Click Click Boom!!!!!

What causes the cranks to break on the new engines? The old mechanical ones would because they couldn't stand being lugged or run under 1600 and that would make a lot of uncontrollable heat. These new engines are designed and programmed to “idle” down the road and are running almost 1000 rpm less than the old ones so I thought the beefier bottom end designs and the electronics were supposed to manage this problem better. Is it still a lugging problem?

 

Crankshafts are subjected to extreme torsional twisting between power strokes.

If sensors were placed at either end, they would read the crank twisting a little even though they’re very beefy.

The newer engine cranks have better metallurgy to them to make them handle the stress of lower rpms. But they still have counterbore issues.

Sometimes cranks that breaks just have a weak spot that never show up when made at the beginning and crack down the road. Quality control issues during forging.

Or a bad harmonic balancer on the front.

 

Even incorrect machining of the main bores will put stress on the crank. If one's a couple thou out of spec, it will cause the crank to flex slightly. Constant flexing over time work hardens the steel and it eventually starts to fracture.

 

I understand. So same as it ever was. Or same stuff different generation.
Thanks for the response @Shawn2130 and @AModelCat. I just thought there was more mystery to it like a new problem that came along with the new tech.

 

Sometimes #### just happens. Engine was covered under warranty, put a new crank and 1 rod in it and back into service. It probably had a very minor defect during machining. Second broken crank ISX crank I have seen with my own eyes. For the amount of trucks that go through our place, it is a very rare failure.

 

Figured it had to be rare. But just like the few rare cranks that broke 40-50 years ago the future oldtimers will talk like every single one of them broke or is a failure waiting to happen. Lol

 

Torsional loading is definitely the precise word for the issue. Cranks get twisted up clockwise then counterclockwise like a twizzler billions of cycles. The trucks today still pull the same 80k but theyre doing it with 200 extra HP and at less rpm. Well less rpm means more microseconds of loaddm durstion on each rod and crank throw, thus a greater degree of torsional deflection. Less guys in a tug of war means the guys that remain work harder. And so it is with lowering rpm to save fuel, less piston pumps carry the load up the same hill so each pump must do more work for longer. Lower oil pressure, less fan, less coolant circulation and more time under strain. =More crank deflection.

A big truck has a lot of flywheel/clutch mass to help dampen the torsion pulses but could use a larger diameter front balancer. On gas engines that are beat on youll see more wear in the main bearings near #1 cylinder.. opposite of the flywheel. Especially when kids pop on one of these snazzy lightweight aluminum crank pulleys. Bearing life dramatically reduced because the torsional harmonic has less mass available to dissipate it. The crank dances and bearings suffer.

 

Had 429 ford in a propane truck doing a clutch job. No engine complaint. We were required to check crank end play on every clutch job. Had zero at rear, 1/4" in the front. Drove in with a broke crank. Darnest thing I ever seem.

 

Was hanging out with a buddy at his in-laws place. His father in-law gets home from work and mentions reverse gear felt weird the last couple days and some weird sounds when he starts it up or shuts it down. We look around the truck, tilt the hood and start/shut it off. Then I noticed when he shut it off, the damper would push outwards about 1/4" - 3/8". Had him look while I bumped the starter. Sure as #### she was moving in and out. Never found out what exactly what failed. I'm suspecting the crank broke or was damaged because they ended up dropping in a replacement ACERT C-15 from a wrecking yard.

This was a strange truck. T800H but had 69k lb Freightliner air ride

 

Not a truck but this one still has me puzzled as to why this happened.

Oil pump of GM 1.6 4 cilinder. Very low miles on engine rebuild, with new oil pump.

Car got hit by another car, engine was still running, and driven home after the hit.
At home the oil pressure light came when engine was idling.

After turning off the engine it would not crank any more.
Turning the engine was possible but only for like 30 degrees crank rotation and then it was blocked.
Clutch depressed or not, no difference.

Maybe hydro-locked, but coolant level and everything was OK.
Removed the spark plugs,still the same.
Checked inside the cilinders, no piston to valve or head contact.
Removed oil pan, crank or rods did not hit anything, nothing strange there.
Removed timing belt, camshaft rotated normally.
Removed transmission, same thing.
Removed pulleys from front of crankshaft, same.
Removed oil pump from front of crankshaft, and crankshaft could be rotated again.

Opened the oil pump, and every single tooth was broken like this....

Cleaned oil passages in the block, put on new filter and pump, checked mains and rod bearing (no damage at all) and engine ran fine again.