I did a brief search on the forum but If I missed the answer I apologize ahead of time. If so, just link to where it is and I can read it for myself.

Here's what I have. A daily driven A100 van with slant six 2 bbl Carter carb, dutra duals, 727 auto, MSD ignition with electronic distributor. I had recently driven the vehicle when this work commenced. It had a very smooth idle before this began.

I cracked the factory exhaust half and had to replace it. After reassembly and the first crank up I have noticed it has a rougher idle. I checked it (with a temp gun on the exhaust legs) and found cylinders #1 and #6 are essentially dead at idle. When I put it in gear it shakes pretty good. I have driven it and while the idle is rough as soon as its off idle it runs smooth with the same or more power than before I started the manifold change.

Here is what has me worried. When I installed the intake/exhaust manifold after having it trued up by a machine shop with a table sander I neglected to clean it out properly. When I fired it up the first time and found the dead cylinder issue I pulled it all apart. I realized there was quite a bit of metal powder still sitting in the runners and feared the worst. Not finding any other reason for the dead cylinders, I pulled the head. I did not find anything of major concern so I wiped down the cylinder walls and head combustion chambers with a little oil to try to remove any shavings/dust that may have made it in there. After all that and doing the checks noted below, I still have cylinders 1 & 6 dead at idle but running great above idle.

I have checked/adjusted the following after final reassembly:

Valves, .010 Intake .020 Exhaust. Adjusted with the engine running and fully up to temp.

Spark plugs, swapped positions problem persists on the same cylinders.

Spark plug wires, swapped, no effect.

Compressions, 87, 95, 92, 102, 96, 95

Vacuum leaks, none as far as I can tell. No open ports on this intake manifold. Manual brake vehicle.

Timing, 12 initial

Carb, minor idle mixture adjustment.

Suggestions?

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1968 A100 Van, 225, 2bbl intake, carter bbd, 727, 3.55 sure grip, Scarebird front disc conversion. Van was originally a CA fire department vehicle.

Most likely cause: vacuum leaks at the #1 and #6 intake runner-to-head junctions.
That won't have helped the longevity of your engine, but neither will it have finished the engine off.
If your gauge is accurate and the compression test was done with all spark plugs removed, the engine warm, and the throttle fully open, these are really low numbers indicative of an engine past due for overhaul.
Try shooting some carburetor cleaner at the #1 and #6 intake-to-head junctions and see if that changes the idle quality any.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Dan,

Thanks for the response. I was leaning towards a vacuum leak myself but I did everything "by the book" this time when installing the manifolds and was hoping that wasnt it. I am sure I caused the old manifold to crack by over torqueing (and not paying attention to washer placement) the last time. Right now they are torqued to 10 ft lbs, I will try bumping them up to 15 or so after confirming a leak is the issue.

On the compression, I did not have the throttle open, but did have all the plugs out and it was warmed up. I will recheck those numbers with the throttle/choke open but I suspect it is due for an overhaul. Just want to get this issue figured out first.

I will report back when I have it figured out.

Thanks again,
Chris

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1968 A100 Van, 225, 2bbl intake, carter bbd, 727, 3.55 sure grip, Scarebird front disc conversion. Van was originally a CA fire department vehicle.

Ok,

I retorqued the intake/exhaust nuts and that solved the problem. I torqued them to 15 lbs instead of 10. Something so simple. Runs great now at idle.

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1968 A100 Van, 225, 2bbl intake, carter bbd, 727, 3.55 sure grip, Scarebird front disc conversion. Van was originally a CA fire department vehicle.

I do not think you will like the long-term results of this what you've done. You have to remove and replace the manifolds, this time with a good gasket (Remflex) and the nuts not overtorqued. Wether you do it now or later determines whether you also have to buy an uncracked exhaust manifold.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Dan.....first post claims Dutra duals. That doesn't relieve him of the responsibility of doing it right, but it shouldn't crack any more manifolds.

Roger

Dan,

I thought I saw somewhere on the forum that 15lbs was recommended. At any rate, I do not want another cracked manifold, that's what started this journey 2 or 3 months ago. I do have a Dutra front half but the rear is a stock modified one that will crack if not installed right I am sure.

Whats the best price for a Remflex? I am seeing $48.99 from Remflex.com, I am guessing it doesn't get much better?

Edit 2: I found a seller that has them for $37.59 + 7.50 shipping. Anyone know of a better price?

Edit 3: I found one on Amazon for $39.99 with free shipping and grabbed it. I think I got a decent deal.

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1968 A100 Van, 225, 2bbl intake, carter bbd, 727, 3.55 sure grip, Scarebird front disc conversion. Van was originally a CA fire department vehicle.

I installed a set of home-made dual exhaust manifolds on my brother's van years ago. You have to be very careful about lining the manifolds up to the ports in the head and with the tightening pattern used to secure the manifolds. What i did was put the exhaust manifolds face down on the new manifolds gasket and feel from the bottom of the gasket if the manifold ports were lined up with the holes in the gasket. When they were aligned I traced the outline of the manifold on the gasket with whiteout. Then when i went to install the manifolds on the engine i could line the manifold up with the white-out lines and carefully torque them down. When torquing the manifold nuts down I followed the same in-to out alternating top to bottom pattern as the regular manifold installation process, but I treated each exhaust manifold separately.

I used a stock Fel pro gasket and haven't had any trouble with sealing.

Thanks for that input. That very well may have been what I neglected to do, properly line up the gasket. At this point I have already ordered the gasket and will use it as it sounds like I will never have to worry about leaking manifolds with it. But, I will use your technique, thanks for that!

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1968 A100 Van, 225, 2bbl intake, carter bbd, 727, 3.55 sure grip, Scarebird front disc conversion. Van was originally a CA fire department vehicle.

With Dutra Duals it is safe to tighten to a higher torque spec as it is the expansion with heat and the contraction with cooling that causes the cracking. Splitting that exhaust system into two parts reduces the expansion by half. In my opinion, those cone washers are a serious design compromise on our beloved slant. Before I replaced my stock exhast with Dutra duals, Vacuum readings were poor and unsteady when cold. It was not until things heated up that the assemly sealed well. I would not worry about 15lb torque on those bolts. I tightened mine to some unkown "very tight" torque ten years ago, and have had no problems. When I thought there was a problem there last year it turned out the exhaust pipe flange gasket had burned. Manifold gaskets were still sealed tight.

Sam

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Sam,

Thanks for the input. It makes sense that the expansion is half with the Dutra modification. If it were not for the fact that I have just experienced a cracked exhaust manifold I would not be as worried about it happening. Previously I had just torqued the manifold without a torque wrench and it cracked right in half after a couple years in service. As it is, I do not want to go through this again any time soon, so I have purchased the high dollar gasket and will be sticking with 10lbs (or less) of torque. Not saying the high dollar gasket is required, but its the route I am going.

Chris

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1968 A100 Van, 225, 2bbl intake, carter bbd, 727, 3.55 sure grip, Scarebird front disc conversion. Van was originally a CA fire department vehicle.

Coefficient of thermal expansion is still the same for one half of a cast iron manifold as the whole. Where exhaust manifold has no center bolt attachment as intake, expansion can be in both directions or one direction depending on where the tightest attachment point is. Where exhaust manifold is close to one half length as its whole, expansion could remain the same if in one direction because of its matting or securing to intake or half the distance of what a whole exhaust manifold would produce. My money is on expansion in one direction due to that center bolt of intake which positions or clocks rear half of exhaust manifold. Same goes for Dutra front casting.

I would adhere to FSM torque specs.


Cold weather wrenching:
Compare cast iron expansion rate to aluminum; this is why it is so difficult to remove a steal bolt from an aluminum casting when below zero; the hole's diameter shrinks about twice the amount the bolt causing binding.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

I installed the new Remflex gasket, torqued to 6 ft lbs, and have no more leaks! Hope I don't have to do that again for a while. I will remember Remflex for any other exhaust manifold gaskets I may need. Very good product.

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1968 A100 Van, 225, 2bbl intake, carter bbd, 727, 3.55 sure grip, Scarebird front disc conversion. Van was originally a CA fire department vehicle.