Okay, so...
As the title says, I am currently building, or rebuilding, my first Ford engine. I have dealt with exclusively GM engines thus far, but a friend of mine asked me to rebuild his 351 Windsor for his old Ranchero, so here I am. In any event, when I got the engine, it was old and worn out, covered in years worth of grime and gunk and stuff but it turned over freely no problems. I tore it all down, put in new bearings all around, gaskets, seals, bearings, the whole nine yards. So far so good...

The problem: in putting it back together, I put the pistons all in, breaker bar turning it with each one and it spun just fine. I let it sit over night and suddenly it's locked up. Thinking something fell in one of the bores, I took them all out and found nothing out of place. So I one again put 4 of the pistons back in and it spun fine, no issuse. The wife and I left for a few hours to run some errands, came back home and once again, I find it locked up. Mind you, the crank and pistons have more oil and lube than a porno set (I'm very liberal with assembly lube). I called a friend of mine and he mentioned that in the cold air - and its about ~30°f where Im at - the metal can shrink and lock up. Does that sound like whats happening to you guys? Have you ever had this issue before with the enging locking up after sitting for hours at a time?

Before you ask: All the pistons that are in right now ARE in their correct bores. The crank is lubbed. None of the associated bearing surfaces have any gouging or deep cuts.


I was able to hand turn it earlier this afternoon. I've never had this issue with any of the SBCs I've built, but come to think of it, its usually warmer when I do so I guess it never came up.

in any event, thanks for your input guys!

(the pics are for reference. Before and after and all that)

 

For whatever its worth, after a painfully careful inspection, I found that one of the rod bearings was oversized .010 while all the other ones were standard. I recall that I had to order one extra pair since I accidentally scratched one from the new set. I guess they sent me an oversized pair and I didn't think to check it for it since I didn't exactly specify. (Usually standard sizes are sent unless specifically asked for otherwise). Live and learn I guess 🤣.

 

Hey that is good detective work. I was thinking the problem sounded like a binding bearing and it doesn't take much.

 

A .010 under bearing should lock up as soon as the bolts are tightened unless the crank is really bad.

 

Did you seat the thrust bearing properly ?
Bearing clearance needs to be checked with a set of mics and a good bore gage reading in .0001". Otherwise your just gambling with your time and money.

 

Thrust bearing location is different (can't remember where it is exactly) from GM. That's come up in the past.....