breaking crankshafts

I have seen it happen once or twice a year over the course of many seasons. Normally break right at the bearing on the flywheel side.

Two in a row? I would make sure I had proper side play.
 
I think I have found a clue in your post from Nov, 17.

Posted by Grasshopper
For Sale
I have a very nice 380 Intimidator series Tilly for sale,, its alcohol, and does perfectly. ive been running it on a big bore stroker billet animal, and its just not big enough. can send
pics to anyone wanting them.. asking $250 shipped. new it is $325 plus shipping.

As far as stock animals, never heard of anyone having a problem with cranks, as long as they run oil in them and change it every once in a while.
But with a stroker, big bore, billet, animal with billet head and HUGE tilly carb, turning a zillion rpms ????? Now that's a different animal. But I understand that you need external bearing supports for that kind of engine. LOL And a few other tricks.
I just realized that I am beginning to sound like Duck. Time to go to bed.
 
One Fast Kat said:
I think I have found a clue in your post from Nov, 17.

Posted by Grasshopper
For Sale
I have a very nice 380 Intimidator series Tilly for sale,, its alcohol, and does perfectly. ive been running it on a big bore stroker billet animal, and its just not big enough. can send
pics to anyone wanting them.. asking $250 shipped. new it is $325 plus shipping.

As far as stock animals, never heard of anyone having a problem with cranks, as long as they run oil in them and change it every once in a while.
But with a stroker, big bore, billet, animal with billet head and HUGE tilly carb, turning a zillion rpms ????? Now that's a different animal. But I understand that you need external bearing supports for that kind of engine. LOL And a few other tricks.
I just realized that I am beginning to sound like Duck. Time to go to bed.
Click to expand...

its got 3rd and 4th bearing supports on it,, I don't turn it way up in rpms,, try to stay around 7500-8000, its a billet crank too, that's whats got me baffled,,,
 
jjchat said:
I have seen it happen once or twice a year over the course of many seasons. Normally break right at the bearing on the flywheel side.

Two in a row? I would make sure I had proper side play.
Click to expand...

side play is fine,,these are breaking right at the rod ,,on the clutch side
 
The stroker Animal I built I used a stock flathead crank and turned it weekly 9000 rpm and never had a problem. I was even running the engine on a 425 lb Champ kart on a 1/8 mile bull ring.
 
How hard is Clutch Hitting , 3rd and 4th Bearing can't have Crank in a bind before tightening down , and a rough track is also tough on them . I have some of the same problems .
 
Grasshopper said:
ive broke two cranks in my animal this year,, wondering if anyone else is having these issues?
Click to expand...

It would probably be helpful if you use a lite weight flywheel to reduce the torsional stresses on the crankshaft. ARC makes some very lite flywheels that might work for this application. The other consideration is how hard the clutch locks up, maybe too hard and this is creating some heavy impact loads on crankshaft.

Steve
www.Bakerracingengines.com
 
Roofer Dude said:
How hard is Clutch Hitting , 3rd and 4th Bearing can't have Crank in a bind before tightening down , and a rough track is also tough on them . I have some of the same problems .
Click to expand...

clutch isn't hitting it hard , no bind in the 3rd and 4th bearings either, ive bout decided that we have built an untamable monster that's just gonna keep breaking them
 
This goes back a few decades but I'm sure it still applies. Billet cranks ( and rods ) do not have as strong a "grain flow" as a forged piece. Don't know the engineering numbers on this but I believe it's a significant difference in strength. Actually, billet pieces have no continuous grain flow.
 
Flash-o-matic said:
This goes back a few decades but I'm sure it still applies. Billet cranks ( and rods ) do not have as strong a "grain flow" as a forged piece. Don't know the engineering numbers on this but I believe it's a significant difference in strength. Actually, billet pieces have no continuous grain flow.
Click to expand...
This is entirely correct.
Billet is constantly raved about. Forged is the superior molecular arrangement.

Nonetheless billets have proved their worth and the kind of breakage being discussed here is not normal, nor characteristic of the well known crankshafts we run....such as the ARC crank.
If you are breaking new forged OR billet cranks, you have a problem other than the makeup of the crank. That includes the stock Animal/WF crank, which is an excellent forging.
 
"There is an old argument that a forged crank is superior to a billet crank because of the allegedly uninterrupted grain flow that can be obtained in the forging process. That might be true of some components, but with respect to crankshafts, the argument fails because of the large dislocations in the material that are necessary to move the crankpin and counterweight material from the center of the forging blank to the outer extremes of the part. The resulting grain structure in the typical V8 crank forging exhibits similar fractured grain properties to that of a machined billet. More than one crankshaft manufacturer has told me that there is no way that a forging from the commonly used steel alloy SAE-4340 (AMS-6414) would survive in one of today's Cup engines."
source: http://www.epi-eng.com/piston_engine_technology/crankshaft_design_issues.htm
 
The cranks used in a Cup, or fuel dragster are a different animal altogether. Our fueler cranks were made in UK.
I expect the Cup cranks come from a very similar supplier.
These cannot be in any way compared to a kart crank.
 
Yes that's true V8's have 7 more cylinders than a Briggs. Other than that obvious fact the theory s very similar to that of your every day vehicle.
The manufacture of a cup or drag car is obviously a lot more complex with the additional 7 cylinders. They are also made of materials such as 4340 steel.
The stock Animal crank is a forged piece but the Briggs stroker crank is cast iron. However, the crank used to stroke the Animal has proven to be quite strong and durable.
The thing that is holding back producing more HP from your typical 4 stroke kart racing motor is crankshaft durability!
At least for now. He He he.
Here's a video of the mfg of a NASCAR crank. https://www.youtube.com/watch?v=hyRBbGb2UDA
 
the problem with that big of a stroke is the 7/8 journal ,, its to small and therefore is the weak point, problem is you cant get a 1 inch journal that stroke and make it fit in the jr billet block, so I guess I will tame it down and change from the 2.887 to a 2.637
 
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