Cracked crankshaft

[firebat45]

A friend of mine's SHO started knocking recently, and we figured that rod bearings were a good bet. There was no oil light, but this engine had spun a bearing before, 40k earlier. It was ground 0.030" under and matching rod bearings were used.

Well, when I got the girdle off, I immediately noticed a big frickin' crack through the crankshaft! This car is completely stock, and the engine was idling/under no load when the noise started.

As far as I'm concerned, crank grinding is a big mistake. Every incident of a broken SHO crank that I can think of involves a ground crank, especially all those failed stroker engines from Vadim.







It's not cracked into two pieces (yet!) as far as we can tell, just a nice thick crack, definitely not a hairline crack. We're not running the motor anymore, obviously the crank is garbage but the rest of the engine is still salvageable.

Might turn the car into a Lemons racer. This engine has blown up twice now, so we should be good through the competition maybe.

What's the easiest way to swap a crank? I was thinking that we could drop the tranny, take off the rear main and the oil pump housing, and do the swap in car. It's probably just easier to pull the engine and rebuild on a stand, right?


Sorry for crappy photos, all I had with me was my cellphone.

 

[zblackbeast]

How the **** did you pull that off? Do you beat the living **** out of it day in and day out? Regrinding the crank should not cause it to crack like that, at ALL.. especially if you use the correct bearings... Jezz man.

 

[firebat45]

Not my car, so I don't know the absolute specifics of what happened. It wasn't beat on though, it was used as a daily driver and driven in a spirited fashion, but not bagged. Normal driving/shifting most of the time, some moderate acceleration and 5k-ish RPM shifting every now and then.

The engine was rebuilt by the P/O, who is a Ford tech, and he did use the proper bearings.

I'm not saying every ground crankshaft fails, but they are a highly disproportionate percentage of failed crankshafts. SHO crank is case-hardened, isn't it? So grinding off the hardened layer logically seems like a bad idea.

 

[zblackbeast]

Well.. a majority of them, as you stated in your OP, were the SHOShop stroker kits.. But daymn doode.. Poor motor.. New crank time..

 

[93rev2sev]

I can't imagine that having anything to do with crank grinding...now if it had cracked at a journal...that might be blamed on shaving off the case hardened steel.

 

[firstgen89sho]

Blaine, what cyl # is the fracture close to?

It was Prime Engine, near Freedom who did the crank grinding.

That's crazy that it cracked like that, when Dave told me last night, I was real surprised...

Throw another stock crank in her, and she will still be good, as the rest of the engine is still rebuilt. I did not have another stock crank at the time, so I had that one reground.

 

[rubydist]

Its going to be less work overall to pull the engine and put it on a stand, imho. The cranks are heavy, and holding one up under the car while your buddy measures bearing clearances, installs bearing caps, etc. is not going to be any fun.

 

[Off Road SHO]

Its going to be less work overall to pull the engine and put it on a stand, imho. The cranks are heavy, and holding one up under the car while your buddy measures bearing clearances, installs bearing caps, etc. is not going to be any fun.

Ditto.

And since you don't know where the knocking was coming from, you will have to have the rods checked for out-of-roundness.

Tom

 

[zak]

I would examine the radius between the rod journals and the throws. It is possible that they ground 0.03 under and left a sharp step at the edge of the jounral bearing surface (a major stress riser). Who ground the crank? What was the source of the core? Ever run undampened with one of those undampened underdrive crank pullies?

Have a couple of other ideas if that is not it - zak

 

[Bob Gervais]

I would examine the radius between the rod journals and the throws. It is possible that they ground 0.03 under and left a sharp step at the edge of the jounral bearing surface (a major stress riser).

My thoughts exactly. Also, at a regrind of .030", all of the benefits of nitriding were lost. I doubt that has much to do with cracking, but it definitely should have been heat treated again after having so much ground off.

 

[sperold]

Did that crank ever run a supercharger?
That crank looks like it was subjected to the wrong firing order for half its life.
I don't think you can blame that one on a regrind.

 

[firstgen89sho]

That crank never ran a supercharger, and as far as I know, it always had the right firing order, the engine had 220,000 kms on it when the bearing spun, and put on around 20-30,000 after the engine was rebuilt

 

[jonheese]

I'd like to see the whole crank out of the block (or at least with all the rod caps off) before drawing any conclusions about exactly what caused the failure.

Can you tell how far the crack goes, or where it starts?

Regards,
Jon Heese

 

[firebat45]

I'd like to see the whole crank out of the block (or at least with all the rod caps off) before drawing any conclusions about exactly what caused the failure.

Can you tell how far the crack goes, or where it starts?

Regards,
Jon Heese

We will be pulling it out and I'll update, but that's a back burner project, we have other stuff to do. Probably a few months down the road. I couldn't see the end of the crack, it goes out of sight up the crank.

Did that crank ever run a supercharger?
That crank looks like it was subjected to the wrong firing order for half its life.
I don't think you can blame that one on a regrind.

No supercharger, car was bone stock. It ran strong up until the knocking, I don't think the firing was off. I can double check that easily enough though, and people seem to mix up 5 and 6 regularly. Especially since that damn Haynes manual has the wrong firing order in it.

I would examine the radius between the rod journals and the throws. It is possible that they ground 0.03 under and left a sharp step at the edge of the jounral bearing surface (a major stress riser). Who ground the crank? What was the source of the core? Ever run undampened with one of those undampened underdrive crank pullies?

Have a couple of other ideas if that is not it - zak

This is what I think happened. If they left the edge straight, then thats a major stress riser, on top of the strength being lost. Crankshaft was the original one from this car, apparently ground at Prime Engine. No underdrive pullies, bone stock engine.

Blaine, what cyl # is the fracture close to?

It was Prime Engine, near Freedom who did the crank grinding.

That's crazy that it cracked like that, when Dave told me last night, I was real surprised...

Throw another stock crank in her, and she will still be good, as the rest of the engine is still rebuilt. I did not have another stock crank at the time, so I had that one reground.

I've got a 3.0 crank from the engine that's donating it's heads to our Bondurant block, so we will put that crankshaft back in when we get a chance to rebuilt it. The fracture is on the piece of crankshaft between the front (relative to motor, not car) 2 pistons. Pistons 1 and 6 I believe. You can see the dampener in the pictures.

EDIT: My bad, pistons 1 and 4.

 

[jonheese]

The fracture is on the piece of crankshaft between the front (relative to motor, not car) 2 pistons. Pistons 1 and 6 I believe. You can see the dampener in the pictures.

I think you meant 1 and 4.

Firewall
1 2 3
4 5 6
Radiator

Regards,
Jon Heese

 

[93rev2sev]

 

[SuperchargedSHOguy]

I would not blame the grinding on that. Seems like just one of those freak failures that happen from time to time. There have been plenty of people in the past that have reground the crank after a spun bearing and were fine. The SHOSHOP ones with stroker cranks were the main failures with maybe 1 or 2 not breaking.

 

[Bob Gervais]

Fine then. Internal crank cancer, caused by TOO MUCH torque on the crank bolt. Next epidemic? I think so....

 

[93rev2sev]

alls i no is itsanother kina shoBOOM.

 

[St Louis SHO]

Fine then. Internal crank cancer, caused by TOO MUCH torque on the crank bolt. Next epidemic? I think so....

This.

Dr Bab says so.