I have had 2 different motors a 351 C & now a 351 M that locked up then later started right up like nothing had been wrong. The C had been rebuilt with only 10,000 miles on it. The 2nd time it locked up I pulled the plugs & it still would not turn over. You could hear the starter engage in the flywheel so that was not the problem. I pulled it & tore it down finding nothing wrong I scrapped it. Now I have the same problem with the M. It has only locked up the one time so far. It only has 80,000 on it & always serviced regularly. Any ideas on a fix? I don't want to scrap this one if I don't need to.

 

Locking up usually is caused by one of 3 things:

1. Hydrostatic lock: A fluid, maybe coolant or even gasoline, gets in a cylinder and prevents the engine from turning
2. Overheated: An engine that is very hot will frequently not want to turn because the components have expanded and there are no clearances
3. Rust: Rings frequently rust to the walls of the cylinders if moisture has gotten in.

 

Thank you Sir. I never found any evidence of fluid when I tore it down. I wanted to know what had caused it & I'm still wondering? Thank you again for your time.

 

Maybe the starter drive locking up?

 

Try turning it with a socket and breaker bar backwards, if the bendix is stuck, that will break it loose.

 

Thank you for responding to my question. I could hear the starter drive hit the fly wheel but would not turn it over.It wasn't hot. I had parked it the night before & went in to bed when I got up it was stuck? I don't remember if I put a breaker bar & socket on the crank. I'm sure I did & I know I did the 2nd time it did it. Like I said some one told me it was vapor locked & to pull the plugs. I didn't do that the 1st time. The 1st time I tried to turn it over by hand with the using the belts belts. I came back in the house & called the guy I got it from to see what he thought I should do about it. He was the one who said it was vapor locked. I went back out & it started up like it always did . Then I'd say about 2-3 weeks later it did it again. After pulling the plugs it still would not turn over. The neighbor & I pulled it down the HWY about 50 mph & dumped the clutch in 2nd & 3rd gears. It would not turn. I couldn't find any thing wrong when I tore it down. I scrapped it wasn't going through that again. The 2nd truck I just got I found out got real hot so that explains this one. Thank you all again for your time responding. You have a good day. God bless you & yours always.

 

. May not have quite enough ring gap and the ends are butting together from heat expansion and seizing a piston... can break the lands out of the pistons... often leaves a super shiny patch on the cylinder bore where it happened... prevention is prevent overheating... and/or more ring gap...

 

sometimes I wish there was a thumps up and down for posts. Well said Buzz!

 

. LOL!!!!!!!!!!

 

Thank you Buzz that is something that I have never heard of & I didn't look for when I tore the motor down.

 

. Here's what can happen if ring ends butt and lock in bore and piston keeps moving downward...

 

I never saw that! But it is a good possibility that is what had happened. Thank you again Buzz