Being very careful here as I bough a used 1977 F100 with a factory rebuilt motor that had about 12,000 miles on it.

To make a long story short, the motor had a rumble in it that came and went. Not a bearing sound, and several good friends/mechanics had no idea.

Well....crank broke between the first 2 rods and the second main bearing after about 5,000 miles.

When the remainder of the crank was pressed from the balancer, it was cracked[balancer] where it attached to the crank.

The heads are rail type, so they should be '77 vintage.

I had the machine shop order a replacement balancer and the box says 80 and up. That is what matches the #s on the old one

What are the differences in the harmonic balancers between '77 and '8X??? The crank I got is from a '77. Regrind w 10 under grind.

I'm wondering if a slight difference in the balancer might have caused the problem. The motor ran well before and did not have any noticeable vibration.

Any suggestions are greatly appreciated! Thanks.

 

I've re-read your post a couple times and if I missed it I'm sorry.

Do you have a 302 or 351?????

If it's a 351 there is NO difference in inbalance in any of the years.

If you have 302 and a 1980 balancer it should be compatable with the '77 crank. Ford changed the balance in '81 and ABOVE 302's to 50oz imbalance. Check your flywheel/flexplate also.

Anything up to an '80 on a 302 should work. '81 and above is a different game.

351's are the same in all years but there's a catch!! 302 balancers and flywheels will bolt up. So, again, if you have a 351 and '81 302 stuff you have the wrong parts..

Sorry if this was confusing.