leaking intake valve

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1 rider
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leaking intake valve

#1

Post by 1 rider »

looking for some help. I have a rear head on a 1949 panhead with plumbers intake manifold. this head was rebuilt with motor. after assembling the cycle and running found out it had intake leaks . remedy peek seals on the manifold. but when I pressurized the heads it blows out the spark plug hole only on the rear head only. I have taken the head off and lapped the intake valve. after filling with water and believing it not to leak I reinstalled the head only to have air coming out the sparkplug hole again. repeat with the same result. what am I missing? I tighten heads in a cross pattern. :?:
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Re: leaking intake valve

#2

Post by RUBONE »

How are you pressurizing the head? Is the piston at TDC when you are doing it? You cannot pressurize both heads at once, one will always have a valve partially open due to the 45 degree design relative to the valve timing sequence.
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Re: leaking intake valve

#3

Post by blewcrab »

1 rider wrote: Tue Aug 15, 2017 12:47 am looking for some help. I have a rear head on a 1949 panhead with plumbers intake manifold. this head was rebuilt with motor. after assembling the cycle and running found out it had intake leaks . remedy peek seals on the manifold. but when I pressurized the heads it blows out the spark plug hole only on the rear head only. I have taken the head off and lapped the intake valve. after filling with water and believing it not to leak I reinstalled the head only to have air coming out the sparkplug hole again. repeat with the same result. what am I missing? I tighten heads in a cross pattern. :?:
lift the pushrod tubes so you can see the position they are in ....rotate the engine so all pushrods are down ,then do the manifold pressure test .....
1 rider
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Re: leaking intake valve

#4

Post by 1 rider »

thx for the response . the pushrods are not in its just closed valves . and pressurized the manifold thus the leaking out the sparkplug hole. when the head was off and the valve lapped I done a leak check by filling the intake chamber with water . waiting a day or two no leaks then re assemble head . I figure if the lapping job was bad it would leak? I pressurize the head by installing manifold blanking it off with an adapter so I can slowly put air in about 10 psi .
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Re: leaking intake valve

#5

Post by RUBONE »

Are the valves deep into the seats? There could be a problem with the rocker arm hitting the pan and keeping the valve off the seat. One more variable to look at.
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Re: leaking intake valve

#6

Post by blewcrab »

1 rider wrote: Thu Aug 17, 2017 1:08 am thx for the response . the pushrods are not in its just closed valves . and pressurized the manifold thus the leaking out the sparkplug hole. when the head was off and the valve lapped I done a leak check by filling the intake chamber with water . waiting a day or two no leaks then re assemble head . I figure if the lapping job was bad it would leak? I pressurize the head by installing manifold blanking it off with an adapter so I can slowly put air in about 10 psi .
you had better take off the head and get a good look at it ....could be a crack ....the problem should show itself . also I have used gas to check for valve leaks , gas will pass thru when water wont ...jus a thought
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Re: leaking intake valve

#7

Post by 1 rider »

thx a crack is what I was afraid of will try the gas and take a closer look.
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Re: leaking intake valve

#8

Post by Frankenstein »

I squirt brake clean into the port to check valve sealing, move the head around 'til all the seat area is immersed in fluid, and count to 10. No wetting around the valve, I figure it's good.
DD
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