Register or Log In To remove these advertisements. |
|
|
|
Thread Tools | Display Modes |
10-25-2012, 12:36 AM | #1 |
Registered User
Join Date: Jul 2012
Location: Marysville, WA
Posts: 294
|
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 |
10-25-2012, 12:59 AM | #2 |
Account Suspended
Join Date: Dec 2008
Location: indisclosed
Posts: 1,515
|
Re: Cracked Exhaust Manifold Questions
Can you weld it back up?
|
10-25-2012, 01:01 AM | #3 |
Registered User
Join Date: Jul 2012
Location: Marysville, WA
Posts: 294
|
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 |
10-25-2012, 01:37 PM | #4 |
Account Suspended
Join Date: Dec 2008
Location: indisclosed
Posts: 1,515
|
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. |
10-25-2012, 02:00 PM | #5 |
Active Member
Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
|
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.
__________________
68 GMC 250/3 speed Saginaw p/b p/s 69 Chevy 350/350 currently in pieces still lookin for a cab 06 Trailblazer I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive... |
10-25-2012, 02:31 PM | #6 |
Registered User
Join Date: Dec 2008
Location: NW-Ohio
Posts: 2,525
|
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.
|
10-25-2012, 02:33 PM | #7 |
Account Suspended
Join Date: Dec 2008
Location: indisclosed
Posts: 1,515
|
Re: Cracked Exhaust Manifold Questions
i would like to formally withdraw any comments regarding the welding of cast iron.
|
10-25-2012, 02:56 PM | #8 |
Hollister Road Co.
Join Date: Apr 2005
Location: Houston
Posts: 6,134
|
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 |
10-25-2012, 03:55 PM | #9 |
Registered User
Join Date: Dec 2008
Location: NW-Ohio
Posts: 2,525
|
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.
|
10-25-2012, 04:07 PM | #10 | |
Active Member
Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
|
Re: Cracked Exhaust Manifold Questions
Quote:
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.
__________________
68 GMC 250/3 speed Saginaw p/b p/s 69 Chevy 350/350 currently in pieces still lookin for a cab 06 Trailblazer I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive... |
|
10-25-2012, 05:03 PM | #11 | |
Registered User
Join Date: Jul 2012
Location: Marysville, WA
Posts: 294
|
Re: Cracked Exhaust Manifold Questions
Quote:
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 |
|
10-25-2012, 05:37 PM | #12 |
Active Member
Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
|
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.
__________________
68 GMC 250/3 speed Saginaw p/b p/s 69 Chevy 350/350 currently in pieces still lookin for a cab 06 Trailblazer I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive... |
10-25-2012, 08:39 PM | #13 | |
Fabricate till you "puke"
Join Date: Jun 2002
Location: Ill
Posts: 9,403
|
Re: Cracked Exhaust Manifold Questions
Quote:
__________________
69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears.... |
|
10-25-2012, 09:18 PM | #14 |
Registered User
Join Date: Jul 2012
Location: Marysville, WA
Posts: 294
|
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 |
10-25-2012, 09:24 PM | #15 |
Registered User
Join Date: Jul 2012
Location: Marysville, WA
Posts: 294
|
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 |
10-25-2012, 09:46 PM | #16 |
Active Member
Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
|
Re: Cracked Exhaust Manifold Questions
The video doesn't work for me...
__________________
68 GMC 250/3 speed Saginaw p/b p/s 69 Chevy 350/350 currently in pieces still lookin for a cab 06 Trailblazer I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive... |
10-26-2012, 12:14 AM | #17 |
Registered User
Join Date: Jul 2012
Location: Marysville, WA
Posts: 294
|
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 |
10-26-2012, 03:17 AM | #18 |
Fabricate till you "puke"
Join Date: Jun 2002
Location: Ill
Posts: 9,403
|
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
__________________
69 longhorn,4" chop,3/5 drop, 1/2 ton suspension/disc brakes,1 1/2" body drop,steel tilt clip, 5.3/Edelbrock rpm intake/600 carb, Hooker streetrod shorties,2 1/2" exhaust/ H pipe/50's Flows , 6 spd Richmond trans,12 bolt/ 3.40 gears.... |
10-26-2012, 12:56 PM | #19 | |
Registered User
Join Date: Jul 2012
Location: Marysville, WA
Posts: 294
|
Re: Cracked Exhaust Manifold Questions
Quote:
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 |
|
10-26-2012, 01:50 PM | #20 |
Active Member
Join Date: Jul 2007
Location: Centrally located between Houston, Austin and Waco. BCS area.
Posts: 7,947
|
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.
__________________
68 GMC 250/3 speed Saginaw p/b p/s 69 Chevy 350/350 currently in pieces still lookin for a cab 06 Trailblazer I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive... |
10-26-2012, 01:54 PM | #21 |
Registered User
Join Date: Aug 2009
Location: Bowser
Posts: 13,522
|
Re: Cracked Exhaust Manifold Questions
Heat riser valve working!
Sounds like cold intake, lean misfire due to fuel puddling. |
10-26-2012, 11:08 PM | #22 | ||
Registered User
Join Date: Jul 2012
Location: Marysville, WA
Posts: 294
|
Re: Cracked Exhaust Manifold Questions
Quote:
Quote:
Adam |
||
10-26-2012, 11:24 PM | #23 |
Registered User
Join Date: Sep 2009
Location: Weare,NH
Posts: 1,589
|
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. |
10-26-2012, 11:28 PM | #24 | |
Registered User
Join Date: Jul 2012
Location: Marysville, WA
Posts: 294
|
Re: Cracked Exhaust Manifold Questions
Quote:
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 |
|
10-26-2012, 11:41 PM | #25 |
Registered User
Join Date: Dec 2008
Location: NW-Ohio
Posts: 2,525
|
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.
|
Bookmarks |
|
|