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Technical Flathead Ford weird vacuum problem

Discussion in 'Traditional Hot Rods' started by Custom Riviera, Jul 8, 2019.

  1. Custom Riviera
    Joined: Jan 16, 2006
    Posts: 35

    Custom Riviera
    Member

    The engine runs badly and there's an unusual situation with vacuum under the intake manifold, in the lifter valley. When I remove the oil fill breather and put my hand over it, it nearly sucks my hand in. When I spray carb cleaner down the oil fill, the RPM increases. Spraying carb cleaner around the manifold makes no difference. The compression is 110-120 in all cylinders except #5 which is 80-lbs. It doesn't idle or accelerate smoothly, it runs like there's a bad vacuum leak. It idles (roughly) with about 5-hg of vacuum, and the needle bounces a bit. The engine is a 59AB, I believe it has low hours, but hasn't been driven in many years. I swapped the intake manifold and installed a new gasket after cleaning the mating surfaces. I tried different carbs, adjusted the timing, but no difference.
    Where do I begin to diagnosis why there's vacuum under the intake manifold?
     
  2. I'm no expert on flatheads, but a cracked intake manifold would explain the condition you describe. The crack could be on the bottom of the manifold. Or a failed intake gasket, again near the bottom of the intake port. Has the engine ever run properly while in your possession or has the intake been recently changed? Maybe a porous casting somewhere or improper gaskets?
     
  3. nice read...will follow......
     
  4. Custom Riviera
    Joined: Jan 16, 2006
    Posts: 35

    Custom Riviera
    Member

    ClayMart,
    Thanks for responding, I replaced the intake manifold and carb with known good units and new gaskets. I looked for cracks or splits, and found nothing. The car is new to me and I never heard it run any better then it does now.
     

  5. So what do you have for crankcase ventilation? Vented fill cap and a road draft tube, or has someone added a PCV system? If there's a PCV valve installed somewhere make sure it hasn't gotten fouled and is always stuck in the open position. Some pictures of the engine from a couple different angles might be helpful as well.

    Now I'm really grabbing at straws here, but... intake valve guides...?? o_O
     
  6. landseaandair
    Joined: Feb 23, 2009
    Posts: 4,409

    landseaandair
    Member
    from phoenix

    Very worn or damaged intake guide or guide bore?
     
    Cosmo50 likes this.
  7. Whew... Thanks! ;) I'm glad to know that somebody's got my back on this. :rolleyes:
     
  8. alchemy
    Joined: Sep 27, 2002
    Posts: 16,270

    alchemy
    Member

    I would think a valve guide would have to be worn to a half inch wide hole before it would make such a sucking vacuum that you could feel it with your hand on the fill stand.

    Is the proper original breather still in the front corner of the pan rail? Are you using a pre-48 intake? Were there any modifications to the venting tube inside the valley?

    you said you replace the intake and gasket again? Did you note anything at all on the ones you replaced? Were does your vacuum brake for the distributor hook to the intake?
     
  9. Yeah, I know. That's why I said I was grasping with my initial reply. :rolleyes:

    It looks like at least some flatheads used a split, two-piece valve guide. Don't know if they were just a press fit or if there was some other way they were retained that might be a common weakness on those engines. :confused:
     
  10. alchemy
    Joined: Sep 27, 2002
    Posts: 16,270

    alchemy
    Member

    Crap, I had a senior moment. Yes his 59A might have split guides. But even if they are worn more than any others in history, it still shouldn't be causing enough vacuum in the valley to hold his hand to the pipe.
     
    Last edited: Jul 9, 2019
  11. 48fordnut
    Joined: Nov 4, 2005
    Posts: 3,895

    48fordnut
    ALLIANCE MEMBER

    With my limited knowledge of flat heads ,all of the up thru 48, 59 A had split guides.8ba,8cm, started in 49 with the single piece guide and regular stem valves. 48 and earlier had the tulip valves and split guides. There are keepers that hold both types in the block.
     
  12. Boryca
    Joined: Jul 18, 2011
    Posts: 688

    Boryca
    ALLIANCE MEMBER
    from Detroit

    Watching this close as I'm having the exact same problem! I too have checked all the usual places. I'm pulling the intake and seeing what's what inside next

    Sent from my Pixel 2 using The H.A.M.B. mobile app
     
  13. drtrcrV-8
    Joined: Jan 6, 2013
    Posts: 1,372

    drtrcrV-8
    Member

    To pull the vacuum described by the owner, there has to be a direct leak into the manifold from the valley SOMEWHERE! Now you just need to find it! Possibly shoot a short squirt of white paint into the oil filler that's pulling all that vacuum, shut off the engine, Pull off the manifold, & see where the white paint went ?? The suction will put the paint where the hole is better than just looking & guessing, & I seriously doubt it's the valve guides : if it was, the motor, if it ran at all, would make enough metal rattles to scare a 1st sergeant.
     
    stillrunners and 48fordnut like this.
  14. drtrcrV-8
    Joined: Jan 6, 2013
    Posts: 1,372

    drtrcrV-8
    Member

  15. Boneyard51
    Joined: Dec 10, 2017
    Posts: 4,752

    Boneyard51
    Member

    Man, that sucks!





    Bones
     
  16. 53 ford
    Joined: Apr 8, 2012
    Posts: 143

    53 ford
    Member

    You said you believe it has low hours so it must have been rebuilt. Maybe someone forgot to put the seals on the valve guides.

    Sent from my SM-G950U using The H.A.M.B. mobile app
     
    Cosmo50 likes this.
  17. Custom Riviera
    Joined: Jan 16, 2006
    Posts: 35

    Custom Riviera
    Member

    898F0FE2-10B2-4FDD-9E93-E843AD64673A.jpeg Just as “landseaandair” mentioned after removing the intake manifold, and looking more closely at the valves, we found an intake guide that was damaged, the bottom was broken and it was floating in the guide bore, hence vacuum in the lifter chamber. The engine seems fairly fresh, and the lifter bore doesn’t seem damaged, we’re changing all the valves and guides. Hopefully, have her back together soon and running well.
     
    Boryca and Petejoe like this.
  18. alchemy
    Joined: Sep 27, 2002
    Posts: 16,270

    alchemy
    Member

    When you put it back together, take a little more care than the last guy on that gasket. Globbing form-a-gasket all over the place is dangerous for engine internals. Those thick paper intake gaskets might need a very thin swipe of sealant, but not really much at all. You aren't sealing out any water or compression, and oil won't leak out of there.
     
    Truckdoctor Andy, 48fordnut and RMR&C like this.
  19. 48fordnut
    Joined: Nov 4, 2005
    Posts: 3,895

    48fordnut
    ALLIANCE MEMBER

    Hope you are going with the later 1 piece guides and not tulip valves.
     

  20. Well I'm taking at least partial credit, since I don't usually get to take any at all. :p

    You said the engine hadn't been run for maybe a couple of years. I wonder if it had a valve get varnished up and stick in the guide. :eek: Next time it gets spun over it raises the valve and moves the guide with it. o_O
     
  21. drtrcrV-8
    Joined: Jan 6, 2013
    Posts: 1,372

    drtrcrV-8
    Member

    Glad you found it! Never seen one like this, but now we all can say we have!!
     
  22. did you find the horseshoe clip????
     

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