Hello, i'm new here. Been looking through the website. One of the best websites i've come across. You guys are sharp.

And i have a couple of questions. I'm rebuilding a 302 out of a 1991 f150 2wd, currently in the process of assembly. Have the new cam in, crankshaft torqued down and just now installing the pistons.

The crankshaft turns freely after torqueing it down and setting the thrust bearing. However after installing pistons #'s 3, 4, 7 and 8, i can barely turn the crankshaft even by grabbing a crankshaft counterweight and heaving on it. As i installed each piston (with the notch forward) it got harder and harder to turn until i could barely turn it at all. Everything is wonderfully lubed up, and i assume its the new piston rings rather than the rod bearings that are providing the resistance. Is this normal? I only imagine after getting all eight pistons in there... there will be no way i'll be able to turn it.

When i first began tearing it down, i could grab the crankshaft with one hand, give it a spin and have it spin several times over... and that was with everything connected. (cam, pistons, everything) Maybe i'm just surprised at the amount of resistance the rings provide.

Thank you in advance.

 

Oh, and my other question. The old cam and lifters were toast, so the new cam i purchased was a comp cam 31-255-5. From what i understand, this cam will work without any modification to the rest of the valve train components... and even though new valve springs are recommended they aren't necessarily needed. Is this in fact true? I will make sure for myself when i get the chance to do a mock up for valve clearance and spring compression, but i did want some of you who are more knowledgable to give me your opinion.

 

well let me say this you must be one strong som a bitch.....to be able to grab the crank with the pistons installed and give it a spin. wow

you have to make sure the rods are installed the right way, there should be numbers on the rod and cap that should face away from the cam when installed.

It will take a wrench to turn it over with new rings and a fresh hone.

 

Indyuke, I just finished a rebuild in a 91 speed density Bronco. That cam will work with no other modifications except the timing. I first started out at the base timing of 10* and the motor seem to be sluggish. After my 500 mile break-in, I started playing with timing and I am currantly at 18* BTDC with no pinging and great throttle response. I also went from 11 mpg to 14 mpg.
I also used my stock rockers and valve springs.
As for the binding, if you only have 4 pistons installed and it is extremely hard to rotate the crank, then you have problems. Like Hemi stated, the rods have to go in order and the numbers on the caps and rods should come together when assembled and face out towards the spark plug holes. Also make sure you are using the proper size rod and journal bearings. I built a motor last year that had this problem, found out the bearing box was printed with .020 undersized but the bearings were stamped .030, somebody had mis-boxed this set. Also make sure your piston rings are gapped properly before installing them on the pistons.

 

I will double check the placement of the rods. I know the bearings are the right size... i actually have between .002"-.003" clearance by the plastiguage because i put std bearings with a "polished" crank. It hadn't been ground. So they're a little on the loose side. The main bearings came in a little tighter, but i didn't have any problems with the crank itself binding on the main bearings. The piston rings are in right... i made sure of that.

The engine was extremely worn out when i took it apart. Cylinders worn mirror smooth, rings had lost all usable wear, the old crank was so worn out it could not be salvaged, and like i said earlier, the cam and lifters were toast. Pretty much every moving part was worn beyond use. I think that's why i was able to just grab the crank and give it a spin with everything connected. I haven't tried to turn it over with a wrench... only by hand.

I will double check everything. Thank you.