ID 273 Commando that's apart

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SlotCarWon

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I'm going to look at a 273 that the original owner has passed away. The engine was partially rebuilt. Other than the valve covers how do I tell a 2-barrel from a 4-barrel "Commando" engine?
 
In addition to the valve covers, a Commando motor has a 4 bbl. manifold & carb, domed pistons, different camshaft, chrome air cleaner, valve cover breather cap & PCV valve holder, & a Prestolite dual point distributor. I think that's everything.
 
Assuming this is a 66 or older motor - the major differences will be the cam, the pistons, valve covers, distributor and the intake. As far as IDing them the cam is pretty difficult to tell without a dial indicator set up to measure the duration. The pistons again are going to be tough to figure out, they will have a taller compression height than the 2bbl version, you need the specs for the pistons to determine whether they are 2 bbl or 4 bbl versions. The valve covers and intake will be obvious. If you can, try to get all the kickdown and throttle linkage parts, these are really hard to find in a complete set. The rest of these 2bbl and 4 bbl motors are the same, rods, crank, heads etc.
 
When I rebuilt my 273 2 bbl. in 1975 I added stock 4 bbl. pistons. I'm pretty sure the 2bbl. ones were flat on top. I know the 4 bbl. ones were domed with valve reliefs cut in them. The difference was pretty obvious. 66dartgt is right about the cam, you'll probably never be able to spot the difference. I put a "Street Hemi grind" cam in mine & had a lot of fun with it.
 
Thanks for the help.
I have not seen the engine but I heard it is only partially assembled.
I think the heads are not on so the piston info will be really helpful.
 
Here's what the 273 dome top piston should look like...

HP273T.jpg


HP273.jpg
 
SlotCarWon said:
Thanks for the help.
I have not seen the engine but I heard it is only partially assembled.
I think the heads are not on so the piston info will be really helpful.
Click to expand...

"65s" and "64cuda" are right .2 barrel pistons are flat and have 4 valve reliefs per piston. 4bbl pistons are domed and have only 2 valve reliefs.

If all the other "Commando" parts are there, I would assume the cam to be the Commando one as well. Unless it looks really good, I'd spring for a new cam if you rebuild the engine.

Here's pic of 2 barrel pistons...

273-2bblPistons.jpg
 
I know that the early 273 2bbl pistons are flat top and have 4 valve reliefs. Can anybody tell me how far 'down the hole" they are supposed to set and how much can safely be milled from the early heads when using a .450 lift cam?
 
By the way, where can you get head gaskets for these small bore motors? Everything is listed for 273, 318, 340 and 360 with gasket bore sizes starting at 4.060".
 
'64 Cuda said:
In addition to the valve covers, a Commando motor has a 4 bbl. manifold & carb, domed pistons, different camshaft, chrome air cleaner, valve cover breather cap & PCV valve holder, & a Prestolite dual point distributor. I think that's everything.
Click to expand...
The 4bbl pistons have a lighter piston pin too...just remembered seeing the 2bbl's as HEAVY walled pins.
 
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