Harmonic Balancer fell off - Part2

SRBCitrusCobra17

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Hello, I posed this event several months ago. I have had time to take a closer look at the carnage and now understand more about it. It appears what happened is the screw broke off inside the crank shaft and what remained of the screw damaged the threads in the CS. This CS is not stock and was part of a stroker kit from Eagle as part of an engine rebuild several years ago. Below is a picture of the inside bore of the crankshaft where the bolt goes. You can see the remainder of the sheered screw and nothing remaining of the threads. This seems very unusual and where the screw broke does not make a lot of sense to me. There is nothing else wrong with the engine, but I am looking at a full disassemble to replace the crankshaft at this point. The car only has 24k orig mi on it. Has anyone experienced this?

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Blkkbgt

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It looks like there is a piece of a thread still there but the others decided to leave with the balancer bolt. This to me looks like one of 4 things.

1. Cross threaded bolt
2. The damper was drawn on with the bolt damaging the threads. I've personally seen this on a cast iron crank!
3. Improper thread pitch on the crank or bolt
4. The crank wasn't manufactured correctly and the metal was to soft to hold the clamp load

Eagle has long had a quality control problem they refuse to address as well. I know some builders say they refuse to use them. At one point in time I had 2 machine shops in my area that wouldn't build an engine with them either.

At this point since you're going to pull the engine for a rebuild I'd try and find a Kellogg crank. Other than those cranks I honestly don't know what other forgings are good these days. Hopefully someone with more recent experience can give you another option.
 
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badcobra

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Man what a mess right there. It's also possible the stock bolt broke and snapped off. There is tremendous load there on supercharged cars and they should have upgraded to an ARP bolt. You can definitely damage crank threads pulling the balancer on using the bolt, even on a forged crank. I for years did that on mine and the threads got boogered up, but fortunately I was able to chase em and get em back in shape. I now have a balancer install tool.

That crank is likely not done for, it can be drilled and tapped and reused most likely. Send it to a competent machine shop to have it repaired. If you need a referral for one, we have an incredible one local to me in Minneapolis called Crankshaft Supply. They can fix about anything so do not be afraid to ship it out.

The benefit of reusing the crank is you wouldn't have to rebalance. But, most likely you are looking at a full rebuild and if that engine is already .020" over on the bores, I would suggest not going more and finding a new block. There is no such thing as just 'replacing the crank'. Prepare to empty that wallet.
 

DCguy

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+1 to above....youre looking at new seals, gaskets, rings, bearings etc for a refresh plus anything else you find while youre in there. At minimum i would also replace the head bolts with ARP2000 studs.

If you had to replace the crank go with Manley/Kellogg...your Eagle unit might be repairable. If the bore is too damaged you could always have it machine for a stud if youre not using the factory caged lower pulley.

GT500 Crank Saver Stud Kit - KINETIK MOTORSPORT
 

SRBCitrusCobra17

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Thanks for the feedback. Great info. The engine work was done back in 2007; stroker kit, .020 bore, cams, pretty much the works for $8k. The stroker kit alone was $2k. So it lasted 14 years before it hit the ice berg. I did speak to an Eagle rep to discuss the damage and options. They also mentioned using the ARP bolts which I am not sure was done during the rebuild. The other thing they mentioned is they could match the crank based on the serial number with the one I have. Intuitively to me you would think it would be very difficult to damage threads on forged steel, evidently not. The one part I do not like about the crank is the recessed key. Seems to me it should go all the way to the end, especially on something that can handle over 1000hp. You can see how it wore into the slot on the HB that fell off (stock damaged HB, pic below). This easily slid back onto the crank shaft with quite a bit of radial slop, which I am wondering was a contributing factor. I should also mention that the set up on this was the Metco pully for the SC and Alt. The stock pully fell apart several years ago and this seemed like a good option at the time. Thanks again.

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badcobra

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Pull the engine and disassemble, then go from there. Chances are you'll need all new parts. My suggestion is find a stock bore aluminum block, a stock Cobra crank and use those as your foundation for the new build. Have the machine shop bore the new block the very minimum amount to make the cylinders true and order a custom sized piston. That's the problem when you go right to .020" over, the block is one and done. If they would have done a minimal overbore, you could have reused the block then. Good luck
 

01yellercobra

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Chances are it was something that was happening over time. The bolt loosened or stretched causing things to loosen up. What you're seeing it a result of everything getting beat up.
 

SecondhandSnake

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I had it happen while torquing it on a stock balancer, stock crank. Snapped off deep just like yours and boogered up some threads. I just drilled it out to the next biggest size, drilled and tapped it, made a sleeve from the new thread to the old one, installed it with threadlocker, and put in a new bolt. It's been running like that for years. I wouldn't hesitate to go that route again. It sure beat rebuilding the engine with a new crank.
 

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