Having an EXHAUSTing day?
Most of you who know me personally and others who know me through this column have figured out the theme for most of these articles. Problems a Club member has experienced and problems that show up in my shop make good column material.
It seems as though exhaust problems have popped up a lot lately. For the most part, about the only way to repair an exhaust system is to replace it.
On the old flatheads, you basically have six pieces that consist of three sections of porcelain that make up the exhaust manifold, the exhaust pipe, the muffler and the tailpipe. In addition, you have various hangers and clamps.
Starting with the porcelain (unless it leaks or you want to get them refinished), chances are that you will leave them be. However, if for any reason you take them off, be sure you use new gaskets and new bolts when reinstalling them. I also strongly recommend that you clean the threads in the porcelain. If the threads donít come out bright, they should be helicoiled. If the porcelain is bad and you send them off to be refinished, you should definitely helicoil the bases using Loc-Tite and let them cure before reassembling.
Of course, if you are doing a full restoration, you will usually do a complete refinish of all the manifolds. When you imagine how many hot and cold extremes these threads have experienced in the last 50 to 60 years, you wonít hesitate to rethread, helicoil and use new bolts. That should take care of the easy part of the job.
As for the lower three sections, you usually canít replace one without doing all three. Most of the time you have to cut them apart anyhow, and old exhaust parts donít have a lot of market value. Anyhow, it is generally quite a bit less expensive to buy the complete set of three. One problem you will run into is that the modern bending machines being used by most suppliers donít get exactly the same shape as the original factory that were stamped with smoother bends. As a result, you will probably have trouble installing and aligning the system.
Letís start with the exhaust pipe. We have talked before about the importance of the insulation on this piece. Since you canít get the original asbestos, you will need to use the replacement material available from McVeyís and others. Follow the written instructions for forming, cutting and fitting. Then with the masking tape still holding the material in place, mount the pipe in a vise and using your propane torch, heat the inside of the pipe to start the curing process. When the material is about dry but still has a little moisture in it, remove the masking tape and handform the material without squeezing out the remaining moisture.
At this point, I will take time out to share one of my secrets with you. Go to a local furnace repair or environmental contractor and pick up a roll of the material they use to cover and seal asbestos-covered pipes. If you canít find that, you can go to a medical supply house and get some rolls of plaster binding that doctors use to make arm and leg casts. The 2-inch width is the easiest to work with and will make the neatest application.
Getting back to the pipe in the vise, while the other material is still moist, wrap the binding around it and spray lightly with water. Smooth it down and mold it with your hands. As soon as it starts to set, use your propane torch and again heat the inside of the pipe until you start getting steam along the whole length of the insulation. Let the whole thing set and cure for a couple of days (at least). I hope you remembered to put the flange on the pipe first or you will have to take it all apart and start over. Also you want to make sure you have about 3/4-inch clearance between the flange and the top of your insulation. Failure to do so, will surely cause a few swear words when you go to bolt the pipe onto the porcelain manifold.
After the insulation has cured a few days, mask the pipe and flange. Using very-high-temperature semi-gloss enamel from a spray can, put about four or five medium coats on top of the plaster. Let this dry overnight. The main reason for the paint is to keep the assembly from showing every little bit of dirt like the untreated insulation will. It will also add a lot of longevity. You can now put on the original-looking straps that came with the kit.
I mentioned earlier about replacement pipe bends not being perfect. Now Iíll tell you the cure. On the exhaust pipe, cut it about 4 inches in front of the second bend from the muffler end then use a pipe-to-pipe splice and a couple of 2 1/4-inch clamps. After you have attached the flange to the manifold a little snug and the clamps the same, you can rotate and adjust to get a perfect fit.
Then hook up the muffler and adjust to align with the holes in the frame. Donít tighten up yet. If you cut and splice the tail pipe ahead of the axle hump, you can adjust to get the best fit making sure you clear the axle and shock absorbers. Put up the rear hanger but donít tighten. Because of the splices, you may need to cut off an inch or so from the front of the tailpipe.
Once you have the best alignment all the way, start tightening up the clamps and hangers after tightening the four bolts holding the flange to the manifold. Make sure you system is centered through the frame holes. Also make sure they stay that way as you tighten up all the way back. Before you tighten the rear section, mark the end of the pipe and cut a downward angle on the tip. This will direct the exhaust downward and you wonít get that ugly smudge on the bumper and trunk you see so many times.
One last tip: use all-new bolts, washers, clamps and hangers. This wonít cost you more than 20 bucks and will prove well worth the investment.
I donít know about you, but after all this, I am exhausted.
See ya next month,