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Broken crankshaft at timing chain gear
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DRR Trophy
Picture of thehueypilot
posted
Just trying to learn from this crankshaft failure. The crank is a Eagle 4.25 - 2.75 main which has been in my bracket car since 2007 (yes 18 years) and I estimate about 4K 1/8 mile passes. The engine is a 351W bored and stroked to 460 cid. The max rpm I shift at is 6400 rpm with a two speed PG and the balancer is a ATI super balancer. If you zoom into the picture you can see cracks in the corner of the timing chain gear key way. The crankshaft snout drives an alternator and vacuum pump only. No warning when it suddenly let go at the finish line. Why did it fail? Why would there be cracks at the key way feature? Any help would be appreciated. Note: not sure how to attach my photos?

Tim

This message has been edited. Last edited by: thehueypilot,


TheHueyPilot(UH-1H) US Army Pilot (Retired)
93 Mustang Coupe
Best Run 1/8=6.353@106.18,1.346 60' NA
 
Posts: 12 | Location: TN | Registered: January 04, 2010Reply With QuoteReport This Post
DRR Sportsman
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4k 1/8 mile passes…that thing should be in a museum, especially for an eagle
 
Posts: 478 | Location: somewhere between been and never was | Registered: November 03, 2002Reply With QuoteReport This Post
DRR Top Comp
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Is the crank gear cracked on the backside? (Closest to the block)


.
Dave



F J B

Wake me when it's over
 
Posts: 4058 | Location: Earth | Registered: February 08, 2006Reply With QuoteReport This Post
DRR Trophy
Picture of thehueypilot
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No the timing gear is in good shape and the crank failure happened right under the gear as it is barely holding onto the crankshaft. I got lucky the gear did not fail/fall off and take the engine out.

Tim


TheHueyPilot(UH-1H) US Army Pilot (Retired)
93 Mustang Coupe
Best Run 1/8=6.353@106.18,1.346 60' NA
 
Posts: 12 | Location: TN | Registered: January 04, 2010Reply With QuoteReport This Post
DRR Top Comp
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quote:
picture you can see cracks in the corner of the timing chain gear key way


Front or back of the gear?


.
Dave



F J B

Wake me when it's over
 
Posts: 4058 | Location: Earth | Registered: February 08, 2006Reply With QuoteReport This Post
DRR Trophy
Picture of thehueypilot
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The cracks in the key way are to the front of the timing gear. One thing I am going to change is the amount of length the balancer sticks out from the end of the crankshaft. The difference between a late model and early model car is about one inch more of length (maybe the width difference of the serpentine belt vs the v-belt). I purchased the early model balancer which should move the balancer and pulleys weight in toward the center of the crankshaft which hopefully takes away some stress from the failed area? Any thoughts?

Tim

PS thanks to Ken Harris for the helpful info!

This message has been edited. Last edited by: thehueypilot,


TheHueyPilot(UH-1H) US Army Pilot (Retired)
93 Mustang Coupe
Best Run 1/8=6.353@106.18,1.346 60' NA
 
Posts: 12 | Location: TN | Registered: January 04, 2010Reply With QuoteReport This Post
DRR Sportsman
Picture of Bob Deniker
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You honestly should be making a post thanking eagle. It broke because you pushed it past its intended use by 2000 passes.
 
Posts: 593 | Location: Latrobe Pa. | Registered: July 30, 2007Reply With QuoteReport This Post



DRR S/Pro
Picture of Big Steve
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That crankshaft owes you nothing, Just gotta hope your next one last that long

This message has been edited. Last edited by: Big Steve,
 
Posts: 1976 | Location: On the the dark side now | Registered: April 30, 2010Reply With QuoteReport This Post
DRR Pro
Picture of RacerVX54
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quote:
Originally posted by Big Steve:
Thank crankshaft owes you nothing, Just gotta hope your next one last that long



This 1000%


"Just Shut Up and Race"

Brian Martin
Martin Racing
5.66 @121.55
 
Posts: 1310 | Location: Va.Beach .Va | Registered: August 03, 2005Reply With QuoteReport This Post
DRR Sportsman
Picture of BD104X
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Yeah, you got 4000 passes out of a Chinese crank.... I'd say you are way ahead of the game.


Billy Duhs - BD104X@gmail.com
 
Posts: 552 | Location: New Jersey | Registered: February 26, 2000Reply With QuoteReport This Post
DRR Sportsman
Picture of Bad News
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Years ago It was shown that multiple position keyway timing gears caused stress risers in crankshaft snouts.
 
Posts: 856 | Location: ft laud | Registered: September 02, 2004Reply With QuoteReport This Post
DRR Sportsman
Picture of 434 olds
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If you`re going to buy anther "cheap" crank, look into Scat. There cranks have come a long way and mic up very nice. I got away from the Eagle cranks.





Worlds Quickest And Fastest 71 Cutlass On The Planet Earth
 
Posts: 368 | Location: Oak ridge, N.J | Registered: February 09, 2003Reply With QuoteReport This Post
DRR S/Pro
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No answers for you, but a good while back I saw a broken crank on a diesel engine on a diesel-electric drilling rig. The engine was still running and the balancer was wobbling like crazy. This is only to say it sounds like a similar failure.


Illegitimi non carborundum
 
Posts: 2291 | Location: OKC, OK | Registered: February 15, 2008Reply With QuoteReport This Post
DRR Pro
Picture of Eman
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When assembled did you check the alignment of the timing gears before installing the chain?
 
Posts: 1295 | Location: E TN | Registered: February 13, 2009Reply With QuoteReport This Post



DRR Sportsman
Picture of TD3550
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Stress risers generated by intermittent bore contact may result in crankshaft failure. This is from even Callies. Aside from that stay away from the 9 slot setup. You will never need it. If your for real on the 15 years and 4k hits. I think and end table will be in order.
 
Posts: 1369 | Location: Under a Truck | Registered: August 23, 2013Reply With QuoteReport This Post
DRR Pro
Picture of Goob
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quote:
Originally posted by Bad News:
Years ago It was shown that multiple position keyway timing gears caused stress risers in crankshaft snouts.


This. ^^^^^^


What vibration dampner you running?

Easy answer is LS swap..... Laughing Hard


"Despite the high cost of living, it remains popular."
Dave Cook
N375
 
Posts: 1173 | Location: Indy | Registered: November 21, 2008Reply With QuoteReport This Post
DRR Trophy
Picture of thehueypilot
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quote:
Originally posted by Eman:
When assembled did you check the alignment of the timing gears before installing the chain?


Yes the gears were checked for alignment during the initial install. The timing gears/chain were in good shape but I will replace them. I have not heard of the multi key way gear causing stress risers but it did fail right under the gear. I guess I got lucky the gear held onto what was left of the crank snout.

Tim


TheHueyPilot(UH-1H) US Army Pilot (Retired)
93 Mustang Coupe
Best Run 1/8=6.353@106.18,1.346 60' NA
 
Posts: 12 | Location: TN | Registered: January 04, 2010Reply With QuoteReport This Post
DRR Trophy
Picture of thehueypilot
posted Hide Post
quote:
Originally posted by Goob:
quote:
Originally posted by Bad News:
Years ago It was shown that multiple position keyway timing gears caused stress risers in crankshaft snouts.


This. ^^^^^^


What vibration dampner you running?

Easy answer is LS swap..... Laughing Hard


ATI super balancer with the late model four bolt set up. I am switching to their three bolt balancer which is about 1/2” shorter.

Tim

This message has been edited. Last edited by: thehueypilot,


TheHueyPilot(UH-1H) US Army Pilot (Retired)
93 Mustang Coupe
Best Run 1/8=6.353@106.18,1.346 60' NA
 
Posts: 12 | Location: TN | Registered: January 04, 2010Reply With QuoteReport This Post
DRR Sportsman
Picture of Busted Knuckles
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IIRC, the multi-keyway gears didn't have enough bevel on the engine side and were actually cutting into the crank when driven on fully.


Organized people are just too lazy to look for their $h!t.
 
Posts: 469 | Location: Texas USA | Registered: November 09, 2002Reply With QuoteReport This Post
DRR Trophy
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Don't run the blower belt so tight.
 
Posts: 176 | Location: Rock><Hard Place | Registered: February 20, 2010Reply With QuoteReport This Post
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