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Lapping valves....good idea or bad?

Discussion in 'The Hokey Ass Message Board' started by Lucky Strike, Apr 13, 2006.

  1. Lucky Strike
    Joined: Aug 14, 2004
    Posts: 1,665

    Lucky Strike

    I have some used heads and the intake valves are a bit rough but may clean up if I lap them some. Anyone ever done this. Is it a possible way to get some extra miles before a full on valve job or is it always a bad idea. If searched the intenet and have found both opinions. What do ya'll think?
  2. rodknocker
    Joined: Jan 31, 2006
    Posts: 2,267


    if you have enough meat on the valve go ahead i do this all the time at work. i usually connect a fuel line hose on a drill to the valve and grease my finger to hold it against the seat,and lapping compund is a must
  3. hayduke
    Joined: Apr 1, 2006
    Posts: 239


    Heck yeah, as long as it's not a diesel or anything goofy (some of the fancier valve materials don't appreciate lapping).

    Be sure to clean everything really well, the valve guides too, it would be a good time to replace or install new stem seals also. Typically umbrella types are sufficient.

    Have fun!
  4. Hackerbilt
    Joined: Aug 13, 2001
    Posts: 6,248


    Depending on the age and hours on the heads your most likely gonna need guide work...either a cheap knurling or some proper guide replacement.

    The old Mechanics would never tolerate someone trying to lap a valve with a drill on the stem.
    Use a lapping stick with a suction cup so that you turn it back and forth gently with the stick between both hands (like Ugg the caveman starting a fire...) instead of powering the crap out of the guide and seat with a drill.
    Makes it easy to pop it out and check progress as you go...or clean and add new compound if needed.

    BTW...Keep the compound off the stem. The guides don't need a lapping! ;)

    If inspection of the guides shows minor wear that you don't want to deal with right away, the umbrella seals will help control the oil a little better but won't last forever. As they get harder from the hot oil, the lose valve stem fit will hog them out and you'll get some oil burning again.

  5. Lapping works good, just more work, and prolly unnecessary if the valves aren't leaking already. If the valves are leaking, it's usually due to mis-alignment caused by worn guides.
  6. Flat Ernie
    Joined: Jun 5, 2002
    Posts: 8,406

    Flat Ernie
    Tech Editor

    I always do it - even on a fresh valve job. Of course, then I go very lightly & just to make sure the surface is concentric & in the same plane - caught a few that weren't that way...

    You've got nothing to lose - it's not like you're going to sink the valves into the head! ;D
  7. On a quick overhaul its ok. On a fresh valve job, it is never acceptable! I think its a sign of a machinist with no self confedece or no tallent.
  8. Lucky Strike
    Joined: Aug 14, 2004
    Posts: 1,665

    Lucky Strike

    Yep, this is exactly what I was talking about. When I searched the net for an answer to this question I found some folks that build race motors that always lap a fresh valve job and others that would never lap anything.

    I'm probably going to give it a shot. Thanks to all for your advise.
  9. Bruce Lancaster
    Joined: Oct 9, 2001
    Posts: 21,682

    Bruce Lancaster
    Member Emeritus

    The old lapping-in okie valve job has a lot you can say against it, but it is capable of keeping an old engine running for cheap--and it's pretty much the way most valve jobs were done except at the best equipped garages until at least WWII.
    There is no way of course to narrow and you can't fix any serious defects in the surfaces. You are widening everything, which would be a no-no in any modern valvery but here is actually a necessity--because the part of valve and seat that do the work with engine hot are somewhat away from where they meet cold.
    I learned valve work from a pre-WWI manual in the early sixties--I had no idea how modern work was done, and it didn't matter because I had no money anyhow. I did pop for about $5 worth of high tech equipment from JC Whitney, including a little giz that held emery paper in a 45 degree cone to clean up the seat. I had no idea how lucky I was to be working on a flathead Ford with hard seats that were basically indestructible...
    Just be aware of why this isn't the best way to go and do the best with what's available. The problems are:
    1. You almost always need guides...but engines do indeed manage to seat wonky valve action.
    2. You are widening seats and can't do anything about it...but the engine will learn to cope for a while.
    3. You have to work in a wide potential seating area because you know the working seat is going to be a bit...elsewhere and you have to hope you're at least getting that area clkeaned up.

    I've been planning an article on how Ford valve work useta was...depression survival machine work is fascinating.
    Oh, you'll need a manual--go get a copy of "The Grapes of Wrath" by Steinbeck. Fully covers auto mechanics for those with three tools and zero money!

    Oh, yes, lapping at the end of a modern valve job is done expressly to see for sure that valve's seat is rounf and concentric, not to move metal. It's a way to see what's going on.
  10. mikeyboy
    Joined: Aug 26, 2001
    Posts: 223


    yep....the man that guided me through the process on the last set of heads i did had me lap the valves...not to seat, but to determine where the actual seat was, and to make sure all of the seats were in the same location on the face of the valve. Was rather surprised to see where the seat was, then got a 20 minute dissertation on flow at low lift......Then the guy that taught James how to do this arrived. Took one look at the valves, ports and determined that "it oughta catch a rabbit"

    he was right :D

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