I am rebuilding a 1986 ford 4.9l 300ci inline 6 that came in a parts truck I bought a while back, I striped it down to the block, rebuilt/replaced everything and have started putting it back together, starting with the crank shaft, after torquing the main bearing caps to spec I tried to turn the crankshaft by hand and it wouldn't budge, even coaxing it along with a rubber mallet didn't do anything. the main bearings came in a kit and are suppose to be a stock replacement, I measured them and they are the same thickness as the stock bearings, at first I thought the assembly lube I was using was to thick so I cleaned the bearings off and used 10w30 oil with the same results. any help with why this is happening would be appreciated.

 

You need to be setting your bearing clearance the right way, with mics and a bore gauge reading in .0001". Put your main bearing in oil and torque the bolts, mic the crank journal you are checking and transfer that reading to your bore gauge & run it through. Now you will be able to see your clearance and be able to see if there is anything more than .0002" taper, anymore than that and I'd be investigating to find out just why. Now you know right where you are at before ever putting the crank in. One other thing, did you seat the thrust bearing ? Pry the crank either way, torque the bearing cap. Find a piece of soft metal (brass) a 5 pound or so sledge hammer. Now strike the front of the crank firm but not hard. Do the same to the rear then check the thrust clearance.

 

Were the main caps marked properly and did you put them back in the same place and in the same direction?

Look at the bearings on the back, are they marked STD or .010? Have seen a lot of parts boxed wrong. Got a set of STD rings once, or so the box said, but turns out they were .030 over.

 

Fixed it! But now I'm at a loss as to why it wasn't turning; all I did was pull all the bearings off, clean all of the assembly lube off, and replace it with fresh 10w30. I torqued every thing down and it turned smooth as butter, the only thing I can think of is that there was some crud on the surface between the block and the bearing that pinched it to tight. As for the thrust bearing, it was at .002 clearance (not sure if that's right or not?) Thanks for all the help.

 

.002 is too tight. Strike it, front and rear.

 

So after coaxing it along I was able to get a total of .004" out of it, hopefully thats enough clearance.