72 + 340 motor

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The balancer that is on some of these is thick with a weight on them. is this the same one that was on the 318 motors? I am asking for a friend who is putting one together from left over parts just to throw in a beater.
 
There is no weight on the 318 motor, so no. And it is not the same as the 360 damper. So you have to have the right one.

There are not-too-expensive ones out there that come kitted with different weights that you can bolt on for either late-340 or for 360.
 
The one you are looking for says “cast crank only” on the front of the balancer.
 
Like sireland said. You need the "Use with cast crack 340 only" If it doesn't say that on the damper its not correct. If the motor is being built you can have in neutral balanced (it doesn't take much, I have a cast crank 340 in the GTS) and run any forged crank 340 balancer. Jegs has a nice SFI one. I think Professional Products has a damper you can add weights too and has the cast crank one.
 
And since this is a cheapo effort.....

You can see how big the weight is here, as well as get an idea of how far out from the center this type of weight would set from the the placing of the bolt holes. The small weight is for the late 340 and bolts to the back of an otherwise balanced damper for a 318. http://professional-products.com/me...78eab33525d08d6e5fb8d27136e95/9/0/90012_1.png

Here is the same but cheaper: https://www.amazon.com/dp/B004BTB4VU/?tag=joeychgo-20

These particular weights bolt on the back side of the hub, so you have to mentally flip the weight over in these pix to figure them out.

To put this type of weight at the right angle relative to the keyway, you can look for a pix of a stock late 340 damper on this site or elsewhere and center it at exactly the same angle as the 'cast weight on the original damper shown here: https://picclick.com/Mopar-340-Plymouth-Dodge-Cast-Crank-Harmonic-Balancer-322421913680.html
 
BTW, OP, are original 340 pistons (or aftermaket, cast, stock replacement pistons, like Silvolites) and stock rods being used? And the later cast crank? Just checking on anything that effects balance.
 
From what I saw, a 1972 340 motor may be neutral balanced with a steel crank. 1973 is cast crank only and requires a special one year only harmonic balancer. Note that people have bolted in 318 cranks in 340's. This requires the crank to be rebalanced. You have to go by the numbers stamped on the block, not the numbers cast into the block to determine the year of the engine.
 
I know this may not be a good thing to ask but can you use a 318 crank and balanecer in a 349? With that be mentioned I am curious for me..
Not that I have one to do but just wondering.
 
Early '72 340's were steel crank, neutral balance. ( I have one )Later were cast crank, external balance. You need to know witch one you have. I think some time in April is when they changed.
 
I have two 72 340's both have cast cranks.
 
From Allpar.

"a forged steel crank (through 1972’s engine #39118000, when a cast iron crank was used)"

"The crankshaft was switched from forged to cast somewhere in the production cycle, believed to be in early April 1972, with engine 39118000 (thanks, Karl Thomas); a milder camshaft was used"
 
My '72 340, steel crank motor has a '71 date code. If I remember right, it's September, but not positive. It came out of a '72 Duster. It was an early production car. The cast crank motors will have a '72 date code on them, beginning in April.
 
I pulled a numbers matching engine from a 72 challenger. It had a cast crank and a 71 block. They used up what they had and then made the switch. MOST 72's will have a cast crank but some came through with forged.
If you have a cast crank 340 its easy since there was only one balancer and it was not used on anything else. Forged crank will be neutral balance. These dampers are much easier to find, just need to make sure you use the right timing cover to match the balancer. I think the change was made in 70 when they went to aluminum water pump. The timing marks went from the passenger side to the driver side.
 
I know this may not be a good thing to ask but can you use a 318 crank and balanecer in a 349? With that be mentioned I am curious for me..
Not that I have one to do but just wondering.
It's always a good thing to ask! Sorry, but no. The 318 crank (cast for almost all of the LA318's) is balanced for around 2140 grams of bobweight + or -, and all the 340 cranks are balanced for approx 2310 grams of bobweight. The 318 crank will fit up just fine, but the crank itself will have to be rebalanced for the much heavier stock pistons of the 340.

Adding external weight at the front and back for the 318 would be a full balancing exercise.

Interestingly, the KB253 pistons for the 340, with the stock 340 rods, works out very well for the 318 crank....around 2150 grams of bobweight for that piston/rod combination... within factory balance tolerance for the 318 crank.
 
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