[font size="1" color="#FF0000"]LAST EDITED ON 13-Jul-01 AT 11:59 PM (EST)[/font][p]I just replaced the main and rod bearings in my 351M. There was no machine work done just new Std. size bearings. I torqued everything down now I can't turn it over. The only thing I can think I did wrong was use to much assembly lube. The kind I used was black and very thick like grease. My friend said the kind he used was thinner. Anyone have any ideas?

 

butaford,

I've never seen a thick, black assembly lube. That could be the problem. If you can't turn the crank with less than 40 ft/lbs torque on the damper nut, it's a bad sign.

Other things to consider:

Did you clean the bearing bores in the block and caps (main) and rods and caps (rod) before you put in the bearing inserts? The bearing bores must be completely clean and dry, with no oil or other foreign matter between the back of the bearing insert and the bore. Even a little oil (or assembly lube) behind the bearing insert will change the bearing clearance and reduce proper heat conduction between the bearing insert and the cast parts.

Also, did you check bearing clearances when you put in the new bearings? I always suggest checking clearances with Plastigage before final assembly, just to make sure you got the right bearings. If just one bearing is the wrong size, undersize in this case, it will sieze the crank and burn up shortly after you start the engine. To check the bearing clearance, the wear surfaces of the bearing insert and the crankshaft bearing journal must be completely clean and dry, as any oil will dissolve the Plastigage and throw off the clearance reading.

And now the obvious: Did you put the grooved main bearings in the block (not the caps)? Did you line up the bearing insert tabs with the grooves in the bearing bores? Did you seat the thrust bearing (middle main) correctly? Did you torque all the bolts correctly?

It may be time to recheck your work, at least check all the clearances with Plastigage, if you haven't already.

Torque spec for the main bearing cap bolts is 95-105 ft/lbs. Torque spec for the rod bearing cap nuts is 40-45 ft/lbs. Clearance spec for all bearings (mains and rods) is 0.001" to 0.003".

Hope this helps.

BubbaF250

1980 F250 4x4 Custom, 351M/NP435/NP208/D44HD-TTB/D60-FF/3.55s 6750 GVW, Rust & White.

 

More obvious stuff: check that all pistons face the right way and that the rod bearing caps are put back on the same way you took them off--they usually have numbers stamped on both halves, and both numbers should be on the same side. Make sure all main caps are installed in the correct order and facing the correct direction. Check everything with plasti-gage at factory torque specifications. Type of assembly lube shouldn't matter; it's got a bind somewhere.

If you're pretty sure you put everything in right, you might try loosening or even removing bearing caps one at a time to isolate the problem.

 

I found the problem. We put a couple rod caps on the wrong rods. Ooopppss. I guess thats what happens when you work in the dark. Thanks for the replys.

 

Probably got undersized bearings. I knew a guy who bought what was supposed to be standard bearings, they turned out to be mispackaged undersized. Big mistake, check that first. Plastigage is the way!