So, I finally decided I needed to spend some quality time on my '52 since I completed the restoration several years back. I knew my first attempt (during restoration) of the exhaust heat riser failed miserable. During restoration, I had discovered that that the riser flap shaft was a very loose fit in the exhaust manifold with worn holes. But, the shaft was in good shape. So, I bored out the holes and pressed in (more like hammered in door hinge bushings) door hinge bushings. I then reamed out the bushings to fit the shaft. Took no time at all for the bushings to back themselves out and cause a large exhaust leak. Lived with it that way for several years.
Fast forward to this past weekend: I pulled the exhaust and intake manifold in anticipation of repairing the heat riser. Well, it turns out that the exhaust manifold was leaking at two exhaust ports, heat riser shaft, and junction between intake and exhaust manifolds...no wonder it was noisy under load! Anyway, my repair this time around utilized 1/4"-18NPT brass plugs. The plugs were hollow (from Home Depot, see photo). I drilled and tapped the exhaust manifold to receive the pipe plugs, installed the plugs with Loc-tight, then cut off the square boss from the plug exposing the hollow section. Finally, I bored/reamed the plug to fit the shaft. The hollow portion of the plug added in effort to get the hole size correct. If I had used solid plugs, I would have had to center punch, and hope I got it right... The shaft is now a very precise fit and I hope not too tight. It moves freely at room temperature, but hopefully material expansion rates, when hot, won't lock the shaft in place.
Here are some photos. Thanks for looking and I hope this helps someone needing to fix their heat riser...
heat riser bushingheat riser shaft installedheat riser assembled
