A method is described for adapting the new reduced diameter stovepipe supplied with Dorman replacement upper intake manifolds for use in 1995-1998 L36 engines. (All decimal values are in inches.)
The reduced diameter stovepipe supplied with new Dorman upper intake manifold replacement kits (part no 615-180) has a .625 shoulder on a .510 pipe that can be directly substituted for the straight .625 pipe in 1999 and newer L36 lower intake manifolds. The use of this new pipe creates a very large (.133) insulating gap between the hot EGR pipe and the new plastic manifold to reduce heat stress on the plastic. The larger stovepipe bore in the lower intake manifold of older L36 engines built between 1995 and 1998 is too big for the new Dorman pipe.
A ring of heavy-wall seamless stainless steel tubing .750 x .620 is pressed onto the .625 shoulder of the Dorman pipe creating a .750 x .510 pipe that can be driven into the lower intake manifold to replace the original .750 stovepipe.
The heavy-wall stainless steel tubing can be purchased in one foot lengths from McMaster Carr in Chicago for about $20 including shipping. http://www.mcmaster.com
Their part no is 89895K759. (Aluminum would probably be better, but I could not find aluminum tubing that would work.) A tubing cutter is used to remove a quarter-inch ring from the tube. The ends are de-burred, and one outside end is chamfered.
To make your own $2 press, you will need to buy a 10mm x fine thread bolt 60mm in length with a nut and a few heavy washers. The washer that bears on the top of the Dorman pipe must be a very close fit to prevent damage to the pipe. I used a heavy 5/16” SAE hardened washer and reamed it out a little with a rat tail file to just slide over the bolt.
Assemble the parts as shown in the image below, sliding on a 3/8” washer, the ring with the red mark down (the other end is chamfered for the pipe), the pipe, the close-fitting washer, a thrust washer, and finally the bolt. A drop of oil between the two top washers and under the nut will make it turn more easily, but do not use any lube between the ring and the pipe. Make sure everything is lined up nice and straight, then using two wrenches, or holding the bolt head in a vise, turn the nut down to press the ring onto the pipe. When the ring is all the way on, undo the nut and remove the pipe. Don’t use much more force than it took to press the ring on as it hits bottom. Too much force may distort the diameters making the pipe difficult to fit or remove from the bolt.
The bottom of the shoulder should be chamfered and the sides lightly dressed to provide a tight, press fit in the lower intake manifold. The outside diameter of the shoulder should be 2 or 3 thousandths larger than .750 for a nice tight fit. You can reassemble the pipe on the bolt without the washers and chuck it in a 3/8” drill to use as a makeshift lathe for this work.
You will need to clean the stovepipe hole in the lower intake manifold of all carbon and oxidation before driving in the new pipe. Find a deep well socket that you can use to apply force to the stainless steel ring to drive the pipe into the hole. Do not drive the aluminum part of the pipe. If you do, the pipe will likely slip through the ring.
Make sure the shoulder is flush or below flush with the deck of the LIM. This will allow you to easily install a metal shield around the pipe to really keep your new plastic upper cool. Go to this link to see how: (Still working on this posting- it will be titled: "Low cost heat shield for L36 stovepipe")
If you do not want to pay $20 for a foot of tubing when you only need a quarter-inch, or if you do not have a cutter that will handle heavy-wall stainless, I will sell you a ring. It will be de-burred, chamfered on the ID for the Dorman pipe and on the OD for driving into the lower intake manifold, with a red mark showing which end is down, for $5 (includes postage and handling) Send me a Private Message at: http://www.bonnevilleclub.com/forum/...de=post&u=2199
if you want one.
Thanks to popatim for providing the Dorman pipe shown above.