I'm trying to find someone with engine balancing experience. Here are the particulars. I have a stock 340 with a stock steel crank from a 340. I know it will balance without the use of much drilling and should use no heavy metal . 340s have a hole drilled from the factory in the end rod journals, parallel with the crank center line(ie, there is weight removed from the rod journal). I also have a 318 steel truck crank. It is a desirable crank. It has no such hole drill where the 340 does.Does this mean weight will have to be added to the counter weight in order to balance this crank in a 340? Input from someone who has made this 318 crank work in a 340 would be helpful.

If your willing to do some changes the crank should work. First off the 340 was externally balanced while the 318 is internally balanced so you will need a 318 torque converter of flywheel and damper. Once you have those parts and the engine disassembled a machine shop can balance the rotation assembly.

Not an expert just thoughts.

The 340 in question is an internally balanced motor. Both are steel cranks. The 73 340 is the cast crank and externally balanced.

I had a friend who had a 318-3 crank and it did not fit in the 340 block and rotate, I know they are supposed to but it didn't. Make sure it works in the block before going any further, is your 340 crank fubared?

Sheldon

As the 318 pistons weigh 590 or so grams and stock 340 pistons weigh 720 grams, while the cranks should interchange, balancing will have to be done to make the ultra-heavy 340 slugs be in balance with the 318 crank.

Best Answer is to get some decent 340 pistons that don't weigh as much as a bigblock, then balance the assembly.

R.


IF the 318 truck crank was a long tail crank, it can't be used. But otherwise, EVERY 318 had the 2.500" main journals, 2.125" rod journals and 3.31 stroke.

I'm not sure if this is a 318-3 or not. It came out of a 68 318 pickup with a three speed. I will check it to see if it physically fits first.I bought my sons AAR and the motor had been rebuilt. It had two new rods and a crank without the hole in the end journals. It had not been run since the rebuild. From the spotty work. I doubt it had been balanced and was probably an exchange from the crank grinder. I have never seen a known original 340 crank without the hole. I assumed it was a 318 crank since both of my known 318 steel cranks at the shop, do not have a hole. I sold that crank to a guy long ago, who used it in a 340 and told him it needed to be balanced. The guy who built the motor and I don't talk much and I doubt he even remembers it. I drove the car so I know it worked out. I just would like to get some info from someone who has actually balanced one of these cranks in a 340. Do you have to use heavy metal? I am selling a 340 and don't want to mislead the guy and sell him this 318 crank that can't be balanced without heavy metal. I'm going to the shop and will get some pictures to explain better.

All I can add is that (drilled hole vs no hole) is alot of grams of material difference & it is in the rotating part of the eng rather than the reciprocating part which means that weight difference is doubled in the bobweight formula for it's actual affect on eng balancing. EDIT You could measure the dia/length of the hole then google the weight of steel then figure the amount (volume) of material that would have been in the hole for a close approximation on how many grams difference there is.

This is the kind of info I need. This is along my way of thinking as well.Light pistons are out there and certainly are easier on the motor.

You could take that 318 crank in & see what it balances to (how many grams) then go to work on weighing your rods/rod bearings etc to see what piston weight you need. HF has a gram scale for $15 & it's on sale regularly for $10. You can rig up a fixture to hold your rods horizontle to weigh the big/small ends. rods can be lightened on the balance pad & some on the small end & deburring the shank on the sides. Pistons can be lightened slightly. BB pins can be shortened 1/4" on each end with no durability issues as the pins are too big to start with. Teh bobweight formula is online & is simple. You may be close as is & this'll tell you if you can get by with or without a lighter piston and with or without rebalancing.

I messed with this situation for years, then got the rotating assembly balanced. Haven't looked back since, night and day, running very smooth now for three years.

In the mid 80's I bought a 340 Duster which I was told had been rebuilt, when I tore it down it had +.060 TRW flats tops, stock rods w/273 or 318 crank w/solid journals and that thing never vibrated a bit. It didn't have any crazy deep holes drilled in the crank either but was .020 under on the rods, not sure why it worked after everything I've always read