Eagle Forged Stroker Crank CRACKED

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T

thomasfouraker

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Built a 408 from a Magnum Platform a few years ago. Recently been running it and dialing in the tune and in doing so making some hard pulls.

It was running really nicely then I noticed a knocking and a wobbly balancer.

Of course I pulled the drain plug and found it full of metal. Pulled the pan and what I found was certainly a surprise. I think tops I am making 425hp with my setup. Its a very mild pump gas low comp build.

Looks like I snapped the crank right after the number 1 main. Brief research suggest this was a common problem for their cast and forged cranks. I suppose its quite thin in this area.
 
Pictures

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363A53AF-906E-4633-AC2F-AFF534CBD660.jpeg
 
In full disclosure, this was a used crankshaft out of an engine that was put together in the early 2000s/late 90s. I did have it ground .10/.10 prior to using it. It was magnafluxed (supposedly) and fine.
 
That Sucks, if you put it back together you might want to consider Scat or Molnar crankshafts. Good Luck.
 
thomasfouraker said:
In full disclosure, this was a used crankshaft out of an engine that was put together in the early 2000s/late 90s. I did have it ground .10/.10 prior to using it. It was magnafluxed (supposedly) and fine.
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That bites for sure. At least it didn't come apart at RPM. I lost a friend at the drag strio many years ago. The 460 based stroker crank broke at the top end and oiled the track. He slid into the end of a guardrail with the driver door and he was gone.
 
I have heard of Eagle cranks snapping in 2 before, I’d steer clear of them.
 
Common issue. Seen several do that on the forum over the years.
 
Super common 20 years ago… the one I personally know of took out everything in the engine… even the heads got damaged… and to add insult to injury took out the converter and transmission…
 
Since I am a Molnar Technologies dealer I thought it would be interesting to hear what Tom Molnar had to say about his thread.

Here was his reply:

"I am eating an early lunch and when I read " Disappointing to say the least on a well known brand. ", I almost had it coming out of my nose. Eagle is quite well known and they sell a lot of parts but mostly to the end user who thinks they are a quality product. Not many real engine shops use them as most of the cranks need to be ground .010 - .010 before they can be used. I cannot tell you how many people say they measure them out of the box and find .002" of taper in the rod pins. The other guy talks about "a big hole for a cross drilled rod main". That's a lightening hole, not a cross drilled crank.

In reality, there can be several things that caused this.

1- What damper was used?

2- It was a used crank with a lot of time on it.

3- It was ground undersize. If the grind shop did not have the radius on the wheel right, it could have left a stress riser.

4- It could also be a cast crank. Even the OEMs use a forged crank in engines that make much power.

5- If the crank was made for a certain bob weight and it was balanced for something else, it can cause problems. As an example, lets say the crank was designed with counterweights for 1700 gram bob and it was balanced for 1900 by adding heavy metal. The middle of the crank is still too light to cover the forces in that area and since the balance machine only reads the forces on the #1 and #5 mains, it does not know what is going on in the middle. Since the middle effects what the balance machine tells you it is light on the ends. When heavy metal is added to the ends to fix the middle, the ends end up being too heavy but the balance machine tells you everything is fine and at 700 RPM, it probably is. At high RPM, the heavy ends pull in one direction and the middle pulls in a different direction. This bends the crank. Rev it up, it bends, go back to idle and it relaxes. This back and forth is jut like straightening out a paper clip and bending it back and forth. After a while it breaks."

Tom
 
Plymouth 65 said:
What damper were you running? Photos of the break face? 65'
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Pro Race Balancer. I haven’t pulled the motor yet but hopefully within the next week or two I can have it broke down and inspected.

Aside from component defect, any thing else I should be looking for as a contributor?
 
PROSTOCKTOM said:
Since I am a Molnar Technologies dealer I thought it would be interesting to hear what Tom Molnar had to say about his thread.

Here was his reply:

"I am eating an early lunch and when I read " Disappointing to say the least on a well known brand. ", I almost had it coming out of my nose. Eagle is quite well known and they sell a lot of parts but mostly to the end user who thinks they are a quality product. Not many real engine shops use them as most of the cranks need to be ground .010 - .010 before they can be used. I cannot tell you how many people say they measure them out of the box and find .002" of taper in the rod pins. The other guy talks about "a big hole for a cross drilled rod main". That's a lightening hole, not a cross drilled crank.

In reality, there can be several things that caused this.

1- What damper was used?

2- It was a used crank with a lot of time on it.

3- It was ground undersize. If the grind shop did not have the radius on the wheel right, it could have left a stress riser.

4- It could also be a cast crank. Even the OEMs use a forged crank in engines that make much power.

5- If the crank was made for a certain bob weight and it was balanced for something else, it can cause problems. As an example, lets say the crank was designed with counterweights for 1700 gram bob and it was balanced for 1900 by adding heavy metal. The middle of the crank is still too light to cover the forces in that area and since the balance machine only reads the forces on the #1 and #5 mains, it does not know what is going on in the middle. Since the middle effects what the balance machine tells you it is light on the ends. When heavy metal is added to the ends to fix the middle, the ends end up being too heavy but the balance machine tells you everything is fine and at 700 RPM, it probably is. At high RPM, the heavy ends pull in one direction and the middle pulls in a different direction. This bends the crank. Rev it up, it bends, go back to idle and it relaxes. This back and forth is jut like straightening out a paper clip and bending it back and forth. After a while it breaks."

Tom
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Great reply from an authority on the subject. I don’t think a forged crank should ever break under any circumstances on a build like this. Especially NA. I’d love a Molnar crank and may have to price out a rotating assembly.
 
mopar head said:
Can you ask of his knowledge, input for their H beam rods?:thankyou:
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I don't want to muddy this thread, but I will answer this question and if a discussion on rods is needed then a new thread should be started.

Eagle rods are assembled in China with supposed ARP bolts and torqued to 50 lb/ft of torque before they are honed in China.

A Molnar rod is also assembled and the big end is bolted together and bored in China. The rod bolts are then removed and the rod and cap are sent in matched pairs.

When Molnar receives them they install real proprietary made Molnar ARP 2000 bolts and torque the caps to 80 lb/ft. Then they do the finally honing which results in

about .001" of overall material removal. Molnar rods are honed to within .0001" of the desired dimension.

You have to look at the honed dimensions on an Eagle rod because a lot of time they need the caps cut and re-honed. Plus a lot of Eagle rods have only supposed 8740 ARP bolts.

Since Tom Molnar started his career at Oliver rods, then work for years at K-1 , and then finally went out on his own and has 41 years of knowledge in this business, as well as, now

having his name attached to his product he knows rods and cranks. This is why I've done business with Tom for over 20-years. I without question trust the quality of his products

100%.

Tom
 
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thomasfouraker said:
Built a 408 from a Magnum Platform a few years ago. Recently been running it and dialing in the tune and in doing so making some hard pulls.

It was running really nicely then I noticed a knocking and a wobbly balancer.

Of course I pulled the drain plug and found it full of metal. Pulled the pan and what I found was certainly a surprise. I think tops I am making 425hp with my setup. Its a very mild pump gas low comp build.

Looks like I snapped the crank right after the number 1 main. Brief research suggest this was a common problem for their cast and forged cranks. I suppose its quite thin in this area.
Click to expand...
Are you positive that's a forged crank? On the front of the first counterweight it'll say 4340 and have the p/n under it.

Looking at the images on Eagles site it looks like a cast crank.
 
PROSTOCKTOM said:
Since I am a Molnar Technologies dealer I thought it would be interesting to hear what Tom Molnar had to say about his thread.

Here was his reply:

"I am eating an early lunch and when I read " Disappointing to say the least on a well known brand. ", I almost had it coming out of my nose. Eagle is quite well known and they sell a lot of parts but mostly to the end user who thinks they are a quality product. Not many real engine shops use them as most of the cranks need to be ground .010 - .010 before they can be used. I cannot tell you how many people say they measure them out of the box and find .002" of taper in the rod pins. The other guy talks about "a big hole for a cross drilled rod main". That's a lightening hole, not a cross drilled crank.

In reality, there can be several things that caused this.

1- What damper was used?

2- It was a used crank with a lot of time on it.

3- It was ground undersize. If the grind shop did not have the radius on the wheel right, it could have left a stress riser.

4- It could also be a cast crank. Even the OEMs use a forged crank in engines that make much power.

5- If the crank was made for a certain bob weight and it was balanced for something else, it can cause problems. As an example, lets say the crank was designed with counterweights for 1700 gram bob and it was balanced for 1900 by adding heavy metal. The middle of the crank is still too light to cover the forces in that area and since the balance machine only reads the forces on the #1 and #5 mains, it does not know what is going on in the middle. Since the middle effects what the balance machine tells you it is light on the ends. When heavy metal is added to the ends to fix the middle, the ends end up being too heavy but the balance machine tells you everything is fine and at 700 RPM, it probably is. At high RPM, the heavy ends pull in one direction and the middle pulls in a different direction. This bends the crank. Rev it up, it bends, go back to idle and it relaxes. This back and forth is jut like straightening out a paper clip and bending it back and forth. After a while it breaks."
Click to expand...
The part about balance I found interesting. Perhaps that is an extreme example. I am not sure. But Molnar cranks for Mopars are not center counterweighted either, so that is exactly how they are balanced, I thought, by adding heavy metal or drilling holes in front or rear.
 
I don't know if this is bs or not but I knew a guy who built small block Chevys and he claimed that he would have his crank shafts x rayed for cracks is this possible or was he full of it? He also said that he had them checked for straightness.
 
PROSTOCKTOM said:
I don't want to muddy this thread, but I will answer this question and if a discussion on rods is needed then a new thread should be started.

Eagle rods are assembled in China with supposed ARP bolt and torqued to 50 lb/ft of torque before they are honed in China.

A Molnar rod is also assembled and the big end is bolted together and bored in China. The rod bolts are then removed and the rod and cap are sent in matched pairs.

When Molnar receives them they install real proprietary made Molnar ARP 2000 bolts and torque the caps to 80 lb/ft. Then they do the finally honing which results in

about .001" of overall material removal. Molnar rods are honed to within .0001" of the desired dimension.

You have to looked at the honed dimensions on an Eagle rod because a lot of time they need the caps cut and re-honed. Plus a lot of Eagle rods have only supposed 8740 ARP bolts.

Since Tom Molnar started his career at Oliver rods, then work for years at K-1 , and then finally went out on his own he has 41 years of knowledge in this business, as well as, now

having his name attached to his product. This is why I've done business with Tom for over 20-years. I without question trust the quality of his products 100%.

Tom
Click to expand...
I like their connecting rods. Wish they'd make a stock stroke (3.31) 340 forged crank.
 
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