273 dilemma

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fireguyfire

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I’m looking for opinions on how to proceed with a problem I have with the 273 commando engine that is matching numbers in my 67 formula S fastback barracuda that I bought recently.

The car is an unrestored survivor, and the car has been stored inside for 30 years by the original owner whom I bought it off.
I pulled the engine to inspect it since it will need a new gasket set and seals at a bare minimum and unfortunately I found that at some point the torque converter must have been ballooning and pushed the crank forward which wore most of the side of the thrust bearing off and unfortunately are 40 thou into the crank.
I took the crank to my trusted machinist who said it is unusable as is, and the only place he knows welding up cranks like that is a marine engine specialty place in California that costs a fortune.
I’m really bummed as it is a beautiful forged crank, but so be it.
So my big dilemma is what to do now. I’m trying to find another forged 273 crank but am having zero luck as I would love to save the matching numbers engine. Another guy suggested you could easily throw in a 318 cast crank but I have to think that because this is a commando engine that has tee HP parts that that idea might be a big can of worms in regards to throw length, balancing etc.
And the 3rd option as I see it would be to find a decent running 340 and drop it in since it was a period correct option and drive the car.

I’d love to hear opinions on all of those options by any of you here that have done it or heard of people’s options in a similar situation.

Cheers!
 
People have told me that a cast 318 crank would fit, but might create issues in regards to balancing, etc because the rods and pistons are different from a size and weight perspective than 318 stuff which could lead to issues.
 
Put an ad in the "Wanted" section, someone close to you probably has a usable crank.
 
Just remember, if you do find a crank it will cost a small fortune to have it shipped. Also in 67 there was no "numbers matching". 68 had the order number stamped and the VIN in 69.
 
If you do find a replacement crank, remember that there are different size torque convertor registers in the rear of the crank.
 
The only issue you will have is the pocket in the convertor flange for the nose of the convertor. In approximately 1968 they enlarged the diameter of the recess in the crank to accommodate a larger nose on the convertor. If you can find a '67 and earlier crank, it's a drop-in; if you find a '68 or later crank, it will require a spacer bushing to be pressed into the crank to let it match up to the '67 and earlier convertor.
 
Professor Fate said:
The only issue you will have is the pocket in the convertor flange for the nose of the convertor. In approximately 1968 they enlarged the diameter of the recess in the crank to accommodate a larger nose on the convertor. If you can find a '67 and earlier crank, it's a drop-in; if you find a '68 or later crank, it will require a spacer bushing to be pressed into the crank to let it match up to the '67 and earlier convertor.
Click to expand...
68 didn't have a forged crank so that doesn't apply. 68 and 69 273's had cast cranks.
 
Although, if your convertor actually was "ballooning" that badly to cause engine damage, you're probably going to be replacing the convertor as well. Know that later convertors will not fit the early transmission, the spline count changed. You could always have a custom convertor built with the early spline count and the later nose diameter to fit a later crank if that's what you end up with.
 
if the rest of the motor is in good nick, i'd scoop up a used crank (318 or 273) and go that route over dropping the coin for a 340.

snapping up a cast 318/273 crank local with a trip to the balancer (just in case) would probably be quite a bit cheaper than a 340 crank or getting something shipped, or going motor swap.

keep the 273, that's what makes the car unique.
 
The Hot Rod Magazine article on the 273 when it was first introduced says the 273 pistons (or pins, can't remember) are heavier so that the 273 piston/pin weighed the same as the 318 poly piston/pin so that the 318 rotating assembly did not need to be rebalanced for the 273 pistons.

Which reminds me - the 273 forged cranks (at least in 64-65) were the same as the 318 poly cranks. So one of them would work, too.

Someone correct me if I'm wrong, but I seem to recall that the 340 had heavier pistons and rods than the 318, and its crank had larger counterweights, too. Same stroke for 273, 318 and 340, but the 340 crank is not interchangeable without rebalancing.

Of course, one really should have an engine balanced anyway.
 
So in my research it shows that the throw is different on a 318 crank than on my forged 273 crank.
Is that correct?
 
fireguyfire said:
So in my research it shows that the throw is different on a 318 crank than on my forged 273 crank.
Is that correct?
Click to expand...
No. 273 and 318 cranks are for the most part interchangeable. Bearing journals and balance. 340 cranks have the same bearings but because of the heavier pistons and rods, their counterweights are heavier.
 
Professor Fate said:
The only issue you will have is the pocket in the convertor flange for the nose of the convertor. In approximately 1968 they enlarged the diameter of the recess in the crank to accommodate a larger nose on the convertor. If you can find a '67 and earlier crank, it's a drop-in; if you find a '68 or later crank, it will require a spacer bushing to be pressed into the crank to let it match up to the '67 and earlier convertor.
Click to expand...
Hard to believe a stock 273 could ''balloon'' a converter. Is it possible at some point the wrong vert was installed and that put all that pressure on the crank? If so, i'd be checking the trans out also. Just a thought?
 
Will definitely be checking out the trans pump pressure; I’ve already checked the tranny cooler lines and they aren’t blocked at all.
Looks like the engine has never been out of the car, and it’s the factory converter by the orange factory paint spray mark on the converter and the flex plate which match up perfectly.
My engine guy said he has seen this a lot from people doing brake stands
 
I put a cast 318 crank in my 273 that I just built. I never planned on running any stock year converters with the little nose, nor a stock 120 tooth flywheel. 318 crank was a 72 year model, drilled for and has a pilot bushing and went 10-10. I used Scat rods which were better rods and cheaper than reworking the old 273 rods. Had it balanced with the custom 30 over flat tops and it's all good. It went to 6 grand on the dyno a dozen times, but I wasn't worried about it anyway. Cast cranks get an undeserved bad name for mild street motors. I had a 73 Challenger when I was a kid, with a cast crank 340 in it. I made that poor thing suffer, and the crank never was a problem.
 
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