The Stovebolt Site Forums The Shop Area Engine Shop GMC 270 intake manifold

I recently detected a manifold leak in my rebuilt 270 - put in a new gasket and found the damned manifold had warped. Took it off again and was preparing to have it milled down at the local muffler shop (they have a belt sander) when I noticed a crack on the carb mount of the INTAKE half of the manifold. Is it possible to weld this (I heard it can be done with a stainless steel rod), or is it a complete waste of time to try?

As a followup, if the head is toast, should I go get another one at the junkyard or am I better off looking for aftermarket separates? Right now I am using a Holly/Weber 2 barrel on it.

Ranger,

Your intake can be welded...this only needs to be done if the crack would cause a vacuum leak.

Another option, and a better option I think, would be to have a automotive machine shop plug the manifold. This is done with a series of holes that are drilled, tapped and plugged with cast iron break off screws in a overlapping fashion.

Brazing the manifold would be a option too. I am not familiar with the GMC, but it sure seems strange to have a crack in this manifold, and especially in the carb base area.

I have never heard of using a belt sander to flatten a warped manifold. If the jimmy setup is like the Chevy ones, both manifolds are usually milled TOGETHER on a specific machine built to mill cylinder heads, flywheels and manifolds.

Eugene is full of machine shops...I have dealt with several of them over the years. Make sure that the intake is really cracked and needs repair and be sure the belt sander deal is going to give you the results you want.

If the manifolds bolt together, they must be flat, true AND the same depth from where they bolt together.

Stuart

The surfacing must be done with the manifolds mated.

If the crack is only leaking vacuum why not try some epoxy? (JB weld)

Stuart, I was also struck by the odd location of this crack - I could maybe see the exhaust part of the manifold cracking, but not the intake and definitely not on the carb mount. (Wonder if it resulted from trying to torque a warped manifold.) I'm not sure it is leaking air, but an intake manifold leak is the reason I took it off in the first place so I think I'm going to try to plug it. I worry about weakening it further with a weld so will try Celtis' suggestion of JB Weld epoxy (thanks.)

I actually surveyed a machine shop or two and landed at a muffler shop that uses an old belt sander specifically for resurfacing exhaust manifolds on rigs they work on, and yes, they also recommend milling the mated ex-in manifolds. Reading your suggestion, Stuart, I'll check around a little more. Any recommendations for gaskets beyond the stock gasket you can get at NAPA? Thanks to both of you for your suggestions.

Roger

Roger,

I would do some more thinking on the belt sander deal. The intake/exhaust combination on these engines is sensitive to alignment. The flanges need to be flat with themselves and flat and true with each other...AND this all has to happen when the two individual manifolds are bolted together and mated properly with each other.

As Cletis notes, the machining operation is done on BOTH manifolds at once when they are mated together..not done separately.

I can understand the muffler shop belt sander scenario, but I truly don't think it is at all appropriate for this situation..I will bet you only want to do this operation once. It must be done correctly.


Stuart

This seems like a lot a work and a little bit of a gamble to repair. Have you compared the time and expense of repair to the cost of a replacement.

Mike
RLTW

Mike, I checked around and the nearest intact manifold pair is in Vancouver, WA, about 100mi north of me. Will probably go look at it. Tom Langdon at Langdon's Stovebolt 6 advised junking the cracked pair and getting a replacement. Should I mill the "new" mated in - ex manifold pair prior to torquing it in?

Roger

Roger,

I thought it was only the area around the carburetor on the intake manifold that looked suspicious??

That would be the only repair!! Milling the manifolds isn't repair, think of it as maintenance.

Sift out the static..unless this intake thing is horrible, you're getting ahead of yourself.

I can't say this enough..sticking the two manifolds together and having them milled is simple, cheap and done all day long. Don't throw the baby out with the bath water.

Mr. Langdon knows much much more than I do..he also has a reputation to uphold. Unless the intake is truly scrap, weigh his advice very carefully.

Stuart

Roger,
If they are new, they "should" seal pretty well and the gasket "should" take up the slack if there is any and I am correctly visualizing what you are talking about. If the milling can be done with little effort, go for it.

My original comment was only a suggestion as to what would be most cost effective and easiest.

MikeE,

My comments sometimes sound rather "gruff". Your comment made perfect sense, and I wasn't trying to challenge it or diminish it in any way.


Stuart

I'm not smart enough to know I've been insulted in any way so this didn't even register as a challenge. I certainly didn't look at anything other than just more suggestions for a solution. In fact most of the comments on this page comprise an international brainstorming session.

bolt the manifolds together and belt sand them,,as far as the vacum leak sand the area and bj weld it...

I appreciate all your comments.

The intake and exhaust manifolds are still together ( I took them off as a unit), and the crack, on the carb mounting body, is real but fairly small, I found a machine shop that will weld it with a stainless steel rod and then mill it. I'll give it a whirl and let you all know how it turned out.

Thanks!

Roger