redhotnrollin

Im rebuilding a 390 and i got the grank in and it rotated fine i put pistons 1 2 3 and 4 on and it rotated ok it was a little hard to move, then i put piston 5 in and i cant even rotate it by hand now.... is that normal or did i screw somthing up? and what can i use to rotate it now?

someone please help.

Flawebmaster

It sounds like you may be installing the connecting rods backwards. Look at the rods down where the two rods would be riding together on the crank journal. You will notice that one side of the rod has a slight bevel and the other side is machined flat. The beveled side must go on the outside against the crank, the flat side goes next to the adjacent rod on the journal. The more rods you install the worse the interference. If you find that you do have them backwards, depending upon what type of pistons you are using you may have to pull out the piston pins and turn the pistons around as well.

kdtrucker

I agree with Flawebmaster, you might also want to platigauge your clearence between the bearings and the journals just to be on the safe side. Check also the main caps to make sure there're on the right journal and all arrows pointing forward to the front of the motor

redhotnrollin

oh man.... after i posted this i neglected to check it because i thought it was just because of the piston rings and the friction on them. i put a breaker bar on the crankshaft snouth with the bolt and i can rotate it that way, its stiff but it seems like it should be like that.

the whole motors together now.

what would you do?

kdtrucker

With every piston you put in it will get harder to rotate but if you hank on it hard enough, it'll rotate and that is normal. Did you oil the pistons and the chambers before installing?? If not that could be your problem! And also you want to put a generous amount of lube (I like to use STP honey oil) on the bearings before installing?? If you don't have any pre-lube on the bearings disassemble now and or you'll be turning the crank again and buying new bearings.

redhotnrollin

yeah i did oil and lube everything. the onlyhting im woried about is the way the connecting rods face, like the whole flat side and concanved side.... i didnt check for that, mainly cause i didnt know. :(



PS... i put a breaker bar on the cranp pully bolt and it rotates its tight cause of it bein a fresh assembly. i made sure the crank rotated freely before i put any pistons in.

redhotnrollin

Is there a way to tell if i got them on right without havin to take them all out?

Flawebmaster

You must look at the flat side of each rod at the big end. One side is totally flat, the other side has a slight bevel. This beveled side goes to the outside toward the crank. If you don't understand this go to a machine shop and they will explain. Very important!

redhotnrollin

i understand it but is there a way to check without having to take the rod caps off? I have the motor all together and i dont really wanna have to take it all apart again.

Thanks for the help. :)

kdtrucker

If your using aftermarket rods you can plainly see the flat side and the champhered side. If your using stock rods there is a square nub on the cap and it is slightly beveled. You'll have to look at them from a side angle. I believe the lower side of the angle goes towards the crank, but get a second opinion in case I'm wrong.