Engine Dss 347 Crank Failure... Possible Causes?

Cobra4B · Aug 9, 2012

This was in my father's road race Panoz with a DSS 347 with a stud girdle, road race build, AFR 165s, custom cam, Edelbrock Performer RPM Air gap, Pro-Systems carb etc. Made 370+ rwhp. Never ran right all last year; never made it through a full track weekend without some sort of problem. Finally the bed this February at VIR on the back straight at the top of 4th. No warning, no issues with oil pressure. Started ticking last fall, but the shop who built the motor swore it was a lazy lifter. I felt it was rod knock. Upon tear down all the lifters looked fine, but the rest sure didn't...

Supposed lazy lifter...

Before...

After... Snap goes the crankshaft. The mains are all intact, rods banged up but all intact as well.

I'm currently earing the car down to the bare chassis and fully rebuilding it with a new LS1 crate motor and TKO600. Tired of blowing up Fords (this is the 2nd one to snap the crank). My 2001 Z06 race car has 123,xxx miles on the longblock and the last 3k have been all track/race use... done playing with Fords.

LS1 currently being prepped...

Build thread - http://ls1tech.com/forums/conversions-hybrids/1559870-rebuilding-dads-panoz-ls1-swap.html

2000xp8 · Aug 10, 2012

What kind of rpm were you running?

That a stock 302 block or race block?

The stock 302 block doesn't put up with any type of sustained rpm for too long.

Not going to try and talk you out of the LS engine, because for your uses, it's probably better than a pushrod 302.
But it wouldn't hurt to consider a 2012 boss 302 crate engine.

BTW, that pic says it all on why girldles are worthless.

Noobz347 · Aug 10, 2012

That's some of the best carnage that I've seen on a DSS yet.

7991LXnSHO · Aug 10, 2012

Possible lessons - Trust your ears and get a mechanic's stethoscope to pinpoint the noise? Skip the stud girdle and go for an aftermarket block?

If you find out what happened to cause the disaster, I'd like to know.

AWESOME carnage. Did you have a vinyl seat cover and extra undies when it happened? I bet most of us would have needed them.

Noobz347 · Aug 10, 2012

7991LXnSHO said:
Possible lessons - Trust your ears and get a mechanic's stethoscope to pinpoint the noise?

A little late for that.

Cobra4B · Aug 10, 2012

2000xp8 said:
What kind of rpm were you running?

That a stock 302 block or race block?

The stock 302 block doesn't put up with any type of sustained rpm for too long.

Not going to try and talk you out of the LS engine, because for your uses, it's probably better than a pushrod 302.
But it wouldn't hurt to consider a 2012 boss 302 crate engine.

BTW, that pic says it all on why girldles are worthless.

Stock 302 block. But it should have been plenty of this power application and 6000 rpm rev range. To my eye it appears the bottom end didn't fail first, the crank did.

LS1 crate engine = $2900 (all aluminum, 6-bolt mains, 430 rwhp with a cam swap, stock bottom end can handle 555+ rwhp)
FRPP Boss 302 crate engine = $7400 (iron, 4-bolt mains)

IMO the LS platform was a no-brainer once I figured I could just get a quicktime bellhousing and run the same style transmission etc. etc.

Are these DSS setups known for failing? The shop he used recommended the setup for a reliable 350-370 rwhp 6000 rpm trackday/road race motor.

rd · Aug 10, 2012

Is that a cast or forged crank? What was it balanced to 28-50 or neutral?

RangerJoe · Aug 10, 2012

There was a discussion on here a year or so back regarding aftermarket blocks with cast cranks versus stock blocks with forged cranks. Many claimed that a factory block will flex so much on the bottom end, that the crank is allowed to roll and flex, causing failure. This same group making this argument claimed that this is why it is worth it to put a 800HP capable forged crank in a 500HP capable stock block. The same group claimed that you can get away with using a cast crank in an aftermarket block because the mains and block are so solid that the crank will not flex like a stock block.

About the same time this discussion was going, one of the populare Mustang mags built up two seperate engines in the same issue. One was a stock block with all forged internals, the other was a Dart based block (built by Dart if I remember correctly) and it used a cast crank. So maybe a little truth to the claim.

My point in all this is to say, the stock block is thin and will give under high stress. IMO, 6000RPM blast down the 1/4 are fine on a stocker, but sustained RPMs is a lot for one to handle. The bottome end probably flexed and let the crank flex as well. Just a thought.

Joe

Cobra4B · Aug 11, 2012

FWIW the crank was a Scat forged 4340 crank.

RangerJoe · Aug 11, 2012

Cobra4B said:
FWIW the crank was a Scat forged 4340 crank.

Scat makes good stuff. Not saying their stuff doesn't have flaws, but that would make me lean towards the block weakness. Ford made alot of block improvements in the mid to late 90's, Unfortunately for us fox guys, it was done in the form of the mod motor. The LS block are definetly tough.

Joe

MFE92 · Aug 11, 2012

Tell us if you see cracks between the main bores and the cam bores, and possibly all the way down the center of the intake valley. That's how the stock blocks fail, and when they do, they open up bearing clearances and things get ugly. IMHO, that crank didn't start the problem, the block did. FWIW, I split a stock 302 block in the typical fashion, but with only 260-ish RWHP, and I did it chasing down a Lotus Elise at Mid America Motorplex. All I initially noticed was a drop in oil pressure, but the other odd thing was the oil pressure gauge acted like a vacuum gauge. When I applied load, the pressure went down.

I drove it home 2.5 hours and even ran it for a few more days before figuring it was time for a rebuild. When I tore it down, the cam bearings were walking out of their bores (and getting banged up by the cam lobes), and I discovered the cracks in the block. The vaccum-gauge action of the oil pressure was because when I applied load to the block, it flexed and opened the clearances, lowering the pressure. 6000 RPM sustained is just too much for a stock block IMHO. I'm still running a stock block though, because I can rebuild it twice more for just the cost of a Dart block, and I just keep the revs under 5800.

Cobra4B · Aug 11, 2012

Funny.... I can't get the cam out because one of the bearings came loose and tries to come out with the cam. I don't see any cracks from the top in the valley area, but the main webbing is completely split from the block. Is that the area you're describing between the mains and the cam bearings?

MFE92 · Aug 11, 2012

Here's how it starts:

lots of good tech in this thread http://forums.corral.net/forums/5-0...r-one-reason-stock-302-b-breaks-pics.html

Here's how it ends, in this case another DSS 347 from this thread: http://www.460ford.com/forum/showthread.php?t=103161

2000xp8 · Aug 11, 2012

Cobra4B said:
Stock 302 block. But it should have been plenty of this power application and 6000 rpm rev range. To my eye it appears the bottom end didn't fail first, the crank did.

LS1 crate engine = $2900 (all aluminum, 6-bolt mains, 430 rwhp with a cam swap, stock bottom end can handle 555+ rwhp)
FRPP Boss 302 crate engine = $7400 (iron, 4-bolt mains)

IMO the LS platform was a no-brainer once I figured I could just get a quicktime bellhousing and run the same style transmission etc. etc.

Are these DSS setups known for failing? The shop he used recommended the setup for a reliable 350-370 rwhp 6000 rpm trackday/road race motor.

I think we are talking about 2 different boss crate engines, i speak of the 2012-13 engine, which i think is like 12 grand, lol.

Where do you get an ls1 crate engine for $2900?

Cobra4B · Aug 13, 2012

Crate Engine Depot . com

elarm1 · Aug 13, 2012

Yup I did the same thing with my 306 last year. Super spinning that stock block is not good!

2000xp8 · Aug 13, 2012

Cobra4B said:
Crate Engine Depot . com

For curiosity's sake, i went to that website to see about the engine you speak of. Cheapest LS 430hp crate engine i could find was $6200, that's no accessories, no computer and no carb setup (i'm assume you need one or the other since you currently run a ford engine).

I like LS engines, but unless i'm missing something, it's not happening for anywhere near $2900.

95Vert383AOD · Aug 13, 2012

I beat the piss out of my 351 based stroker. Its def. seen 7000RPM spinning tires around corners and keeping the pedal to the floor as i straighten her out tires still spinning.

Mishimoto · Aug 14, 2012

We need to see pictures of the car this engine came out of, please.

Engine Dss 347 Crank Failure... Possible Causes?

Cobra4B

2000xp8

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

7991LXnSHO

wanna catch the space herp

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

Cobra4B

rd

RangerJoe

I leave the horn on while driving

Cobra4B

RangerJoe

I leave the horn on while driving

MFE92

Cobra4B

MFE92

2000xp8

Cobra4B

elarm1

2000xp8

95Vert383AOD

Mishimoto

Member

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