[parts man]

WE bought a MF 65 for parts with a broken crank. A real shame, because the PO had obviously just done a motor job on it, the bearings were like new, and the cylinders still had the honing marks on the walls. I would think less than 100 hours on the rebuild.
The break seemed to have been from metal fatigue. I was wondering if there was any way to detect this before the rebuild, or if the machine shop that turned the crank should have caught the problem? Magna-fluxing catch something like that??

<img src=http://www.chowntractorparts.com/images/busted1.jpg>

<img src=http://www.chowntractorparts.com/images/piece.jpg>

 

[MowHoward2210]

Not sure about how to forsee the problem, but great pics. Hope I never see that with anything I own.

 

[bear]

magna flux should have caught that

 

[Ingersoll444]

Had that happan to my old truck. Just in two peices though. Funny thing, is it still ran. Knocked a bit, but still ran.

 

[Wingnut]

That sucks file

Magna Flux should or did show the anomaly, whoever didn’t realize what they were looking at or were never train in looking at it. The unfortunate part is that if the machine shop refuses to pay for their neglect, it would cost you more for an expert witness than the damage caused. If is hard for someone with strong mechanical knowledge to prove that the machine shops negligent in the theater of a court room. You will probably calk it as a “lesson learned” for us here at Tractor Forum”.

Try to keep smiling

 

[Live Oak]

Magnaflux or a dye penetrant test should have caught that as Bear said but who know what the previous owner was doing with the machine when this happened? What a mess!

 

[parts man]

THanks for the input! I don't know if the PO had the crank checked or not, I just was wondering if having it magna-fluxed would show the crack. And it seems it should have shown up if it HAD been checked. Good to know for future use.
Thanks guys!:thumbsup:

Paul, I've heard of broken cranks running with a knock, and as I understand it, a crank will ussually break acroos a journal, or right down along the edge of a journal. This is the first I'd heard of breaking both webs to a rod journal right off! "Course, this IS the first broken crank I've seen too!

 

[jodyand]

My brother in law had a 86 blazer with i think a 2.6 V6 and he had two cranks break in it. It ran also but sounded bad very bad knock.

 

[Ingersoll444]

Parts.
Mine broke just like that, right on the crank arm mid way down. NEVER seen it before. Tolorance's were so tight that the two peices were held together enough to run,


Jodyand.
Those old 2.8's were know for that. In the front drivers they were a fine engine, but in the rear wheel drive cars, and the s10's it was JUNK. Hard to find one that stil runs.

 

[jodyand]

2.8 Sounds more like it:duh:

 

[parts man]

Thanks for the update Paul. I supose with the increased compresion of a diesel, it caused the other side to let go as well. When that happened, the piston came down through the bore beyond the bottom oil ring and broke the skirt ( the rod of course was already bent), and the piece of skirt from that piston flew to the adjacent cylinder and damaged that piston too!
Ah, well, got 2 good pistons, 3 good rods, and head ect, price was right!

 

[AlbanyBob]

Not in a tractor

:night:

I had almost the same thing happen to me in a drag bike engine I used to have......frown

I had done the engine myself and even had the crank Magna-Fluxed and dyed......:clap: Found no crackes or weak spots according to the shop.....:wow:

Finished my 1260 big bore kit :quiet: Which started out as a GS1100E......:crazy:

After running it for a week at time trials and then on street night, I pushed it to the limit red line at 10,500outta here

Had the crank come apart at a journal and almost threw me off into the pavement........:argh: :argh:

:fineprint Never trust only one person for anthing this major

Just my 2 centsa worth.....

copy and paste the link below if you would like to see some of my pics....

Bob

 

[aguysmiley]

Parts man,

Just a thought here. From what I see in that picture, it looks like that crank had a lot of force on it when it broke. I'm kinda wondering if the cylinder had filled with fluid. I don't know a whole lot about deisels. I have heard about fuel injected outboard boat engines having a problem filling a cylinder with fuel and bending rods, breaking cranks, etc. I haven't seen it myself, but have been told that if the injector sticks open on one of these, it can partially fill the cylinder. Fluid doesn't compress. It would be just like submerging a running engine.

 

[parts man]

aguysmiley, that's a thought for sure! The picture isn't terribly clear, but you can see the shiny part on one side where it had been broken and working against the other half for a while before it let go. The top of the piston wasn't damaged or scarred like I would expect if there had been any kind of obstruction in the cylinder. The bend of the rod was to side also, from the crank letting go on the weaker side first so I think it was just a case of metal fatigue. A tired crank!