Eagle Forged Stroker Crank CRACKED

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Icetech said:
Not what i expected inside at all... more research to do...

The thing that always surprises me is guys running (including myself) 30+ year old rubber type stock ones and they still hold up most of the time..
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They hold up but are they really working? It’s hard to say without seeing the bearings but many times you can see the distress in the bearings and it’s because the damper isn’t doing its job well enough or isn’t tuned for the application.
 
K.. that was a interesting read about how they work
 
I put a Mopar Performance damper on my stroker engine over 10 years ago has a rubber ring like an original damper. I have a Sharpy mark on there to check if it slips and has not. Engine aint blown up yet but you'all got me wondering about my damper choice....Scat cast 4" crank.....I guess I am lucky....I wind it up pretty good on empty unpopulated country roads not been to any track and skinny all season radials cause aint built up chassis drive train enough for sticky tires...yet....
 
340sFastback said:
I put a Mopar Performance damper on my stroker engine over 10 years ago has a rubber ring like an original damper. I have a Sharpy mark on there to check if it slips and has not. Engine aint blown up yet but you'all got me wondering about my damper choice....Scat cast 4" crank.....I guess I am lucky....I wind it up pretty good on empty unpopulated country roads not been to any track and skinny all season radials cause aint built up chassis drive train enough for sticky tires...yet....
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Threads like this have me sooo paranoid about a cast crank... it makes me want forged/h-beam for a motor that probably won't make 420hp :) Overthinking/worrying is my thing...
 
Icetech said:
Threads like this have me sooo paranoid about a cast crank... it makes me want forged/h-beam for a motor that probably won't make 420hp :) Overthinking/worrying is my thing...
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Forged a lot heavier then cast and H beams a lot heavier then I beams. I running Scat cast crank and Scat I beams lighter faster revs less weight less stress on mains ect ect. My new at the time Scat cast crank was turned 10/10 to improve run out, taper, out of round ect. Had local high end speed shop balance crank rods and inspect rotating assembly. Then I bought tools checked clearances, run out, end play etc myself during assembly. During assembly I ran oil pump with a drill with crank in block but no pistons/rods and got a bunch of metal shavings in oil pan which would have been stuck in rod journals otherwise.....
 
Rat Bastid said:
They hold up but are they really working? It’s hard to say without seeing the bearings but many times you can see the distress in the bearings and it’s because the damper isn’t doing its job well enough or isn’t tuned for the application.
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Spent the last hour reading up.. think i will try a rattler, i like the design idea and really can't find anything bad about them.
 
340sFastback said:
Forged a lot heavier then cast and H beams a lot heavier then I beams. I running Scat cast crank and Scat I beams lighter faster revs less weight less stress on mains ect ect. My new at the time Scat cast crank was turned 10/10 to improve run out, taper, out of round ect. Had local high end speed shop balance crank rods and inspect rotating assembly. Then I bought tools checked clearances, run out, end play etc myself during assembly. During assembly I ran oil pump with a drill with crank in block but no pistons/rods and got a bunch of metal shavings in oil pan which would have been stuck in rod journals otherwise.....
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Yeah.. plus quite a bit less money to start with :) I just worry too much. Good call on running the pump to clean it out.. easy to miss stuff like that :) I won't be doing the stroker thing til next year anyway, every shop around here is WAY backed up and i want my bank account to heal a little bit :) Just doing a 318 for this year to get on the road and upgrade as i go..
 
340sFastback said:
Forged a lot heavier then cast and H beams a lot heavier then I beams. I running Scat cast crank and Scat I beams lighter faster revs less weight less stress on mains ect ect. My new at the time Scat cast crank was turned 10/10 to improve run out, taper, out of round ect. Had local high end speed shop balance crank rods and inspect rotating assembly. Then I bought tools checked clearances, run out, end play etc myself during assembly. During assembly I ran oil pump with a drill with crank in block but no pistons/rods and got a bunch of metal shavings in oil pan which would have been stuck in rod journals otherwise.....
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The Scat I-beams are nice. The Summit branded ones are the same (even same number forged into the side of the rod) for about $16 cheaper. I think if I ever got to the point where I needed an H beam rod b/c power output is beyond what a good I beam can take, I'd skip the H beams and go with aluminum rods.
 
kdeboy said:
The Scat I-beams are nice. The Summit branded ones are the same (even same number forged into the side of the rod) for about $16 cheaper. I think if I ever got to the point where I needed an H beam rod b/c power output is beyond what a good I beam can take, I'd skip the H beams and go with aluminum rods.
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Yeah, i believe they are pro-comp sport or something like that.. good rods. And yeah, i will probably end up with cast/ i-beam.. the last motor i did a long time ago was all forged but i had a procharger on it. I would love to run a turbo or blower again but too much money for me :)
 
90-percent of crank breakage in the front half of the engine is due to a balancer that is too large in diameter, too heavy, has moving parts, and cannot be balanced with the crankshaft. Moving parts include both fluid and mechanical pieces. These dampers cannot react fast enough to rapid acceleration and deceleration. Therefore, they create harmonics that will eventually fatigue a crank and break it. These dampers were designed for industrial applications that run constant speed in narrow RPM ranges. So, that being said, the smallest diameter, lightest weight, and an elastomer design is best.
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Interesting...
 
Personally I'll just stick with my ATI dampers and rebuild them ever now and then. This thread is turning into one like, "What Cam Should I Use".

Everyone has their preference, there are pros and cons to every type of damper the problem lies in the fact that most people honestly do not understand how important

this component really is to the life of an engine.

Tom
 
PROSTOCKTOM said:
Personally I'll just stick with my ATI dampers and rebuild them ever now and then. This thread is turning into one like, "What Cam Should I Use".

Everyone has their preference, there are pros and cons to every type of damper the problem lies in the fact that most people honestly do not understand how important

this component really is to the life of an engine.

Tom
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well.. since you brought it up... i'm trying to figure what cam to use right now :) and regretting my rocker decision.. but i own em now :)
 
I disagree with his answer to question #4. Since you don't know the resonant frequently of the engines MES you can't optimize the tuning of the damper. That goes for rubber or viscous type dampers!
The only real way to confirm the frequency is to perform torsional vibration measurements. 65'
 
Resonant frequency of the system doesn't change with engine RPM. 65'
 
Yes, I know its a lightening hole, but it looks really big to me. Its a whole lot larger than the lightening holes in my stock 340 crank. And I will say that the cross section where it is cracked looks really on the thin side. And the crack runs right through the lightening hole. No matter what material it is, it just probably fatigued because of the small cross section. I also noticed the deep scratches left from the drill in the lightening hole, stress risers.
 
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 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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I appreciate them/you being forthright with the nature of the Molnar rods.

How come they can't just make 'em here, 100%?
 
Engine RPM absolutely matters. The system resonant frequency will be found somewhere within the operating RPM. With a V8 engine you'll be looking at a predominant 4th order which is due too the engine firing frequency. 65'
 
The crank failed through the ligthening holes because that was the weakest point. It became a failure point because for whatever reason, the dampener was not dampening......
 
Your not alone. Here's a K1 crank (which is just a glorified Eagle that they do the finish machining work on to give them better tolerances than Eagle does). But the chinese metal is the same and still breaks.

20220927_155518.jpg


20220928_104457.jpg
 
Isn't Scat made with the same forgings pretty much? rarely hear of issues with them.. or is scat different?
 
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