The Stovebolt Site Forums The Shop Area Engine Shop Exhaust leak on heat riser valve shaft

Hello fellow Stovebolters,
I have a 47 gmc 216.
I have a exhaust leak where the heat riser valve shaft comes thru on the weighted side of the shaft. It's a large enough leak to hear, and feel. I've done some interweb searching for a replacement shaft and bushings, coming up short. I see them for the jeep and mopar stuff, anyone know of an in line 6 chevy/ gmc source for these parts? Thanks Al

Hello Al,
First of all, you can't "seal" a rotating shaft running thru a hot manifold without extreme measures. It will always be under pressure and will always leak some. You can make the "fit" tighter somewhat. If you think it is worth the effort, you take off the manifold to the bench and search websites like McMaster-Carr to find a bushing to use or modify. Then try to redrill/line drill the manifold casting so as to press in the new bushing(s)...provided riser shaft is not worn in to several diameters..... and provided you don't run into broken block studs/bolts and etc.

Or you can buy a good used manifold with tight heat riser, no cracks and no broken ears....

Or you can forget about it and work on something else.

Click

The flapper valve is welded to the shaft, so it needs cut off and rewelded to install bushings or a newer shaft. Not sure what material grade the shaft is, but you might be able to just make one or find a replacement from a new manifold and make it fit.

Joe if you mean the inside butterfly, how did they assemble it?

I have replaced the shaft and flapper with stainless steel parts running in brass bushings. I make the bushings from 1/8" NPT pipe nipples, threaded into the manifold and line-reamed so the shaft runs true. Lots of work, and fairly expensive, but that fix lasts about 3 days past forever.
Jerry

Thanks for the input folks, I'm gonna enjoy the truck for now, I'll tackle it this winter, along with some other items...

Yes the inside butterfly valve, sorry for not being clearer. The 230/250 manifolds use a solid shaft, I had to replace the butterfly on mine, looked like it was brassed or silver soldered to the shaft. I used a better flap out of a broken manifold to repair mine.

Mine was rotted off on one end and egged on the other. I happen to have an old stainless steel bbq grill grate slightly larger diameter to rob from. Cut a piece a little longer than original. Drilled the manifold to the correct size, slotted the one end of the rod for the spring. Ran the same bit through the flap as it needed just a little bigger hole. Mine was originally drilled and riveted so I did the same(as you install). The counter weight was enough oversized without drilling but its installation in relation to the flap is important so make note before tearing the original one apart. The weight should pull it to a fully open position and the spring will tighten and pull it up closing it when it is cold.Drill shaft for the counter weight and use a roll pin or cotter pin. With the extra length I mentioned, I made the slot for the spring deeper, so it does not fall off. Bench test it using the propane torch on the spring to make sure it opens correctly.

Hi Jerry, just wanted to let you know that I'm giving your procedure a try, got the manifold off, lots of slop where the shaft goes thru the exhaust manifold. Have some 1/8 " npt nipples coming, just gotta to find a stainless rod, and will get to work. When you threaded the nipples into each side did you apply anything for a sealant to the threads to promote a good seal? 2ndly, when you line drilled thru the bushings (once they were in place) did you just use a long drill bit the same size as your stainless rod stock? How did you get an acceptable alignment?
A jig of some sort, or freehand? Thanks for the advice Jerry!

The pipe thread in the manifold and the brass fittings work without any kind of sealer, particularly since the exhaust gas it's exposed to is far too hot for any kind of locker to work- - - -even red LocTite. Just screw them in firmly. I set the manifold up in a drill press, and line-drill both fittings a few thousandths undersize, then finish-cut with a chucking reamer about .005" bigger than the pivot shaft. Too tight, and the shaft will seize up- - - - -especially after some carbon builds up there.
Jerry