Bob, inspired by your breakthrough, I did a little research and found that stainless steel tubing is available mail order in a pretty wide range of wall thicknesses, ODs and IDs. Your idea and Harry'* information about GM'* revision got me to thinking that while any air gap is good, a little more might be better. GM apparently just went from a 3/4" pipe to a 5/8" pipe and called it good. When they did that, they produced a .063 air gap between the pipe and the plastic.

I was also thinking about deposition of carbon over the long haul. The inside of my plenum was pretty evenly coated, from the back of the throttle body, all around the runners and even the EGR pipe with a pretty good layer of the black stuff around the top of the tube and down into its I.D. I don't remember if the carbon extended down around the outside of the pipe into the .015 gap I observed between the pipe and the plastic. And, what I thought was hard carbon on the plastic might have just been deteriorated plastic. (I wish I had taken a picture.) Because I bought the car at 127K mi, I don't know if my engine had a problem or if this buildup is "normal." If this is a common thing, and it extends to the gap you are trying to create, a little bigger gap might be better.

I know this complicates your elegant idea, but what do you think about using a piece of 5/8" (.625" O.D., .035 wall) tubing for the new EGR pipe? I was thinking that a short (1/4" high) ring of 3/4" O.D., heavier wall (.065" wall, .620 I.D.) could be heated up with a propane torch to expand its I.D. and the 5/8" pipe slipped in for a shrink fit to produce a really cheap shoulder to fit in the LIM. I don't know if this would work, just thinkin' out loud. But, if it did, and you use the 7/8" .035 wall sleeve as you planned, you would end up with a gap of .090" around the pipe. This is probably more gap than we need, but it would still provide as much EG flow as GM does in their revised pipe. If 13/16" .035 wall were available for the sleeve, we would only have to ream the plastic out to .810, and, with an I.D. of .743, we would still have a .059 gap. But, I have not yet been able to find any tubing with an O.D. around 13/16".

I don't know if the shrinking process would expand the O.D. of the ring so that it would not easily fit in the LIM, or what other extra work this would make, but the numbers are really close and it should not add significantly to the cost of the method as the 5/8" .035, 3/4" .062, and 7/8" .035 are all shelf items. The stuff I was looking at would have to be purchased in 3-foot lengths making the initial investment about $50 with shipping, but this inventory would produce 24 sets of pipes, rings, and sleeves, with a lot of ring and sleeve material left over. $2 per set, and everything in stainless!

Just something else to think about.

Bill: My machine shop guy doesn't have the proper reamers, so I'm off to Harbor Frieght this morning to buy a set ($70). I'm sure these are your basic el cheapo Communist China tools, but we're only reaming plastic here, so no biggie.

However, it occured to me that if the reamers are fairly decent, I can ream the ID of the 7/8" tubing our for a little more air grap. If not, I'm going to go with the idea as I proposed. My current UIM is not leaking, and I'm using the (Delphi) manifold Vital sent to me as the test mule, so, if it doesn't work on what is my daily driver, I can restore it to original.

As soon as I get this done, I'll select an upcoming not-too-busy weekend and install the kit in my own '99 SLE, which will be our test mule.

As I said, if it works, I'll provide the parts (which are dirt cheap) to those on the board who wish to do their own repair, or, if they can't find the proper reamers, I can repair the manifolds of those who care to ship them to me.

I'm not overyly concerned about the small air gap. As '57 remarked, and break in the thermal conductivity will be beneficial, and as he posted in the 2000+ forum, The General finally seems to have caught on.

Interesting that the Ken-Co part appears to be carbon steel. I just naturally thought of stainless because exhaust gases won't corrode it under any circumstances.

Also, so many people here have had LIM gasket failure it occurs to me I prolly ought to replace them while thrashing on the UIM. Can some posters please put up what brand gaskets they've used and the results?

Also, I've seen some posts on gaskets bought on e-Rape, but haven't been able to find them. What keywords did you guys use?

You're probably right, Bob. I tend to overanalyze sometimes. And your gap should be .028, not .025 like I first mis-stated. The important thing is that you will have a sleeve to protect the plastic. I would take a .028 air gap with the sleeve any day over the General'* .063 radiating to plastic.

[edit: I used Felpro upper and lowers when I did mine.]

Bob, could you take some pix as you are doin' the work for the benefit of the many who will be following your path?

Again, great work - and let us know how it turns out.

Bob, before you start reaming, you might want to buy a new Upper gasket set and take some measurements around the hole that seals the EGR pipe passage. Just to make sure you will still have an OK seal.

Bob...

I used Felpro for the upper and lowers.

I also used Felpro sets for upper and lower. This is a fantastic thread. Buttermore, I may pay you a visit when I get back to Ames from Muscatine next Monday... this is GREAT stuff!

Don’t forget the GM # 89017554 upper intake gasket set is new and improved. The gasket material around the two coolant ports that leak have been changed. The new material is black and works like an o-ring not exposing the hard plastic to coolant. Now if GM will do the same thing to the coolant passages on the lower intake gaskets things would be Jake.
This gasket set comes with the new improved gray throttle body gasket that is supposed to prevent flange warping. There is also a new PVC tube in the kit.

Wonder whose gasket Dorman uses with their replacement upper intake?

The inside diameter of the EGR pipe hole in this new gasket kit is .775”.

OK, Upper is at the machinist'* (couldn't find a set of reamers) and will be back tomorrow.

After getting that ugly, greasy mess out of the parts washer I did a little measuring with the Mark I eyeball and a precision-engineered paper clip probe and I'll be surprised if the .879 bore-out hits coolant. There appears to be sufficient material not to.

As soon as it returns, I will cut off the 7/8" stainless tubing sleeve to the correct length and epoxy it in. I will then cut of the 3/4" stainless tubing to the length recommended by Bill, buy some gaskets, and get set for a weekend thrash.

Bill, BTW, no worries on the sealing for the UIM gasket for the sleeve. Using my dial calipers, it appears the diameter of the o-ring seal in the gasket is about .980.

Excellent! Let us know how it turns out - and don't forget the pix!

All: I have a digital camera and will chronicle the event-when it happens. This is my daily driver and I need to schedule a three-day weekend just to make sure.

But pix of the installation?

sure.