Cranks

[Fingers]

So, If some of you would actually go back and read, you would see we looked at the loading. The pressure from a piston in a performance Dmax is ~45,000 lbs applied to the crank per ignition event. By and far the largest first order force the cranks sees. Even then, the factor of safety exceeds 3 times what is needed to support that force. This max is only in the very small range around TDC too.

The reciprocating forces are more an issue for the connecting rods their bearings and the pistons than the cranks. IMO

And I need to add that STOCK motors are breaking cranks. Think stock forces people. Stock

 

[Mike L.]

What about TCC force at the back of the crank VS the accessories mounted on the front of the crank. Be interesting to know if the crank let loose during or after TCC apply. Just thinking out loud guys.

 

[SgtKilroy]

This might be a silly question, but are the Cummins motors experiencing these problems, or is it limited to the V type motors?

 

[countrycorey]

Has anyone broke a crank in a truck with a manual?

 

[duratothemax]

There probably arent enough manual transmission duramax's out there to make an accurate comparison. Interesting thought though, for sure.

 

[juddski88]

Didn't Caleb Baker break one in his 05 Zf?

Dylan broke one too

 

[Fingers]

Stock motors put out about 750 ft-lb of torque. So that would be the ballpark load at the converter end that has broken cranks.

Belt driven accessory torque is limited by the capacity of the belt.

 

[Dave c]

To have different failure areas at different levels of HP and RPM, there are MANY areas of issue with this crank, not one.

I bet its a combination of things.

 

[Fingers]

The overwhelming majority of the failures across all power levels are on the first throw or the crank. Nearly all are towards the 2nd main. Handful towards the #1 main.

Second most common from what I can tell is on either side of the #4 main.

I am sure there are other locations, but very, very few.

 

[IdahoRob]

What about TCC force at the back of the crank VS the accessories mounted on the front of the crank. Be interesting to know if the crank let loose during or after TCC apply. Just thinking out loud guys.

The one I cracked the snout off of, had a converter that had issues after a long life and was not right. Happened the day of when the converter was locking up on it's own accord in the wrong timing. Mike, This was our first thought at the time on why it broke.

 

[zf>allison]

if you look at crank breaks in zf transmission trucks. make sure you know if they had a stock dmf flywheel, and a light stock clutch, or dual disk triple disc ect with a solid flywheel. I know when my dmf was going out it shook the motor so bad I could hardly drive it but I limped it to work for a few weeks like that, just five miles up the road. I now have a dual disc and the shaking is gone and I hasn't broke yet. I would think shaking caused by the flywheel being unbalanced would move me to the top of the list for mine to break next. but a lot of zf trucks go though this vibration of the dmf going out so I actually wonder if they could be more prone to it?

 

[Fahlin Racing]

How many others have picture of broken cranks ? preferably close ups on the break pattern.

Has anyone cared to measure the journal for taper or barrel shaping from the connecting rod at all?

Is the connecting rod end close enough to the radius for wear to cause an increasing stress concentration at the radius? I doubt the lower mileage engine will show this.

How much is the overlap of the con-rod journal and the crankshaft main journal?

 

[EDP]

Many Sled pull guys have all switched over to ZF or other manual setups and still breaking them.:thumb:

 

[Fingers]

I don't think we are going to learn much more, if anything from any more post-mortem examinations. Fatigue failure originating on the inside of the rod journal across the crank throw. Matches the high stress point on the crank from either torque or bending forces.

 

[DieselmafiaLLY]

Isint there a better crank out there to use?

 

[coker6303]

^^^ ya, cummins! Lol

Keep up the technical debates and ideas. I obviously don't understand the level some of you are on but it it interesting to read. :thumb:

 

[delong_1]

How many others have picture of broken cranks ? preferably close ups on the break pattern.

Has anyone cared to measure the journal for taper or barrel shaping from the connecting rod at all?

Is the connecting rod end close enough to the radius for wear to cause an increasing stress concentration at the radius? I doubt the lower mileage engine will show this.

How much is the overlap of the con-rod journal and the crankshaft main journal?

i still have my crank, i can email a pic to you if you want it

 

[zf>allison]

so alternate firing order cam, and a billet crank isn't going to hurt to just add for extra insurance.

 

[PACougar]

so alternate firing order cam, and a billet crank isn't going to hurt to just add for extra insurance.

Based on previous statements in this thread, billet cranks don't really help. It certainly appears the alt. firing cams do.

 

[zf>allison]

Based on previous statements in this thread, billet cranks don't really help. It certainly appears the alt. firing cams do.

yes I read that, im saying do an alternate firing cam, and a billet crank also. just for no worries.