The Stovebolt Site Forums The Shop Area Engine Shop 216 exhaust riser repair

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 bushing

heat riser shaft installed

heat riser assembled

Great job! Just got to think outside the box. Great blueprint for the next stovebolter with this problem. Pictures say it all. Should think about making it a Tech Tip.

I have to put my riser back together on my manifold and heard people use brass bushings. Did the manifolds come with any bushings from the factory? My manifold does not look like it has any bushing and the shaft was frozen solid to the manifold. I was able to get the shaft out and got a new one and it seems like a nice fit but do I need to drill and use bushings or do I leave it as is? Don’t want to make more work but don’t want it to get stuck a year down the road...

No bushing from factory. If the shaft is not loose, or the holes in the manifold not worn out, clean it up and put it back together without suing bushings.

Ok that’s what I thought. Is there any info on where the flap should be relative to the weight and at what temperature? I took some pictures before I cut it apart but is there some scientific approach?

I’ve read that but think I need more info than that. I have to drill the hole for the weight in relation to the slot where the spring goes then tack the flapper back to the shaft. So unless there’s no technical drawing I’ll just refer to my pictures and try to get it close.

On cold engine, the weight should be near horizontal at the top with rounded side up. As the engine warms, the weight rotates downward in toward the engine. When all said and done, the spring should need just shy of 1/2 turn to hook on the pin. There is a photo on the forum if you search.

Great work! One small suggestion- - - -since the way to break the bond of Loctite on a part is to heat it to 500+ degrees, using it on an exhaust manifold accomplishes nothing. Normal running temp there would be 1000 degrees or more under load. The tapered pipe thread will be sufficient to hold the bushing in place without locking compound if it's tightened sufficiently. I've fabricated heat riser parts from stainless steel at times which assures a long lifespan in a very hostile environment.
Jerry

Thank you for the info.