273 Commando Rebuild Or Not?

[junkyardhero]

i like the compression numbers and the fact that it's a runner right now.

open it up and you just might let the magic out of it.

personally, i'd throw some seals and gaskets at it, fresh chain and oil pump then paint it up and ship it. then build something on the side that's a little more value for money.

 

[66fs]

I was thinking perhaps it could be a leaking head gasket on the passenger side bank. Why not replace the head gaskets? From what I understand, the Commando came with longer valve springs then the 2 barrel version. What will putting 340 valve springs on the engine do? Isn't anything related to 340's in the unobtanium price range?
Thanks for the ongoing help

The head gasket is not you problem on the low side. Check your head castings. If you run the engine as is and start using good oil and a good filter, the compression may come up to match the other side. Commando head gaskets are special .020 thick head gaskets. The bore of the Commando head gasket is not round, you will not find another set like, or as good. 2 and 4 barrel springs are different, but still lacking in spring rate. 340 valve springs are great on any HP small block and were readily available at a reasonable price. You can also run aftermarket copies, see post #13. There is no down side to running 340 valve springs, and if you are replacing the valve seals it is easy to swap the old springs out for fresh better springs.

 

[cudamark]

The head gasket is not you problem on the low side. Check your head castings. If you run the engine as is and start using good oil and a good filter, the compression may come up to match the other side. Commando head gaskets are special .020 thick head gaskets. The bore of the Commando head gasket is not round, you will not find another set like, or as good. 2 and 4 barrel springs are different, but still lacking in spring rate. 340 valve springs are great on any HP small block and were readily available at a reasonable price. You can also run aftermarket copies, see post #13. There is no down side to running 340 valve springs, and if you are replacing the valve seals it is easy to swap the old springs out for fresh better springs.

The possible downside to running heavier valve springs is the extra wear on the cam and lifters. If it's just going to be a cruiser and not going to be revved way up, why do it? No upside IMO. The existing cam and lifters are used to those springs.

 

[66fs]

The possible downside to running heavier valve springs is the extra wear on the cam and lifters. If it's just going to be a cruiser and not going to be revved way up, why do it? No upside IMO. The existing cam and lifters are used to those springs.

Not much different at .425 lift, but less false motion. I pretty much run them on everything. But I don't run anything but a 4 barrel carb and rev to 6,000 rpm. When you use good parts, longevity is a non issue in my experience. Most of my engines last forever with oil and filter changes at 3,000 miles and 20w50 Valvoline VR1. Actually I have never had one fail yet, except the cam and lifters in the stock 318, and that was a small tick at idle. To be fair it was a factory engine with 30,000 miles and it sat for years before I bought it. Fixed it with a small Mopar Performance cam and lifters, still running like new or better 20 years later...

 

[Blue62Val]

273 head gaskets are no longer available, you will have to use 318 ones or have Cometic make custom ones..$$$$

Just curious……so they don’t make 273 head gaskets, but you CAN use 318 gaskets.
So what’s the difference between them ?

 

[4spdragtop]

The difference is bore size. Orig 273 steel gaskets were "wallowed" and not perfectly round and near extinct.

Just curious……so they don’t make 273 head gaskets, but you CAN use 318 gaskets.
So what’s the difference between them ?

 

[Blue62Val]

The difference is bore size. Orig 273 steel gaskets were "wallowed" and not perfectly round and near extinct.

Is it “better” to use them ?

 

[4spdragtop]

I can't say which is better, I've never used Cometics, just Felpro.
When we redid our 273 12 years ago I can't remember whether 273 or 318 gaskets were used. No issues with 318 gaskets.
More knowledgable will chime in.

Is it “better” to use them ?

 

[66fs]

Is it “better” to use them ?

Since you can't find the OEM steel shim .020 thick gaskets it does not matter. I don't like steel shim stamped steel gaskets. I always felt they seeped oil. You pretty much need a 3.91 bore gasket on a 273 because of the head chamber opening. I always used the Fel-Pro small block gaskets on a 273. They are .040 thick and seal everything up, never a problem. My engines make plenty of power, so a tad lower compression does not seem to matter much.