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?)