Broken Crank

[RJYork]

I have broken a crankshaft twice in less than 7 months in my Yanmar 2010. The first break was in August 2006 on the original, I suppose, crank. It is back in the shop after breaking the new one I just replaced from Hoye Tractor parts in August. It has had very little run time since I replaced it in August.

Hoye said they will not refund unless the manufacture finds a defect when I return the crank to them. I really do not expect a refund. If they do not make good on the crank, I will sell the Yanmar and buy another brand. I can not afford to keep replacing crankshafts this way.

There is no sign of seizing, no burn marks, no visible damage other than the broken crank. Looking inside at the break, all I see is that the metal seems to be very grainy. Not a solid mass as I would expect.

My question: Has anyone else had any trouble like this?

 

[LMTC]

How soon after purchase did the original crank break? Any other symptoms at that time?

 

[DieselPower]

Can't say I have ever had that problem. Have you had the block checked for straightnes between the crank main journals? Do the bearing's show any abnormal wear? Where the crank broke are there any visable signs of air pockets or casting flaws?

 

[normde2001]

Never heard of it in 5-6 years of following 4 Yanmar forums. Did the new one break in the same place as the original?

 

[RobS]

How many hours on the original? Assuming lots of hours, and a fairly quick second break, I'd suspect something in the block. As Norm asked, was the break in the same place? Any chance the block froze recently? Any coolant leaks? How's the flywheel/bellhousing? Anything out of the ordinary to stress the crank could contribute.

 

[MJPetersen]

That is NOT normal at all. There Must be some sort of problem with alignment or stresses that are out of specs. You need to find the cause of the breakage. Was there any vibration like somethng is out of balance before it broke. If you said where it broke ie after first rod journal or before rear main journal, it might give a clue on where to look. Also it would be VERY interesting and important to know if the first and second broke int he same place.

Mike in Warsaw

 

[RJYork]

I did not really watch the run time, but I am sure less than 40 hours.

No, the bearings do not show abnormal wear or any kind of unusual markings. No sign of any kind of binding at all. The bearings are dinged just slightly where the shaft wobbled after breaking. Inside the crank break, it looks like tiny bubbles. Almost a sandy texture look and feel.

I was not able to get information on the first break location from the first mechanic. So I am not sure about both breaking in the same place. The first break occurred while the unit was in idle. I went inside to get a drink and left it in idle. When I came back out after a few moments, it was dead and would not start. Second break, it was in idle as I stepped off to hook up 3 point. I got back on, raised speed slightly and put in reverse. Tractor lurched and died. I was never able to get it started again. I felt the same thing had happed again. It did.

No leaks, coolant and oil levels all good. The flywheel and bell look good. No missing fly weights. The fly even has a hole bored for counter balance. No addition weights appear to have been added or thrown.

I will ask the mechanic to do something to have the block checked for straightness between the crank main journals before reassembly. There are no obvious defects showing.

I will try again to contact the first installer and see if I can get location of first break. I agree that is a critical piece of information that I would like to have also.

Thanks for everyone’s input.

 

[kenmac]

Inside the crank break, it looks like tiny bubbles. Almost a sandy texture look and feel.



This would indicate to me that this is (mabe) a cast crank instead of a forged crank. Does anyone know if these cranks are forged or cast ?

 

[oldmech]

Hi! Everybody! My opinion. Is it not a crankshaft problem! Yanmar are direct injection engines. So Injection timing are very Important. Bads injectors (check opening pressure), bad injection timing pump. (Check advance and regulator timing)May be some Injector or bad injection pump( no the good one) Check every parts numbers with original OEM engine parts manual. So Check block! Dont fit new crankshaft before find the trouble! Good Luck! Oldmech

 

[normde2001]

Hi! Everybody! My opinion. Is it not a crankshaft problem! Yanmar are direct injection engines. So Injection timing are very Important. Bads injectors (check opening pressure), bad injection timing pump. (Check advance and regulator timing)May be some Injector or bad injection pump( no the good one) Check every parts numbers with original OEM engine parts manual. So Check block! Dont fit new crankshaft before find the trouble! Good Luck! Oldmech

My thoughts exactly, pre-combustion on one cylinder could cause it, putting undue strain on the crankshaft. That's why I was curious where it/they broke. (Between the cylinders?)

 

[LMTC]

If there's any question about the possiblity of cobbled together parts, I'd be curious as to the origin of the machine. Have you spoken with the seller? How long did you have it before the first crank broke?

 

[CAT793]

G'day gents,
Are there any pictures of the fractured crank ??? There is a lot to gained from the failed iron. The crank will most likely be a forging, forging created flow lines (steel grain) parallel to the fillet and journal surfaces resulting in a stronger crankshaft.

There are quite a few different failure modes associated with crank failure . Basically the crank will see two types of load , Bending ( During combustion) and torsion ( caused by the resistance to crankshaft rotation by flywheels, pulleys, transmissions etc.)

I'll list a few types of failure that we look at.

Slow failure ( over time)
Bending Fatigue
Torsional Fatigue

Quick failure (can happen at anytime)
Contamination
Misalignment
Heat
Grinder cracking
Straightening cracks
Welding
Inclusions
Flaking
Forging burns
Quench cracks

I could keep going on but that should do. If any photos are available can we see them.

Your first crank could have failed from Fatigue, second cranks unless it was used would not have failed from fatigue, but more than likely from one of the others on the list above. There is a lot that goes into a crank shaft it is a very involved process, a problem during the manufacturing process if not caught will cause a low hour failure. I usually work with engines from 100hp to 3500 hp but the same principals apply to a small engine.

The iron will tell you what happened if you know what to look for. Let me know if I can be of any more help.

Cheer's
Pete

 

[LMTC]

For those of you--like me--whose technical level was just exceeded by light years in this last post, Pete is an engineer with Caterpillar. And that accent in his typing (G'day gents).....he's from that island where they all say "G'day", thus eliminating the totally useless and time wasting double "O".

And you should see some of the stuff he gets to play with. Machines bigger than my house.....

 

[phatgemi]

For those of you--like me--whose technical level was just exceeded by light years in this last post, Pete is an engineer with Caterpillar. And that accent in his typing (G'day gents).....he's from that island where they all say "G'day", thus eliminating the totally useless and time wasting double "O".

And you should see some of the stuff he gets to play with. Machines bigger than my house.....

Yep, it sure sounds like he knows his stuff. There could be one reason missing from his list however. But we can't be sure........

- Improper VN rebuild!

Would be interesting to learn the orgin of this tractor........

 

[RJYork]

Thanks again for the input. I will try to post a picture of the crank before I send it back to Hoye Tractor.

New information:
The crank has broken on both sides of the engine. First in front, latest in back.
Mechanic says there is no misalignment or any sign of a misalignment.
He is taking the flywheel to a racing shop to test that component.
He had the injectors tested and found them in good condition. He had the same thought as some of you. Good guess, but no cigar on that one.

Yes, I really want to find out what is happening before I put it back together. That is why I am having it checked thoroughly.

I ran the unit for two years before first break. But hardly any time before the second break. I will let ya’ll know as things progress along.

 

[CAT793]

Mate,
Make sure the photos are very good quality close-ups we really need to see what happened , need to see both side of the fracture ........... if the size exceed what's allowed on the forum , you can email them to me direct and I can have a look at them for you.

We all want to see the iron..............

Let us know how you get on.

Cheer's
Pete

 

[RJYork]

I just got off the phone with my mechanic. He was installing the new crank, from Hoye, when the light hit the new crank just right. He discovered a crack in the brand new crank. He was able to put a knife blade into the crevice. The location of the crack? Glad you asked. Same place as the break in the crank being replaced, which was also purchased from Hoye. I asked Hoye to contact the mechanic and let me get out of the middle. I will send both cranks back to Hoye for their analysis. Stay tuned for the next installment.

 

[mark777]

Incredible!

If Aaron at Hoye has two bad cranks form their supplier, wonder how many, and from what source are on the shelves.

I'd bet my next paycheck We'll hear from Hoye and let us know what actually happened. Obviously nobody is safe from faulty manufacture regardless of how big (or small) the volume of your business is.

I'm sure I would Zy-glow AND magna-flux any crank shafts from that, or any particular supplier.

Good luck,

Mark

 

[kenmac]

If I were Aaron, I would check the rest of my stock. Not just these cranks , all my cranks

 

[MJPetersen]

Incredible!! I for one would still like to see those pics up close and personable for the first second and third cranks. If at all possible.

Mike in Warsaw