273 Commando Piston Reuse - L2222N /.040

[PocketAces]

I picked up a 273 block with domed Commando pistons. The pistons are stamped L2222N and they are .040 over. I think they might be older TRW replacement pistons which would be forged, but not sure how to tell for sure. The bores look good with no scoring but some of the bores have a pretty good ridge and I was told the engine was smoking.

I'm wondering whether it would make sense to try to reuse the pistons in a different block. I assume I have to remove and inspect them, but I'm not sure what to look for.

• What diameter should the pistons be if they're .040 over?
• Does the diameter vary from the top to the bottom, or is the skirt the same diameter as the crown?
• What diameter should the wrist pin holes be?
• How do I tell the difference between forged and cast pistons?

 

[PocketAces]

What, no opinions?

 

[toolmanmike]

Sorry, I was going to respond but got real busy the last few days. If the engine was .040 over the next step up is .060. You should have a good machine shop sonic check the block to make sure there is enough material to go that far. The earlier 273's had some core shift problems but your's might be ok. The pistons may have some resale value if they are still in good condition and would be a welcome buy for a guy that has a .030 over block that needs a bit more. I don't have the specs you need handy so I can't answer your other questions right now. I may have some extra time later tonight. tmm

 

[PocketAces]

ToolManMike, I was hoping you would see this thread.

I'm more interested in the pistons. 273 blocks seem to be cheaper than pistons. If I can find one that will clean up at .040, maybe I can use these pistons?

I showed the engine to a machine shop in the area. They said the pistons looked like TRW's. He said that Egge doesn't stamp them the way TRW did. The machinest said to pull them out and he would check them out for me. But if you have the specs, that would be great.

From what I've come across online, the TRW pistons were rated for higher compression than the Egge pistons. But don't quote me on that. It could just be that the web page I found was quoting the nominal compression ratio and not the actual value like you measured on your build.

I actually would prefer something lower like between 9 to 9.5 to 1.

 

[Double M]

L2222N is the TRW part number for the 273 -10.5 replacement piston. The pin is the stock MOPAR size. The only difference from stock as far as design goes, the factory piston had off-set pins, the TRW's had 0 off-set, and were forged. It's a good piston, you can run the hell out of them. Make sure to have them balanced if you're going to use them.

Russ.

 

[RustyRatRod]

The old forged pistons from TRW required a pretty good amount of clearance. I think on the order of .004"-.006". Seen as high as .008" and RUN as high as .012". LMAO But that joker didnt burn a lick of oil because I file fit the rings. It was noisy when cold but got better when warm. Those old forgings are heavy and TOUGH. They can get by with some clearance.

 

[toolmanmike]

I picked up a 273 block with domed Commando pistons. The pistons are stamped L2222N and they are .040 over. I think they might be older TRW replacement pistons which would be forged, but not sure how to tell for sure. The bores look good with no scoring but some of the bores have a pretty good ridge and I was told the engine was smoking.

I'm wondering whether it would make sense to try to reuse the pistons in a different block. I assume I have to remove and inspect them, but I'm not sure what to look for.

• What diameter should the pistons be if they're .040 over?
  
  Stock bore 3.630. .040 over= 3.670
  
• Does the diameter vary from the top to the bottom, or is the skirt the same diameter as the crown?
  
  Piston diameter is measured .500 in. below the wrist pins on the skirt side.
• What diameter should the wrist pin holes be?
  
  Small block wrist pins are .9842 in. diameter
• How do I tell the difference between forged and cast pistons?
  
  Kinda hard to tell but forged pistons are usually smoother than cast pistons with fewer sharp edges. If you compare the two side by side you can pick out the forged ones.

Hope this info helps. The TRW's are a good strong piston and I've heard they are closer to the 10.5/1 compression ratio which may cause you problems with today's gasoline. The Egge's may be a better choice. You could find a different block but I wouldn't bore it .040 over unless it was already .030, and needed to go bigger, just to reuse the pistons. I wouldn't be too concerned about the ridge for now until the machine shop measures everything. You may have a broken ring or even loose valve guides or bad valve seals that is causing the smoking.tmm

 

[PocketAces]

Now that's what I expect out of FABO. You guys rock!

 

[Double M]

I guess I should have mentioned what Stroker said. Run them loose. I ran .007 with new slugs on all my 273's way back when with the TRW L2222N pistons. I always went .060 over, never had a heating problem. I also went .011-.011 on the crank. Lots of clearance, .003 rods and mains, the little 273 can be a revving SOB with the right heads and cam, big carburetor. The only motor I broke was 3 1/2 years old and I let a friend race it in Hemet and it broke a rod, put the cam in three pieces. It still beat a 396 Camaro doing it. This was back in the early '70's. Also, I worked at a machine shop at the time so I did my own engine work.

The only correction I would like to make to TMM's post is that the 273 should have a stock bore of 3.625, not rounded off to 3.63. But that shouldn't matter, the machinist shouldn't bore any motor before first putting a mic to the slugs.

Russ.

EDIT: Also, if you don't want to spring for a Cloyes True Roller timing chain setup, use the 354 Hemi setup, it bolts right on and the chain is one inch wide. You won't stretch it. Numbers popping into my head are HOOF, #273 and #274 timing gears with a #348 chain. I reserve the right to be wrong, as these numbers just popped into my head and I could just have CRS.

 

[toolmanmike]

The only correction I would like to make to TMM's post is that the 273 should have a stock bore of 3.625, not rounded off to 3.63. But that shouldn't matter, the machinist shouldn't bore any motor before first putting a mic to the slugs.

You're correct Russ. I had to go down 2 flights of stairs at midnight to look it up in the service manual. lol 2 of my books and my desktop dyno listed it as 3.63. Exact bore size is a relative measurement because it is controlled by the piston diameter and the piston to cylinder wall clearance. Like your last sentence states, mike the slugs, add the clearance and bore to that dimension leaving a bit for honing.

Another note to 65Dart, make sure the machine shop uses a torque plate to bore and hone the block especially if it is going .030 or over. The main caps should be torqued also. (good machine shops wouldn't do it any other way) Nite all! tmm

tmm

 

[stillrunners]

Have a set of Ross pistons that were made awhile back.....Ross still pulls up that job # though.