justinp61
Well-Known Member
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- May 15, 2009
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What stroke?
Eagle Forged Stroker Crank CRACKED
- Thread starter thomasfouraker
- Start date
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What stroke?
pettybludart
Well-Known Member
Last winter while doing a refresh on my 410 stoker build,my builder magnafluxed my forged Eagle crank.This is the crack he found.I was lucky to have caught this before catastrophic failure.I replaced the crank with a forged Molnar crank.You can really tell the difference in quality by just comparing.Oh I,ve also been running an ATI Super dampner for 12 year without issue.Molnar crank on right
Kris1234
Member
That one is a 4.625 stroke.
Look at the meat in the crank on the right versus the undercut one on the left
Hey Scott
And you guys wonder why I’m happy shifting at 6700-6800 rpm. Lol
I'm gonna stick with 3500... just gonna run it like a old diesel after all of this
Dale Davies
Well-Known Member
Quality for many products went south or east a number of years ago.
A service station I worked at years ago, brother to the owner, had a backhoe and dump truck. The truck was a Ford with a 391 engine. The crankshaft front pulley came loose a couple of times, so I torqued it again. Then the bolt came out on the road. I was able to get another bolt and torqued it in with loctite. Three days later it stalled while driving so he stepped on the clutch. With a load on there is lots of momentum, so he let engaged the clutch again. The angle on the fracture on the crankshaft just behind the #1 main bearing pushed the front piece of thecrank out the front with the main bearing web still bolted together and on the crankshaft. Timing cover was a writeoff as well. Those 391 engines had steel forged cranks and the front snout is larger diameter to support driving the air compressor and other truck options. Seems for some reason the crank developed a crack that allowed excess torsion to the torsional damper causing the bolt to work loose. When I loctited the bolt and started it up there was no discernable noise and the timing only varied like you expect with a bit of a worn timing set.
It looks like from the pictures there’s more of a chamfer on the Scat crank as well. Are my eyes deceiving me?
Looks like it.
Dale Davies
Well-Known Member
The aircraft overhaul industry xray checks recip engine cranks, rods and sometimes engine cases for subsurface cracks and irregularities. Those engines are built to stand up to 75% load for hours on end, similar to heavy duty truck engines. Automotive engines get a quick blast at full power for a few seconds and then are in cruise at say 10% to 20% load the rest of the time. That is why certified aircraft engines have a TBO of 1500 to 2000 hours generally and the xray NDT examinations. When an automotive componenent fails, we pull over to the side of the road. An aircraft comes down. This is also why they are mandated to have dual ignition systems, usually magnitos.
Dale Davies
Well-Known Member
When you look at the overlap of the rod and main journals on the stroker cranks, there is not a lot of metal there. Also the Eagle crank is saving weight and metal in the web area. The white marker appears to be following the oil hole drilling from the outlet. Appears to be a substandard crank. The Molnar crank tapers nicely from the main journal area to the outside of the rod journal. This helps reduce the possibility of unwanted flexing which will lead to stress cracking. That Eagle crank was born with C4 in it.
David Vizard has a video that he discuses C/S balancing for power and mentions companies he has not had problems with. Scat and Molnar are on the list. The Scat 9000 series he recommends for quality and affordability. A good video to watch.
I noticed the Molnar crank is aero contoured with the cut angle throwing displaced oil toward the main webbing to slid down the web and into the oil pan. This gets the oil out of the air around the rotating assembly where it resists the motion of the components.
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Rat Bastid
Dunamis Metron
What damper were you using? When they fail like that it’s almost always a torsional vibration issue.
Just like a tuning fork will break glass, a damper that is tuned wrong or worn out, you get failures like that.
I‘m frigging surprised we don’t see way more of this stuff. It shows how good this stuff really is.
If it was the garbage some think it is, they wouldn’t make it past 1000 miles at best.
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Rat Bastid
Dunamis Metron
If the Eagle crank didn’t have the hole in the rod throw or a smaller hole it still would have failed. It would have found the weakest spot (which is right where they all fail because all the torsional vibrations end up at the crank snout) and failed anyway.
Rat Bastid
Dunamis Metron
I can say without any reservations that your damper is NOT functioning like it did when it was brand new. It can’t be. The rubber has lost a bunch of durometer and several of the bands are probably fractured.
One of the better things about the ATI damper over other elastomer dampers is it can (and should) be rebuilt. Rubber is not a lifetime materiel.
Not sending it in for a tune up is pressing your luck.
lead69
hopeless car junkie
Bobzilla
Well-Known Member
Does too much or too little press fit of dampener onto the crank snout affect it’s efficiency? Say the dampener was perfectly tuned and suited for the application but was really tight going on during installation and that was not addressed. What would happen?
Bobzilla
Well-Known Member
I highly doubt the SCAT crank is the same forging as an Eagle. They look totally different in the details.
Looks like parts have been made in China for quite awhile, but quality of those parts depends on the company finishing the parts and selling them here. Anyway, kind of an interesting read: https://www.enginebuildermag.com/2019/06/a-look-into-manufacturing-in-china
Dale Davies
Well-Known Member
The press fit or interference fit should not matter. Being a slip fit could be a problem as it could work loose.
Rat Bastid
Dunamis Metron
Too tight and it usually fractures the snout at the keyway.
Too loose and they don’t work.
They need the correct amount of press fit to work correctly.
Rat Bastid
Dunamis Metron
No, it matters.
Dale Davies
Well-Known Member
In the 70s we were importing Japanese steel. When you tried to cut it with the acetylene torch, now and then there would be some rust buried in the rolled steel. Seems that Chinese manufacturers are going through the same QC issues. The responsibility comes down to the American company getting product manifactured in China to verify QC. Now if ypu purchase really cheap cast parts, you get what you pay for. Look on some rod and crank manufacturers sites and they state xrayed. That is part of their QC to verify the steel.melt was done properly to ensure no voids or inclusions that would be subsurface and not detectable by magnaflux. These will allow cracks to develop and spread.
thomasfouraker
Well-Known Member
Aside from some marks as a result of interference with the water pump (assuming it occurred when the crankshaft became compromised and it wobbles) the damper looks fine to my eyes.
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