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Valve clearances

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  • Valve clearances

    Just doing the valve clearances on the project bike before putting her back together.

    Most of the clearances are right at the 'tight' limit and a few at the 'loose' limit, and one is way off. I've just lapped the valves lightly and get a nice silver ring the whole way around, so they should be sitting nicely in their seats.

    Before I order new shims, am I best to set the clearances at the 'tight' or 'loose' ends of the range, or should they ideally be right in the middle?

    Say the range is 0.10-0.20mm, should I be aiming for 0.10, 0.15 or 0.20?

  • #2
    Hmmm, punt I say 0.10mm as will settle in.


    • #3
      So they'll loosen up as carbon/dirt builds up on the seats/valve faces?


      • #4
        No they usually close up as the valve stretches pounds itself into the seat. Typically they don't move much but on the larger side is a good place to be. If they end up too close the valve won't close properly and the gases rushing around mainly the exhaust valve will burn it. Open just makes it a bit tappy and they won't quiet run as well as it should but you don't burn anything.
        Harvey community radio has a motorcycling show listen over the web here ,Facebook here yes I am the goose that hosts it.


        • #5
          ^WHS^ In the middle or towards to loose setting. Would not recommend leaving any on the tight limit.
          Being an Australian is not an excuse for being dumb and racist.


          • #6
            I agree with Nero Diablo. Always towards the loose side. The worst that will happen is a bit of extra noise for a while. Performance loss is insignificant or even unmeasurable except on a dyno at full noise and then maybe not even.

            Closing up is also as a result of valve seat recession as the mating surfaces wear away through friction and micro-welding. This is where the surfaces get hot enough to fuse in places and pull microscopic little pieces away. Exhaust valves especially need to have enough clearance as the gap will close up when the engine is hot due to expansion along the length of the valve.


            • #7
              The recommendation is between 0.10 - 0.20mm right???

              Im sure the manufacturer would allow for expansion etc etc..
              to give those specs right???


              • #8
                If you have lapped an old valve on to an un-cut seat there will be negligable settlement. I always set these type of motors toward the middle/top of the range as it tends to maximise the valve's cooling time. If they are all at max or even slightly bigger there will be bugger all noise, it's only when one is a lot larger clearance wise that there will be an audible 'tick'. You don't need to buy shims.... I have tons of 13mm shims if you need to exchange some. Got to remember, you will only get .05mm adjustment increments whatever you do unless you surface grind them to a custom thickness. The other way to do it is top the stem a smidge.... What sizes you chasing?


                • #9
                  Ordered valves yesterday afternoon. Spent a little longer googling, and decided to go with 0.15mm clearance as that requires me ordering the least number of shims.

                  Might need to swap one more shim once I've got the new ones as my feeler gauges have fairly coarse steps in their size once you get past 0.25mm...

                  Not going to grind valve stems or shims, I don't *need* them to be perfect, just decent enough as I don't want to adjust them again in a hurry.