I have the carbs off for some work and noticed that an air passage has been drilled between runner 1 and 2 but none of the other runners.

This probably why I've had a hard time balancing the No#1 carb in the past. So while I have it off the car I would like to plug it, but with what?

 

I could drill out the end plug and tap threads but only want to that as a last resort. JB Weld and Silicone gasket maker will both break down eventually with contact with gasoline, maybe a neoprene plug of some kind.

I'm open to any ideas.

Thanks,

Chris

Edited March 24, 20159 yr by grannyknot

Perform a search on Thermosteel.   This stuff might do the trick.

Perform a search on Thermosteel.   This stuff might do the trick.

Devcon Plastic Steel Putty also works well. Used in Porting and polishing of Cylinder heads and manifolds to repair holes and modify port shape. It is not affected by Fuels or Oils. Make sure that you get the standard set time Putty. Do not get the 5 minute Epoxy or the 5 minute Putty. They are different formulations and I do not believe that they are as resistant to fuel and oil as the original Putty.

 

http://www.itw-devcon.co.uk/index.php?/devcon_mro/epoxy_maintenance_repair_and_overhaul_systems/devcon_plastic_steel_putty_a/

 

Expensive, but worth it.

 

http://www.amazon.com/Devcon-10110-Plastic-Steel-Bottle/dp/B00065TMTO/ref=sr_1_1?ie=UTF8&qid=1427214624&sr=8-1&keywords=devcon+plastic+steel

 

 

 

 

Available in a 500g size as well. Part #10112, although it's a bit more difficult to find.

Edited March 24, 20159 yr by Chickenman

Maybe it's just me, but I'd be skittish about using any type of plastic or rubber to plug that hole. I'd want something with a positive retention feature of some sort. If a chunk of something comes off or out of that hole, it's going straight into your intake valve. I'd want to use some sort of metal and I'd want it welded into place or retained with threads of some sort. I know I'm conservative when it comes to that kind of stuff, but I'd sleep easier.

 

Some ideas?
Drill out the end plug and tap the hole as you already suggested.

 

Find or make a tap short enough to be able to stick it into the hole and tap it with quarter turns right through the circular runner opening. That way you won't have to drill out the end plug? Then use a set screw to plug the hole (with thread locker) and grind off any excess.

 

Make a two piece tapered plug contraption, one with a male thread and one with a female. Put one in runner 1 side and the other in runner 2 side and then thread them together (with thread lock) from one side to the other? Grind off any excess.

 

And of course, the obvious of weld one side shut. Someone trained in the art of aluminum welding ought to be able to make easy work out of that.

 

Wonder why they only connected 1 and 2...

DatsunZguy and Chickenman, those both look like good products but the more I think about it the more I think I should have a permanent obstruction in there.

 

Captain, as you say, I may have to have one side welded shut but while reading your post it made me think of this: flip over the manifold and drill down 90* to the air passage, through it with a slightly larger drill say

1/8th - 27NPT plumbing tap and then use a brass plug to close it off. I shouldn't have to break through the top surface and there is plenty of webbing between the runners so it shouldn't weaken it too much.

And if if it ever backs itself out it won't head toward the intake valve but will just fall to the ground.

I put a red dot where I would drill, can you guys see any potential problems? 

 

Absolutely. Cross drilling and plugging that way would work great too. I was gonna mention that, but I thought for some reason that you didn't want the modification to show. I was reading too much into it, and even so, you could always do the plugging from the underside and that way it'll be invisible after installation.

 

I'm not sure you're going to want pipe threads though for the job though. You're need to drill and tap deep enough that you'll completely eclipse the cross hole and I'm thinking that straight threads would be better for the application.

 

Another cross plug option would be to drill (without tapping) and shrink fit an aluminum plug into the hole. Size the hole and the plug such that with a little heat on the manifold and a little cool on the plug... Press the plug in, grind off the excess, and it'll be pretty much invisible when done. Just make sure you use aluminum for the plug so the thermal expansions are matched.

 

or cross drill and weld it full - easier to get in there from that angle than in the hole. after welding shut you can grind it clean and nobody will be the wiser.

 

or just chewing gum...

If this were mine i woud tap it and install a decorative pan head screw with thread locker.  Brass, chrome or maybe zinc coated like the other fasteners if you can find one.  super simple, wont get sucked into the motor and looks like it belongs there..  I think im less of a perfectionist than some people here though.. 

The Devcon product I mentioned won't go anywhere and will never chip or break when properly applied. It is an Industrial grade product made to permanently repair Industrial machinery and should last the life of the equipment.  It is a tough as steel and can be tapped, drilled or machined just like steel after installation. It is much, much stronger than any product such as JB Weld.

 

As I mentioned, Tuners who port Cylinder Heads and Intake manifolds have used this particular product to repair cracks holes and reshape runners for decades. I was using it back in the 1970's to repair/modify Cylinder heads and manifolds when I was racing Datsun 1200's. The FIA head and manifold that I patched with Devcon ( in 1976 ) is still being used in Vintage racing to this date at a local Track. Still with my original patch.... FWIW.