Broken SBC crankshaft
 

Well my season ended early at the Jackson pro am last weekend. The crankshaft broke right behind the #8 rod journal. Several runs before the broken crank I had an oil pump snap off at the neck and fell into the pan. The engine was completely freshened and had the crank turned .010. Might have been some residual damage from the oil pump hitting the crank. Also the #4 main bearing was burned pretty bad. Other than the #4 main all of the other bearings looked good. What are some of you using for crankshafts. I think the one in the engine might have been an Eagle lightweight. Super Stock 350/295/313 SBC 2.00" rod journals. Thanks.

Re: Broken SBC crankshaft
 

Callies has a really good stock and superstock crankshaft from what I have seen.

Re: Broken SBC crankshaft
 

BRC 4340 .........which has chromed rod journals. This crank has been through hell.........passes mag check , straightness every time.
First time , ( in '01 ) a Manley aluminum rod broke. Crank kicked it right through the block.
Last year.......
I lost an engine from what I thought was a rod failure ( aluminum ) and turned out to be an oil pump bypass spring breaking ( no oil pressure ) .
Sent the rod through the block , again.
Last time.........recent , apparently the damage from the previous carnage above fractured / cracked the oil pump drive shaft and I didnt see it.............it broke , and I lost oil pressure AGAIN , only this time I caught it before it killed everything. Polished crank , sent rods to GRP for evaluation.........they replaced 2 rods because they were a little out of shape on the big end. And let me just say this.........GRP is a stand up company because they replaced those 2 rods at ZERO charge to me.
Those rods had 14 runs on them at the time.
So as you can see , my crank / cranks take a beating and come back for more.........:D

Re: Broken SBC crankshaft
 

if crank wasn't magnafluxed when ground, may have been cracked and then broke.
#4 main bad and others good sounds like crank was cracked and rubbing bearing before it broke, if look closely may see where #3 and # 5 main bearings have been rubbed some,most of the time when you have a few main bearings rubbed/wiped out the crank will be cracked and flexing.
Was the radius left in crank when reground?If had 1/8 radius and it was cut less or square that weakens the crank also.
When I tear into engine with broken oil pump,I check balance of rotating assembly,clearance between oil pump shaft and block and oil pump pick up/pan clearance.
but there is chance since most bearings were OK that crank broke and vibration from that broke oil pump.
Mike Taylor 3601,

Re: Broken SBC crankshaft
 

Unfortunately we did not magnaflux the crank before it was ground. The radius on the crank was real nice when we got it back from the grinder. The break was right in the same area that would have been damaged from the oil pump breaking off. the burned bearing has me puzzled though. Maybe the cracked crank was pushing some metal through the system but the two rod bearings next to the broken area were still good. The newer model of the Melling M55 pumps are known to break. I replaced that with a moroso billet pump on that last freshen up. I also put a low oil pressure warning light in the car. I shut the engine down as soon as that lit up.

Re: Broken SBC crankshaft
 

That's why I like the guy that grinds cranks for my shop. He simply WILL NOT grind a crank without magnafluxing it first. He has found plenty of cracked ones over the years, they go in the scrap pile :)

Re: Broken SBC crankshaft
 

It has been my experience that the vast majority of crankshafts that fail from fatigue fail either in front of #1 rod journal, or behind #8.


For an aftermarket crank, I strongly suggest Callies, I don't think you'll find anything better for Stock Eliminator or Super Stock.

Re: Broken SBC crankshaft
 

You probably already know this, but just in case... Be sure to have the converter, front pump bushing and front pump checked (assuming the car uses an automatic trans) before you put the car back together. With the rearmost chunk of the crank wobbling around when the failure occurred, they may have gotten hurt.

Re: Broken SBC crankshaft
 

A quick way to check for a crack on a forged crank is to hold it off the ground and tap it with a hammer. If it rings like a bell it's good. I it gives a thud sound it's cracked. If it's a cast crank you have mag them.

Re: Broken SBC crankshaft
 

Never reuse a crank, especially in a racing motor, without magging it even if you are not grinding it or even if it did not blow up.