Bent valves

Discussion in '40- & 55-Series Tech' started by Mace, Aug 3, 2005.

  1. Mace

    Mace rock scientist.. Staff Member s-Moderator

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    2f Motor.

    What are the common causes of bent valve shafts on a 2F?

    newly rebuilt motor.
    "high horsepower" cam ( I have no idea if it is a regrind or a custom cam)

    Can Timin of the motor actually bend the valves?? This was offered as an explaniation but I cannot see how it would happen. By the time ignition occurs the valves are very much in the closed position..

    :confused:
     
  2. Mr. Toad

    Mr. Toad

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    Yes, if the timing gears got out of whack. But ignition timing cannot bend the valves.
    Well, if the performance cam increases performance because it has larger lobes and you did not readjust the valve clearances after replacing the cam, this might possibly be a valve-bending problem.
     
  3. Mace

    Mace rock scientist.. Staff Member s-Moderator

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    I actually should have specified..
    In timing I was referring to ignition timing.. Not camshaft degree timing.
    Theoretically the camshaft can only be put together one way. And that way shoudl be perfect. unless of course the lobes were not ground properly...
     
  4. Poser

    Poser Oh...Durka Durka Durka. s-Moderator Supporting Vendor

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    I am aware of a person that installed a 'performance' cam, and did not re-adjust the valves afterwards......dropped a couple valves by snapping the stems off at the keepers....He purchased a new block and head from me....He said that he was not aware that the Land Cruiser had solid lifters...as if that would make any difference... :rolleyes:



    Do they look like they have been struck? Are there marks on the pistons? You would think that something would have needed to hit them for this to occur.



    Good luck!


    -Steve
     
  5. andrewfarmer

    andrewfarmer

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    Quite easy to get the cam timing wrong...

    The other thing to check is the cam gear. The rubber strip can delaminate causing the gear to 'walk' from the correct position. This would change the cam timing and cause the problem you refer to.

    My pick - either incorrect cam timing or valves not adjusted correctly.

    you did adjust the valve clearances before you started it up?
     
  6. Mace

    Mace rock scientist.. Staff Member s-Moderator

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    First hint, this is not my truck..

    :D

    there was no impact on the pistons.
     
  7. Poser

    Poser Oh...Durka Durka Durka. s-Moderator Supporting Vendor

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    What condition is the cam gear in?


    Who did the engine work?


    Was it running fine before this, for how long?



    ????????????????


    :)
     
  8. Mace

    Mace rock scientist.. Staff Member s-Moderator

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    no idea on the cam gear,

    Engine work was done by a shop in Vegas. No clue how good of a job they did.

    Engine has been nothing but trouble since the rebuild.

    siezed lifters, bent valves, etc..
     
  9. Poser

    Poser Oh...Durka Durka Durka. s-Moderator Supporting Vendor

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    Well with that little nugget.....


    I would bet that things in relation to cam and crank gear timing have not been correct from the get go....


    Start over from scratch, new parts, toss all the trash, and try again.



    Good luck!


    -Steve
     
  10. Pin_Head

    Pin_Head

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    Unless the valves were already bent when they were installed it almost has to be due to interference with a piston. If the cam gear was installed out of phase, you would think it would have been noticed when turning the engine over by hand. I vote for valve float causing the interference; either from testing the RPM limit of that :high performance" cam or by missing a power shift.
     
  11. Mace

    Mace rock scientist.. Staff Member s-Moderator

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    interesting point.

    Personaly I could not see any way of the valve shafts bending without impacting something (unless the lift of the cam was sufficient to bind the valve springs)

    Hmmm.. I'll go take a look at the motor with a fin toothed comb before it goes back together.
     
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