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Valve Clearance Question

Discussion in 'Tech' started by x_files, Jan 9, 2006.

  1. x_files

    x_files Active Member

    My experience with DOHC 16V motorcycle engine valve clearance has been they tighten up as the engine accumulates running time. I believe this is due to the valve face wearing against the seat and therefore closing up the gap between the valve and tappet.

    Well, I am now working on a FZR race engine that hasn't been run in two years. The head was built by EDCo and the clearances apparently set to 0.010". The clearance I measured on all valves is above spec - not below spec like I'm used to seeing. In 2 cases the intakes are 0.005" more than spec.

    Are deposits on the sealing face of the valve or seat enough to open up the clearance this much? Looking down the intake ports I don't see excessive deposits on the top of the valves, but I can't really see the face of the seat well enough.

    Other ideas why the lash has grown? Any guidance is appreciated!

    Scott
     
  2. RB

    RB Well-Known Member

    Once you start thinking you have all the answers something like this will pop up to straighten you out.

    Define 'apparently set' . Did you actually check them yourself ?

    On a new motor with lots of new parts the clearances can go any which way. The norm is tight but maybe you get a valve that the stem is not perfectly square where the bucket contacts it and it wears in a couple of thou until it is square.
     
  3. x_files

    x_files Active Member

    Thanks RB . No, unfortunately this is the first time I've laid hands on it. I recently bought the engine from the person who had it built.

    Great pointer on the stems! This supposedly has custom valves in it that had to be cut down in length to fit the head. Maybe the stems were not cut perfectly square as you suggest. This would explain alot.
     
  4. Gumby647

    Gumby647 SeƱor Member

    It could also be rust on the seats.
     
  5. x_files

    x_files Active Member

    Thanks, good point. If it were, any reasonable chance it could clean up (without loosing too much sealing surface) by just running the engine?
     
  6. Don Nees

    Don Nees Well-Known Member

    I'd suggest two simple checks:

    1. Do a compression check on all cylinders. If it hasn't run for a while make sure you spin it a few times to insure adequate oil on the cylinder walls.

    2. Measure the cam lobe height on all lobes against spec. ("custom valves"...., maybe custom cams...), what is it that they were trying to improve (?).

    Just trying to suggest some simple checks to help you avoid chasing a dragon.
    Don
     
    Last edited: Jan 9, 2006
  7. x_files

    x_files Active Member

    Thanks Don for the recommendations. I'll do the compression check and that should tell me how well the valves are sealing up to the seats. I did check the valve lift on the lobes and it is in spec.

    Scott
     

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