Manifold test

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Weston1955
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Manifold test

#1

Post by Weston1955 »

Hello there. Got my heads back on and motor buttoned up but upon doing a manifold test I can across something that's stumping me. Upon pressurizing the manifold to test for leaks I'm noticing a small amount of air escaping past the valve into the chamber. The heads are brand new std panhead replicas with new valves and seats and guides. I heard a small amount of air coming though the spark plug hole and I'm wondering if pressurizing it is pushing the valve open just slightly? All pushrods are removed and the motor is out of the bike. I know the air has to go somewhere when going through manifold but didn't know if 12lbs was enough to open valve. Thanks again everyone for your time and help
    Weston1955
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    Re: Manifold test air pressure

    #2

    Post by Weston1955 »

    Weston1955 wrote: Tue Sep 12, 2017 1:17 am Hello there. Got my heads back on and motor buttoned up but upon doing a manifold test I can across something that's stumping me. Upon pressurizing the manifold to test for leaks I'm noticing a small amount of air escaping past the valve into the chamber. The heads are brand new std panhead replicas with new valves and seats and guides. I heard a small amount of air coming though the spark plug hole and I'm wondering if pressurizing it is pushing the valve open just slightly? All pushrods are removed and the motor is out of the bike. I know the air has to go somewhere when going through manifold but didn't know if 12lbs was enough to open valve. Thanks again everyone for your time and help
      Bigincher
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      Re: Manifold test

      #3

      Post by Bigincher »

      No, 12psi won't push a valve open.
      Weston1955
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      Re: Manifold test

      #4

      Post by Weston1955 »

      Bigincher wrote: Tue Sep 12, 2017 6:06 am No, 12psi won't push a valve open.
      So in your opinion, what could be causing this?
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      Re: Manifold test

      #5

      Post by Bigincher »

      Wish I could tell you, but I'm not there.
      Have you researched older threads? This was just recently discussed. Below the last post in this thread you should see "Similar Topics". Start reading there, that's all I can say.
      If it was mine, I'd make sure the manifold and seals don't leak, put the fukker together and run it. Brand new motor, not broke in, none of the mating surfaces worked together yet- give it a chance, but watch it.
      Otherwise, tear it apart and chase a ghost. If there's really a problem it will show up, tear it apart when you know what it is.
      But that's just me....
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      Re: Manifold test

      #6

      Post by Excalibur »

      I'd slide the head off and pressurize its' intake port. Use soapy water to determine where the leak is coming from. If it's coming past the valve-to-seat, use grinding paste to lap the valve in. Typically I lap valves by hand just to be 110% sure. Lapping valves in, isn't done much these days but I still have some paste and a valve grinding stick in the shed. A quick-and dirty method of checking valves for sealing is to tip gasoline into the port and carefully observe from the combustion chamber side.

      PS. you may be aware that I had a pin hole in my front STD head from new. It was in the oil gallery to the rocker feed. It made a large leak in short order. Hoping a pin hole isn't your problem!
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      Re: Manifold test

      #7

      Post by Northman »

      Weston, are your push rods installed? Just asking, you could have one lifting a valve slightly.
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      Re: Manifold test

      #8

      Post by Mark44 »

      Northman wrote: Tue Sep 12, 2017 11:08 am Weston, are your push rods installed? Just asking, you could have one lifting a valve slightly.
      In post #1, he said all pushrods are removed.
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      Re: Manifold test

      #9

      Post by Weston1955 »

      I appreciate all the responses. Since the motor was out and on the bench I figured I would just pull the head to investigate. I pressurized the intake and noticed the front intake valve was not completely seating so I pulled the springs and did a light lapping of the valve/ seat surface. Put it back together and tested again and all is well. So back together it goes.
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      Re: Manifold test

      #10

      Post by Northman »

      Mark44 wrote: Tue Sep 12, 2017 5:54 pm
      Northman wrote: Tue Sep 12, 2017 11:08 am Weston, are your push rods installed? Just asking, you could have one lifting a valve slightly.
      In post #1, he said all pushrods are removed.
      Yep, blew over that part.
      Sounds like you have taken care of. Were the seats cut or ground on your job?
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      Re: Manifold test

      #11

      Post by Mark44 »

      Weston1955 wrote: Tue Sep 12, 2017 10:54 pm I pressurized the intake and noticed the front intake valve was not completely seating so I pulled the springs and did a light lapping of the valve/ seat surface. Put it back together and tested again and all is well. So back together it goes.
      That would have been my next question, were the valves lapped into the seats.
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      Re: Manifold test

      #12

      Post by Weston1955 »

      Looks like they were ground with a slight oversight of lapping the one valve completely. After doing that it's air tight and blows the plug out before lifting the valve.
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      Re: Manifold test

      #13

      Post by Bigincher »

      Excellent! Thanks for posting the results of this little exercise. It's good for everyone.
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