Correct harmonic balancer?

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swingingdart

swingingdart

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I have a 1972 date 318 with a '69 340 forged crankshaft. My harmonic balancer that I got off the original 72 engine spun the outer ring. So I'm shopping for a new one. But I guess there is a difference in them depending on if the engine is internally or externally balanced. I haven't drove the car hardly at all since engine build. But it does have a mysteries bump and thump almost like its missing but not, I notched that up to the spun balancer. Any input is much appreciated! Thanks everyone!
 
swingingdart said:
I have a 1972 date 318 with a '69 340 forged crankshaft. My harmonic balancer that I got off the original 72 engine spun the outer ring. So I'm shopping for a new one. But I guess there is a difference in them depending on if the engine is internally or externally balanced. I haven't drove the car hardly at all since engine build. But it does have a mysteries bump and thump almost like its missing but not, I notched that up to the spun balancer. Any input is much appreciated! Thanks everyone!
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You can have the original rebuilt..
 
swingingdart said:
I have a 1972 date 318 with a '69 340 forged crankshaft. My harmonic balancer that I got off the original 72 engine spun the outer ring. So I'm shopping for a new one. But I guess there is a difference in them depending on if the engine is internally or externally balanced. I haven't drove the car hardly at all since engine build. But it does have a mysteries bump and thump almost like its missing but not, I notched that up to the spun balancer. Any input is much appreciated! Thanks everyone!
Click to expand...
Professional Products has a good one for around 115$.

Jake
 
swingingdart said:
I guess my question would be, would the 72 318 balancer still be correct if I'm using a 69 340 forged crank? Even if I went back with a 72 328 crank I want to make sure the setup is correct. Thanks!!
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Somehow I want to say I've heard something about different harmonic balancers for 340? We're going to need a guru to step in and answer that one...
I just know they can get rebuilt in people do re build them...
 
Cast 340 cranks have their own special balancer. There are forded 318 cranks and cast 318 cranks and some are internally balanced and other are external depending on year. Since this is a mismatch of parts, was the engine balanced with the 340 crank? I think rebuilding the one you have might be the best bet with mismatched parts.
 
Isn't an internally balanced 340 crank, going to have vibration issues if you use it in a 318. Assuming you did have it balanced ?

you may need a heavy duty Harmonic balancer to handle the extra vibration.
 
trapster said:
Isn't an internally balanced 340 crank, going to have vibration issues if you use it in a 318. Assuming you did have it balanced ?

you may need a heavy duty Harmonic balancer to handle the extra vibration.
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Been so long I cant remember if I had it balanced. I can do some digging and probably find my paperwork somewhere.. I hope! I did have it turned, I would hope he checked the balance when he did that!
 
dano said:
Cast 340 cranks have their own special balancer. There are forded 318 cranks and cast 318 cranks and some are internally balanced and other are external depending on year. Since this is a mismatch of parts, was the engine balanced with the 340 crank? I think rebuilding the one you have might be the best bet with mismatched parts.
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To the best of my knowledge, ALL 318's cast or forged cranks ARE internally balanced, ALL 340 forged cranks ARE internally balanced, ALL cast 340 cranks ARE externally balanced, therefore you can swap a balancer from a forged 340 crank to a 318 crankshaft cast or forged, you can swap a balancer from a 318 crankshaft, cast or forged to a forged 340 crankshaft.

Hope this sets you straight
 
JBurch said:
To the best of my knowledge, ALL 318's cast or forged cranks ARE internally balanced, ALL 340 forged cranks ARE internally balanced, ALL cast 340 cranks ARE externally balanced, therefore you can swap a balancer from a forged 340 crank to a 318 crankshaft cast or forged, you can swap a balancer from a 318 crankshaft, cast or forged to a forged 340 crankshaft.

Hope this sets you straight
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There's some clarity! That does set me straight. Thanks!
 
Keeping the internal and external parts matched across the two engines is important. I believe however the 340 crank was factory balanced with the heavier 340 piston and rod combination. Putting the lighter 318 piston and rod assemblies on the 340 crank will work but I would suggest checking the balance with all of your parts to ensure all is within spec to avoid unwanted vibration.
 
The rotating assembly would need to be balanced when installing the 340 crank in the 318. The 340 pistons are heavier than the 318. If its a forged 340 crank you just need to make sure its a neutral balance (internal) balancer.
 
I am going off my old memory, but a 340 neutral balance dampener is narrower than a 318 balance.
If you know for a fact you have a 72 318 balance, just buy a new one.
 
Lost my post in net space. !!!!! --------------------- 340 cranks only work with 340 engines unless they are rebalanced. 340 pistons are over 100 grams heavier than 318 pistons [huge]. Use your 318 crank/rods/ and pistons and your good to go.
 
pt70 said:
Lost my post in net space. !!!!! --------------------- 340 cranks only work with 340 engines unless they are rebalanced. 340 pistons are over 100 grams heavier than 318 pistons [huge]. Use your 318 crank/rods/ and pistons and your good to go.
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Still haven't found my paper work yet, but if the crank wasnt balanced for the lighter pistons will this ruin the engine in time? Or just cause unwanted vibration?
 
If it is 100 grams difference that’s not good. My balance guy shoots for 1/2 gram. Which I know is really not needed, but he’s old and tighter tolerance is not going to hurt.
 
furrystump said:
If it is 100 grams difference that’s not good. My balance guy shoots for 1/2 gram. Which I know is really not needed, but he’s old and tighter tolerance is not going to hurt.
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Guess I better find my paper work before I drive it anymore! I'm sure he balanced it because he had the whole set up at the same time. But better safe than sorry! Thanks for the input guys!
 
swingingdart said:
Guess I better find my paper work before I drive it anymore! I'm sure he balanced it because he had the whole set up at the same time. But better safe than sorry! Thanks for the input guys!
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Your inbox is full. Trying to message you about your headliner you have for sale
 
The 340 crank would of needed Mallory metal to balance it, probably 3 sticks. At $100.00 a stjj in close and $100.00 a pop to install them ur already at $600.00. I m ow this as I was gonna put in a 318 forged crank into a 340. It needed 3 sticks. Didn’t do it. Got a 340 crank coming. Kim
 
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