2F Broken Crankshaft!! (1 Viewer)

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Thanks for all the replies. I didn't look at it any yesterday or take more pictures. Hopefully tonight. I'll definitely be checking out the harmonic balancer. Hopefully this weekend I can pull motor and remove crank and measure it.

Starting to shop for cranks now. Are all 2F cranks the same? I am looking at one out of an 1985 2F but want to make sure there weren't any changes between my crank and it.
 
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I'm the 40's nut behind the wheel
What a bummer.

Looks to me like a classic fatigue fracture. Given the crank's former near-death experience I'd be pointing the finger at its previous resurrection for these reasons:

a) being at the end of the row, No,6 journal is usually the first to suffer if the engine is run when starved of oil, so its been ground down in indeterminate amount. (could even have had metal added and built up, with lots of localized heat applied?)

b) failure to maintain the correct fillet radii, both at the journal edges and around the oil gallery hole, can induce stress cracks over time. The oil hole fillet looks OK here. This crack is concentrated around the journal edge fillet area and IMHO was probably just a slow moving train wreck waiting to happen. Another 'good' crank, balanced with the flywheel sounds like the go to me.

Cheers
 
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I thought that a lack of oil would heat the shaft around the journal and give it a bit of a blue/purple tinge...

Seems like an overground, weakened and old shaft pulling more torque than originally intended and just finally cracked it.

Looks nasty mate hope you get it all sorted soon!
 
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Have a freshly machined 2F crank coming from a fellow Mud member in New Mexico. Gathering other parts I'll need when I replace the crank. I'm going to check out the harmonic balancer and replace it needed. Will also have flywheel balanced. May not need it or make much of a difference, but I'd rather be safe than have another broken crank. Will update with more carnage pics when I pull the engine and crank. Thanks for all the replies thus far.
 

4Cruisers

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Have a freshly machined 2F crank coming from a fellow Mud member in New Mexico. Gathering other parts I'll need when I replace the crank. I'm going to check out the harmonic balancer and replace it needed. Will also have flywheel balanced. May not need it or make much of a difference, but I'd rather be safe than have another broken crank. Will update with more carnage pics when I pull the engine and crank. Thanks for all the replies thus far.
Per FedEx tracking, showing it out for delivery 10 minutes ago, let me know how it looks when it gets to you.
 

RAYJON

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My guess is the fillet on the crank journal was cut wrong weakening the crank. hopefully it didn't hurt anything else... might also want to check the trans/belhousing alignment....
 
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Well, finally got the broken crank out. Figured out it had been welded on in a previous life. Pretty plain to see looking at the crank up close. Pics show it too. Guessing in the previous rebuild the crank, or at least the #6 rod journal where the failure occurred, was badly scored or undersized, so the whole journal was welded up then machined back down to size. Pretty sure crack started at a grind mark (red arrow in pic below). Beach marks/smoother area was fatigue, then the rough and jagged area was the final instant fracture. Also interesting that the fracture followed the oil hole.

I checked the old harmonic balancer and the rubber is still in good shape. Will probably get the flywheel balanced for good measure, but I am 99% sure the failure happened because the crank had been welded on before. Sure was glad to find the smoking gun. Have the other parts on order to reassemble. Crank was $200, bearings, gaskets, and misc parts were $500. Hah. Counting my time as free, I'm getting out of it for $700 total. Guessing it would be quite a bit more had I taken it to a shop.
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65swb45

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The fact that it broke on a radius is not proof of misfeasance or malfeasance. Cracks are more likely to happen in a radius than on a flat surface. Nonetheless is is good that nothing else was damaged. I would want to check that the wrist pin is 1000% parallel to the big end of the rod on #5&6.

Best

Mark
 

cruisermatt

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I would have that block out of the truck and on a line bore.
I do not think that putting another crankshaft in that block is a good idea at all.
 

Mace

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If you are balancing. Balance the entire rotating assembly. Pistons, rods, crank, flywheel and harmonic balancer.

What RPM do you usually take the motor to?
 
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Rarely over 2800 rpm. The limited highway cruising I do is limited to 2700 rpm. 95% of the time it is under 2400 rpm.
 

steffan

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I don't think this was brought up yet: was the run-out between the flywheel and I put shaft for the transmission ever checked? I don't know how much of an issue it is with your set up but with a lot of aftermarket bell housings the alignment can be off considerably which can cause a lot of grief
 
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I have seen a few broken crank shafts and I have been amazed at how well they run. Most cracked at a main bearing.

I would completely disassemble the engine and install the crank and main bearings first. If the crank does not spin with less than 20 inch pounds of torque, I would have the crank checked for straightness and then line bore the block if necessary. I would also have the big ends of the rods resized.

You might get lucky just installing the new crank, but I don't like to depend on it with that much time and money invested.
 
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The whole rotating assembly still spun freely by hand after the failure. It seemed to be all contained by the big end of the #6 rod other of course, then the scored up #6 rod bearing.

I have the engine on a stand. Crank and cam are out. I was planning to do exactly that-install main bearings and crank then check for torque required to rotate crank. I already had the new crank checked for straightness/runout at a machine shop. Checked out good. Going to flush oil galleys.
 
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If the crank had not been turned, then the crank probably had a weak spot in it from the factory. When the crank journals were turned (if they were) it is always best to have a radius at each end of the pin rather than a sharp edge. Sharp ends of the crank pins are a stress failure point.
 
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Update, got the engine put back together with the new crank and ran it today for the first time. Crank went in easy, after I got the thrust bearing width issue fixed. See 2F Thrust Bearing Width. Cleaned out galleys, put in new rod and main bearings, seals, gaskets, etc. Rotating assembly turned over smooth and easy as can be once everything was torqued.

First fire up was neat because I had put oil in the cylinders while I had the engine out to keep them from rusting and I had the timing retarded a bit and the idle low. Started up and was puffing plumes of oil smoke and took all of the cylinders a few seconds to all be firing. Looked and sounded like a radial engine starting up!

No strange sounds yet and leftover pieces.
 

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