273 dilemma

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Dave_J said:
Its been said many times before. But if you are reusing the 273's pistons, wrist pins and rods then any Poly 318, or forged 318/340 crank will fit but still should be balanced.

It is true that in 1962-63 when they were doing the engineering of the 273 they used the Poly 318 crankshaft and connecting rods as they had them all tooled up and on the shelf.
But the mass of a Poly 318 piston bob weight is a lot more that the smaller bore 273 so they tooled up some very thick walled wrist pins to match the Poly's bob weight

But if you want the best, replace the 273's HEAVY wrist pins with some light full floating pins, do the David Vizard's crank weight reduction trick and rebalance it. They will be able to remove over 6 pounds of rotating mass
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Even using the original crank, I would rebalance. The factory balance was only so good. Up to 6000 RPM fine, but, above that, rebalance for sure.
 
cudamark said:
Even using the original crank, I would rebalance. The factory balance was only so good. Up to 6000 RPM fine, but, above that, rebalance for sure.
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I know this for sure and have gotten into PI$$ING matches with others that state the factory balance is not too far off.

Yes, good enough for a street engine working between 2500 and 5500 RPM. But even if ran above 4500 RPM for long times I think its not good enough.
 
About 'half' off subject... Can someone shed light on the change in Torque Convertor 'Mounting Lug/Pad' thickness that happened around 1978 or so? It's significant when visually inspecting the convertors, and would either pull the convertor away from the Transmission or push it toward, depending on which Convertor.

T's, Bruce
 
fireguyfire said:
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!
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340's did not come out until the 68' model. A 318 and 340 crank will work, but they are not the same as others stated. Same stroke but shot ping and other machining on the 340 crank. Just make sure they are forged, 71 and down. A 273 crank should not be difficult to find at a fair price.
 
If I was to just re-ring and re-gasket I probably wouldn't rebalance. If you change pistons I would for sure (and I did) The .030 Egge slugs were lighter so some material needed to come off the other end.

I know it's done right. Who wouldn't want that?

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toolmanmike said:
If I was to just re-ring and re-gasket I probably wouldn't rebalance. If you change pistons I would for sure (and I did) The .030 Egge slugs were lighter so some material needed to come off the other end.

I know it's done right. Who wouldn't want that?

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Mike, did you see and maybe take pictures of the 273 wrist pin compared to the Egge setup?

I have searched my garage for my 273 pistons/rods in a box but they may be at my sons house.

When my son did the 78-318 build with light weight pistons and wrist pins we weighted all 8 of his new wrist pins and they weighted just a little more as 4 of the 273's. So just about 1/2 the mass at the top of the rod. All 8 of his pistons, Hypereutetic, were about the same weight as his factory 273 pistons. None of his 273 pistons weighted the same maybe 10gr high to low. All his new .040" over 318 pistons were about 2-5 grams but were equal when he was done. They took 4 pounds out of the crank when balancing it.
 
Dave_J said:
Mike, did you see and maybe take pictures of the 273 wrist pin compared to the Egge setup?

I have searched my garage for my 273 pistons/rods in a box but they may be at my sons house.

When my son did the 78-318 build with light weight pistons and wrist pins we weighted all 8 of his new wrist pins and they weighted just a little more as 4 of the 273's. So just about 1/2 the mass at the top of the rod. All 8 of his pistons, Hypereutetic, were about the same weight as his factory 273 pistons. None of his 273 pistons weighted the same maybe 10gr high to low. All his new .040" over 318 pistons were about 2-5 grams but were equal when he was done. They took 4 pounds out of the crank when balancing it.
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I didn't take any comparison photos. If I did weigh them, I didn't post it. My notes are buried in the basement somewhere and I haven't seen them for 10 years or so.

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Dave_J said:
Mike, did you see and maybe take pictures of the 273 wrist pin compared to the Egge setup?

I have searched my garage for my 273 pistons/rods in a box but they may be at my sons house.

When my son did the 78-318 build with light weight pistons and wrist pins we weighted all 8 of his new wrist pins and they weighted just a little more as 4 of the 273's. So just about 1/2 the mass at the top of the rod. All 8 of his pistons, Hypereutetic, were about the same weight as his factory 273 pistons. None of his 273 pistons weighted the same maybe 10gr high to low. All his new .040" over 318 pistons were about 2-5 grams but were equal when he was done. They took 4 pounds out of the crank when balancing it.
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It was balanced because the +.030 Egge's were 68 grams lighter.
 
Makes you wonder how much money Ma Mopar saved by increasing the weight of the wrist pins rather than re-balancing the 318 poly crank. Probably not as much as when they kept the poly 318's valve angles when casting the 273 and later wedge small blocks.
 
fireguyfire said:
I’m going to hunt for a forged 273 crank, but if that doesn’t work out I’ll consider the 318 option.
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I just acquired an early 67 273 (2-8-67) I have no current plans for. But I don't think we could be farther away from each other, so it may not be practical for you.

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Dana67Dart said:
My bet is it was rebuilt as it's not red
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While I agree with the logic, I can't be certain either way. There are NO indications of any red paint anywhere on the motor (other than the 4bbl intake I set on top). If it was a rebuild, they stripped the oil pan and valve covers as well, and there is no indications of any blue or red overspray.

Maybe a marine or industrial engine???

I once had a 64 4-door d100 truck that was labeled as a Navy vehicle. the truck and motor were painted gray.
 
Dana67Dart said:
My bet is it was rebuilt as it's not red
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I hope you are making a joke, HA- HA!!! Maybe that is a 340 intake because it is painted Hemi orange. Years ago a installed a stock 69' 340 in my 72' van and I painted it blue to match the 72' color, to look original for that year. Block #'s don't lie, Colors do. Does not have to be rebuilt to change the paint colors.
 
My son does not have a picture of the 273 wrist pins but has notes of when he weighted them.

Full floating without the keepers they are 320 grams each. Not sure how much the keepers weigh. 5.64 POUNDS for all 8

The Light weight ones he got for his 318 were from Manley and are Pressed In and are 117 grams. 2.06 pounds for all 8

Easy to see the weight that you can remove from the crank. Even more if you do some work on the rods.

More too if you do some grinding on the crank like what David Visard did for the 318 Uncle Toni engine. End up with a much lighter rotational mass and less windage too.
 
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