251 vs. 264

[RonaldC]

Block says 264 (C5363), but cant tell for sure when looking at the connecting rod. Anyone have a better eye than I?

 

[Plymouthy Adams]

measure the stroke....

[RonaldC]

Looks like a 251 CUI. to me

 

265 had a different nut on the connecting rod. Had more of a stamped nut, where the 251 had a "regular" nut on it

[dpollo]

you may be thinking of the "pal" nuts used as lock nuts.  Measure the stroke.  41/2 for 251,   43/4 for 265 

[Loren]

Besides measuring the stroke there are some quick and dirty ways to tell what you're looking at.

1) if you can turn the crank, the rods fit very closely onto notches in the block pan rail.

2) the center counter weight has a very deep groove to clear the oil pump/distributor drive shaft.

3) the most telling of all are the connecting rods. First they are shorter because of the stroke but you don't have to measure them. The main difference is where the head of the big end bolts are. The 265 rods are cut way back in this area to clear the cam and the bolt heads are not "T" shaped but are round with a tab that fits in a notch in the rod. If your engine has these rods its a 265.

 

When I think of all the clearance issues with the 265, I figure the Chrysler engineers where trying to get the last cubic inch out of it. Also if I ever encountered one that had bearing problems, I repair right away! If one of those rods made contact with something the damage would be catastrophic.