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  1. #1
    Join Date
    Oct 2003
    Location
    Saco River, Maine
    Posts
    118

    Default Vent on Distributor Cap

    My 5.7 Mercruiser has a thunderbolt ignition and the distributor cap has a vent on the side of the cap. What is the purpose of this vent and is it supposed to attch to anything? It look like the vent is setup to attach a hose but in my case there isn't one. RMB :) :)

  2. #2
    Join Date
    Jul 2003
    Location
    Jacksonville, North Carolina
    Posts
    4,145

    Default

    My distributor doesn't have the vent, but my service manual has the Thunderbolt ignition shown in it. They don't say anything about the vent, more than just to show it and mention its existence. There is nothing showing the vent with any kind of hose attached that I can see. In the instructions on removing the distributor cap, they don't mention pulling any hoses off of the vent.

    I can only conclude there is nothing to connect to the vent. It must only be there to possibly vent condensation to keep it from building up, the best I can tell. I'm sure it had something to do with a mistake in design, but the looks of it. Looks a little tacked on, if you know what I mean.

    I was reading something in here about using silicone for sealing the distributor cap to the distributor. They say that the curing process of silicone sealant gasses off acidic fumes and that can corrode the inside of the distributor. Just in case anyone thought about doing that. Not to mention considering that for other sealing processes in corrosive areas.
    Charles
    1981 14' Fisher john boat with 30 hp Mariner
    http://flickr.com/photos/71806267@N00/

    Find out just what any people will quietly submit to and you have the exact measure of the injustice and wrong which will be imposed on them.
    Frederick Douglass

  3. #3
    Join Date
    Oct 2002
    Posts
    1,664

    Default

    Easytime: Thanks for the reply. I guest you somed it up well. I know you can buy vented and unvented caps and the vent on mind is knurled for a small dia hose. It has to have something to do with moisture control. Thanks; RENE

  4. #4
    Join Date
    Jul 2003
    Location
    Jacksonville, North Carolina
    Posts
    4,145

    Default

    Possibly it's for a hose to run any dripping condensation away from the area, rather than having it drip straight down. I can't imagine what would connect to it... certainly not a vacuum hose or anything like that, by what I'm seeing in the manual. There is nothing there, that they show... just the vent.

    I'm sure a connected hose would keep moisture from migrating into the inside of the distributor, better than a plain fitting like that one. It's also possible that yours is either a later iteration or an initial modification. This is a 1998 manual. If yours is an older setup, it could have had a hose and they found it unnecessary for later models. No telling what's going on there.
    Good luck,
    Charles
    1981 14' Fisher john boat with 30 hp Mariner
    http://flickr.com/photos/71806267@N00/

    Find out just what any people will quietly submit to and you have the exact measure of the injustice and wrong which will be imposed on them.
    Frederick Douglass

  5. #5
    Join Date
    Jan 2003
    Location
    Vancouver Island, BC, Canada
    Posts
    2,555

    Default

    Rene:

    I once had a 351 cu/in which had a screen vented opening in the distributor. It was intended to allow moisture to escape, there was never a hose on mine, and I had it from near new. Ironically, that distributor was the most moisture prone beast I've ever owned. Until someone came out with electrical spray seal, I had a devil of a time with it.
    Enjoy,
    Tony
    1981 20ft Cuddy,
    4.3L Chev V-6

  6. #6
    Join Date
    Oct 2003
    Location
    Saco River, Maine
    Posts
    118

    Default

    Well folks here is the rest of the story. Bought a new distributor cap(with vent), rotor and plugs. Had no trouble taking old plugs out and putting new in. Used forum suggestion of using a 3/8 double knuckle, extension and socket to take out and a 12" section of a 1/2" air hose to start new plugs in. Then tightened with the socket. Went well. Now I'm about to learn a lesson.

    I started to change plug wires one at a time from the old distributor cap to the new one. After changing a few wires I started to run into problems because the distributor caps were getting in the way of each other and the wires wouldn't reach the new cap. Now the problem arisers, I started taking off more than one wire at a time without flagging them. Big senior moment; I lost track of the cylinders the wires went to. It took me an hour to track and flag the wires with cylinder no.s and finally get them where they belong. Re-tracking the wires is pain in the neck. Can't see them so it has to be done by feel and everything gets in the way.

    Lesson learned: FLAG THOSE PLUG WIRES with cylinder numbers as you take them off the distributor one at a time the first time you remove them. This mistake more than doubled project time and could have been avoided.

    PS: I did put a small 5" hose on the distributor vent leading to nowhere. It's long enough to hang just below the distributor housing. RMB :) :)

  7. #7
    Join Date
    Jul 2003
    Location
    Jacksonville, North Carolina
    Posts
    4,145

    Default

    Does it run?

    Sounds like ya done gud... hope everything works fine for you. That's probably a good way to use that vent. Just thinking about it. I don't know anything about it, but it sounds good to me.
    Charles
    1981 14' Fisher john boat with 30 hp Mariner
    http://flickr.com/photos/71806267@N00/

    Find out just what any people will quietly submit to and you have the exact measure of the injustice and wrong which will be imposed on them.
    Frederick Douglass

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