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Crank Snout Breakage
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DRR Trophy
Picture of deadon1578
posted
OK guys I've heard of this happening but my first time to experience it. 412 Small block chevy, 3.750 stroke Scat crank in Reher Morrison engine. Freshen up about 50 passes ago. This is chain driven with new Cloyes hex adjust timing set. This engine was dynoed this year at 697 HP. Broke crank behind timing gear, disassembled and everything looks perfect. Not really looking for cause because it might be just fatigue, Looking for the best replacement for this application. Howards offers the billet reaper crank for $1500, everyone else is 3 to 4 grand, anybody have experience with this crank at that HP?
 
Posts: 47 | Location: md | Registered: July 23, 2013Reply With QuoteReport This Post
DRR Top Comp
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Of course, best replacement would be a big block snout. Also, make sure the crank gear has a heavy chamfer so it's not "etching" a line on the crank where it transitions into a snout.
If all seems ok there, take a look at the snout, and inside the damper for any fretting/chatter marks....a loose-fitting (and just some brands of damper) will do this when it's not "happy" with the application...
Last, but not least, crankshaft balance can be an issue. I always put an "over balance" in race cranks. If you've ever reached down and touched a damper after a dyno test. or dragstrip run, you'd get an idea of just how much energy/harmonics a damper actually has to deal with. It doesn't just show timing marks lol...
The amount of overbalance depends on the engine size, rpm and component weights..


.
Dave



F J B

 
Posts: 4480 | Location: Earth | Registered: February 08, 2006Reply With QuoteReport This Post
DRR Sportsman
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Broke out first SBC snout last season in our 434. Ended up going with an Ohio crankshaft billet BBC snout crank because it was what was readily available.

I'd be willing to bet my finish line driving was a factor in the failure.


Denis LeBlanc

 
Posts: 475 | Location: Manchester, NH | Registered: February 03, 2006Reply With QuoteReport This Post
DRR Sportsman
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Bullit Cams can convert to a BBC snout if there is enough parent metal left.


Checkered Flag Machine and Ceralli Competition Engines
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Posts: 110 | Location: Paterson N.J. | Registered: September 21, 2006Reply With QuoteReport This Post
DRR Top Comp
Picture of Curly1
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I have seen two SBC crankshafts broke right behind the timing gear. Timing gear caused it. A good crankshaft has a radius where it tapers down and the timing gear butts up to it causing a sharp edge and that right there is where the stress fracture starts.
I talked to Reher and Morrison about it, two different engine builders here, ATI and Callies (it was Callies Magnum crank and new ATI bamancer) all said it was most likely the timing gear that started it. That was my opinion before I called them but wanted to verify.

Make sure you get a good timing gear and that it is not hitting in the radius when installed.


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Posts: 4060 | Location: United States of Texas | Registered: April 02, 2011Reply With QuoteReport This Post
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Picture of Curly1
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A little more information. Both of the Callies cranks that I saw break the snout off had about 75 passes and were really good cranks. The second one was a Callies Magnum. Was not the fault of the crankshaft that it failed it was the timing gear that caused it.

I to would like to know if anyone has experience with the Howards Billet crankshaft?


https://postimg.cc/gallery/np3zpruo/
"Dunning-Kruger Effect"
-a type of Cognitive bias where people with little expertise or ability assume they have superior expertise or ability. This overestimation occurs as a result of the fact that they do not have enough knowledge to know they don't have enough knowledge.

Before you argue with someone ask yourself, "Is this person mentally mature enough to grasp the concept of a different perspective?" If not there is no point to argue.

4X NE2 CHAMPION. 2020 TDRA NE2 Champion
 
Posts: 4060 | Location: United States of Texas | Registered: April 02, 2011Reply With QuoteReport This Post
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Picture of deadon1578
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Curly, the timing gearset was a Cloyes hex adjust and there is a large chamfer on the rear. I can't seem to be able to post a pic of it, (lack of knowledge)but it's going back together with a Jesel belt drive. I also didn't state that it was an ATI balancer and it was internally balanced
 
Posts: 47 | Location: md | Registered: July 23, 2013Reply With QuoteReport This Post



DRR Sportsman
Picture of 391T
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We've broken the snout off of 2 scat cranks on our small block ford engine. Both cranks were internal balance with ati damper and both had 5+ years on them. Went back with a callies magnum and also switched to cogged belts for the alternator and vacuum pump. V-belts can put a lot of strain on the end of the crank.


Scott Smith
 
Posts: 301 | Location: Barbourville, KY | Registered: December 01, 2002Reply With QuoteReport This Post
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Scott, this engine has a cogged vacuum pump belt and a fuel pump belt, mechanical injection, so nothing with a lot of tension, I appreciate the input
 
Posts: 47 | Location: md | Registered: July 23, 2013Reply With QuoteReport This Post
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Picture of Curly1
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In the future any new SBC cranks I buy will have the BBC snout on them.


https://postimg.cc/gallery/np3zpruo/
"Dunning-Kruger Effect"
-a type of Cognitive bias where people with little expertise or ability assume they have superior expertise or ability. This overestimation occurs as a result of the fact that they do not have enough knowledge to know they don't have enough knowledge.

Before you argue with someone ask yourself, "Is this person mentally mature enough to grasp the concept of a different perspective?" If not there is no point to argue.

4X NE2 CHAMPION. 2020 TDRA NE2 Champion
 
Posts: 4060 | Location: United States of Texas | Registered: April 02, 2011Reply With QuoteReport This Post
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I've never really come up with the smoking gun on why a crank snouts break off. The one that broke in my motor was a SCAT forged crank with a 250 blower, broke right behind the timing gear. Fracture surface showed beach marks indicative of a fatigue failure. I've seen the same failure on a NA small block Eagle forged crank and heard stores of similar failures on NA BBC's. I've heard in blower applications you should not use 3 steps in the burn out, due to the pulses it causes on the blower belt, I've since stopped using mine on the 250 blower.

Better metallurgy and higher quality forgings is one way to combat fatigue, or as many have stated increase the diameter of the snout to a BBC diameter, this will likely eliminate the possibility assuming all other things remain the same.
 
Posts: 395 | Location: Pride, La | Registered: April 18, 2006Reply With QuoteReport This Post
DRR Pro
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quote:
Originally posted by Triple Nickel:
I've never really come up with the smoking gun on why a crank snouts break off. The one that broke in my motor was a SCAT forged crank with a 250 blower, broke right behind the timing gear. Fracture surface showed beach marks indicative of a fatigue failure. I've seen the same failure on a NA small block Eagle forged crank and heard stores of similar failures on NA BBC's. I've heard in blower applications you should not use 3 steps in the burn out, due to the pulses it causes on the blower belt, I've since stopped using mine on the 250 blower.

Better metallurgy and higher quality forgings is one way to combat fatigue, or as many have stated increase the diameter of the snout to a BBC diameter, this will likely eliminate the possibility assuming all other things remain the same.


I know I'm on borrowed time with our SBC snout & a ProCharger. We have about 80 runs on it with the supercharger. Before that the crank had had 1k+ passes naturally aspirated. The crank was Magnafluxed before using it with the ProCharger.

That being said, the plan is to race the motor for the 2024 season. Then have it freshened & install a BBC snout crank in it.

2BKING
Relaxing


1980 Camaro
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Posts: 2601 | Location: NV. | Registered: October 20, 2006Reply With QuoteReport This Post
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Do most of them that break run timing chains, if your spending good money on a crank why wouldn't you run a belt ?
 
Posts: 121 | Location: Indiana | Registered: November 13, 2009Reply With QuoteReport This Post
DRR Sportsman
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quote:
Originally posted by sittin duck:
Do most of them that break run timing chains, if your spending good money on a crank why wouldn't you run a belt ?


My Manley crank broke with a jesel belt drive


Denis LeBlanc

 
Posts: 475 | Location: Manchester, NH | Registered: February 03, 2006Reply With QuoteReport This Post



DRR Sportsman
Picture of Dave Koehler
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I have seen cast snouts break just because.
I have seen blown cranks break due to lack of a crank support.
I have seen cranks break due to a solid weighted Harmonic balancer.
I have seen multi slot timing gears fret the snout until it breaks.
I have seen snouts break due to snout length, rpm and sketchy balance. Fords usually.

I am surprised to hear of NA steel cranks here breaking. Are over tightened accessory belts contributing to the mayhem?


Dave Koehler - Koehler Injection - http://www.koehlerinjection.com
Fuel Injection - Nitrous Charger - Nitrous Master Software - Balancing
99% of fuel injection problems are electric.
 
Posts: 354 | Location: Urbana, IL 61802 | Registered: December 03, 2003Reply With QuoteReport This Post
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Picture of deadon1578
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Dave, Thanks for your input. I did use a new Cloyes hex-a-just gear set. This engine also uses the Star Vacuum pumps front mandril, it does not use the crank bot to mount it. It uses the 3 mounting bolts on the balancer and that was ATI. The only accessories on this engine are a vacuum pump and a mechanical fuel pump, both using cog belts and just the slack removed. I have been told by a machine shop that does a lot of sprint car stuff that the chain was probably too tight. They stock several chains to get the right tension.
 
Posts: 47 | Location: md | Registered: July 23, 2013Reply With QuoteReport This Post
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