1961 364 Nailhead Valve Float

Discussion in ''Da Nailhead' started by Rockable, Nov 19, 2022.

  1. Rockable

    Rockable Well-Known Member

    I am not new to cars and engines but I am new to Nailheads. The engine in my LeSabre is a rebuilt stock (as far as i know) 364 low compression. It has a 4 bbl intake and Edelbrock 600 cfm carb on it. Timing is at 30 degrees, all in with vacuum plugged. Distributor is connected to the ported connection.

    I finally got to get out and drive my car some today and decided to "get on it" a little and see what she'd do. What she does is about the time she starts making good power, the valves float. Fortunately, it doesn't appear that it did any harm. I don't have a tach, so I can't tell you what RPM it's floating at but I believe it's less than 4000, maybe 3500. The engine would rev willingly if the valve springs didn't give up the ghost. Is this normal for this engine? How close are the valves and pistons?

    I am trying to optimize the governor in my TH350 but it looks like that is not gonna happen unless I fix this other issue. Advice?
     
  2. gsgtx

    gsgtx Silver Level contributor

    if you really think the valves are floating just put new springs in. you can do it with out pulling the heads. how you know it not an ignition miss or running out of fuel
     
  3. wkillgs

    wkillgs Gold Level Contributor

    Do you have a recommended valve spring compressor to do this?

    I kinda doubt your getting valve float at that low of a rpm as well. Valve clearance is tight in these engines tho.
    If you have the butterfly valve at the exhaust manifold (heat riser), make sure it's not stuck closed.
     
  4. 69WILD

    69WILD Gold Level Contributor

    I would suggest this type of compressor possibly to get accessibility to the rear springs by the heater box and brake booster clearance issues.

     

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  5. gsgtx

    gsgtx Silver Level contributor

    mine was like this, it was a pain to do but it can be done, i didn't have power brakes if that matters i don't know.
     

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  6. gsgtx

    gsgtx Silver Level contributor

    like this
     

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  7. rmstg2

    rmstg2 Gold Level Contributor

    You might have to much gap in the points!

    Bob H.
     
    philbquick likes this.
  8. Rockable

    Rockable Well-Known Member

    It has a points conversion and a new fuel pump. I guess it could be fuel but it sure seems like valve float. I am capable of replacing the springs and have the tools. I was just curious if that was a common symptom. I may upgrade the fuel pump first. An electric will make hot starts a little easier.
     
  9. gsgtx

    gsgtx Silver Level contributor

    doe's it feel like a miss fire breaking up or more like a surge.
     
  10. Stevem

    Stevem Well-Known Member

    Are you sure you floated the valves,
    This if it did take place it would accompanied with Valvetrain noise and once the motor first dropped back to close to idle rpm would be running ruff for a bit.

    did this take place?

    If yes, you do not want to keep bouncing the lifters off the cam lobes!

    the valves at full stock lift on a nail head are still a long way’s away from the piston tops, so no worries there.
     
    Last edited: Nov 19, 2022
    Rockable likes this.
  11. Rockable

    Rockable Well-Known Member

    It feels like it just falls on its face and then runs rough for a few seconds after i get off the throttle and then straightens up.
     
    Last edited: Nov 19, 2022
  12. Rockable

    Rockable Well-Known Member

    I am going to try to eliminate ignition and fuel from the equation before going any further.
     
  13. Rockable

    Rockable Well-Known Member

    Well, I am 99% sure its valve float. I recurved the distributor to get all in by 2500 rpm. Full mechanical advance is 30 degrees.

    With my digital timing light and no load, all it would do is 4500 rom. Once it got above 4200, it started to miss and just wouldnt go higher than 4500. After each run like this, it idled rough for a minute or two until the lifters normalized. I guess I am going to have to do some engine work that I didnt want to do.
     
  14. Mark Demko

    Mark Demko Well-Known Member

    You weren’t revving it to 4500 rpm in neutral were you?
     
    TrunkMonkey likes this.
  15. Rockable

    Rockable Well-Known Member

    Park
     
  16. Mark Demko

    Mark Demko Well-Known Member

    Same thing, bad thing!
     
  17. Rockable

    Rockable Well-Known Member

    So, how would you have ascertained that it was valve float? I eliminated ignition and fuel, as much more fuel is required under load. I didn't over rev the engine and I didn't do any damage.
     
    Super Bald Menace likes this.
  18. Mark Demko

    Mark Demko Well-Known Member

    You have to drive it, the engine has to be under load.
    You can wind it out in first gear to whatever rpm it happens.
    Revving it to 4 or 5000 rpm in neutral is a killer on rod bearings.
    Yes, rpm is rpm, but there’s a difference in the TYPE of rpm, under load, or free rev.
     
  19. Stevem

    Stevem Well-Known Member

    In terms of those rebuilt heads you have with what might be reused 61 year old springs that you do not know the history of, I can relay this info.

    I have rebuilt a lot of those heads in the early 70s in the shop that I worked in.

    Those 364 springs are marginal at best and if the motor was ever overheated, well you can stick a fork in them because there DONE!!

    if they are shot I bet that on a good number of them you can use two Thumbs to apply enough force to get the valve to move up & down a bit.
     
    Rockable likes this.
  20. JESUPERCAT

    JESUPERCAT No Slow Boat

    I would check what the Springs are at for tension open and closed. Eliminate the guess work, use a proper gauge.
     
    Rockable and Smartin like this.

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