Nice pictures!

Bill is there a red coating of something in your new tube or does it just look that way?

That red coating was on the original I.D. of the 1/2" schedule 80 ss pipe we turned to make the new pipe. We figured the I.D. was just about right, so it required no machining. Don't know what it is.

Gentlemen, our worries are over. I visited the local metal stores again today and also got a piece of 7/8" 304 stainless tubing in addition to my previously garnered 3/4" piece.

Both are .035 wall. That means the .750 piece, which fits into the port in the LIM, has about .050 clearance when a piece of the 7/8" tubing is used to sleeve the UIM.

Therefore, the only maching required is to cut the piece to length, and as Bill has posted, length is not critical, and a little longer may be better.

I will drill the used UIM I have out for the 7/8" (.875) sleeve Saturday. I don't think that I'll hit water when I do so based on some of the posts here, but if I do, of course, the sleeve and epoxy will contain it.

I'll keep all posted, of course. If this works, I'll be happy to provide the pieces for the cost of the materials and shipping, and that'll be a hell of a lot less than $80.

Bill, I've finally realized that the air gap between the two pieces is to cool the sleeve and prevent cooking the UIM. I don't think that'* necessary, as stainless, according to a website, does not transport heat well, but as you're up and running trouble free, I bow to your experience in the matter.

Excellent work, Bob! I too looked for stainless tubing for a cheaper way, but all I could find was really thick stuff for hyudraulic hoses - you got it done! .

And...I'm pretty sure I know why we need the sleeve. As well as repairing an actual burn-through if you have one, the sleeve acts as a heat shield for radiant heat. I realized this when I thought of my parlor stove, a nearly perfect radiating black body that sits about 18" from a nice piece of woodwork. When I used the stove, the wood used to get really hot. I was not worried the woodwork would catch fire, but I was afraid the varnish might be harmed. So I taped a piece of aluminum foil flat against the wood (no air space) to reflect the heat, when I fired the stove. It worked unbelievably well. Even when the stove is really cookin', the woodwork stays cool to the touch. So, I'm thinkin' the sleeve is there to work the same way, i.e., to reflect the heat and keep the plastic cool. There may be some heat conduction, too, but I'll bet radiation is the primary mechanism.

If that is so, that means that it is important to keep the I.D. of the sleeve clean and shiny so that it can do its job and when installing it, don't get any JB weld on the ID, like I did. As an item of maintenance, like when we pull the throttle bodiy to clean it or service other parts, we might take that opportunity to clean any carbon buildup (which would absorb heat) from the I.D. of the sleeve.

Finally, if this is how the sleeve works, I'm not sure it is necessary to extend the sleeve up into the air stream. As long as it can reflect the heat away, flush with the top should work fine. And, that way, the pipe gets the full benefit of the cooling air stream. BTW, you will note that the hole where the pipe comes through into the air stream is not flat. To gain the full benefit of the sleeve, it should at least cover all of the plastic. That would leave a little of the sleeve exposed at the bottom of the curve. I suppose you could JB weld it in, then carefully grind or file the protruding sleeve to be perfectly flush with the top of the hole, if you wanted.

Now I am inspired to pull mine out and re-do the sleeve. For those of you who have a friend in a machine shop, there is a tool called an adjustable ream that we used to clean out the hole in my UIM. We used it by hand, and it worked great.

HeeHee! Way to go Bob! I think we've got this one figured out, boys!

Just a few more words: because I don't know if it is critical, I tried to keep the length of the new pipe exactly the same as the old one (1.420") by having Joe make the piece a little long, then carefully adjusting the length as the last step. If the length is the same as the original, in Bob'* method, there should be no difference in the airflow compared to the original pipe, as they are the same diameter. And as far as the sleeve is concerned, I think the length of the sleeve needs to be whatever is required to completely cover and protect the plastic ID of the hole in your plenum. If you remove your original pipe the way 57Chevythunder did, by slipping a close-fitting deep socket inside the pipe before grabbing it with pliers to keep from squashing it, you should be able to re-use the original part and just add a sleeve to the UIM.

Be sure to keep track of the measurements, Bob. I sure hope it is possible to go out to .875 without cutting into the cooling passage. That would be cleaner.

[edit: I think using the stock 3/4" and 7/8" tubing, the air gap around the center pipe would be about .025 - not as much as my .086, but a whole heckuva lot cheaper and 10x the gap that GM gave us!]

Hey Guys !! -some awesome discussion going on here !! Good job everyone. (-Yup, it'* old '57chevythunder back again,,,) Have been away from the forums for quite a while, but came back again, since I now have a '02 in addition to the '99. I'm just finishing getting the '02 back together, -the EGR mod, and LIM gaskets. -I'll post a topic over on the 2000-newer forum, especially since I made a VERY INTERESTING discovery on the '02, as compared to the '99.

Thinking of your discovery about heat shielding with the parlor stove, let me say that years ago I installed an old wood burning stove in my garage, which, due to "radiated heat" was making the sheetrock wall get really got to touch. I picked up a sheet of galvanized from the local HVAC shop, and attached it to the wall, with about a 1 inch space behind it, and about a 2 inch gap at the floor. I am here to tell you, that no matter how hot I run that stove now, not only does the wall stay cold, THE GALVANIZED METAL IS COLD TOO !! -I never would have believed the effectiveness of "radiant heat shielding." Isn't science way cool !! (yeah I know, poor pun,,)

Just last night I put the micrometer to the parts and pieces, and as I remember, here are my numbers: The stock EGR tube is .750". The stock (virgin/new) UIM hole is essentially the same size, and sorry I don't have that number right handy here at work today. But the stock tube definitely touches the plasitc. Now here is another interesting dimension: The "sleeve" that comes with the Ken-Co kit measures a strong .755" Which explains exactly why I cussed so much when forcing the sleeve into the new plenum. Looking back on it, I wish I would have thought up some way of slightly reaming out the plastic. And yup, the replacement egr tube in the ken-co kit is quite a bit smaller, just like the pictures at the beginning of this thread shows.

To my way of thinking, you guys have got it all figured out excactly right. The air gap is probably the most important part, plus you are breaking the thermal conduction path to the plastic (-don't forget to go over to the 2000-new forum and see my story there,,,,) and I'm sure the radiant heat shielding effect of the sleeve helps a lot too, with the added benefit in conjuction with the epoxy, of sealing off any potential coolant leaking through. As far as the height of the sleeve goes, I really doubt it matters that much. I'll bet that once you have those mods made, it'll never fail again.

C'Ya Later !!

and just to re-affirm - per the part print, there should be a gap along the middle section of the pipe to help with the cooling. i'm fairly convinced (in my own mind, anyway) that this could all be rolled down to a lazy supplier who didn't want to machine a little piece of pipe that could fall within tolerances on the print without having to machine a small amount away from the centers. oh how horrible it would be, if that was the case, and everyone who'* had a failed upper had tolerance stacks to thank... and a supplier who took advantage of that.

of course, that'* pure conjecture on my part, but whatever

The man himself! It'* good to know about that GM revision. It really confirms our suspicions that the airspace is really important. You really had this figured early on, Harry. So, GM went to a .625 OD pipe, a .063 gap and no sleeve. I'm wondering about the relative importance of the sleeve and the air-gap in protecting the plastic.

Bob Dillon is thinkin' about trying a .025 gap with a sleeve. It has to be way better than the stock setup of .0025 or .000, depending on who'* plenum we're measuring.

Harry, I'm curious, did the KenCo sleeve completely cover the plastic in the plenum? Did it stick up a little bit into the airflow? And did the KenCo material look like stainless?

Bill, thanks for the reply. Let'* see if I can answer the questions: I'd say that the Ken-Co part certainly is not stainless. It looks to me maybe like Cad-plated steel. And honestly, from my perspective that should be just fine, -you have to figure that no matter what the egr standpipe is made of, it will be transferring it'* heat into the LIM'* aluminum anyway. And for the material of the sleeve, there again I really don't think it matters. Heck, I even entertained the thought of reaming out the plastic just enough to insert a section of copper tubing. But I do feel that a "ferrous" material makes a better choice, especially when it comes to reflecting radiant heat.

Say, I'll have to bet that Bob'* approach will work just fine and dandy. I mean afterall, don't you have to figure that breaking that thermal conduction path is most of the deal anyhow, and providing any air gap at all is even "bonus points."

No, the Ken-Co sleeve does not extend at all above the edge of the plastic, in fact if anything it seems to me to be just a tad short of flush. I wonder if mybe they do that to help ensure that a person will drive it in at least flush with the bottom of the hole, which of course would be VERY IMPORTANT, so as to not interfere with the gasket below. But, again, my opinion, no sweat about it not sticking up above the plastic. You have to figure that ANY metal lining at all has to be way better than bare plastic !!

What do you think ?? :?:

I think you're right.

I would only be a little concerned about the size of the air gap. I would want it a little bigger than .025, I think. [edit: calculates to .0275, not .025 ]