Manifold heat contol valve

Engine, Transmission & Driveline

  1. ALLAN

    ALLAN New Member

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    Just found out that the righthand manifold heat control valve is 'Well seized' shut, questions :- any gotcha's to watch out for when I simply remove and fix ?
    What does this do ? The car has been difficult to start when hot.
    A similar setup on my 235 C...y had been removed, is this a route to a cure.
    Engine is a standard 318 with a/c in a 70 Polara
     
  2. FURYGT

    FURYGT Senior Member

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    You most likely just found your hot start problem. Unless you drive the car a lot in very cold weather, just remove it and plug the holes (some people use short bolts).

    This is also cold an exhaust manifold heat riser. It's function is to help the engine warm up quicker by restricting the exhaust flow to build engine heat. A spring on the counterweight is supposed to open the valve once the engine is up to temperature. You may be able to lubricate it and free it up if all of the parts are still there but its rare that you can free them up. You can buy a replacement kit.
     
  3. jct

    jct Senior Member FCBO Gold Member

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    Lube it up really good and tap on it with a hammer
     
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  4. mr. fix it

    mr. fix it Old Man with a Hat

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    Reason it is frozen is the shaft(steel) rusted and impregnated the bronze bushings on a microscopic level.
    There used to be a heat riser spray. could be still
    PB blaster should free it up.
    I suggest you hit it with graphite spray once freed up.
    Keep an eye on it and lube as required.
    Don't be surprised if it starts to leak afterwards.
    Mine does a bit.
     
  5. CBODY67

    CBODY67 Senior Member

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    When we had the valve replaced on our '66 Newport (back when Chrysler still built the parts to do that), when reassembled, the supplied bronze bushings for the exhaust manifold were "tight" and didn't allow the shaft to move fully with just thermostatic spring tension. So, the shaft was removed and the bushings reamed so the valve moved freely and easily.

    Typically, the valve will remain mostly closed during normal operation. The spring will keep it that way, until exhaust flow opens it. The valve plate is slightly off-set to help move the counterweight to open the valve. The earlier ones had such a counterweighted system, but later ones just had the spring with a round "weight".

    So most valves will stick in the 1/3 open position, from my experience. It sends exhaust heat up through the intake manifold's "heat riser passage", which is ALSO where the carb's automatic choke thermostat is located! If no heat goes up there, then the automatic choke won't come-off as soon as it should, which can cause poor performance and fouled spark plugs. 318s that only see town miles will eventually coke-up the passage, which will require the manifold to be removed and the accumulation chiseled out (which many '66 Belvederes the local dealer sold to older ladies needed after a few years of operation, just to get the automatic choke to work.

    So, get things free'd-up to get the shaft out of the manifold. Ream out the bronze bushings (which should be the friction interface between the cast iron manifold and the steel shaft) so that the cleaned-up shaft will move freely in the bushings. This is important! Then reinstall everything with some high-heat lube. THEN, every oil change or so, make sure the valve is working freely.

    IF you have a carb with a full electric automatic choke, then no exhaust heat to the intake manifold passage is not a big deal.

    The OTHER function of keeping that passage working is for fuel atomization in the manifold plenum, during warm-up. Until the engine block's heat convects into the manifold itself. An aluminum manifold tends to quicken this, though.

    In our moderate N TX climate, I never could tell one way or the other if hot restart performance was really affected. Of if normal drivability was really impacted with the valve being just less than 1/2 way open/closed. Never did need to get much past 1/2 throttle anyway.

    Consider the heat riser valve to be a part of the supporting cast of characters for efficient engine fuel system performance. Take ONE part out and it can mean the rest will have to be re-tuned a bit to compensate.

    By observation, Chevy engines also have had heat riser valves, too. Even the 6 cyl engines. Most stuck about 1/2 open/closed, too. No starting issues that I have known off. Generally didn't get fixed, either.

    My '77 Camaro had a heat riser valve that was vacuum operated, which I thought was a plus. Keep it working. Until the linkage fell off after several 100K segments. Ball stud wasn't round any more. That valve made a big clanging noise, due to exhaust flow pulses in the manifold. Certainly NOT a smooth flow! Which is probably why Chrysler used that "couinterweight" to dampen the valve's rotation against a spring.

    Just some thoughts,
    CBODY67
     
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  6. Ross Wooldridge

    Ross Wooldridge Senior Member FCBO Gold Member

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    Kits are available at www.dynamicrenovation.net

    They're not cheap, but they're correct.

    Having a working heat riser is a good thing for all the reasons listed above. Keep it lubed up properly and you'll be good for years with it.
     
  7. dart1962_440

    dart1962_440 Member

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    The heat riser spray is still available - part number 04318039AE . It's called Rust Penetrant now. I got mine from Amazon.
     
  8. HWYCRZR

    HWYCRZR Senior Member FCBO Gold Member

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    My local Dodge, Chrysler dealer had 7 cans in stock. About $9.00 It worked great. Very smooth action with only the spring resistance now. I was reluctant to use other lubes or penetrates with the high heat. I didn't want it to burn off the solvent and leave a sticky residue.

    Edit
    Sorry, didn't notice you were in UK, Local Dodge dealer may be difficult to find.
     
  9. HWYCRZR

    HWYCRZR Senior Member FCBO Gold Member

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    Service manual does a good step by step process of changing the heat control valve. (at least in the '68 manual)
     
  10. Davea Lux

    Davea Lux Senior Member FCBO Gold Member

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    It would be a good idea to keep the heat riser if you can as your automatic choke will not function properly without it. The heat riser forces exhaust under the carb to warm up the intake and the choke spring to cause the choke to release. A heat riser that is stuck shut will cause the carb to boil which in turn dumps fuel into the engine after the engine is turned off. That is most likely the cause of your hot start problem. Back in the days of leaded fuels, the heat riser would stick from lead deposit fouling. These days it is mostly rust that makes them stick. If necessary, you can disassemble and replace the heat riser as noted above, usually some patient tapping and a good rust penetrating oil will do the job. If the little spring on the heat riser has failed you will need to buy a replacement kit. The other option would be a wrecking yard complete manifold as 318 exhaust parts are usually pretty cheap.

    Dave
     
  11. ALLAN

    ALLAN New Member

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    I'll have a nose around our turbine shop, should have some useful lubes in there:thumbsup: I don't think this engine has been looked after for some time other than oil changes, It'll give me something to do on these soggy June days...
     
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  12. ALLAN

    ALLAN New Member

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    That went well :thumbsup: soaked it over night then gently persuaded it to move, a few light taps and a gentle wiggle, then I started on the job :) I removed a lot of carbon from around the butterfly. It now moves well and returns under the spring. I feel a fraud as I didn't skin my knuckles at all. Thanks again for the info, I now know to keep a check on it.:thankyou:
     
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  13. mr. fix it

    mr. fix it Old Man with a Hat

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    well if it makes you feel better go and scrape your knuckles on the bricks somewhere to give you that feeling that we all love to hate as the blood trickles down our fingers.:lol:

    Glad you got it working.:thumbsup: