Clyne_duster72

Hi I'm new to this forum, wanted some expert advice on rebuilding my 72 340

My dad had it rebuilt a few years back, he made it a mild strip build. Bought X heads had it ported and polished. Bored .03 over, TRW forged domed racing pistons. Steel crank, rebuilt rods, new bearings all around. High volume oil pump, deep sump pan. Cam was .512 lift or around there. single plane dominator, 750 holley dp, compression was 10:5:1. He raced it, ran right around 12.9. It only had 5k on it.

So anyways I took the engine apart, looks real good except as I went to take the crank out and it split in half ...literally. Before I took it out, it cranked and would turn over perfectly. All the other internal look good though so I was confused. We used proper toque converter and tranny so this is weird.

I'm thinking about just making it a mild street car, mild cam, scat cast steel mild stroker crank, check rods, forged pistons. Have the machine shop hone the block to the new pistons. Hot tank block and heads, new bearings, clean everything. Then rebalance the assembly

Do any of you experts have any advice for me? I can do all the mechanical operations myself.

78doubleR

all you'll need to do, since your getting a new crank, is line hone the main journals.

TVLynn

I would bet It was a cast crank originally.. Cast will work fine up to a point.. I would look for an early 340 forged crank if possible or you can go the stroker route for a mild street car..

Clyne_duster72

Yes I have been looking for a 340 forged on eBay, found a couple I'm just scared about what the condition there in. If I bought a new cast one it would be ready to Install other then rebalance and hone the mains, but I would have to hone the mains for the forged also.

I also know I can use a forged 318 crank as the stroke is the same 3.31 inched. I'm rebalancing the entire assembly anyway so that might be an option also.

Clyne_duster72

Yes forgot to add that, thank you

Chryco Psycho

The Ball is really in your court , you have to decide if you want to fix what you have , a 318 forged crank will work fine as long as you balance the assy , if you want to spend the extra you can buy a new stroker kit , crank rods & pistons & take it up to 408 - 426 ci . Your call !
The 87-92 308 heads will make a lot more power over the X heads , there may be a more suitable cam as well .