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I recently replaced the manifold gaskets on my '56 235 and am currently trying to start the engine. It runs very rough and backfires through the carb. It also has an exhaust leak. I will be going through the usual timing checks to see if that's the problem with the rough running condition but I was wondering if maybe I did something wrong when I installed the manifolds. I don't believe the exhaust leak is coming from the pipe-to-manifold connection. That is on straight and torqued down good and tight. I had trouble getting the gaskets on and lined up and it was slightly misaligned at one spot so that it was very tough to get the bolt to go through the hole in the gasket. I'm wondering if maybe I don't have both an exhaust AND an intake leak at the manifolds. I found it to be a big pain in the neck getting the gaskets on and lined up. I used a tiny amount of Permatex and hung them on the alignment studs where possible. What technique is generally used here and has anyone else experienced this problem? By the way, the exhaust leak sounds like it's coming from somewhere near the exhaust pipe but a little further back, like around cylinders 4 and 5.

Did you install the alignment rings between the intake manifold runners and the cylinder head? If they were not installed, it's very possible the gasket slipped during installation and you've got a major vacuum leak. Try putting a stream of gas from a Propane torch (not lit) around the intake-to-head area and see if the engine smooths out or increases speed. Some folks use starting fluid or carburetor cleaner for this check, but Propane or Acetyline is a lot less messy.
Jerry

Yes, the rings are installed.

was it running good before you put the new gaskets on or is this a new issue after installing them? If this is not a new issue then you could try many things. Valve adjustment, fuel issue, timing.

One other thing to look at is the gasket at the heat riser.

...pic...

My 235 had an exhaust leak; you can see evidence of the leaks in this pic.
...pic...
I had to take the manifold to a machinist for a little mill work. You can inspect yours with a straight edge.

With the manifold split you can torque in sequence between heat riser and manifold.
Good Luck

The gasket for the heat riser came with the kit and that is installed. Was the leak in your picture at the two middle exhaust ports? Gaskets look slightly blackened there.

Good Eye
yes thats where my leak was.

Sometimes the rings can hang up and the manifold doesn't make a good contact. If there appears to be a space between the intake manifold ends and the head then that is probably what happened. I find it necessary to loosen the for bolts holding the two manifolds together untill the manifold is snugged up to the head. I keep the gaskets in place by using the rings in the head and inserting two of the smaller bolts in the two holes near each end of the head. The gaskets stay in place and the bolts are replaced after it is stable.

It would be nice if that's the cause. I'd like to be able to repair it without doing major disassembly, if possible.
I assumed that torquing the bolts down would overcome any friction with the guide rings and snug everything up tight. I have it snugged up pretty good and still have a leak somewhere.
I guess I should mention that my tail pipe is missing. Everything from the muffler back is gone. But I doubt that's related. The sound definitely seems like it's coming from the manifold area.

I recently learned a painful lesson on installing the manifolds on my newly rebuilt GMC 228. While the construction is a little different than that of the Chevy they are basically the same. After installing and torquing them I had an exhaust leak at the number 1 cylinder so I tightened a little bit more and the leak got worse, so I took everything back apart and found I had cracked the exhaust manifold at the outter ear. I had used alignment rings on the intake, but one was not seated properly and found it was bent when I disassembled the manifolds. So I took the exhaust manifold to the machine shop to see if it could be repaired - it could not. He asked if I had separated the intake from the exhaust before installing them. I had not. He told me that was most likely the problem as with the two bolted together it is very difficult to to get them to line up and install properly. He said that the two should be loosely assembled together, installed on the block and then the bolts tightened up.

It might be a pain to disassemble and reinstall but worth the effort if it keeps you from cracking the manifold and dealing with that problem. The cast iron manifolds can be broken easily as Huck has written. Proceed carefully.

Huck, I did exactly what your guy said not to do. I had the two bolted tightly together and then tried to fasten them to the block. I, too, am using the rings I checked them out carefully before installing them and they looked fine. There was a lot of varnish in this engine so maybe they aren't seated all the way in.
Could I possibly redo this without taking everything apart again? I was thinking I could undo the bolts holding the intake to the exhaust (or at least loosen them) and then fasten both to the block. Then tighten the two together. I guess at this point, I'd have nothing to lose. If it didn't work, I could just take everything apart.
I did notice that there is a lot of play in the heat riser shaft. The weight looks blackened, too, like it's been getting blown by exhaust. Could sloppy bushings cause this kind of a leak? I see smoke in that area but can't pin it down.

Right. You don't have anything to lose. However it sounds like you may have to replace/install bushings in the exhaust manifold for the exhaust thermostat shaft which means you will have to take the manifold off anyway.

Do you happen to know how much play is allowed in those bushings? I've got one on my 49 Plymouth and if my memory serves me, they aren't all that tight.

I checked the Chevy Shop Manual and it really doesn't say much at all about the manifold heat control valve. The GMC Maintenance Manual goes into a lot of detail on replacing it and discusses new bushings and reaming them to proper size. I can wiggle the shaft on my GMC so there is definitely some play, but I am not noticing any exhaust leak from it and I think that is the key.

Thanks, Huck. I checked the Chevy shop manual, too, and there isn't much at all. I did some calling around to the usual vendors and haven't found anyone who sells a repair kit like they do with vintage Mopars. But I did find 1/4" bushings at my local Lowe's, along with 1/4" round stock. So I'm thinking of making my own. My only question at this point is there are bronze bushings and steel bushings. Since expansion will be a factor, which should I use? The round stock is, of course, steel. Which material would not give me any trouble with binding?
If this works, I'll post pictures. If it doesn't, I'll swear and throw everything across the lawn.

I don't know what size the shaft on the Chevy is but on the GMC the manual talks about reaming the bushing to .3135 to .3160 inches in diameter. The shaft passes through the valve (flapper) and is welded to it, so the shaft may need to be larger than a 1/4 inch in order to fit properly. I had to free up the shaft on the replacement manifold I got and re-weld the valve to the shaft. It might be easier when its all said and done to get another manifold or the shaft from one. There are a lot of people who are up-grading to Fenton headers and probably have one sitting around.

I believe I found my leak. Check this out:

[IMG]http://i7.photobucket.com/albums/y261/bohon/56%20Chevy%20truck/ExhaustLeak001.jpg[/IMG]

It looks like I never had it squared up to the block to begin with. I have to think that was because I had the two manifolds bolted together and was trying to fasten them to the block as one assembly. I put a straight edge along the mating surfaces of the exhaust manifold and it is not warped. I still want to replace the bushings for the heat riser shaft but just saw that the flapper is welded to the shaft like Huck says.

Well it looks like I'm in the market for a replacement exhaust manifold. I was just checking out the heat riser on mine and I found a massive crack. I don't know how I missed it before. My first thought was, I hope I didn't do it. It looks like it's been there for a while, though. Any pointers on what years are compatible with a 1956 235? I might be prowling the boneyards this weekend.

Just got back from the salvage yard where I scored a manifold for my truck. It's got some pretty heavy rust on the bolts. I'm going to have to give it some PB Blaster for a few days before I can separate it from the intake. The heat riser valve is frozen in position, too, but I hope I can free that up as well.

So after freeing up the heat riser valve, I realized that this manifold I just got from the salvage yard might be warped. When I put a straight edge on it, one port stands away from the straight edge by 1/16 of an inch. Can anyone tell me if it's possible to have that much machined off the other three mounting surfaces? The port in question is the one that mounts at the front of the engine.
Thanks for any advice you can give.

On the 216 I rebuilt, the engine would not idle. Leak at the intake ports was the problem. My fix was an extra set of gaskets. Ultra Copper sealer on intake surface and between the two gaskets. {intake ports only} Great idle at 450/500.
Good luck and follow the torque specs.

I have machined considerably more than 1/16" off manifolds to straighten up warp problems. The shop where I worked had a BIG belt sander that would work on cylinder heads, manifolds, etc, and we used it pretty often. Try disassembling the intake/exhaust assembly and have each one milled flat, then leave the joint between them slightly loose while you're installing them. That should solve the misalignment problem.
Jerry

Thanks very much, Jerry. That's a load off my mind.

When I had mine done the machinist looked at me with a "what a noob" smile then had me join the intake and exhaust together so they would be milled evenly. After he explained why I smiled right back with a "yep I am".

I'm not exactly a noob but I'm always running into things I've never seen or done before, like this. I'm always learning something new. But I have to admit also that my capacity for bone-headed screw-ups amazes even me. Who's the forum member that says,"If it ain't broke, fix it until it is?"

If you have the intake manifold milled, be mindful that the alignment rings might need to be made "shorter" (otherwise, they might hold the manifolds out from the head, resulting in leaks).

A straight milled edge should allow modern manifold gaskets to seal the joint area. However, Cuthbert's suggestion/observation of using two sets of gaskets is a reasonable option, if the leak is small (1/16" might be too large a gap?). The original manifold gaskets were thicker than the modern gaskets (I had a NORS set for comparison). I have used exactly what Cuthbert describes and it was a satisfactory long-term solution.

I see a lot of manifolds where the intake and exhaust flanges are not straight across. I have also doubled up the gaskets on the low flanges with good success.

I think that is what the machinist was trying to teach me. I'm sure his reasoning was as long as he was doing everything else it just made sense to true up both (while assembled) to eliminate the hassle of 'making it fit' and being as I was/am a noob messing that up and then burning a valve or something.
I believe he milled it as opposed to using the belt sander, I don't know for sure as I wasn't present for any of that.

I don't know if this is of major or minor import but thought I'd add in my experience for what it's worth... I believe about .02 cents or so.

My methods and techniques have been reliable over six decades being a gear-head. Have followed Motor Manuals suggestion of selecting suitable tool. Often, that straight edge proves positive. The trio intake ports may not be absolute. The detent grove in the head / intake port for the ring does come into play when torqued to specs. A milled surface may create problems. Any leak at the intake ports will change the air/fuel ratio to lean and the desired idle will suffer. I like your " satisfactory long-term solution". Leaks suck !

So it might not be a good idea to mill the intake as well?

The guy who did mine had me mount them both up to the block and tighten them up then pull them back off as one unit. I didn't question him as I figured anyone who once ran 30,000 rebuilds a year through his shop knew wtf he was talking about. (He had one of six shops on the west coast that ran numbers like that but its now just him and his son... I guess times have changed ) If the alignment rings are a a factor then take them in with the manifold and have them dressed up as well.

I went to the machine shop today and I was told that to take 1/16 inch off three of the four mounting surfaces to make it flat would take hours and likely cost me way more than a new manifold. The guy said that is so much material to remove that it would take hours because they'd have to keep waiting for it to cool. I'm just curious to know what those of you with shop experience have to say about this.
What he recommended was that I use what he called orange RTV, which he swore by. He is sure that will take care of the difference. I have to say I was surprised. I looked up orange RTV and it seems it is Permatex Ultra Copper. I'm going to give it a try over the holiday and see what happens. I read the technical data sheet for it and it is supposed to be used for this application, so I'm hopeful it will work.

If you are going to make a try with what you have, use the Ultra Copper on two sets of gaskets (both sides of the gaskets and inside the "sandwich").

Let us know how this works out for you.

Good luck.

Have you considered the Remflex gasket?
It's also available from Larrowe and Son. link
I have one but haven't used it yet.

regards,
Leon

Labor cost at the machine shop X number of 'big' bucks. Cost of the Ultra Copper "on what you have" less that $10.00.The Ultra C worked well, had good results and smooth idle. Good luck with your effort.

That's exactly what the machinist told me. Haven't had a chance to install everything yet but will post when I do.

While not a professional machinst, I've managed several shops over the years. I can't imagine taking 1/16" would take that long. Nor can I imagine it causing that much heat, especially if they use this stuff called coolant. I'd guess an hour tops for getting it setup and about 10-15 minutes to make one pass, and it might take 2-3 passes. Should be cool to the touch the whole time with coolant running. Even without it, it should be touchable when done.

Based on things I've read and heard elsewhere, his response surprised me. I'm not a pro, though. Most of what I'd heard was that it's not that big a deal to take 1/16 off, like you say. In any case, if I can make it work without paying for a machinist, I'll be happy.

Yesterday I installed the manifolds with the gasket and Ultra Copper and there are no leaks. I was almost afraid to turn the key because I didn't want to tear it down again. But the stuff works, even with an exhaust manifold that is warped 1/16 of an inch out. Idles fine and accelerates well. Thanks for all the advice.

Joe