The Stovebolt Site Forums The Shop Area Engine Shop 1950 3100 manifold install Kremlin

I recently posted a thread concerning the reinstallation of a 216 manifold with new gaskets. The exhaust manifold gaskets were blown out. Several of you commented with helpful install tips. After removing the fender brace and making more space between the head and the carb and oil filter canister it went on evenly over the 2 guide pins and the rings lined up. Bingo. Success as far as no leaks go. But..........there's more. after I started it.

Upon startup it ran very rough and would not idle. It has never run this rough over the many years I have owned it. It felt like either timing was off or a plug wire was disconnected to me. I may be totally wrong. I don't think the carburetor was at fault. However, now I need to figure out what is causing the problem.

I checked all of the plug wires and connections at the distributor and coil. I'm not aware of changing anything else during the removal and reinstall of the manifolds. I [did not] include the heat deflector that was an (add on) to reduce vapor lock in the summer. I am not referring to the spacer between the intake manifold and the carburetor. I plan to reexamine today and resolve or at least attempt to do so.

I am really curious to see if any of you have some helpful ideas to consider before I as try to diagnose the problem. Thank you for your advice in advance.di

Trying be logical, I'm thinking the rough running must relate to the carburetor. I installed a new correct gasket under and on top of the spacer prior to reinstalling the carburetor. Nothing new as far as wires or electrical go.

So I may be totally wrong in thinking that the rough running is electrical. It stands to reason that it is something that I actually removed or installed. Hence the carb.

A buddy of mine thinks it's a vacuum leak from my descriptions.

I agree, go over what you changed, including the manifold gaskets, and see if you can see an issue. The gasket under the carb has a slot that must line up with a hole on the bottom of the carb in order for it to work correctly.

Stick a vacuum gauge on the windshield wiper tube. Should get <> 18 inches of vacuum. If way low you have a leak.

I was thinking about that top gasket. I really hope that's it.

Pretty sure that is the pipe beside the valve cover that I plugged when I converted to an electric wiper years ago.

Spray WD=40 around the base of the carb and the where the intake manifold attaches to the head. If the engine behavior changes you have a vacuum leak at that location.

Thank you. will try that. Will have to increase the idle to keep it running.

WD 40 is messy. Use the tip of a Propane torch with the gas turned on but not lit. Move it around the intake manifold to head mating surfaces and the base of the carburetor. When the gas finds a vacuum leak, the engine will speed up and/or smooth out.
Jerry

Thank you. That sounds like a good way to check for leaks. I will give it a go. Yes, the WD40 as messy. I checked vacuum hose clamps and fittings. I didn't check at the gaskets between the head and the manifolds. Could be the problem even though it looks good and I don't hear sounds of leakage.

I rechecked the carb gaskets. no problem there. The top gasket has 4 notches so there is no way to put it on wrong. I checked vacuum connections with WD40 but that showed no change. Will use propane gas to check the manifold gaskets for leaks next.

If you find the leak/leaks in/at your manifold gaskets, you might want to try this gasket. It is worth the $$

So I have checked for vacuum leaks and even replaced the plugs just in case though it's throwing parts at the problem.

I believe the manifolds did not seat on the bottom side even though they looked great from the top. The guide rings may have been the culprit. I think I will have to remove the manifolds again and and try again. Unfortunately the guide pins on either end are short and make the job harder for 1 person. I will try to enlist an assistant today. I actually need to complete this in order to get hay rolls for the goats.

Jameschevypickup50 You might take those end pins out and screw a bolt in to help hold things. Idone a seat (valve) job on my 48 2 ton assembled head,and manifolds on the bench then with a helper put the whole assembly on the truck. Used a 2x4 to carry. Be sure your alignment rings are not holding your manifolds off. Make pins with slots,hacksaw, scew in with scewdriver,might even slot the old ones. On those rings it's a temptation to leave those out but if you do later you'll hit a chuck-hole and manifolds will shift engine will start missing--vacuum leak ! good luck

I thought about trying to remove the pins but removal may be a seemingly impossible task. Doubt they have ever been out.

DO NOT REPLACE THE GUIDE PINS WIH BOLTS! They are there so the long end runners can expand/contract slightly with temperature changes. Bolting them down solid can result in the intake warping and/or cracking. If you're firmly convinced that you're smarter than the guys who designed the engine, the pins can be removed with plenty of heat, penetrating oil, and vise grips. They're 3/8-16 thread like the rest of the manifold bolts. If someone has milled the manifold mating surface to straighten the face of it sometime in the past, it's possible the alignment rings are a little too thick and the manifold is bottoming out on the rings before it clamps the gasket tight. Don't remove the rings- - - - -just shorten them a little with a file or a disc sander.
Jerry

Thank you. I wasn't planning on replacing the guide pins, but did think they could be a little loner to make the install easier. Advice all appreciated. especially the rings being being too long.

The rings don't do anything to seal vacuum- - - - -they're only there to keep the intake ports in the head and the manifold runners aligned correctly. I have made rings from slices of exhaust tubing with a diagonal cut to adjust the circumference of the ring to the correct size to be a snug fit in the counterbore. Some online vendors sell stepped rings to adapt a 216 manifold to a 235 head which has larger ports. You can make longer pins by cutting a 3/8" bolt off to fit the threads in the head, leaving the unthreaded shank a little longer than the original part.
Jerry

Install unsuccessful. Checking for fit prior to connecting the two manifolds, the intake alone lined up nicely with the head ports with rings inserted. After combining the intake and exhaust lousily the exhaust seemed to prevent the intake from seating properly. The intake is an official GM part but the exhaust is not. The exhaust did seat but the intake just didn't line up causing it not to seat properly with the rngs. So I am curious if others have had problems installing after market manifolds that have been purchased as replacements.

My next attempt will be to try using a GM exhaust manifold that may become available.

I just used the stock guide pins. A 1/2" inch longer would have been nice.

Got any pictures?

jameschevypu50 Are your plug wires crossed up ? Also can use your acetylene torch-not burning-to look for vacuum leaks.

So the big problem was manifolds weren't official GM manufactured. They did not match up well with the head ports. What a wiast of time and frustration. In the end I had a GM intake and a GM exhaust manifold I was able to install the combo and slowly torque them in. The truck ran wonderfully. I reconfigured the vacuum fittings so that my brake booster hose came straight into the heat riser portion of the manifold along with two other vacuum lines T'ed off. The brakes were better than ever before.

If anyone is replacing manifolds I recommend that you take care to insure that they are GM parts.

Your experience is far from unique. Some of those aftermarket parts create a whole laundry list of problems that could have been avoided with OEM parts. Good on ya for hanging in there!
Jerry