engine knock found

[69ranger]

So, the 48 cub that I recently bought with the slick knock got some attention today, and you all are not going to believe this.

I wanted to try and trace down the source of the knock, so off with the oil pan.

Once I got the pan down, and started to roll it around with the crank, I noticed that the front end of the crank moved forward some.
On closer inspection there is a break, across the crank right behind the front main. The crank would literally be in two pieces, if not for the mains holding it in place.

Here is the weird part.. This engine really made very little noise, and it carried very good oil pressure. I have never taken a running engine apart on anything, that had a broken crank.
The good news is that the rest of the engine looks good, from what i can see. I pulled the rest of the mains down, and number one rod, and so far so good.

So I will take the engine out, and tear it the rest of the way down, and look thinks over.
Apparently the engine has not run much in this condition, and the fact that its a low RPM engine apparently save the engine from coming apart.

I hope all the rest is ok, and will follow up with more info, after I get the engine out of the tractor.

Now for the $64,000 question... So was this was a casting flaw, or an abuse issue, and if so what the heck where they doing that cause this?
Has any one else has ever encountered a problem with cranks shafts in the little cubs?

[Jim Becker]

Broken crankshafts have happened before. But they are so rare that it never comes to mind when somebody has a strange knock. Any comments I make on the cause would be a pure guess.

Here is one thread about a broken crankshaft.
http://www.farmallcub.com/phpBB2/viewtopic.php?f=1&t=71799&p=579036

Here is another about one broken crankshaft and has mention of another.
http://www.farmallcub.com/phpBB2/viewtopic.php?f=1&t=22208

[ricky racer]

What caused the crank to break may remain a mystery but the good thing is you found it. Find a new crank, replace the bearings, seals and rings and you'll be good to go.

[tst]

A guess would be maybe to much end play ?? if it was bouncing back and forth a lot due to bad thrust bearing ?? make sure to look over the rods carefully that they are not bent, could just have a flaw in the casting that has been there for a long time and finally let go ?

[muleboss]

I do have a couple of extra engines. Don't know anything about them. expect they are not stuck.

[ScottyD'sdad]

I recall reading that there was a short period of time, that the cranks were defective, and broke as mentioned. I believe it was George Willer who described it.

Ed

[phill_mi]

Discussion of a recall due to bad crankshafts
https://farmallcub.com/phpBB2/viewtopic.php?f=1&t=86409&p=688789&hilit=broken+crankshaft#p688785

[69ranger]

Thank you everyone for the info and for taking the time to reply. I am grateful, and will keep you all posted as I begin trying to fix.
I was going to work on it today after Church, but ended up working with my buddy on his car. I did start the tear down so I can remove the engine.
Maybe work some this week, if time allows.
Looks like I must have got one, that slipped by the recall all those years ago. The rod and main bears from what I can see, at this time look fine, but I will look carefully at everything before making a decision weather to save or part it out.

Mule Boss: Glad to know you have an engine. I would love to get up and see you, and yes I may be needing a replacement engine, if this one is not fixable.

Again, thank you all!
Brad

[BigBill]

Running a engine with lots of bearing wear puts stress on the crank. I’ve seen spun main and rod bearings for it being out of balance.

[Clark Thompson]

Line bore on the mains can cause a crank to crack.

[BigBill]

I seen a v8/350 Chevy crank crack along the forging lines. My newly built 350 using forged pistons needed .005” clearance and my machinist let them go at .002” that’s for fast pistons, I’m up in vt with the truck when she started knocking. The #7 piston cracked the skirt along the skirt to the forged vee shape. These were new TRW forged pistons. I had 90 lbs oil pressure, I trusted my machinist. I started doing my own work soon after. I made it 300; miles to home. Another set of pistons .040” over. I never am cheap when I build anything. This was my firewood truck.

[69ranger]

Since I last posted, I have not had time for the Cub, the last few days, as the wife's car needed some work.


So tonight I had my night to myself. My buddy came over, and we got the crank into the block, and the timing marks both lined up.
The mains set up at .002, and all seems good so far. So with the mains set up, I will set the rods up, as soon as they arrive.
Hopefully this week, the rest of the parts will get here. Looking forward to getting this thing put back together.

All for now, more as parts arrive..