67' 318 crank in a 69' 340

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WTH.... golly that IS special. I wonder if they were trying to do some sort of external balance equivalent to what one would have with the standard external balance TC for the later 340. If they were, they put it about 30-40 degrees out of place.

I would see if that can be filled. Since the rest of the flange looks intact, it might be just fine.
 
"I read somewhere that in '71, the 340 compression dropped from 10.5 to 10.25."

Very possible, going off memory here. But anyways, 72 was the big drop in compression.

Yep, looks like a forged crank you have there but the low comp pistons. Man, how could someone cut the crank like that? A good welder may be able to weld that up with nickle rod. Would need some good preheating prior to. I would probably give it a shot if the journals were all in good shape. If the journals have already been cut and possible needing to be cut again, would be best to start from scratch.
 
Part of the 340 compression confusion is in some of the aftermarket pistons.... there are some Sealed Power cast pistons, PN 428P, which have 4 valve reliefs but have a compression height that is only .011" lower than the original hi comp pistons. So those are still fairly high compression.

Then the Sealed Power L2385F forged one are 2 valve reliefs but the CH is a full .100" shorter than the high comp ones....
 
If that was mine and I was just putting around town with it I'd run that **** as-is, but that's just me. The flywheel is going to hold that crank together. Unless that cut goes past the flywheel mounting flange and into the root of the shaft and into the crank seal area I don't see much of the strength being lost, but I can't really see all the damage so it's hard to tell how much of a butcher the hack with the torch was so take my advice with a grain of salt. Probably going to need a crank seal at the very least though.
Now if you'll be dumping the clutch at 6500 rpm occasionally and shiftin' without liftin' you might want to find another crank.
 
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I believe the last photo clearly shows the thin parting line of a cast crankshaft. In my opinion, that one is not worth fixing if you have to pay someone to weld it. Use a different crankshaft.
 
If anyone knows a good cast crank welder in the So.Cal area that will work for beer, I got a old school stroker (360 to 340 mains) that has a chipped flange. Fed Ex dropped it on its end. I still got the piece. I had a 318-3 crank once. Also had a forged 318 poly crank that P.A.W. 'remanufactured' to 340 specs. Worked great.
 
I wonder if any forged high compression pistons would be light enough to not need balancing? Worth checking, to see if there is something light enough to be within acceptable limits. Save money on balancing, put towards better pistons !
 
aftermarket forged pistons are usually lighter than the cast stockers as the forging is stronger so they can use less material for the same strength. you could add weight (MIG wire weld) to the centers of the pins if you went that route.
 
daliant said:
If that was mine and I was just putting around town with it I'd run that **** as-is, but that's just me. The flywheel is going to hold that crank together. Unless that cut goes past the flywheel mounting flange and into the root of the shaft and into the crank seal area I don't see much of the strength being lost, but I can't really see all the damage so it's hard to tell how much of a butcher the hack with the torch was so take my advice with a grain of salt. Probably going to need a crank seal at the very least though.
Now if you'll be dumping the clutch at 6500 rpm occasionally and shiftin' without liftin' you might want to find another crank.
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I may check around town to see if there is a shop that could weld up this crank . I automatically considered this crank junk because I have always thought that anything cast could not be welded but there may be a process where it could be repaired .
I also wondered with the damage to the crank being so close to the center of the crank if it would be measurable or noticeable when balancing ? The flywheel would add stability and remember this car is just going to be a cruiser .
I'm just thinking out loud . I appreciate everyone's thoughts !! A lot of great ideas and comments here !! Thank you !
 
I wouldn't weld a cast crank...at all.
You could buy a "good" cast one for the price the welding will cost.
 
daliant said:
If that was mine and I was just putting around town with it I'd run that **** as-is, but that's just me. The flywheel is going to hold that crank together. Unless that cut goes past the flywheel mounting flange and into the root of the shaft and into the crank seal area I don't see much of the strength being lost, but I can't really see all the damage so it's hard to tell how much of a butcher the hack with the torch was so take my advice with a grain of salt. Probably going to need a crank seal at the very least though.
Now if you'll be dumping the clutch at 6500 rpm occasionally and shiftin' without liftin' you might want to find another crank.
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I will try to get a better close up picture but I'm certain the cut did not go all the way to the crank seal surface .
 
seems a flywheel would work to hold the thing together, but not a flexplate. But its just a cast crank. its nothing special. I sold one for $50 that was already 10/10 and polished.
 
72Dart6pack said:
Stroke it out to the max with a forged crank. Cast cranks are for mail box posts. :rolleyes:
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I ran a 73 low comp engine in a duster than ran mid 11's with a cast crank. Many of the 360's running today in stock in the 10's are running a cast crank.
 
gregsdart said:
I wonder if any forged high compression pistons would be light enough to not need balancing? Worth checking, to see if there is something light enough to be within acceptable limits. Save money on balancing, put towards better pistons !
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Not sure what the thought is... if lighter pistons are put in, it needs to be rebalanced.

Are you thinking that the external balance weights can be done away with? I.e., go to neutral balance damper and flywheel/flexplate? For the cast 340, there is some chance. 70aarcuda has reported coming pretty close to neutral balance with the cast 360 cranks with the very lightest pistons and rods, and it would be easier to reach that point with the cast 340 since the external imbalance weight is a lot less.
 
pishta said:
seems a flywheel would work to hold the thing together, but not a flexplate. But its just a cast crank. its nothing special. I sold one for $50 that was already 10/10 and polished.
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Sounds like that is the way for the OP to go.
 
Vince Gillespie said:
I may check around town to see if there is a shop that could weld up this crank . I automatically considered this crank junk because I have always thought that anything cast could not be welded but there may be a process where it could be repaired .
I also wondered with the damage to the crank being so close to the center of the crank if it would be measurable or noticeable when balancing ? The flywheel would add stability and remember this car is just going to be a cruiser .
I'm just thinking out loud . I appreciate everyone's thoughts !! A lot of great ideas and comments here !! Thank you !
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Just adding material to stabilize the cut is the idea. The main area of stress is down at the base of the flange where it joins to the crank; the stress decreases the further you go from the center. But if you can find a good low-priced crank like Pishta says, that would be better.
 
nm9stheham said:
Not sure what the thought is... if lighter pistons are put in, it needs to be rebalanced.

Are you thinking that the external balance weights can be done away with? I.e., go to neutral balance damper and flywheel/flexplate? For the cast 340, there is some chance. 70aarcuda has reported coming pretty close to neutral balance with the cast 360 cranks with the very lightest pistons and rods, and it would be easier to reach that point with the cast 340 since the external imbalance weight is a lot less.
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I thought the OP wanted to use a 318 crank which has a lighter balance stock. If a guy was real lucky, there just might be a piston that would weigh the right amount so no balancing would be required. Magnum pistons come to mind as something to look at. Magnum rods are also lighter. There are a lot of ways to skin a cat: Hbeam rods are lighter, some sbc parts might make a combo, but that would be getting into territory for veteran engine builders that have seen a zillion parts. For instance I currently have a 5.9 cast crank, a set of sbc h beam 6.2 long 2.00 rod bearing rods. Find a sbc piston with the right deck height and enough meat for valve notches, and with luck I just might come up with a little stroker kit with a pretty light bob weight!
 
OK, I see. I ran over a bunch of common rod and piston combo's with the OP in a PM to see; nothing was exactly on the 318 standard bobweight. Here are those combo's:
Comparing bobweights in approximate numbers:
- Stock early 318 is 2147 grams
- Put in the KB pistons but use the original 340 rods and you end up with 2160 grams.... a tad heavy; the rods could be ground a bit to get there but that is some work and cost
- Put in the smaller 318 rods with the KB167 pistons and you end up with 2105 grams; now you can take weight off of the crank
- Just for grins..... the bobweight for the KB167's and the SCAT rods like we used is 1893 grams.... that is a LOT of weight off of the rotating assembly.
 
"...Put in the smaller 318 rods with the KB167 pistons and you end up with 2105 grams; now you can take weight off of the crank..."
Which is exactly what I'd do IF I were in the OP's situation, and with what he wants out of the economy build.....I believe that combo has been done before... :)
 
Roger. And looking at the numbers again, it is to wonder if 13 grams could be taken off of the big end of the rod.... that would bring the big rod and KB piston right in on target.
FWIW... my numbers are very close but I would re-check one thing before using them... the small end/big end split on the lighter 318 rids weights. They might be off a few grams + or - which would throw off that 2147 stock bobweight a couple of grams.
 
No way I'd run that garbage. It's a cast crank anyway so it's really totally worthless now. Disassemble it and buy a 318 cast crank kit from any big box parts store throw that one at them for the core and have it all rebalanced. Done deal.
 
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One thing to do to figure out a combo is come up with some solid numbers on how far off (overbalance?) the bobweight can be. A one percent OB would be what, 20 grams? That allows some fudge room. I am not a balancing expert so don't go by my 1 percent idea. But there must be someone on this board that has an idea of what can be done.
 
gregsdart said:
One thing to do to figure out a combo is come up with some solid numbers on how far off (overbalance?) the bobweight can be. A one percent OB would be what, 20 grams? That allows some fudge room. I am not a balancing expert so don't go by my 1 percent idea. But there must be someone on this board that has an idea of what can be done.
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The man is a genius LOL. Consulting the magic spreadsheet here, and change the balance factor to .49 instead of the standard .50, and the bobweight for the KB167 piston with the heavy 340 rod becomes 2140 grams which is now slightly under the standard 318 bobweight. So looking at it the other way, that 2160 gram bobweight represents approximately a balance factor of .507 applied to a piston/rod set that would have 2147 grams bobweight with a balance factor of .50 even. (Did I make that confusing enough?)

So your thoughts and number are pretty much spot on, GD.

The .50 factor minimizes the peak magnitude of vibrations for a 90 degree V8 engine. (See the middle pair of diagrams on page 8 of this article: https://www.tonyfoale.com/Articles/EngineBalance/EngineBalance.pdf) Using that .507 factor, one would expect some increase in some vibrations at some RPM's. I don't know what they are, but the above is really stating the obvious: it is gonna be a bit imbalanced compared to normal simply because it it not optimally balanced... like everybody knows, duh! But whether that would be bad is the question; I bet there are lots of uses where it would be a non-issue, like a budget drag car. I just cannot say if it would or would not have an annoying level of added vibration at your main cruising RPM, for instance.
 
I appreciate everyone's time , thoughts and opinions !!! Correct me if I'm wrong but I think the KB167 piston is for a 318 bore , I will be using a 69' standard bore 340 so it looks like a KB243 piston will be needed and I'm certain the bob weight will be different than previously thought .

I am totally out of my element here and I wont pretend that i know what it takes to figuring out what is necessary to balance this short block but so far I can see me using the KB243 piston in the 69' 340 block with the 68' 318 crank/rods that I have . The cylinders looked to have been ridge reamed and walls deglazed ( cross hatching is quite visible ) . The current pistons in the 69' block are 72' factory pistons . The bores will need to be confirmed as whether they are straight or will need to be bored to straighten .

For me , this 70' Dart Swinger is just going to be used for cruising around , going to car shows and the occasional blast throught the four speed (mostly under 5500 rpm ) ... You know , the typical fun we have with our mopars !!

Thanks again to everyone who have taken the time to pass on your thoughts and opinions , very much appreciated !!!
Take care everyone !!
 
I have not gone back through all posts but the KB243's were what I was using for bobweights in post #43 and beyond... DUH! I see I said KB167 from that post onward but meant KB243.....sorry for the confusion! You ARE paying attention; awesome!

So, recapping: if you used the KB243's and stock 340 rods, they will be a tad heavy for the 318 crank.....around 2160 grams bobweight (And, I forgot to add that the more oversized you go the more the pistons typically weigh, so that bobweight gets a bit further off.

I'll put this idea in front of you again to chew on: Buy KB43's and SCAT rods. Then your bobweight will be well under the 273/early318 target bobweight; it is around the 1893 grams I cited before. What I like about this is:
1) if you recondition the 340 rods, you will be spending about 1/2 to 2/3 of the price of the new SCAT rods
2) The SCAT rods come weight balanced end-to-end and for total weight. So no money is spent on balancing the rods (which gets done on a performance balance)
3) The balance work becomes 50% -70% cheaper because all the machinist needs to do is weigh one piston-pin-rod set (with rings and pin locks) and compute the bobweight and balance the crank to that. Done. Between this and the savings on reconditioned rod work, you have paid for the SCAT rods.
4) The lighter weights save on stress on the rotating components with all those benefits. And with a 4 speed, things will rev better, and shift better: when you shift, the lighter rotating mass will make the synchros work less... faster shifts.

That is the route my son and I went on his 340. The crankbalance was something like $95 total....CHEAP! I weighed the pistons/rods/etc. myself and gave him the bobweight to work to so that saved some cost. But him weighing the parts and computing the bobweight should not be much time or cost. He took off about 82 grams IIRC from each of the large end counterweights and that was that.

So we have been down this road before....
 
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