrong gasket kit and timing chain it was for a pre 1006 any chance the crank was soft?

Thanks

Nov 25, 2007 | 04:51 PM

joelster

10 Second Club

Joined: Oct 2007

Posts: 2,630

Likes: 28

Hrmm, maybe possible, but most likely a badly machined crank. I've had this happen to friends of mine before. Put a .010/.010 crank in, engine runs for 5 minutes, then, clunk, clunk, clunk. All on stock non-performance motors.

Nov 26, 2007 | 07:33 AM

8a8mfh

Banned

iTrader: (3)

Joined: Feb 2006

Posts: 1,943

Likes: 0

How do you figure a soft crank caused a thrown rod?
The only thing that would do is wear the journal down faster.
I've seen a lot of turned cranks put in and waste bearings because the oil galleys are not properly cleaned, but you say there was no sign of a spun bearing.
I'd say it was a weak or over torqued rod bolt.

Nov 26, 2007 | 02:05 PM

1997bird

TECH Fanatic

iTrader: (2)

Joined: Nov 2006

Posts: 1,360

Likes: 0

From: Aztec, NM

Why would you only recondition 4 of 8 connecting rods? Thats an expensive mistake. I agree with 8a8mfh on a weak rod bolt. You would have to have a crank that was turned .030" or more before running into a problem with the crank. Did the motor start knocking while you were out driving the truck just before the rod let loose?

Nov 26, 2007 | 05:55 PM

edcmat-l1

Banned

iTrader: (10)

Joined: Jul 2006

Posts: 4,782

Likes: 4

From: Va Beach

WTF do you mean 'throw a rod'? Did the rod break? Thats not the cranks fault. Did a cap come off? Again, not the cranks fault.

Nov 26, 2007 | 06:49 PM

02fastbird

Teching In

Joined: Dec 2006

Posts: 21

Likes: 0

From: elizabethtown,ky

vortec motors have cracked cap rods and cant be reconed...maybe your prob

Nov 26, 2007 | 09:14 PM

CNC BLOCKS N/E

On The Tree

Joined: Oct 2006

Posts: 124

Likes: 0

From: NORTHEAST

Quote:

Originally Posted by 02fastbird

vortec motors have cracked cap rods and cant be reconed...maybe your prob

All the P/M rods we have seen that have come out of the newer engines the caps have not been cracked as they are machined and can be resized but can not be straightened if they are out of alignment as they will break.

Double check and make sure the rod was not installed on the piston backwards