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  #1  
Old 12-06-2000, 04:22 AM
Duster_340 Duster_340 is offline
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CAN ANYONE ANSWER THIS-
How do the 340, 318, 273, 318 Poly canks differ? They are all forged. Are the the same basic forgings???
I had a 1967 318 truck crank 67(FARGO)1/2. The only diff I I could see is that the 318 crank counterweight was not drilled due to the lighter rods of the 318.
And What about the famous 318-3 truck crank?? Was it different than my 1/2 ton crank??


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  #2  
Old 12-06-2000, 05:45 AM
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JVMopar JVMopar is offline
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Well I don't have my book with all of it's specs here with me so I can't give you any specific informations on those A motors but I would assume that the cranks are all forged. I would also assume that the 318-3 truck crank's only difference is that they used electricity to make the bearing surfaces physicaly harder. I've heard of them doing that on the early Hemi motors and switching to a chemical method. The difference between the electric and chemical is that the electric hardening goes deaper into the metal than the chemical hardening. Sorry I couldn't be more specific but I hope this helps somewhat.
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  #3  
Old 12-06-2000, 06:16 AM
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Orange Bee Orange Bee is offline
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As I recall, the 318-3 and the pre 73 340's were the only small blocks with forged cranks. If you're worried about breaking one - don't bother. How often do you see a Mopar crank break. I've only seen one break - a forged one in a 383 that was balanced incorrectly. After 6 years and 145K miles of HARD use in a 70 Road Runner it sheared at the #4 main bearing - and the car STILL drove! When Steve broke it he had been cruising at 4000+ rpm for more than 4 hours non stop too. Good machining and common sense RPM ranges will keep it together.
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  #4  
Old 12-06-2000, 06:42 AM
Brian Mills Brian Mills is offline
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The pre-72 318, 273 and poly cranks are all forged generic pieces. That means the forgers intended to make a crank by forging, and they did. The 340 crank done by the same forgers was built with higher strength in mind, I don't know if it was achieved with better metal or a different process, just that it is different. The famous 318-3 crank is the generic ordinary piece, the forgers wanted it to be stronger, and the easiest way at the time was to design it stronger. They chose to make the same piece with radius fillets. Look at the bearing surface of a crank,the edge of the surface, where the crank goes from horizontal to vertical, in that corner is called the fillet. Normally the fillet is machined square, there is a 90* corner in there. With radius fillet, that square corner is rounded in the forging process making that corner stronger. All extreme performance cranks need to be radius fillet for the extra strength. May have actually been overkill on the 318-3, but work trucks of old had some tough pieces.
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Old 12-06-2000, 02:55 PM
Comp Chassis Comp Chassis is offline
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The 340 forged cranks have lightening holes of about 1" in diameter drilled in the first and fourth rod throws. The 318 and 273 cranks do not have this.

My machinist just attempted to balance a 340 with a 318 forged crank using stock rods and pistons. There was not enough weight in the counter weights to be able to balance it in stock form. He would have had to use heavy metal to balance it. But, he did say that with race pistons and rods, he would have been able to do it.
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Old 12-06-2000, 03:25 PM
Billydelrio Billydelrio is offline
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273 and 318LA forged cranks seem to be identical. The early 318 poly cranks have a longer demension from the rear main to the flange. Later 318 poly cranks are identical to the 318LA forged cranks. This information did not come from a book, but I am pretty sure based on my notes. Also, I seem too remember seeing my 318 poly crank having radi mains. (did not write a note about that in my notes)
Billy
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Old 12-06-2000, 05:43 PM
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pishta pishta is offline
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The 318 poly (late, I guess) and the 273, 318-3 and 340 forged are all interchangeable (with balancing). All but the 340 are neutral balanced to the stock rods. The 340 crank had to have holes drilled to make up for the heavier 340/360 rod on the rotating end. As to balancing, Comp Chassis, did he lighten the rotating side with holes? With light rods (360-2bbl or early 273-318) he would not need these. Good luck.
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Old 12-07-2000, 03:39 AM
BugEyedValiant BugEyedValiant is offline
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You guys forgot that the 67 and earlier had a smaller hole in the crank for the converter......I think. Can anyone back me up?
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Old 12-07-2000, 06:23 PM
Billydelrio Billydelrio is offline
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Yep, I forgot about that. The pilot hole is smaller on some early cranks. I had to chuck my 273 crank into the lathe and open it up to fit the later torque converter. Could be a difference between Auto or Manual crankshafts back then. I have no way of knowing what year the change was made, but BugEyedValiant says 67 and that sounds reasonable.
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Old 12-07-2000, 07:45 PM
Brian Mills Brian Mills is offline
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Sounds funny, I used to have 4 speeds, I thought the pilot bushing was the same one from the 40's on up. Also I've never had a tourque converter that used the pilot hole.
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Old 12-07-2000, 09:46 PM
RDABIKE RDABIKE is offline
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I would not worry about using a modern cast crank. The new Mopar Performance 4" stroke crank is cast and is a great deal at $300. It is made by Scat and I talked to them at the SEMA show. They said it can easily handle 800 horsepower.

Mark
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  #12  
Old 12-08-2000, 01:46 AM
Billydelrio Billydelrio is offline
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Pilot Bushing - The cranks in question have two pilot holes, one for automatic and one for manual. The small one is about .9" in diameter and is deep in the crank. This hole requires a bushing when using a manual transmission. The larger one is about 1.8xx" in diameter and is for the pilot on the front of the torque converter. The converter has a small ring on the pilot that is machined to about 1.8" and enters the crankshaft a little less than half an inch. The small hole is the same on all the cranks that I have seen, but the larger hole has been different. This means that the torque converter will not enter the crankshaft that .400" and there will be an interference fit between the crankshaft, converter pump drive, and the pump. The pump will feel the worst of it!
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Old 12-08-2000, 06:25 PM
Brian Mills Brian Mills is offline
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You live and learn! I never noticed that, I've always been on my back doing flex plate bolts through the inspection cover. I still haven't figured out how to get that 4 bolt pattern to line up on the first try.
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  #14  
Old 12-08-2000, 09:08 PM
ChristianCuda ChristianCuda is offline
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lol Brian
If i am removing one I just spray paint one of the bolts, converter, and flexplate arm so that I put it back in the same spot when put back together. Works to if replacing flexplate with a new one as you match the old one with the new one and paint also.

Christian

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Old 12-09-2000, 05:29 PM
Brian Mills Brian Mills is offline
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I like it! Wonder why Dodge never thought of it! lol
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  #16  
Old 12-09-2000, 09:11 PM
obsessed obsessed is offline
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Quote:
Originally posted by RDABIKE:
I would not worry about using a modern cast crank. The new Mopar Performance 4" stroke crank is cast and is a great deal at $300. It is made by Scat and I talked to them at the SEMA show. They said it can easily handle 800 horsepower.

Mark
Hi Guys:
It is just the new old guy here, Mark is right on the money with his statement. Chrysler done a lot of wierd shit in the old days and nothing was consistent,one thing was for sure though ,they made tough parts and cars. A buddy of mine out west in B.C. Canada had a rear engine dragster with a 30 over 360 in it . It had Millers rods,Venolia pistons,a set of Bill Mulligan used w2s,a tunnel ram with two 850 Holley's and a 300 hp nitrous plate under each one,It had lots of other work done But the point that I am getting to is that it went to 11000 thousand when it shifted from low to high on the 2 speed glide,It finally blew up at the end of the season but it was the block that let go,a cylinder let go and the rod and piston cut the pan in half and 1/2 the block. Jims engines in Prince George B.C. took the engine appart and there wasn't a dam thing wrong with the crank!! and that is no fairy tale. It was the stock(except for the ballancing) 1972 360 CAST!
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