Bing Bang Pow!

[clark_bailey]

Well i got this old bucket of bolts apart tonight. Looks like it made quite the commotion when it came apart. Hoping to save the crank but...

These parts were in the pan.

I'm trying to put the story together... Was told it started knocking on a uphill pull, stuck supposedly... Anyway, the knock out plug in the front of the block I found in a wad of oil and dirt on the frame under the front of the engine. I put it back in so i would loose it during the rest of the tear down.

Wondering if the plug came out during the big bang or before, then motor ran a little low on oil before it began knocking, the uphill thing just set it in motion? Any other ideas?


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[North Idaho Wolfman]

That motors a goner!
That thing ran for quite a while without oil would be my guess!
I would almost guarantee the crank is toast.

 

[skeets]

Hully blowed motor batman

 

[Dwarner]

I have had much worse gasoline engine crankshaft bearing journals rebuilt at a local machine shop. Worth having it checked.

 

[L.C. Gray]

Damaged crank journals can be repaired.

https://youtu.be/UYGzVzpWrw4

That's neat, never got to see submerged arc up close before.

 

[D2Cat]

Kubota has .2mm and .4mm underside bearing available.

Local machine shop (been in operation for 2 generations) didn't suggest/want to weld the journals on a 4 cyl diesel. They indicated all crankshafts deflect some from the heat of welding and if they thy to true up the shaft a crack is invited to form.

I guess everyone's mileage may vary.

 

[lugbolt]

The crank is scrap. Having had some cranks repaired before, they never last. And they were repaired by reputable shops. One being Hank the Crank and another Crankshaft Specialties....these guys know their stuff and they still didn't get the service life out of them that I'd expect. Most times they develop cracks at the journal fillets. From there, it's a ticking time bomb. Diesels are hard on cranks anyway due to how they operate. Only time I'd put any money into a failed crank like that is if it was a really rare one-and even then I'd search high and low for a good used one before I had one welded ground and nitrided.....

 

[CaveCreekRay]

Weird how they use sand for a welding atmosphere. Is that for heat dissipation or to contain spatter?

Looks like a gas-less wire welder using fluxed wire? The slag looks like what you'd get from fluxed gas-less wire.

Man! That machine must be from the 60's or early 70's. Cool!

 

[North Idaho Wolfman]

Weird how they use sand for a welding atmosphere. Is that for heat dissipation or to contain spatter?

The "sand" is metal powder, and that is a plasma arc welder, it's welding the metal powder to the crank.

 

[CaveCreekRay]

Aha!

Yeah, it makes sense that the heat stress from the added metal would introduce stress lines on the rank. I doubt heat treating would get those out and heat would likely introduce more problems.

 

[clark_bailey]

My bad, I held camera too low, it's actually a 4 cyl, the number two cylinder crank bearing surface is the destroyed one. I will eventually get it out, put it on crank grinder and measure to see if a under bearing will make the crank usable. From just glancing it looks way more than .4 mm worn. I just can't believe you could continue to run the darn thing with it making such a commotion. It had to have run a while making a horrific noise since the piston rod is worn into at least 1/4 inch where the crank struck it every go around. All I can say is wow, really!

 

[clark_bailey]

V1903 IDI from a L3600, it's essentially a boat anchor once I rob the essential parts from it to replace with a V2203.


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[Yooper]

First time I've ever seen a block without half caps for the main bearings. Crankshaft must come out of the end of the block like a camshaft. Interesting!

 

[North Idaho Wolfman]

First time I've ever seen a block without half caps for the main bearings. Crankshaft must come out of the end of the block like a camshaft. Interesting!

Yes most, if not all kubota engines are set up like this, it makes for a very strong bottom end!

 

[Wild and Free]

Yes most, if not all kubota engines are set up like this, it makes for a very strong bottom end!

Bottom end of the 1702 I am replacing was not too strong. Usually a broken crank is due to bad finish machining and not grinding down the stress risers and sharp edges.

 

[North Idaho Wolfman]

When disassembling the Kubota engine does the crankshaft come out from the front of the engine as the camshaft would.

I'm rather intrigued with the engineering that went into these engines.

It comes out, back of the engine, all of the main bearing holders same size.

 

[North Idaho Wolfman]

Bottom end of the 1702 I am replacing was not too strong. Usually a broken crank is due to bad finish machining and not grinding down the stress risers and sharp edges.

Yea I agree in your case it was the weak link, I don't think that's a normality on these engines.

 

[clark_bailey]

I think i found the problem! Just needs a little tac weld and it's good to go? [emoji106]


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[Wild and Free]

Ha Ha, thats actually pretty neat.

I should finish tearing down my 1702 to show the broken crank shaft carnage.

 

[cviola2005]

WOW! That brings a whole new meaning to "bent rod".

I've never seen that before, usually slightly bent or snapped in half.

I think that's a Hall of Fame type picture.





I think the real question is: Can you do it again?