1967 cast intake manifold problem

[Timothy B.]

I was trying to remove one of the small cup plugs I installed in the hot slot on my 300 HP cast intake and it turned sideways and fell into the small hole.

I am not a happy camper at this point and I would like everyone's opinion if they think I should remove the intake and find/remove this cup plug. I don't know if it will present any problems down in that cavity but I am not sure.

The plug did not fall down the runners of the manifold, it turned and fell down the small hole it was plugging (hot slot hole).

[John H.]

Re: 1967 cast intake manifold problem

Tim -

The bottom of that hole communicates with the exhaust gas crossover passage (the center port on each side of the intake), and the continuation of that passage through the cylinder head joins with an exhaust port.

If the 7/16" diameter plug is small enough to get through the passage in the intake to the head, in theory, it should blow right out of the exhaust port (positive pressure in the port will keep it away from the exhaust valve end of the port).

That said, if it were mine, I'd pull the intake and try to remove the plug.

[Timothy B.]

Re: 1967 cast intake manifold problem

Thanks John, This little plug is shallow and I suspect it could blow into the head. If I decide to pull the intake I am going to drill and tap the holes. I just created a whole lot of work for myself...

[Stuart F.]

Re: 1967 cast intake manifold problem

Tim;

While you have the intake manifold off, why not use plugged gaskets instead to block off the exhaust cross over altogether? Have you just found a combination that works good for you by plugging off the exhaust at the carb base? Just wanted to know your reasoning and remind there are other options.

Stu Fox

[Timothy B.]

Re: 1967 cast intake manifold problem

Stu,

This is the cast manifold on my 67 300 HP car. I think these cast manifolds need as much heat as you can get to them under normal operating circumstances. I don't think it's a good idea to reduce exhaust flow under the cast. I am thinking of running the engine with new gasket/shield under the carburetor and also leaving the hot slot open.

I had a problem before with a old wore out shield under the carburetor so I am aware of potential problem here. I am not a happy camper and I really don't want to pull the manifold but my mind tells me I really don't have a choice.. With the manifold off, I will tap these small holes for plugs.

[Stuart F.]

Re: 1967 cast intake manifold problem

Tim;

I don't recall where you are located, but it doesn't seem to matter much this year. It seems we all have cold ambient conditions to deal with. I guess you know what works best for you for your year around conditions. I too use the 300 hp phenolic spacer on my 63 340 hp, but along with gaskets above and below. I have also tried the plate, but it serves no real purpose on mine because I don't have the small holes in the aluminum manifold. But, what I have learned is that there are a number of ways you can seal off the small holes without plugging them simple with the use of different base gaskets. As a for instance, the 340 hp piece will seal off the holes and the chamber in the spacer very well. There are also different thickness plates - some, specified as being repro, are almost paper thin while others are much more substantial. This may be what you will eventually want as it will appear completely stock outwardly (if that is a consideration).

Have you exhausted every method to extract the plug as yet? I realize going with a magnet is not an option, but they do make some very thin ones that are on the end of a flex stem. I have one that has saved me a lot of time. Can you see it and possible hook it to move it into a position where you can get a needle nose on it - even to just bend it into a shape that will allow it to pass up through the hole better?

Has the manifold ever been off before, i.e. are you trying to save the orginal gaskets, etc.?

I feel your pain whatever the situation is it is an unwanted dilema. Perhaps John H. has the best idea of blowing it out, but I too have lost a valve and piston once due to debris and the thought gives me the jitters.

Stu Fox

[Timothy B.]

Re: 1967 cast intake manifold problem

Stu, I went fishing for it with a magnet today and that little plug is gone. I almost got the magnet stuck in that little hole. Looks like I will remove the intake, find the plug and have it cooked out at the machine shop to clean it up a bit..

I do not want to have to worry about it when driving the car.

[John H.]

Re: 1967 cast intake manifold problem

Tim;

While you have the intake manifold off, why not use plugged gaskets instead to block off the exhaust cross over altogether? Stu Fox

Stu -

Unlike pre-'66 Corvettes, the '66 and '67 use a divorced choke thermostat mounted in a well on the intake manifold which actuates the choke and fast idle cam via a rod; if you block off the crossover passage on a '66 or '67, that well won't get any heat, and the choke won't work.

[Timothy B.]

Re: 1967 cast intake manifold problem

Took the manifold off my 67 this afternoon and could not find the little plug inside the manifold. I used my magnet inside the cylinder head and guess what, came out with the plug and I believe it was either next to or on the exhaust valve.

I want to take the manifold to the machine shop to have it cooked out and I need to remove the rivets holding the splash shield. Can anyone tell me the best way to remove them without bending the shield and can I reuse them??

[Stuart F.]

Re: 1967 cast intake manifold problem

John;

This is probably why great advocates of using blocked gaskets say that you should just use one on the driver side, I suppose. Not sure if that would solve any problems though.

Stu Fox

[John H.]

Re: 1967 cast intake manifold problem

I want to take the manifold to the machine shop to have it cooked out and I need to remove the rivets holding the splash shield. Can anyone tell me the best way to remove them without bending the shield and can I reuse them??

Use the end of a sharp chisel under the head of the rivets to work them loose and remove them. New splined drive rivets are available from GM - P/N 10229247.

[Joe R.]

Re: 1967 cast intake manifold problem

Stu,

This is the cast manifold on my 67 300 HP car. I think these cast manifolds need as much heat as you can get to them under normal operating circumstances. I don't think it's a good idea to reduce exhaust flow under the cast. I am thinking of running the engine with new gasket/shield under the carburetor and also leaving the hot slot open.

I had a problem before with a old wore out shield under the carburetor so I am aware of potential problem here. I am not a happy camper and I really don't want to pull the manifold but my mind tells me I really don't have a choice.. With the manifold off, I will tap these small holes for plugs.

Hi Tim:

When I blocked the hot slot on my 300 HP engine, I worried about the plug dropping in as yours did, so I used a threaded plug as shown in the attached photo (intake was of the car at the time).

I had to buy a box of 25 plugs to get the right size with an allen socket, so I have a lot of spare plugs. If you want a couple, send me a PM with your address and I will mail them to you.

[Clem Z.]

Re: 1967 cast intake manifold problem

Took the manifold off my 67 this afternoon and could not find the little plug inside the manifold. I used my magnet inside the cylinder head and guess what, came out with the plug and I believe it was either next to or on the exhaust valve.

I want to take the manifold to the machine shop to have it cooked out and I need to remove the rivets holding the splash shield. Can anyone tell me the best way to remove them without bending the shield and can I reuse them??

good thing the exhaust valve was not open or you would be also removing the head. you can tap the manifold on the engine by using grease on the pipe thread tap and have someone hold a shop vac pickup near the work area. you should not get any chips in the engine doing it that way

[Timothy B.]

Re: 1967 cast intake manifold problem

I am glad I removed the manifold, it had 1/2" of oil crud inside the oil splash underneith. Had it cooked and then machine with steel shot cleaned it like new. Got new GM rivets (thanks John for the part #) and reinstalled the shield.

Water fitting was corroded and will be replaced plus temp sender was oxidized bad and needed to be cleaned (brasso), it looks like new. Should I use permatex #2 for thread sealer or never seize for the water fitting and temp sender?? I really don't think this sealer will keep the temp sender from grounding..

Agree about the exhaust valve not being open, had this happen to me a long time ago with a carburetor nut and got lucky the same way. Funny, the feeling was the same when the plug dropped down the hole, it was like going back in time..

I am going to tap for a plug before I install back on the engine, but I plan on running without the plug for now and let the heat get to the carburetor. New correct heat shield and gasket of course..