Crankshaft problem on Y395??

[Bob Rooks]

There are many contributing factors involved in broken crankshafts aside from bad forgings, which is highly unlikely, (crankshafts are not cast) which are not limited to unbalanced firing pressures from defective fuel injectors, mis-calibrated fuel injection pumps and worn piston rings/liners, defective/unbalanced clutch packs and flywheels, harmonics generated from the drive train, etc., etc.

[Ranch_Hand_Supp]

Originally Posted by Johnny P

Hello all,

The crankshaft has broken across one of the counterweights, Don't know why, maybe a fault in the casting!

Johnny P

Could have been a fault casting or forging flaw but, I would be more concerned with the main bearing Housing Bores in the block to help determine the cause. The bearings wear pattern can tell a lot sometime.

If the line bore is off then the crankshaft main bearings will have excessive clearance that can and will cause the crank to jump / flop, (cranks don't like that). Piston connecting rods need to be checked / corrected when this happens. Crankshafts are so hard they are brittle.



Ronald
Ranch Hand Supply

[Bob Rooks]

FYI: Crankshafts are not brittle, that's why they are forged from billet steel - to allow for the grain to follow through the webs and shaft line continuously. The journals are only hardened ~.050" to allow for ductility.
Ronald is correct about the line bore. Cranks will only tolerate so much repeated deflection before breaking.
I have never heard of an engine crankshaft made from cast iron - or cast steel for that matter.

[IH3444]

Remove crankshaft halfs. Box up and ship to "RRL Chinese Tractor Expert, Experienced Repair Remanufacture Facility" Wait several weeks for crankshaft to return repaired. Reinstall crankshaft. There is nothing Rob can't fix.

[Ranch_Hand_Supp]

Originally Posted by Bob Rooks

FYI: Crankshafts are not brittle, that's why they are forged from billet steel - to allow for the grain to follow through the webs and shaft line continuously. The journals are only hardened ~.050" to allow for ductility.

I have never heard of an engine crankshaft made from cast iron - or cast steel for that matter.

I am not and engineer ........ just have spent my whole life trying to repair / maintain what engineers have designed (grease monkey).

I have just always assumed that diesel cranks had to pretty dang hard to be able to take the beating that a diesel puts on a crank and the ring tone it has when tapped on the end with a wrench ???.


But. I did do a Google search using ; Cast Iron Crankshafts , Cast Steel Crankshafts & Crankshafts are not brittle.



Ronald
Ranch Hand Supply

[IH3444]

Bob, what's the difference between billet steel, and cast steel?

[Bob Rooks]

Ronald,
It was not my intention to seem condescending, I apologize. I too am a grease monkey.

IH3444,
Cast steel is solidified in a form (casting) and has no granular strength, whereas a billet is solidified as a bar, plate, etc., and forged into a shape by a press or rolled into various forms such as channels, angles, H-beams., etc. In a forging the grain of the steel follows the line of the forging from end-to-end and has much greater strength and resiliency. In both cases machining is still necessary to obtain dimensioning & finishes.

I shouldn't have made such a blanket statement that all crankshafts are forgings, as I know this to be true. There are light duty applications and extreme heavy duty segmented crankshafts where there are a lot of castings.

[IH3444]

Thanks Bob!

[Johnny P]

Hello,

Can any body supply the torque settings (Y385 engine) on the attached list,

Thanks

Johnny P
(Hope the attachment works)

[Rich Waugh]

Crankshafts have been forged for somewhat over a hundred years now, I think. I have a couple of old forging books that show the entire sequence for forging the things, not that I ever plan to do it.

I agree that probably all ordinary crankshafts are forged, and that forged is better than cast, but I wouldn't completely agree that the grain lines follow the forging - at least, not after heat treating. Once the steel has been taken above the A3 point, the grain of the steel becomes random again. It just can't help itself. :-) Prior to normalizing though, the grain of the steel definitely does flow with the forging forces to some extent, depending on the manner and amount of forging. Open die forging generally will develop more grain flow while closed die forgings develop somewhat less. As a general rule - there are no real absolutes in forging work, in my experience.

It is my understanding from my metallurgist buddy at one of the biggest industrial forging joints in the country, that after forging the cranks are normalized to relieve stresses, then sent out for rough grinding. After rough grinding they are then induction hardened at the bearing and rod journals and finish ground to tolerance. The remainder of the crank is left in the normalized condition so that it can handle the stresses of reciprocation.

I haven't asked him what he thinks the reason is for a crank to break, but my guess would be a bad forging or bad line bore. During the forging process it is possible, though very unlikely, that a "cold shut" could get forged in at one of the transitions, resulting in a stress riser that later cracked under use. It is also possible that the original billet could have been flawed prior to forging, but that is usually caught by X-ray on QC check. In the US, anyway. :-) It is also possible, and maybe even likely, that the crank was improperly machined after forging, leaving a sharp inside corner at a transition - this becomes another stress riser in use.

With all the possible ways that the crank might have been flawed, it still might well have performed fine if it was operating in a perfectly bored set of journals. But the least little bit of misalignment in the journals would set up stresses and harmonic vibrations that would cause it to self-destruct for sure. Even a perfect crank won't tolerate an out-of-line bearing line for too long.

That's my take on it, anyway. I'm **** sure no metallurgist, mechanic or engineer, just a blacksmith who's been around a bit, so you can take it for what it's worth. I'd definitely have the line bore checked, no matter what else you do. Put a new crank in a bad bore at your peril, in other words.

Rich