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Do built motors use tighter valve clearances

Discussion in 'Tech' started by mike-guy, Dec 19, 2017.

  1. mike-guy

    mike-guy Well-Known Member

    I was told that my bike has a ss build on it. After 2 seasons (probably should have earlier) I decided to check the clearances. Everything was near perfect on the tight side but the exhaust had 3 that were tight. Suzuki spec is .18 - .28 mm and I had two that came in at .127 and one in at .152. Bike ran great and makes good power. No weird idle or anything, cam lobes and from what I can see the bucket looks good too. So to adjust or not to adjust?
     
  2. fastfreddie

    fastfreddie Midnight Oil Garage

    Short answer? Put 'em back in spec.
     
    5axis likes this.
  3. RM Racing

    RM Racing Tool user

    Race spec is always close to or at maximum lash. But that may require more attention. You have two that have some wear, if they are Ti, you have probably lost the coating. Set them to specified lash and if they tighten up again, time for a valve job.
     
    JJJerry likes this.
  4. Kurlon

    Kurlon Well-Known Member

    Now granted, my experience comes from pitbikes... but I always thought a BUILT motor you went looser than OEM as everything was going to be hotter and will tighten up more than normal?
     
    shadyaj3 likes this.
  5. mike-guy

    mike-guy Well-Known Member

    That does make sense in a logical way but I'm going to follow orders here and just adjust them.
     
  6. mike-guy

    mike-guy Well-Known Member

    Ok if I'm understanding correct you mean the valve has lost coating where it seats in the head and is coming up further hence the smaller gap? I know this is not a black and white question but should I check it after a few weekends or is this something that damages at an exponential rate?
     
  7. Wheeliest

    Wheeliest ʍɥǝǝןıǝsʇ

    Lets use an american system.

    0.23 +/- .05 metric = 0.009" +/- .002" american.

    You can safely run to the .140" shims on the zukis but valve stretch.. and seats will be toast..

    I ran .004" ex & .008" in, on my little 190hp gsxr1k so I could keep with the new era hp bikes and the head needed new seats after 2 seasons. running in spec will prolong the head/valves.. no youre not going to experience catastrophic failure because one of your exhaust valves on cyl 4 tightened up (common) remember, .004" is the thickness of a piece of paper..

    Make sure you mic the shims and adjust to the findings and not the mathematics of "What it should be" via the shim labeled size.

    Tighter = valve open more/longer/freq maint
    Looser = Less pwr / less maint.
     
  8. RM Racing

    RM Racing Tool user

    Looser does not mean less power if everything is within the spec. I've done dyno testing strictly on valve clearance and there is not a noticeable or quantifiable difference in power. As a matter of fact, there is some evidence to suggest that the valves stay closed longer and you increase dynamic compression, but my testing was inconclusive.

    For the OP, yes, if the coating has worn off (with 2 years of track use this is probable) then the valve will begin to wear much faster and will begin to "tulip". If it was my racebike, I would check again after 500-1000 miles. If it's very slightly tighter, don't worry too much.
     
  9. Wheeliest

    Wheeliest ʍɥǝǝןıǝsʇ

    Yeah wont argue with you about static testing.. waste of time for the category imo.. I've raced a big old bike vs big new bikes and every little bit counted.. and the tighter my valves got, the faster my bike went.. my bike was a SB Build done by yours truly and tuned by yours truly and raced by yours truly.. I guess my 2cents should be argued.
     
  10. Robby-Bobby

    Robby-Bobby Steeltoe’s Daddy

    You were correct according to my testing also. However, I have only tested that theory on
    CRF450
    675 Daytona
    Vintage Triumph
    Hayabusa

    Yes, all motors are diffeeebt and little things can make differences.

    But I agree with you 100% and always set my valves in the "tight side"

    The only downfall is that I personally check the clearances more frequently
     
    Wheeliest likes this.
  11. fastfreddie

    fastfreddie Midnight Oil Garage

    Small price to pay for a 30 minute job...with a beer. :D
     
  12. humblepie

    humblepie Well-Known Member

    It has been my experience that engines prefer valve lash clearances at the looser end of the spec.
    Sometimes, past the loose end of the spec. Certainly worth doing a lash test on the dyno.
     
  13. PistolPete

    PistolPete Fuck Cancer...

    Loose is safer, tight is faster! Tighter they are, the further they open. But like RB said, keep an eye on them, because too tight is not only slower, it's expensiver...
     
  14. mike-guy

    mike-guy Well-Known Member

    I just got a “starter kit” in the mail and will probably adjust not only the ones out of spec but the ones that were on the tight end as well. Kind of looking forward to it since the bikes torn down and the motor is sitting on stands.
     
  15. fastfreddie

    fastfreddie Midnight Oil Garage

    Before you open it, are you confident the shims aren't made of pot metal? If it says China anywhere on the package, send it back.
     
  16. mike-guy

    mike-guy Well-Known Member

    Nah it’s the good stuff.
     
  17. fastfreddie

    fastfreddie Midnight Oil Garage

  18. RM Racing

    RM Racing Tool user

    What do you know anyway?
     
  19. Robby-Bobby

    Robby-Bobby Steeltoe’s Daddy

    lol I'm not arguing that with an R6 with you! Lol
     
  20. humblepie

    humblepie Well-Known Member

    As I said before, there's a ton a guys who know way more than me about the R6.
    BTW, just ended 5 seasons at GMS. Now at Honda MX. And in the end, its all just nuts and bolts :)
     
    MELK-MAN likes this.

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