Cracked Exhaust Manifold Questions
 

Hello,

Background:
Finally getting my 67 C10 w/ L6 250 ready to drive. There had been a nasty off-idle stumble. Changed the points and set it up and it started and ran and drove great. Got rid of all the problems. I was loving it for a day. I was so excited that I went and changed everything else you would do in a good complete tune-up (plugs, wires, cap, rotor, air filter, fuel filter, pcv, breather, even a new coil). Much to my disappointment I started the truck and instantly it had a bad miss really noticeable right off idle. Worse than anything before. I started changing everything back figuring something was bad and it was still there after putting all the original parts on. I figured I'd start looking for a vacuum leak and when I started looking around I saw a big crack in my exhaust manifold. Right near the center.

Questions:
Could this crack in the exhaust manifold be causing this miss? Or is it likely that I have multiple problems? Do I need to find a good used one or are these produced anyplace? Or, is there a better alternative to replace this with-- that would bolt on and not require extensive modifications.

Thanks,
Adam

Re: Cracked Exhaust Manifold Questions
 

Can you weld it back up?

Re: Cracked Exhaust Manifold Questions
 

I don't do any welding myself, but maybe it's possible. It's an original cast iron manifold. Maybe?

It doesn't seem to be leaking horrendously, but I know it's not right. I just don't know if it's possible it's my problem with the miss or if I have other issues possible.

Adam

Re: Cracked Exhaust Manifold Questions
 

Actually, that was an irresponsible response on my part; i hear cast iron, especially exhaust manifolds, is difficult to weld.

You may be better off looking for another manifold. i don't think they produce them anymore but you should have not too much difficulty finding a used one.

Re: Cracked Exhaust Manifold Questions
 

Yes they still reproduce them or look on ebay. If you're a member you can post a want to buy in the parts section of this site.

As for welding, there are some places that can weld it for you. They have to specialize in the sort of work. Used to be they'd have to heat the metal to a certain temp because cast iron tends to crack fairly easy. I've heard of some that can braze it with good results. I have used metal set before with decent results.

I have a leak in my gasket between the carb and exhaust and the engine runs fine without a miss. Check your ignition again. Maybe use a timing light to observe the spark of the different plug wires. Do a compression test also to make sure there isn't a burnt valve and check for vacuum leaks carefully.

Re: Cracked Exhaust Manifold Questions
 

Welded cast many times with my mig, never any problem, think its a myth to get people to buy new parts.

Re: Cracked Exhaust Manifold Questions
 

i would like to formally withdraw any comments regarding the welding of cast iron.

Re: Cracked Exhaust Manifold Questions
 

It ran fine till you changed plugs, wires, cap, rotor, air filter, fuel filter, pcv, breather, coil.

Go back a see which item is bad before you look at something that was there when it ran good. Bad coil. wrong coil, mis gapped plug cracked cap. wires not seated or damaged while changing all this, any of that could cause a miss but not usually a exhaust manifold

Re: Cracked Exhaust Manifold Questions
 

though id braze it, softer, will expand n contract with it, so it don't crack more if the part is under stress, though drill the end of the cracks with a tiny drill bit to give them an end point.

Re: Cracked Exhaust Manifold Questions
 

No need to withdraw. You're correct in that it's difficult to weld compared to regular iron stuff. It seems to depend on the experience of the welder.

Many years ago, I had an engine throw a rod and put a small hole on the side of the block. I had it welded and you could see hairline cracks around the edges of the weld. It held, but oozed a tiny bit of oil from the cracks.

Re: Cracked Exhaust Manifold Questions
 

Thanks for the replys.

This is what is really throwing me...I figured something I put on was bad so I went and changed everything back to what was on there before (except the fuel filter). And it still runs bad. I rechecked the timing and dwell-- both are good. Dwell is about 31 degree and timing is about 12 degrees. That is when I noticed the crack in the manifold.

I don't have a good idea of how the intake and exhaust and carb are all connected, so I was thinking the crack may be causing some type of vacuum leak?

The engine ran so good for a day and then this happened -- I was hoping it was something simple.

Adam

Re: Cracked Exhaust Manifold Questions
 

First thing I would do is to change the timing back to specs. 12º BTDC is too advanced for that six with points. You can play with it and advance it slightly to 2º or maybe 4º but even on my 250 with HEI I keep it at around 8º BTDC.

Re: Cracked Exhaust Manifold Questions
 

I dont feel that the crack in the manifold will cause you a missfire.....you can weld or braze it to "plug the leak", but short of replacing the manifold , anything is short lived;) Going into my Long lost points playing....you will get a little wear really quick...maybe recheck the dwell & timing. Play for what you can find to "fit", but I do agree that your pionts dist has more mechanical advance , than an HEI does....you will to trim the initial back a tad, to make it right. Figure 8-10 initial, on the HEI, with a slower curve....lots of good info goin in the post, just roll with it:chevy: best of fun, crazyL

Re: Cracked Exhaust Manifold Questions
 

Ok, got some news. Not sure good or bad, but it is news.

I don't believe the manifold is cracked anymore. I looked closer at it and I think I was looking at the surface that is machined down where the intake meets up with it under the carb. I think that is good news.

Bad news, I still have the miss. I reset the timing to 4 degrees (which I believe is factory spec) and no change. I rechecked the dwell again and it is at about 33 degrees. I have absolutely no idea what to do next with this thing. I am completely lost on how it can go from running great one day after changing the points to having this nasty miss off idle.

The only vacuum lines on here are to the distributor (hard line off of carb, and I changed the short piece of rubber line from hard line to vacuum canister), and the PCV. The PCV has great suction, but I also plugged it at the manifold to see if it ran different and it didn't get rid of the miss.

Anyone have any suggestions other than to start taking things apart and changing gaskets???

Adam

Re: Cracked Exhaust Manifold Questions
 

Maybe it's not a "miss" and I'm describing it wrong.

I took a quick video, not sure if this helps of not...

You can hear me open the throttle and the engine seems to choke and then catch up. I do this a couple times and then the third time it actually backfires.

http://img411.imageshack.us/img411/2...ycgpmadvma.mp4

Any ideas?

Adam

Re: Cracked Exhaust Manifold Questions
 

The video doesn't work for me...

Re: Cracked Exhaust Manifold Questions
 

Sorry about that. I tried it a couple places and it's showing up for me. Let me upload it someplace else and see if I can get it working.

EDIT: Try this-- http://www.flickr.com/photos/72375543@N03/8123975745/

Adam

Re: Cracked Exhaust Manifold Questions
 

hard to really tell., but it sounds like a "tip in problem"...Maybe the acc pump on the carb? If you advance the timing, does it get better? Could be that you have a bad vac advance canister? crazyL:chevy:

Re: Cracked Exhaust Manifold Questions
 

I had the timing at 12 before and is now at 4. I haven't driven it since setting to 4, but it acts the same. So I would say that advancing the timing does not change it.

Would that make you think the vacuum canister is ok and lead you to the carb?

Is it possible for it to work ok one day and then not the next? All of the sudden stop working ok?

I have never rebuilt a carb, is this the direction you would go based on what I've given you guys for symptoms?

Adam

Re: Cracked Exhaust Manifold Questions
 

The monojet is a very easy carb to take apart and clean. Get a kit from the local auto parts and dive in. We should be able to help you if you have questions.

I have taken several of those apart and rebuilt. Buy at least 2 cans of carb cleaner. You should also replace the float if it has the black phenolic one. I've heard they get fuel logged even though I've never seen it. Check the gasket between the top half and lower half to make sure it's tight or not leaking (two phillips head screws from the bottom of the carb).

After you do that, adjust the idle speed and idle air screw for best, smoothest idle or highest vacuum. Keep resetting the idle to specs if the engine rpm goes up and recheck the adjustment.

Other things that can cause bogging, hesitation and/or backfiring are burned valves, weak valve springs, worn cam and or cam gears, bad distributor. An HEI distributor would help if that were the case.

Re: Cracked Exhaust Manifold Questions
 

Heat riser valve working!
Sounds like cold intake, lean misfire due to fuel puddling.

Re: Cracked Exhaust Manifold Questions
 

I believe this carb is actually a Carter-- maybe a YF. Any experience there?

Is the heat riser valve you are talking about the one at the top of the exhaust manifold? I noticed it was a little sticky, but it doesn't seem to run any different if it's opened or closed. How should it operate-- boucing back and forth or should it either be open or closed depending on temperature?

Adam

Re: Cracked Exhaust Manifold Questions
 

Tip in issue? Like others said, could be an issue with your carb.

My personal experience with this issue you describe is on my 1986 305. When I did a teardown to install a new cam and the TPI, I found an extremely worn original timing chain. That would explain why my timing would sometimes jump around when I was setting the ignition timing.

Re: Cracked Exhaust Manifold Questions
 

I don't believe these engines have timing chains, just gears. But I don't see any issues with my timing, it seems to set easy enough and I see it move when I open the throttle.

I don't see any difference in movement with vacuum connected or not, but I'm not sure I would either. Haven't tried driving without vacuum on the dist.

Carb or Dist., and now heat riser, seem to be the only ideas floating around here and I'll just end up taking a stab at one unless more come up.

Adam

Re: Cracked Exhaust Manifold Questions
 

I gut the heat riser valves when I find them, and just weld the shaft holes shut so its just a pass through.