Issues installing THUMPR cam

[LilSpann601]

I am currently in the process of buidling a sbc 400 and I ordered a Comp Cams Big Mutha Thumpr cam .486 ...The cam installs smoothly but when I rotate the engine I can tell the cam is binding on something and it locks the rotating assembly. I put the crankshaft sprocket dot at the 12 o clock position and the cam sprocket dot at 6 o clock....i put cylinder 1 at tdc which places the dot at 12 o clock position i also notice that cylinder 6 is at the top too...does this sound like i have the cam timing incorrect???

 

[LilSpann601]

when rotating the crank it will spin may be 1 or 2 times and then the cam lobe is making contact with something

 

[Jshock]

Ok dumb ? Here. Are the heads installed or not? Just making sure you aren't fighting compression. Anyways #1 and #6 will be up at the same time one is on compression stroke the other on exhaust stroke.

 

[hurst1979olds]

Are you using stock rods? Your rod bolts might be hitting the cam. Rod 2 and 6 are the most common on a 383 Stroker.

 

[Pontiac455]

Do the easy first, remove the timing chain and turn each seperate. That will narrow down if its the crank or the cam..

 

[79malibubbctt]

If the heads are still on did you check to see if you had proper valve to piston clearence. If the cam is to big the valves can be hitting the top of the pistons. Otherwise put it on tdc with the chain off and spin the cam to see if its hitting.

 

[LilSpann601]

The rods I used are 5.7 Pro Comp I Beam Rods...The heads are not installed. The cam will spin freely if I leave the crankshaft at one position. But soon as I connect the timing chain to the cam and crank and give the engine a turn or two..The cam binds up somewhere. Im going to remove everything and give it a closer look

 

[jrm81bu]

Are you using stock rods? Your rod bolts might be hitting the cam. Rod 2 and 6 are the most common on a 383 Stroker.

x2! Even though they aren't stock rods and it's a 400 it's still the same issue.

 

[hurst1979olds]

The rods I used are 5.7 Pro Comp I Beam Rods...The heads are not installed. The cam will spin freely if I leave the crankshaft at one position. But soon as I connect the timing chain to the cam and crank and give the engine a turn or two..The cam binds up somewhere. Im going to remove everything and give it a closer look

Definetally sounds like the cam cam is hitting. You just need to clearance the 2 and 6 rod bolts. You will be able to see which ones are hitting when the engine is upside down.

 

[LilSpann601]

what is required to clearance bolts??? I hope I dont have to spend money with the machine shop again