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Discussion Starter · #1 ·
with only 9 passes on a professional rebuild-only a polish & w/checked for cracks-the # 3 rod journal broke out of the crank [completely]on a short 6000 rpm burn out-this WAS a 514 svo crank.just wondering what would have caused this to happen-is it a common problem ? this engine was in a rear engine dragster,shifted at 6650 rpm and had been running without any problems--the rods were still attatched and turn freely rods were still full length.any thoughts.
 

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The 514 had a cast steel crank didn't it? I had one (a 4.500 stroke Scat cast) do the same thing two yrs ago. 3/7 rod journal snapped completely off. It had been magnafluxed less than 50 passes before and no cracks were found. Just it's time to go.

They all seem to break on the 3/7 or just behind the front counterweight.

Harmonics of some sort? Who knows.

Good time/excuse to step up to a 4340 steel crank.
 

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Does it look something like this?



This was another guy's recent failure.
 

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I would guess that its just a plain old fatigue failure. Cast material has poor fatigue resistance when compared to forged material.
I’d be happy to run some tests free of charge on the failed pieces, if you’re up to shipping them to me. It would be interesting to test a piece of a forging also. Generate some good comparative data.

Let me know

Jason
 

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broken crank subject

Question for the pros, the cranks seem to break not from a bearing spinning, but for some other reason? I see for sale fully grooved mains, and coated mains and coated rod bearings, does any of that help against breakage of this kind? Most of the cranks seem to break at the front of the engine at a rod journal, I'm wondering why its so common. If its was a cast 514 crank M-6303-a514, its the bigger 2.5 rod journal than the cast 2.2 eagle/scat unit . Both rod journal sizes have had breakage in the same areas, its funny you don't see this breakage in the stock 460 cast cranks that many people run very hard. I'm curious as to the cause.....
 

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Discussion Starter · #11 ·
fluiddampner-I've heard of some grumblings about those from others w/broken cranks-Chrysler-Chevy-my damage was not as severe as that.
 

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Question for the pros, the cranks seem to break not from a bearing spinning, but for some other reason? I see for sale fully grooved mains, and coated mains and coated rod bearings, does any of that help against breakage of this kind? Most of the cranks seem to break at the front of the engine at a rod journal, I'm wondering why its so common. If its was a cast 514 crank M-6303-a514, its the bigger 2.5 rod journal than the cast 2.2 eagle/scat unit . Both rod journal sizes have had breakage in the same areas, its funny you don't see this breakage in the stock 460 cast cranks that many people run very hard. I'm curious as to the cause.....
The stock stroke cranks have more overlap between the two journals.....stouter crank. The stock stroke deals are not making as much power also. Scat is not a fan of dampers with moving inertia weights.
 

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DAMPERS WITH MOVING INERTIA WEIGHTS
A. Fluid, balls, springs, inertia rings with rubber O-Rings, etc. Can
you balance a wheel on your race car if the tires are flat???? How
can your rotating assembly be balanced if to quote one
manufacturer, “These units (Dampers) should not be on the crank
for balancing as the inertia weight may not be centered until the
engine starts.” NEWS FLASH!!!! Centrifugal force will always take
the inertia weight off center no matter what RPM. Your assembly
is never balanced. TELL TALE SIGN!!!! Metal transferred on nose
outside diameter and damper internal diameter . . . A fatigue crack
starts. SNAP!!!! The crank breaks

copy-paste from Scat catalog.
 

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Thanks, Lem!

Appreciate the info! I had a fluid dampener on my 460 jet boat, sold it long ago, I don't use a dampener on my blower motor, engine is balanced with a steel drive hub on front, I'm currently building a copy of FRRP's 514 short block, and will balance it the same as my old 460 was with the steel hub for the blower drive. In your years of dyno experience what should max rpm be on a cast Ford 514? Didn't Ford rate its top hp at 6200? I run the stock 460 crank higher, but the overlap you explained makes sense, less internal leverage on the crank throws= strength/reliability. Any other suggestions for the cast crank applications for a proper build?
 

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I think what possibly happens is that the shorter stroke stock crank by being stiffer tends to resonate at a higher frequency than a crank with smaller crank pins and that is more flexible. I just wonder if it's possible that the stock crank resonates at a frequency that's higher than what can be reached in most applications running with the cast crank. As an example let's say instead of 5500rpm it's at 7500rpm, the engine never goes that high and if it does it's only for a very short period of time.

I've noticed before on circle track Chevy engines running with a stock cast crank to 7200rpm that the damper really takes a beating even when only making 400 or less horsepower. This means to me that the engine must run at, near or around the resonant frequency for the crankshaft during operation..
 

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I was going to say about this thread.....


...the likelihood of that particular cast crankshaft breaking under the circumstances noted (less than 10 passes, less than 7000 rpm) is extremely rare and unusual (ie virtually non-existent). It simply had to be something else serving as the culprit, such as poor tune or--as is often discussed--that damn fluid dampener to which SCAT so vehemently objects.

It wasn't so much the crank as it was other external factors.

Paul
 

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Paul, he said that it was 9 passes since a rebuild.......the crank could have many more cycles than the 9.
 

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more cast crank questions

Well you guys have given some good insight to the breakage, the balancer must be chosen carefully, and the balance job must be accurate. In a cast crank, manual transmission application, would using a aluminum flywheel be a good idea? I was planning on using 40lb steel external balance style for my D9TE block. 3000 lb approx wt. of vehicle. Any tips on making the FRRP 514 motor live as long as possible are appreciated.
 

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Discussion Starter · #19 ·
the crank did have more passes than 9-had probably 450 since new -just been checked - mag fluxed and black lited-when polished and balanced before assy.was in a hardtail rear engine dragster-now in a 4 link red-tune was on the lite side but had run an 8.27 @ 163 mph at 3800 ft w/34 deg timing. 12.6:1 comp w/a429 heads
 

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450 passes

At 450 passes thats more stress than ever would even be remotely seen in our street machines. Still what is learned at the track can absolutely help us build our motors better. I would say this site has helped us all avoid expensive mistakes, and we constant learn more to improve our engines. I learned from this about balancers, prior I thought Fluid Dampener was a good part, now I see that some manufacturers don't recommend them in certain applications. Everything I can learn is going into my new motor which is in the machine shop right now, so thanks to all that chimed in with helpful info!!
 
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