HELP QuadraJet experts weigh in...

olds307 and 403 said:

Don't worry Donovan, I forgive you for building a chebby. At least you used modern heads, something not out there with Olds 350 sized chambers and ports. Curious what intake did you use? Most Vortec intakes are square bore from what I have seen. I know the Vortec heads are crack prone but not as bad as the Dodge Magnum heads, I think. The Ram EQ heads which flow 233/188 cfm on the 5.9 in my Dakota are proof of the stock heads cracking.

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Christian, the intake manifold is kind of a unique piece. About 10 years ago, I was working for a natural gas compression company, and they used a variety of marine and industrial engines to power their portable units. One of the models used the Vortec version of the venerable Chevy 350, but they were converted to run on the natural gas that came out of the ground. Every once in a while these engines would grenade itself beyond the point of repairing, so the good parts were canibalized for spares and reuse. This intake manifold is one of those pieces.

It’s a “Kodiak” brand aluminum intake, and because it’s for marine and industrial use, it’s dual drilled for both square and spread bore carb patterns. My buddy Mike (whom I met when I started working there) still had this intake and a pair of the desirable casting Vortec heads in his possession that he wasn’t using. He was in need of a refrigerated dryer for his shop compressor which I found for him, so a trade was set up.

When I went to use it on the build, I simply ground off the Kodiak logo and painted it Corporate blue to match the rest of the engine. It’s patterned off of the popular Edelbrock dual plane, but at a fraction of the cost. I can vouch that it performs extremely well, no issues with it whatsoever.

As for the cracking issue that Vortec heads are sometimes known for, it’s caused by negligent drivers overheating the engine. Even tho I got the set of used heads in the trade, I chose to buy new GMPP heads so that I didn’t have to worry about their past history and got all new parts in them as well. I monitor my engine temps very closely when I’m driving the car to make sure I never overheat and possibly crack these heads.

Alright guys, so an update on the original reason for this post.
I’m doing this for closure and resolution to the problem, as well as to hopefully help out anyone else that may come across this problem.

So after pulling the carb off and getting it on the bench, this is what it looked like. You can clearly see my hastily done JB Weld job to get it temporarily sealed up.



The earlier plug pics I posted were NOT of my carb, they were taken from a friend’s. I honestly could not remember what the plug looked like before I covered it over, but as it turns out it’s an all aluminum plug, no plastic anywhere in it.
This is what it looked like after I got the JB Weld off:



I chucked it up in the vise upside down, and started by drilling a pilot hole in the center of the plug. By drilling it upside down, it kept most of the chips and swarf out of the inside.





My initial thoughts were that it would probably accept an 1/8” pipe plug, but after opening up the hole to the required size for the tap and grinding off the outer flange, I found that an 1/8” plug wasn’t going to be big enough to replace the existing plug.

Here you can see how much larger the existing plug is than my “1/8” plug tap hole” by the slight difference in colour of the materials:



Since I had the hole sized for the 1/8” tap already, I started tapping it anyways hoping it would dislodge the plug from the body.



And that’s exactly what it did. Perfect.



With the old plug finally outta there, I compared the size of the hole to the 1/4” plug I had. It was slightly larger than the recommended pipe tap hole size, but smaller than the 1/4” plug so I knew it would work.
After carefully tapping the hole upside down again and test fitting the plug several times, I got it to just the right depth. A little Loctite 567 on the threads, and I ran it in and snugged it down.



If you’re doing this yourself, resist the temptation to crank down on the plug. There’s not a lot of casting material around the outsides of the hole, and it wouldn’t take much to crack the housing. Just a little more than snug with some good thread sealant is all it’ll need.

Also be aware of the depth that you tap the hole to. On a pipe plug tap, the more you turn it, the deeper the plug will sit in the hole. Most of the time this usually isn’t an issue, but in this case I didn’t want to go too deep and have the bottom of the plug interfere with the spring or filter.
Looking inside the bore, you can see the bottom of the plug is going to be nowhere near either one (yes it’s in there!):



After thoroughly flushing the bore with carb cleaner and compressed air, I reassembled everything, and now it’s back on the car.



I’ll give it a day or so for the sealant to set up before I expose it to fuel, but I don’t anticipate any problems. I’ll report back if I do.

This should totally do the trick, my thanks to everybody that commented, made suggestions and helped out. I’m extremely grateful.

D.

I fired it up tonight and ran it for a fair bit.
No leaks whatsoever, everything is nice and tight and dry.
Looks like the repair was successful!