How to repair a cracked Intake Manifold

hank14 · 06-10-09, 04:58 AM

I bought a used stock intake and exhaust manifold, only to find a 3 inch hairline crack in the intake manifold where the isolator plate goes.

Can this be repaired properly to prevent future cracking? I know the SOR.com stainless steel insulator is designed to prevent future cracking.

I did not find any forum info here about repairing a cracked intake.

eventhough · 06-10-09, 05:17 AM

I'm not sure about the intakes but some have welded the exhaust manifolds.

I have an extra intake manifold if you want it - PM me.

Stumpalama · 06-10-09, 05:41 AM

I had my intake welded about 10 years ago and it is still good. Find a good aluminum welder and they can do it while ensuring the manifold doesn't warp.
Also, you have to remove the likely culprit: the thermo nuclear reactor, or the exhaust diverter thingy. They invariable fail in the up position directing the hot exhaust directly on to the manifild below the carb.

GLTHFJ60 · 06-10-09, 05:49 AM

Definitely a good thing to point out. I have a hairline crack as well, but I ignored it. I probably should have had it repaired / replaced, eh?

Cruzerman · 06-10-09, 06:01 AM

I had a crack in my intake on my 40. Took it to a good aluminum welder and he stiched it right up.

zuluzeugma · 06-10-09, 08:10 AM

I have one for sale if you want to go that route.

Stumpalama · 06-10-09, 08:23 AM

Quote:

Originally Posted by GLTHFJ60

Definitely a good thing to point out. I have a hairline crack as well, but I ignored it. I probably should have had it repaired / replaced, eh?

Yeah, that little crack caused me all sorts of frustration when trying to chase down a vacuum leak. the truck would alternate between exhibiting signs of running rich, then running lean.
Also, if the intake is cracked, have the mounting face (against the head) checked for true.
If it needs to be milled, I recommend having the machine shop mill the intake and exhaust as one unit, that way they are sure to fit tight on the head.

GLTHFJ60 · 06-10-09, 08:24 AM

Quote:

Originally Posted by Stumpalama

Yeah, that little crack caused me all sorts of frustration when trying to chase down a vacuum leak. the truck would alternate between exhibiting signs of running rich, then running lean.
Also, if the intake is cracked, have the mounting face (against the head checked for true.
If it needs to be milled, I recommend having the machine shop mill the intake and exhaust as one unit, that way they are sure to fit tight on the head.

Damn. I gotta go back in there and pull it off I guess.

NLXTACY · 06-10-09, 08:44 AM

If you guys are noticing cracks in the intake, like I had, make sure your carb fan is working properly.

GLTHFJ60 · 06-10-09, 09:29 AM

Quote:

Originally Posted by NLXTACY

If you guys are noticing cracks in the intake, like I had, make sure your carb fan is working properly.

Did that about a month ago, or whenever you posted up that easy solution, and just got installing my Remflex on Sunday. At least I think I can get the manifold off without taking the header all the way out.

NLXTACY · 06-10-09, 11:26 AM

Quote:

Originally Posted by GLTHFJ60

Did that about a month ago, or whenever you posted up that easy solution, and just got installing my Remflex on Sunday. At least I think I can get the manifold off without taking the header all the way out.

yeah if you have the bolts and not the studs then its actually pretty easy, relatively

GLTHFJ60 · 06-10-09, 11:36 AM

Quote:

Originally Posted by NLXTACY

yeah if you have the bolts and not the studs then its actually pretty easy, relatively

Were there ever two options? I thought the stock config was two studs top + center with the rest as bolts.

NLXTACY · 06-10-09, 11:48 AM

Quote:

Originally Posted by GLTHFJ60

Were there ever two options? I thought the stock config was two studs top + center with the rest as bolts.

The option is an aftermarket option. I originally went with studs because its supposed to be easier to get the manifold back onto the head because you aren't sitting there trying to align it, holding it up, trying to thread in a starter bolt. In retrospect its a PAIN IN THE ASS to use studs with the engine still IN the truck

GLTHFJ60 · 06-10-09, 11:56 AM

Quote:

Originally Posted by NLXTACY

The option is an aftermarket option. I originally went with studs because its supposed to be easier to get the manifold back onto the head because you aren't sitting there trying to align it, holding it up, trying to thread in a starter bolt. In retrospect its a PAIN IN THE ASS to use studs with the engine still IN the truck

With only the two top studs? I could think of no other way for installing headers. It would be impossible to install headers with one person without the studs.

Think JB weld would hold the crack?

NLXTACY · 06-10-09, 12:01 PM

Quote:

Originally Posted by GLTHFJ60

Think JB weld would hold the crack?

To be honest, yes I do. Or try FastSteel. I was gonna try it if Mark A. didn't have a good one.

GLTHFJ60 · 06-10-09, 12:14 PM

Quote:

Originally Posted by NLXTACY

To be honest, yes I do. Or try FastSteel. I was gonna try it if Mark A. didn't have a good one.

The last thing I'd want is to have that JB weld get sucked into my motor. What if I sealed the crack from the bottom of the manifold? I could definitely get away without taking the whole shebang off

hank14 · 06-10-09, 06:15 PM

Thanks for the offers on the other intakes. I don't think my original one has a crack, but one I bought to replace it does.

I replaced the intake and exhaust manifold gasket and rebuilt the carb 6 months ago. New SS J-tube fixed that pesky leak, but I didn't replace the gaskets or insulator between the intake and exhaust and I didn't replace the gasket/washers on the swivel ends of the exhaust manifold. I'm getting some very minor leaking from all 3 of those. So, I wanted to rebuild the replacement intake and exhaust manifolds and swap them out for my original ones. I don't want to have to do it again.

Now, I'm tempted to go new OEM, or get a header to avoid all this mess.

I also have some minor backfiring when I first get out on the road- letting off the gas to shift gears- when the engine is cool and the choke is off. I don't know if that's related to the intake/exhaust or my homebrew carb rebuild.

Stumpalama · 06-10-09, 06:29 PM

Indicates a rich mixture... but better a little rich than too lean. If you don't have one, go out and get a vacuum gauge (they're cheap) from autozone/sears. Hook it up to your brake booster line after you've got your engine up to operating temp. It and a timing light will tell you and amazing amount about the running condition of your engine. There is a great write-up in the tech section about using a timing light and a vacuum gauge to tune your rig properly. I swear by it... I averaged 14.65 MPG at an average speed of 70MPH (by GPS) with 2F, smogged, headers, 4.11 gears, 4spd and 35" BFG MT's on a recent trip to Hilton Head.

Michael Hanson · 06-10-09, 06:39 PM

If its aluminum,clean and weld it.It will be fine. Mike

hank14 · 06-10-09, 08:17 PM

Quote:

Originally Posted by Stumpalama

Indicates a rich mixture... but better a little rich than too lean. If you don't have one, go out and get a vacuum gauge (they're cheap) from autozone/sears. Hook it up to your brake booster line after you've got your engine up to operating temp. It and a timing light will tell you and amazing amount about the running condition of your engine. There is a great write-up in the tech section about using a timing light and a vacuum gauge to tune your rig properly. I swear by it... I averaged 14.65 MPG at an average speed of 70MPH (by GPS) with 2F, smogged, headers, 4.11 gears, 4spd and 35" BFG MT's on a recent trip to Hilton Head.

Good info. I have checked the vacuum. When the timing's set per the FSM, I get some pinging under load, so I have adjusted it to prevent that (not as advanced).

I think I'll have someone weld the aluminum intake as suggested.