stock 360 2 brrl wanting to go to a 390 4 brrl. is there a difference in the cam's from the truck 360 and the 390 4 brrl?? also i've heard of the truck 360 and truck 390 cranks that have heavier counter weights for the trucks-do i get a 390 truck crank or do they exist?? or are the rods the difference? is the balancer pulley for the 360 the same for the 390?? thanks guys!

 

The only differnce inbetween the 360 amd the 390. Is that the 390 has a deffernt crankshaft and rods.

 

well when my dad built the 390 for his '67 fastback, he pulled a 390 crank out of a truck in the yard but when he assembled and ran the motor it had a bad vibration. after tearing it down and balancing the crank 4 times he then realized his machinist wasn't doing him right so he took it to our current machinist which told him he had a truck crank but just balanced the crank by drilling out the counter weights....my question is being that if i'm turning my 360 into a 390 thats going into a truck should i make sure a get a truck 390 crank that has larger counter weights?? if i get a car 390 crank will it wear out sooner by working harding pulling a truck around all the time??? thanks!

 

I've been told over and over that the 360 and 390 can interchange cranks/flywheels/etc.

However, I had a 360 in my '74 highboy, my brother rebuilt it using a '68 360 from a pickup as a donor (NOT an FT!), and the flywheel had this big counterweight on it - which is NOT SUPPOSED TO HAPPEN.

But it did, in my case. I used that flywheel on my 390 build and it vibrated like heck.

Check your current flywheel, and see if it has a cast-in counterweight on it - I don't remember exactly what it looks like, but should be easy to figure out. If you do have a counter-weighted flywheel, make sure you get a "neutral" flywheel to mate with the 390 crank.

I still think some externally balanced motors are out there somewhere... I know, I know, it shouldn't happen, but I went over it with my brother and he said the exact same thing - used a 360 and flywheel from a donor truck (and the 435NP as well) and it had a counter-weighted flywheel. It was NOT rebuilt previously, and my brother did NOT have it balanced, and it ran fine without any vibration (and lasted over 150K miles). And no, he didn't have to have the snout turned down, nor use an FT timing cover.

Better safe than sorry, always check your flywheels! A 390 should have a neutral flywheel, no counterweights. If your 360 has a neutral flywheel, use any 390 crank - and then get it BALANCED to make sure.

 

The crank swap is true only if the engine has a light truck crank. The heavy duty truck engines (FT) are not the same as car engines and light trucks (FE). The FE 360 and 390 cranks are all internally balanced so a nuetral flywheel and balancer will work. The 428 is external balance with the flywheel. I don't know what your Dad's problem was, but I suspect the first machinest screwed things up some how.

 

ya the first machinist (whom i never met) must have either had sorry equip, sorry workers or just been a sorry worker himself but anyways our current machinist is flawless...7 engines he's done and they've all come out like butta! thanks for the info!!

 

When I built my 390, I took a '68 360 block and bored it .030 over. Then dropped in a 390 crank and rods from a '72 390 (block was in bad shape). I used the 390's flywheel and balancer, although the 390 and 360 balancer looked identical the flywheels *looked* different although I suspect they would interchange. I'm positive both engines originally had dished pistons. For pistons I used 390 car flat tops. Basically it became a car 390.

 

I also think the machinst screwd things up. a 390 crank is a 390 crank car or truck is the same as far as I know.