View Full Version : Any reason I HAVE to solder in a threaded short tube?

October 03, 2001, 20:50
I've got a threaded STG-58 short gas tube I want to install on an R1 barrel with a threaded gas block. Looking at the tube it has a line of solder that proves that it was definitely soldered into it's previous home.

Why can't I just thread the tube into the R1 block, and tap in a retaining pin?


October 03, 2001, 22:33
Unless you have a brand-new tube, and a brand-new gas block, the short tube will almost surely be too floppity in its fit to the gas block. This causes erratic blow-by and friction. Those problems send reliability down the tubes.

Be absolutely sure the tube is correctly aligned with the gas tube collar and receiver before you solder. Use silver solder paste.

There is no reason not to use a long tube, and you probabaly won't need to solder it. I think the short tube is a really bad idea for a kit-builder. There is no reason to use a short tube other than to maintain "correct" appearance of an STG configuration.

October 04, 2001, 17:27
Thanks for the info Gary!

Anybody else have a comment?

October 08, 2001, 03:09
Sure. A rope main bearing oil seal is perfectly adequate in your Pontiac... as long as the engine is regularly used. Don't let it sit for long periods or it will dry out and begin to fail. You can adapt a 472/500 Cadillac rubber main seal to fit a 421/428/455 Poncho block without much trouble at all.

Oh... comment about your GAS TUBE?!? Sorry. :D

The long tube functions just fine without solder because it's supported at both ends and thus has no alignment problems. The short tube is soldered to keep it rigidly fixed in one position... of course in an aligned attitude. Without some method of stabilization, an unanchored short tube will flex and wobble, with an unpredictable gas seal at one end and wild variations of friction against the piston at the other. Describing this theoretical condition in technical terms: "this be bad juju man." Solder the son-of-a-gun! Perhaps employ a wooden dowel to align and lock it in place during soldering.


October 09, 2001, 13:39
Is high-temp (1100 degrees +) solder required?

Or can I use the 500 degree stuff?

October 09, 2001, 15:57
Here I go again, but this time I'm serious.

Back in the early 60s when car manufacturers were still openly competing in racing, EVERYBODY was looking for an advantage. Weight cut at the drag strip line was just like free horsepower. These were the days of factory-made aluminum front fenders and hoods that would dent like a pop can if you leaned on them. Pontiac actually released exhaust manifolds made of aluminum. Since these were for drag racing only, they only had to withstand the heat of combustion for a few seconds... start the engine, heat the tires, stage and go, then shut down. Even so it wasn't uncommon to find little puddles of aluminum under the outlets.

Federal regs require a permanent attachment of muzzle brakes or barrel extensions; 1100-degree solder is mandatory in these cases. Not so with your gas tube. However, ask yourself how hot is that tube going to get? How do you shoot? Bottom line: how close to 500-degrees do you think the gas system will be exposed to, and for how long? Pontiac got away with aluminum exhaust manifolds, maybe you'll get away with a lower-temp solder. Just pointing it out.