6 cyl (292) manifold questions/issues

[May70]

Hello,

I have a 70 c20 with the 292. It had a bad exhaust leak where the two manifolds flange together (along with a valve cover leak). I began taking the manifold apart and found one of the studs looked like it had been broken off previously. That left a nut and a single bolt on the forward side for me to take off and the manifold should have come apart... The only size that somewhat fit the bolt was a 14 metric? The head wasnt rounded off either so I am not sure what happened there... Well the bolt head broke off when I was trying to take it apart. Tried soaking in PB blast, heating etc and it was firm.. I still was able to pull the two apart and see the flange. It looks like its had some history with repair attempts. a couple hair line cracks, some sort of gasket making materiel that resembles jb weld, maybe some actual welding was done. Any way, I did some grinding to get what you see in the pictures and its still not flat.

Does the bolt that broke off (pictured below) go all the way up through to act as the carb mount? The bolt looks STUCK good up in that hole, not even sure if I could get it out. Ive read a lot about these being prone to issues.

Thoughts? is this one worth messing with? What are some alternatives? I see ebay and even rock auto has some re manufactured exhaust manifolds but they have bad reviews for fit etc.. If I bought headers I would have to buy a new intake manifold etc. Not sure if that is an easy swap with orig carb.

[Wrenchbender Ret]

The exhaust manifolds on 292 engines that are worked hard run extremely hot. They get all warped out of shape. It is best to get some manifolds from a 250 or 230. They are generally in much better condition & fit fine with little differences.
George

[Jason Banks]

The bolt does not go all the way through and act as a carb mount. The carb mounts to separate studs.

The rest of that bolt could be taken out. I'm not sure if just welding a nut to it would work. It might need to be torched out. I used to take things that had rusty broken bolts to a tractor repair shop that had an old guy that could get anything out.

I have the ATP 101140 Manifold. You can see my review on Amazon. The casting was rough and I cleaned it up with a carbide rotary file. Basically porting it...but not really. I checked it for flatness and it was fine and installed with no leaks.

https://www.amazon.com/ATP-Automotiv...dp/B000IYCY3E/

You say yours was leaking between the intake and exhaust. Mine was leaking where the flapper shaft was sticking through. Probably could have come up with a way to put new bushings in the shaft.

[May70]

Thanks for the feedback. I hopped on amazon chat and confirmed they would provide a free no hassle return via my prime membership if it doesn't fit properly or as expected.

Will check back in with am update when I get it. Ive got a little sand blaster, not sure if that would smooth it out. Will see how it is when it arrives Tues.

[geezer#99]

Do you know that If the exhaust manifold doesn’t work out you can use headers with your stock intake. Not a bolt on but it can be done.

[May70]

Originally Posted by geezer#99

Do you know that If the exhaust manifold doesn’t work out you can use headers with your stock intake. Not a bolt on but it can be done.

The holes in the bottom of the intake pictured are all clogged up. Not exactly sure what the best way is to unclog them with all the soot. Not sure what they are supposed to look like normally. Might hit it with the sand blaster.

I would assume its possible to do but then you would just close off the bottom of the intake. Reckon ill see how good I can get the intake cleaned up and what the quality is of the

[Coley]

If you have the manifold off the truck and available for repair...then you shouldn't have any problem fixing that broken stud issue.

I would file it slightly flat then take and carefully punch a center hole in it and drill it out with a couple of progressive drill sizes.
After the first size you can try heating it and using an 'easy out' (reverse type extractor)....and if that doesn't work, then upsize the drill bit slightly and keep going. Any remaining material in there will give up at some point.
Then, if it was a tapped hole....re-tap it and put it in a new stud.
OR
Simply take it to a machine shop and they will do this for you in short order.

When it is an actual, real bummer is when you are hoping for a couple of quick changes to the arrangement with it still on the truck and that broken stud happens....that is the real drag, lol

My two bits....
Coley

[May70]

Thanks coley, yeah I was just thankful nothing broke while it was still mounted up. Its apart and off the truck now.

My neighbor has a bunch of machine shop type stuff in his shop. Ill swing by him this afternoon to see if he wouldn't mind pulling it out.

Any idea what bolt size/ threads that is supposed to be? I dont think ill be able to get a gauge on the little bit of threads left. looks like its pretty jacked up haha. Might be able to get some taps out and tell what threads based on the hole but wont know till I get there. Not sure if its the right bolt anyway. A 14 metric fit the head so I assume that is not the original lol?

[Steeveedee]

The bolts are 3/8-16 UNC thread, that's why the head can take a 14mm, though the correct wrench size is 9/16". If you need to drill the bolts out, start with a left-hand twist drill bit, because sometimes when drilling the bit will catch and unscrew the bolt. If you use a right hand twist drill, it won't have that loosening effect. If you want to clean up the thread, a chasing tap is what you want, not a regular threading tap.

[May70]

Thanks for the responses. Got the intake sand blasted and painted today. Bolt came out with oxy acetyl torch and clamping it as tight as the vice would go and twisting it. Just enough nub!

The exhaust manifold should be in tomorrow and Ill do a test fit before giving it a make over

[May70]

What is the inside of the heat riser supposed to look like? I stuck the nozzle of the sand blaster in it and just got 4 holes, not opening up to anything. I didnt know if the exhaust was actually supposed to mix, cause the 'heat riser holes' dont open up into the intake, they just surround it. I am assuming just to heat it up via heat transfer?

[Steeveedee]

The heat riser closes with a bimetallic spring to retain some exhaust heat for carburetor preheat. It blows at least partly open with exhaust gas flow, though. Once the spring warms up, the valve flap should be all the way open.

[May70]

I found a good video on someone explaining how it works. https://www.youtube.com/watch?v=9tepFx1uMJo

The re-manufactured manifold sold by rock auto/amazon is made by ATP did come with a very rough casting, especially on the inside. For me it really was not a deal breaker because i'm not looking for performance. I just wanted something I didn't have to worry about cracking/getting worse with time. The original would likely have continued to crack.

The re-manufactured manifold design added a LOT of strength in the weak spots. Where the old flange is about 1/4 inch thick (where the bolt goes through) the new one is close to an inch thick. It comes with 2 studs for the intake manifold to bolt on, and 3 studs for the exhaust side with 4 or 5 holes for many different exhaust applications. It includes the heat riser weight with spring. It does not include the 'auto choke' id call it for the carb or mounting hardware but it does have the spot for it and tapped holes. I easily removed it from the old and made two bolts for it. Like I said if you're not looking for perfection its a good deal for 167$ shipped. I don't think you could ever get the inside smooth with even a carbide bit, some areas are unreachable, i didn't bother. Also the flange is completely straight, I checked it with a straight edge. If the manufacturer would take the time to clean the surface up on the cast this would be an incredibly nice reproduced manifold. Pics later

[RichardJ]

>> ATP did come with a very rough casting, especially on the inside.<<

You are looking at something that is often debated.
To some extent,
"a rough intake port keeps the fuel/air atomized to burn a hell of a lot faster! smooth intake ports form droplets that as we all "should know" don't burn as fast or efficient".

A rough intake passage creates some turbulence, which can only help a single carb, long inline intake manifold. Inline engines tend to run lean on the end cylinders and anything that can help keep the fuel atomized is of great assistance.
Smooth, polished intake runner turns will have fuel droplets form when the air/fuel mixture tries to make the turn. Outside radiuses are sometimes dimpled to create turbulence.

Do not fully tighten the intake to the exhaust, until the pair are bolted to the head and don't over tighten.