Lash pad calculations | The Z Club of Great Britain
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Lash pad calculations

Discussion in 'S30 (240Z,260Z,280Z) Engine' started by johnymd, Apr 26, 2018.

  1. johnymd

    johnymd
    Z Club Member

    Is there a simple method for working out lash pad thickness required?

    For example: I will be fitting a used cam to my new engine and its not a standard cam. It will probably be a regrind so maybe the base circle has been reduced. The head has currently not been skimmed. How do I work out what size lash pads to order?
     
  2. jonbills

    jonbills
    ZClub Administrator
    Staff Member Committee Member

    I think if you’re just changing the cam, you can approximate extra lash pad thickness as the difference between old and new base circles (cos that’s how much the rocker has to be raised at both ends)
    But to do it right, you need to mock it up: one ex and one inlet rocker installed and mockup springs and existing lash pad (or just the inner spring) rotate the cam checking the wipe pattern and increasing the adjuster at the one end and feeler gauges as shims on the valve end. When you’ve got the wipe pattern right, add the thickness of the feeler gauges to the lash pad and thats the size of the new pads you need. Might be different for ex and in valves.
    Clear as mud?
     
    AliK likes this.
  3. johnymd

    johnymd
    Z Club Member

    Thanks Jon. Just what I needed to know.
     
  4. Mr.F

    Mr.F
    Z Club Committee
    Committee Member

    Or have a box of many mixed lash pads of various thicknesses and trial fit while checking wipe pattern (the Samuri method for irregularly reground cams)...
    Or - buy a new cam ground off fresh billet where all lash pads should be the same +/- a couple of thou.
     
  5. johnymd

    johnymd
    Z Club Member

    When I changed the cams in my 1jz I had none of these issues as the cams were correctly ground with exactly the same base circle.

    I'm guessing when an old cam is reground that all the base circles will be reduced by exactly the same amount therefore all lash pads will be the same. Unless the regrind was done by a blind man in his shed.......or equivalent.
     
  6. jonbills

    jonbills
    ZClub Administrator
    Staff Member Committee Member

    Yep. My reground cam has about 7 mm lash pads on all valves.
     
  7. Mr.F

    Mr.F
    Z Club Committee
    Committee Member

    "I'm guessing when an old cam is reground that all the base circles will be reduced by exactly the same amount therefore all lash pads will be the same"

    I'm guessing you've never dismantled a cam from a Samuri engine...
     
    AliK and johnymd like this.

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