72 Demon slanty-to-340 Resto

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To be perfectly honest, unless you plan on spinning it to the moon (routinely north of 6500 on purpose), or feeding it copious amounts of nitrous, or both, get a cast crank and roll...I can't think of a time I've heard or read about where a cast crank actually came apart in a 318...apart from power handling capability north of about 450-500, the only thing that forging will net you will be a lighter wallet.

EDIT: Ya know what? Come to think of it, there's a member on here who has a turbo'd 360 pushing 9s...pretty sure he's running a stock crank
 
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Unless your planning on high HP and a stick shift. The shock loading from running a high HP V8 with a standard shift can break the back end of the crank if its cast.
 
Yeah I know that for a street engine a cast crank will do and about half the price, I just first wanna see if this one can be saved, and if it's still cheaper than buying a new one. I got it in an electrolysis bath right now to pull off as much rust as is safely possible Rust removal by electrolysis
 
The following will probably sound a little snarky, so please pardon any perceived attitude:

moparmat2000 said:
Unless your planning on high HP and a stick shift. The shock loading from running a high HP V8 with a standard shift can break the back end of the crank if its cast.
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Which is why I phrased my reply the way I did. High HP is a subjective term when talking to different people, but the reality is that unless you're beating the absolute **** out of it (routine 6500+ rpm clutch sidesteps/shifts), a properly balanced and prepped stock 318 casting is still a beefy unit and more than well enough equipped to handle up to and including the number I threw out above, and I'll stand by that assertion until you show me more than anecdotal evidence that one *needs* a forged crank for building a mild or even healthy 318/340.

...even a 400hp 318 would be more than enough to yield lots of smiles, and not break the bank.

knote72 said:
Yeah I know that for a street engine a cast crank will do and about half the price, I just first wanna see if this one can be saved, and if it's still cheaper than buying a new one. I got it in an electrolysis bath right now to pull off as much rust as is safely possible Rust removal by electrolysis
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...you do you boo boo, but if you're spending more than $200 for a ready to go cast 318/340 crank (apart from balancing, which you'll need to spend anyway for any engine you actually care about), you're overpaying. And yes, the cast 318 crank shares part numbers with the 73 340 castings

Having a forged crank is great, but at what cost? If you have to have it retreated due to grinding, how much more will you spend?
 
To add to my previous statement, a stock 302 cast crank is a spindly little twister, but I had exactly 0 issues with 6500+ rpm shifts in a 5 speed, under boost no less with a crank over 150,000 miles, and I've never heard of someone splitting the flange. I've seen them break at both main and rod journals, but usually it was due to abuse or oiling system failures under duress, not just random breakage. With as many people like to brag about mopar's overdesigned parts, something tells me one would have exactly zero issues with flange separation under the same circumstances when properly prepped, so please forgive my scoffing cynicism.
 
No offense taken Jeff. I should have been more specific. However you described it for me. 450-500 hp or more, side stepping it all the time, beating the ever living dog **** out of it. Basically driving it like a ******* animal.

I however have seen and heard of cast crank flanges breaking on dirt circle track cars. Not sure if thats the constant on and of the gas loading against the crank, coupled with severe useage or not. Or the fact that they are the usual 350 chevys with a typical stocker cast crank.

If your combo isnt above 400 you should be fine w a cast crank just get it magnaflux checked for internal defects, get your rotating assembly balanced to minimize any vibration.

Jeff is right. At what cost? Is it so you can have bragging rights at the local sonic or other car hangout, or do you plan on hitting it with a 100 or 150 shot nitrous on a regular basis. Base it on what you intend to do with it.
 
roundy round cars are running constant high rpms, with constant throttle transitions, under heavy loads...apples and orangutans...
 
Just to clarify, if my last post wasn't clear:

IF this crank can't be saved, or if it ends up costing more than a brand new cast crank, I'll just toss it and buy the cast crank. I DO NOT plan to buy a forged crank, I was only linking that as a comparison, to give an idea of what value that crank may have if it can be saved. I got this crank free with the deal, and if I can save it for less than a brand new crank then HECK why not!?

I got the crank in the electrolysis tank right now, got a good deal of rust off but still more to go. I did get journal measurements, but stupid me misplaced the paper I wrote em down on (can only remember rod journal, about 2.138" IIRC).
 
OK so update on the crankshaft, I got it outta the tank, sprayed it down with diluted vinegar (neutralize the soda), and after drying off gave it a full wipedown with lacquer thinner (get off the gunk left behind by electrolysis), then gave it an oil coat.

Here's before going in the tank
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20180725_061530.jpg


And after tank and wipedown
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My only concern now is the journal measurements I took. Mains were all 2.497"-2.500", and the rod journals were 2.122"-2.125" EXCEPT the front half of the front journal that pegged 2.107". One of you said they could be safely taken down 0.020" under, but that's really cuttin close. Just so you know I wasn't completely opposing the last few posts, I did search and find a few options CAST CRANKSHAFT W/ BEARINGS Fits: 1976-1989 DODGE CHRYSLER 318 5.2L OHV V8 | eBay
 
Question: on an A body 8-3/4" housing, what's the measurement from flange to flange?
 
I'm looking at a 8-3/4" for $400, and I wanna be sure it's really for an A body. The 489 3rd member is the later model unit, right?
 
Dartsun said:
Yes later model. 489 considered to be best. An A body most likely would’ve came with a 741.
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I was led to believe the early axles had the 741 and at some point after the late 60s switched entirely to the 489. What exactly is the difference between the two?
 
Dartsun said:
52 5/8” small bolt pattern wheels. Dustin
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Actually 52 5/8 is housing flange to housing flange, that number stays the same regardless of what axles you use.

Wheel mounting surface to wheel mounting surface (“drum to drum”) the SBP axles are 57 1/8”, if it’s been converted to BBP then ~57 13/16”.

If you need to check out an axle, most of the 8 3/4 dimensions are listed here. Both housing flange to flange and drum to drum measurements-
An accurate 8 3/4" rear axle width list

knote72 said:
I was led to believe the early axles had the 741 and at some point after the late 60s switched entirely to the 489. What exactly is the difference between the two?
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The 741’s were around until ‘72 in the A-bodies at least. My ‘71 Dart has one and it was the original.

The 741, 742 and 489 have different pinion diameters. 741 is the smallest. The 742 is the next largest, then the 489. The “which is stronger” thing is more complicated though because the 489 has a tapered pinion.
 
72bluNblu said:
Actually 52 5/8 is housing flange to housing flange, that number stays the same regardless of what axles you use.

Wheel mounting surface to wheel mounting surface (“drum to drum”) the SBP axles are 57 1/8”, if it’s been converted to BBP then ~57 13/16”.

If you need to check out an axle, most of the 8 3/4 dimensions are listed here. Both housing flange to flange and drum to drum measurements-
An accurate 8 3/4" rear axle width list



The 741’s were around until ‘72 in the A-bodies at least. My ‘71 Dart has one and it was the original.

The 741, 742 and 489 have different pinion diameters. 741 is the smallest. The 742 is the next largest, then the 489. The “which is stronger” thing is more complicated though because the 489 has a tapered pinion.
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In the article Dustin linked:

"The two Sure Grip types can be interchanged between the carriers if the matching differential axle bearings are retained. The outside diameter of the cups are the same between the '741'/'742' and the '489'; the inner cone differs. "

So what I'm drawing from that is as long as I keep hold of the bearings I can swap the different diffs. My question is, what about the different pinions? Like the carrier bearings, can they too be swapped? That part is still unclear
 
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knote72 said:
In the article Dustin linked:

"The two Sure Grip types can be interchanged between the carriers if the matching differential axle bearings are retained. The outside diameter of the cups are the same between the '741'/'742' and the '489'; the inner cone differs. "

So what I'm drawing from that is as long as I keep hold of the bearings I can swap the different diffs. My question is, what about the different pinions? Like the carrier bearings, can they too be swapped? That part is still unclear
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You can switch the sure grip if you use the right bearings for each unit, but that’s it. Everything else is specific to the 3rd member, they have different gear sets and pinions and those can’t be interchanged.
 
Well I'll talk to the guy saturday before I go up and get it, ask if it's the 741 case. If it is, and I REALLY decide on a 489, then I can make a trade somewhere for a 489. Funny enough, somebody has a 489 + 3.23 gear for $200. Seems that anything not A-body specific is relatively cheap around here, go figure
 
FYI 741 and 742 are plenty strong for a light A body IMHO unless your planning on some serious dragging. 489 requires a crush sleeve or crush sleeve eliminator when you rebuild. 741, 742 do not. All 3 can use the same limited slip. Its interchangable between all 3.
 
moparmat2000 said:
FYI 741 and 742 are plenty strong for a light A body IMHO unless your planning on some serious dragging. 489 requires a crush sleeve or crush sleeve eliminator when you rebuild. 741, 742 do not. All 3 can use the same limited slip. Its interchangable between all 3.
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Yeah only spirited drives here, plan on staying under that 500hp mark. I do plan on a sure grip no doubt, and did plan on 3.55 gears, but I guess I can see how quick it'll wind up on 3.23
 
I am doing a 408 stroker 4 speed. 742 sure grip 3.73 gears. I prob wont break it. They are way overdesigned.
 
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