1991 F450 Super Duty-Broke Crank shaft

[towjoe42]

Last night my super duty suffered a major breakdown. The Crankshaft broke just behind the Pully. I also found out last week it had two very low compression on two opposing cylinders. I was thinking of rebuilding the motor.
I decided to replace the motor and found a good used one. It will be installed today. I will do a motor autopsy at my home shop to see what else may have caused the crank to break. More later. Joe

[denisond3]

I am eager to hear. I have a 90 F350 with the 351 in it that I plan to rebuild. It had a rod knock, but was also otherwise badly maintained. Actually not maintained at all.

[towjoe42]

I won't be doing an autopsy on my motor. I told them I wanted to take it home and take it apart. The wrecking yard that did my swap had to send the motor back to where they got it as a "CORE MOTOR". I was a little upset with them on that. I really wanted to see if I could figure out the cause of the crank breaking.
The replacement motor runs real good so far. And Actually with all cylinders firing, my Engine mounted PTO actually works much better to operate the tow lift.
So it would seem that the compression being almost zero in two cylinders caused the motor to lug down and actually quit when the lift was operated.
I will be doing a complete tune up on it next week.
Going to get it out tonight and run it through it's towing operations.
So, looks like this wraps up this thread. Tow Joe

[globaltruckdealer]

Ohhhh bad luck!!
its a fun to assemble and open a engine parts.

if you open you engine at home for first time then note down the assembly step by step as you opens it!