The Stovebolt Site Forums The Shop Area Engine Shop Exhaust manifold stuck flap

I forget what that flap it the manifold is called but mine for the 235 I'm putting in is stuck, I've tried wd40, transmission fluid mixed with accitone and a three pound hammer and didn't move even a little bit. It's stuck open so should I just leave it or find another manifold or someone got another idea?

It's called a heat riser valve, and it's important for keeping the fuel vapor from condensing back into liquid gasoline on a cold start. The engine will run lousy when it's cold if exhaust gas isn't directed up against the bottom of the intake manifold during warmup. Try tapping the shaft back and forth (not rotating it) with a medium-sized hammer until the rust breaks loose. Heat is also your friend- - - -either work with the shaft while the manifold is hot from running the engine, or use a torch to heat the area around the shaft before working with it. I like KROIL- - - -been using it for 40 years, and I haven't found a better penetrating oil yet.

www.kanolabs.com

Jerry

Ok jerry thanks

Ian, it will come loose. May take a couple of weeks of daily PB. Blaster, Kroil or some other concoction and hammer tapping to get it to finally free up. After you get it free remember to give it some love every so often to keep it moving.🛠

The shaft gets choked up with cooked on carbon which is a very hard, durable and almost impervious to solvents. Since it is created by heat, it won't melt by adding heat.
Having said that, the combination of everything which HRL just suggested will eventually break it free. Don't be in a hurry. You will just make it angry.
Kroil is absolutely amazing. It is the Chuck Norris of the penetrating fluid world. I used to think the same thing about PB blaster. It is like spitting on rusty parts when you can't make any spit compared to Kroil.
The cooked on material is hard and therefore brittle, so firm blows with a medium sized hammer, striking each end of the shaft back and forth will improve the penetration of the Kroil.
Carl

Ian, just adding to the already given great advice. Since the carbon builds up on the inside, I find that it helps on really stubborn ones to split the manifolds so that you can get at the flapper from the inside. Use a small screwdriver to scrape away all of the carbon deposits around the shaft. Get down to bare metal. Then apply the Kroil to both the inside and the outside where the shaft goes through the manifold and do the tapping.

As stated, persistence and patience pays off. Spray and tap a few times a day. I have had them take over a week to break loose, but they always do.

And as Martin stated, give both sides a generous shot of penetrating oil and wiggle the flapper as part of your regular future maintenance.

Good luck,

Matt

Ian,

I found that was a chronic problem in the exhaust manifold of my'36 Chevy pickup when I restored it in the early 1970s and others I spoke with were having the same issue. The hammering and penetrating oil did solve the problem temporarily but it kept happening again.

If you decide to split the manifolds as Matt suggests it's only a little more work to make a permanent fix. If you put stainless steel bushings in the manifold and make a heat riser shaft from stainless steel you won't ever have to deal with this again. I did that on my '36 PU about 35 years ago and the heat riser valve still functions perfectly without any "persuasion".

I don't know how cold it gets in Tennessee but on cold mornings a functional heat riser valve does help.

I got it broke loose today doing what y'all said, thanks!