Making A Metal Primary
Block-Off Plate
Steel is a bit more difficult to cut, but if you are going to make frequent header repairs, it's more durable than a plywood header block-off plate. We decided to make one of those as well, from a used piece of 3-gauge mild steel large enough to cover the primary flange. It was cut down to size by Steve DuSold using a cut-off wheel, since the heavy-gauge metal is 0.2391-inches thick.
The bolt holes were drilled using the same method described for the collector block-off plate bolt holes. Then the back-side of the block-off plate was deburred for safety sake using a grinding wheel. The plate was degreased and a light coating of black primer was applied.
A new Mr. Gasket D-port header gasket (PN 720-550G, retail $10.95 per pair) was placed on the header block-off plate and the plate was retained with 1-inch long bolts and used for the driver's side header repair. This was not because the plywood wouldn't work, but rather to simply test another method and to make sure the 3-gauge steel would seal properly, so we could recommend it.
Steve Dusold On Ceramic Coating
"Many headers are ceramic-coated, but the specific formulation of it determines the exterior color, finish, and ability to retain heat within the header. In most cases, a ceramic-coated header can be repaired with additional heat and elevated air pressure. Although no coating is rated to over 5,000 degrees, it is unusual that an aluminized-style coating or an advanced thermal barrier, such as the 'White Lightning' coating offered by Swain Tech Coatings, has any problems with discoloration on the pipes after being heated.
"In rare cases, the thermal barrier offered by the coating dissipates the heat to such a degree that a repair can't be made unless the coating is removed from the damaged area. Through the years, there have only been a few instances where the coating prevented the repair; in each case, it was a header that had been coated both inside and out. Since so much money had already been invested in the header, the customers requested the repair ... which was done by removing the outer coating, doing the repair, and sending the header out to be coated again."
Tools & Supplies
3-Gauge mild steel sheetmetal
Plywood
Measuring tools
Clamps
Drill bit or wood-boring bit
NPT tap
Air-pressure gauge (optional)
Air-compressor fitting
Header gasket or seal
Collector gaskets
3/8-in bolts, lock washers, and
matching nuts
Torch
Standard open- and box-end wrenches
Cutting and grinding tools
High-temp spray paint
To remove any burs or splinters...
To remove any burs or splinters that may affect the seal, Steve ran the plywood over a belt sander. You can hand sand if need be.
Next, the vinyl wall base...
Next, the vinyl wall base "gasket" was sliced in half with a razor blade and positioned on the plywood. It was clamped down, and the point of the wood bit was stuck through each hole and into the vinyl, slowly rotating the drill until it cut out a neat gasket hole for each one.
The homemade plywood block-off...
The homemade plywood block-off plate and vinyl gasket are ready for installation on the header, using six 3/8x11/2-inch bolts with lock washers and nuts.
Conclusion
For those who would rather have their damaged headers repaired, DuSold Enterprises can do it for a reasonable price. According to Steve DuSold, "We've repaired headers with compressed air and heat since I owned a bodyshop back in the mid-'60s in Chicago. We can restore them to cosmetically 'new,' send them out for coating, and have them drop-shipped back to the owner."
For hobbyists who enjoy working on their Pontiacs and have a desire to save money, however, the header repair procedures shown here can be done in an afternoon for under $50 using a MAPP torch and an air compressor. If you don't have access to a torch, MAPP gas torch kits retail for under $70, as do oxygen propylene (propane) torch kits capable of welding.
Depending on the severity of the dent, your header may turn out perfect or end up cosmetically challenged yet functional. In either case, the header will flow properly. If you use the cash saved on repairing versus replacing the headers to have them coated, it will pay dividends in reducing underhood temperatures and improving their appearance.
The plate and gasket were...
The plate and gasket were placed against the header and each of the six bolts were slipped through the plate and fastened with a lock washer and nut using two 9/16-inch wrenches.
C-clamps were used to provide...
C-clamps were used to provide additional clamping force between the plywood plate and header flange so as to reduce the likelihood of any minor gasket leaks. Since we will ultimately be applying between 15 and 50 psi of compressed air, the more we can clamp at key areas, the better our chances are to get a leak-free fit on the first try.
Unfortunately, plywood can't...
Unfortunately, plywood can't be tapped and trusted to hold an air fitting under pressure, so 3-gauge steel was used to make a collector block-off plate. A Mr. Gasket collector gasket was placed onto the spare piece of steel and traced. The metal was cut (you can use a hacksaw or Sawzall) with approximately a 1/2-inch of additional clearance around the circumference of the gasket. The three collector bolt holes were made by drilling an 1/8-inch pilot hole, opening it up to a 1/4-inch hole, and finally to a 3/8-inch hole. Since the bolts' diameter is 3/8-inch, a round-file opened the holes further and provided some wiggle room for the bolt to fit through. Next, two 7/16-inch diameter holes were drilled on the face of the collector block-off plate and tapped with a 1/4-inch NPT (18-thread) tap.