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| DESPERATE over head-exhaust manifold leak https://slantsix.org/forum/viewtopic.php?t=68137 |
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| Author: | Daddiojoe [ Wed Mar 26, 2025 12:47 pm ] |
| Post subject: | DESPERATE over head-exhaust manifold leak |
Sorry, but this is going to be a fairly long post. I have been working on this since September. I really need some help and suggestions before I remove the head and take it in for machining (final thing I can think of, although there are no obvious blemishes). Besides the exhaust, my 225 2bbl is running just fine. Problem: significant exhaust leak at last lower stud. (Second to last total--towards the firewall). History: started after having exhaust work done to go back to a half stock exhaust manifold instead of rear Dutra Dual. I felt that the Dutra exhaust was too close to the starter. The mechanic pointed out some obvious places where the exhaust gasket had shifted, so it needed to be replaced. I do not think that the current leak was manifesting at that time. Attempted Solutions: This is going to be long, as I have been working on this particular problem for months. NUMEROUS Remflex gaskets (literally lost count). Some got torn at installation, or afterwards. Also tried using two gaskets at once ONE Fel-pro gasket, just to make certain. Liberal amounts of hi-temp RTV on head, gaskets, and manifolds, in different configurations. Replaced stud Replaced nut Had exhaust manifold trued level at machine shop--both the surface near the problem area and then the whole thing machined. Cleaned out and tapped the bolts that hold the manifold (stock 2 bbl) to the exhaust manifold and bolted the two together again. They weren't bolted together initially. Had exhaust manifold welded inside around where it was leaking. Returned to welder and had possible hairline cracks on the manifold welded from the outside. Decided to go back to the Dutra Dual rear manifold w/ its nice thick flange (wrapped started in heat protection). Dutra Dual was known previouly not to leak. Also fabricated new exhaust connection. My fabricated exhaust works fine, but the same old leak is back worse than ever. I need some magic beans or special sauce or something. Please help. Thanks, Joe |
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| Author: | SlantSixDan [ Wed Mar 26, 2025 1:08 pm ] |
| Post subject: | Re: DESPERATE over head-exhaust manifold leak |
Starter clearance/heat with a rear Dutra Dual exhaust is a non-issue with the starter shown and described here and here. What year cylinder head are you running, and how certain are you (from what evidence) that the exhaust is leaking out through the rearmost manifold runner/head junction? |
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| Author: | Daddiojoe [ Wed Mar 26, 2025 3:06 pm ] |
| Post subject: | Re: DESPERATE over head-exhaust manifold leak |
Dan-- The head is from an early 70s slant six. Does have the spark plug tubes. Does not have the holes in the far back. I am using a starter from a 90 Dakota, and it does come pretty close. But that's not my biggest concern right now. I am certain of the leak location because I am using a rubber fuel line to listen to where the leak is coming from. All other studs and also exhaust pipes and connections are fine. I spent a lot of time on this. Glad that you are helping out, Joe |
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| Author: | Dart270 [ Thu Mar 27, 2025 7:33 am ] |
| Post subject: | Re: DESPERATE over head-exhaust manifold leak |
I wonder if the bottom edge of the manifold is hitting the top of the block or the starter and preventing seating of the manifold? Sounds like you've tried all the normal stuff. Lou |
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| Author: | Reed [ Thu Mar 27, 2025 9:55 am ] |
| Post subject: | Re: DESPERATE over head-exhaust manifold leak |
Have you felt with your bare hand around the area you suspect is leaking (obviously on cold startup before the metal gets too hot) to confirm that there, in fact an exhaust leak? This is another way of asking "how sure are you that what you are hearing is an exhaust leak?" Have you double checked mechincal causes such as valve lash? |
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| Author: | Rick Covalt [ Thu Mar 27, 2025 1:29 pm ] |
| Post subject: | Re: DESPERATE over head-exhaust manifold leak |
Spray a little something down the carb over towards the back 3 cylinders that will create some smoke. Sea Foam spray does Ok. Watch the problem area for smoke. If you have / had 2 cracks in the exhaust manifold I would probably get another one. Is there any possibility that you are tightening the top side bolts to much before the bottom? Just thinking out loud. |
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| Author: | Reed [ Thu Mar 27, 2025 1:44 pm ] |
| Post subject: | Re: DESPERATE over head-exhaust manifold leak |
Also, are you following the corrct manifold installation procedure? https://www.slantsix.org/articles/manif ... unting.htm |
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| Author: | Rick Covalt [ Thu Mar 27, 2025 2:58 pm ] |
| Post subject: | Re: DESPERATE over head-exhaust manifold leak |
Honest truth is you should have a lot of forgiveness with the Remflex. And they probably don't like to be over tightened. I always use the thick green gaskets that Jim Cox / Brian Droshak had made up. They are harder and you can crank them down tighter than called for if needed. I have used them mainly with headers, but have used them with Dutras and stock manifolds without leaks. The only time I ever had a problem was with the lugs at the top of the block interfering with the gasket and not letting it pull back tight. I always cut those off now. |
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| Author: | Daddiojoe [ Thu Mar 27, 2025 3:49 pm ] |
| Post subject: | Re: DESPERATE over head-exhaust manifold leak |
Thanks everybody for your thoughtful replies. Rick and Reed: yes, I am absolutely certain about where the leak is coming from. I can hear it through old fuel line hose, feel it with my hand, and see sparks coming from the area when I open the throttle up. I have used proper procedure and tightening. I have used both a modified stock exhaust manifold and a Dutra exhaust manifold with the same results for both. Where can I get the green manifold gasket that was mentioned? Not sure how valve lash would create an exhaust manifold leak. Wouldn't whatever amount of exhaust leaving the cylinder go out the exhaust manifold? Lou: I thought of that, and have moved around the manifold and tried both the stock (modified) and Dutra dual. Same leak in same place. I appreciate your ideas about helping me solve this problem, Joe |
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| Author: | Rick Covalt [ Thu Mar 27, 2025 7:25 pm ] |
| Post subject: | Re: DESPERATE over head-exhaust manifold leak |
Username "Brian" on here is Brian Droschak. He is the gentleman that last had them made. Since you have changed out several gaskets, could you see the spot where it is leaking? Burned black where it was leaking? Quote: I wonder if the bottom edge of the manifold is hitting the top of the block
I agree with Lou on this possibility, because it happened to me too. If you had the manifolds trued flat and you have a good gasket ( Of anykind), and you draw it up flat and even against the head, then I don't see how it can leak unless something is holding it out. After going through all this work over and over, I'd take some pictures coming apart. And for sure I'd take a grinder and cut off those lugs at the top of the block. At least that eliminates that possibility. Good Luck! |
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| Author: | Reed [ Thu Mar 27, 2025 10:53 pm ] |
| Post subject: | Re: DESPERATE over head-exhaust manifold leak |
I mentioned valve lash before you said all the rest about feeling it and seeing sparks. I though you might be hearing a loose rocker arm and calling it an exhaust leak. However, given what you say you have observed, I also agree it sounds like something is physically keeping the exhaust manifold from sealing against the head. |
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| Author: | ceej [ Fri Mar 28, 2025 6:34 am ] |
| Post subject: | Re: DESPERATE over head-exhaust manifold leak |
If the deck has been cut, make certain the manifold is not interfering with the casting surfaces on the side of the block. I ran into that with a heavily cut deck. Relieve the pads on the block as needed to allow the manifold to run down flat.. CJ |
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| Author: | Dart270 [ Fri Mar 28, 2025 7:31 am ] |
| Post subject: | Re: DESPERATE over head-exhaust manifold leak |
I like the idea of a cracked exhaust manifold too, but the not seating idea is still my favorite. |
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| Author: | volaredon [ Fri Mar 28, 2025 9:49 am ] |
| Post subject: | Re: DESPERATE over head-exhaust manifold leak |
What's this green manifold gasket you guys speak about? Anything comparable to reflex or something else? |
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| Author: | Rick Covalt [ Fri Mar 28, 2025 10:04 am ] |
| Post subject: | Re: DESPERATE over head-exhaust manifold leak |
No it is a much stiffer gasket. It allows you to draw up the bolts much tighter and not cut or tear or smash out. I think Jim Cox had the first ones made years ago for their racing efforts. I grease the face of mine and I can usually reuse them 2 or three times when removing my headers. |
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