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Thread: crankcase vent valve

  1. #1
    Private point's Avatar
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    Dec 2015
    Vancouver Canada
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    Default crankcase vent valve

    Hi guys. I have a Canadian M37 with a few problems. I am trying to take the vent valve apart and I would swear that it is one solid piece and will not come apart. Any advice?
    Also, should the vent valve completely block air flow or just restrict it? When cranking the engine I get very little suction at the carb unless I block the vent valve tube. Any info would be great.

  2. #2
    4 Star General frank8003's Avatar
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    May 2012
    Ft. Lauderdale, Florida
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    PCV vs NCV
    Is it designed as positive crankcase ventilation or negative crankcase ventilation?
    A specific engine and application would be nice to know with particulars..................
    Photos and pictures for tho old guys too!
    Last edited by frank8003; 08-18-2019 at 00:01.
    I was here, had a good time.

  3. #3
    Sergeant Major
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    Jun 2015
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    I believe you are talking about the valve that connect to the manifold, right below the carb. This should be a pcv valve with some brass fitting , and it may or may not be connected to a swivel valve and then into the 3/16 hard tubing if i'm right. This is for the fording system and since you said if you shut in, believe the shut off valve should be still in the connection line. First you have to remove the whole assembly there, just unscrew from the hard line and then the manifold. When on a bench, use heat as needed and remove the brass fitting (don't damage them). Once down to the round pcv, you can unscrew the top, if you wire wheel it, you will find the marking and arrows to tell which way to unscrew and arrow for installation.

    The pcv valve will block about 98 % of the air, but that for back flow purpose to keep water and what not from getting in, you brass swivel valve is what truly cuts or enables the flow. If you are having vacuum issues, i would not really be looking at the pcv, check to be sure, but remember engine suppose to be able run just fine (lower rpm) with the valve closed. I would suggest you mainly check pistons, and of course check for vacuum leaks on the carb its self. Also remember to check vaccum, the engine needs to be up to running temp, or any vac gauge reading will be off. Also the crank speed is a bit lower than running, so that is not the correct way to check. Once again check your pistons for cranking vac.

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