Just looking for ideas as to what the cause was. I was only the guy hired to swap out the parts that got wiped out when it failed, so the only history I have on the hoe is second‑hand, and as it comes out over time it may be unintentionally—or possibly deliberately—distorted from the truth. When it went, it left the torque converter attached to the flywheel by only two bolts, and the owner drove it back to the shop. Judging by the damage, it tore up the pump/converter and the flywheel. My concern is the cause. I dialed everything in for runout and anything else I could think of when installing the used powershuttle that was provided. The flywheel had to be replaced but came from a different doner then the trans did, the flexplate came with the trans and is in good condition. The crank has 0.015" endplay —could this have been the cause, or was it caused by the failure? The rear main doesn’t leak (yet), but I’ve had two seals on the pump fail badly—not immediately, but the next day, almost right after startup, I’m told. I don’t want to spend another couple days pulling this pig out again. I’ve now put a new pump on the unit, everything dialed in with runout less than 0.010" at the converter hub , and I’m hoping it isn’t going to bust another flexplate or eat another seal due to something I’m missing. Any help is appreciated.
It is normal for flex plates to crack and eventually break. It may not have been centered on the torque convertor. when it was installed.
No, I totally get that and agree. What’s exceptional about this is that he was able to keep running it long enough to drive it back to the shop, and the increased magnitude of damage that likely caused. As I’ve said, I’m limited in my knowledge of its operational history beyond the events that followed this particular catastrophic failure—but those events speak volumes about the potential for improper operation and abuse, if not just a lack of understanding of what you should do when a machine starts making those kinds of noises and its behavior changes the way this one must have. I’ll take some pictures of the converter and pump. Honestly, I don’t know how it made it 10 feet, much less the 10 minutes it probably took to get it into the shop. But I digress. I don’t know what the upper limit for crankshaft thrust clearance is on this little 4‑cyl diesel, but 0.015 feels like it’s at or beyond it. I installed a wear sleeve on the torque converter boss, and the witness mark it left was way wider than I’ve ever seen any seal make—even after years or decades of use, failed or not. This was after maybe 2 hours of total operation, if that. The first thing I did after pulling it apart the second time was make sure I hadn’t damaged the seal installing the powershuttle. I carefully examined it under magnification to see if the lip showed any sign of alignment issues or irregular wear. The lip was completely gone, uniformly. The sleeve used is the correct one for this application and for this seal, and it was installed with plenty of lube. I even used white grease to ensure the sleeve placement was correct on the hub after installation. The only thing I can see that would cause the seal to fail twice and leave such a wide mark on the hub is excessive crankshaft thrust. I even checked the torque converter supply pressure and the cooler bypass to make sure they weren’t responsible. Both were normal, although I didn’t let it get fully up to operating temperature for obvious reasons. I just don’t want to put it back together and hand it over, only to find the problem is still there if it’s anything other than an engine issue. I don’t believe he’ll want to tear into the motor—he’ll probably just liquidate the backhoe if that’s the case. If anyone has any ideas—right or wrong—please chime in.
.015 is the absolute limit for the crankshaft end play in a Case 336 CID engine. The ONLY way to obtain an accurate measurement is by using a dial indicator and a pry bar. The crankshaft has to be exposed and the pry-bar is then applied between a main bearing cap and the crankshaft. There are other reasons a flex-plate will fail prematurely.
Welcome to the HEF. The crankshaft end play is getting close to the limit as Tinkerer mentioned, but that’s not why the flex plate cracked. They just crack. It’s a feature of the creature. It’s good to be concerned about root cause, but don’t overthink it.