Anybody had to do this ?



  • Elo guys, has anyone had to replace their PV and bushes/holders ?
    It says on a lot of parts websites that this is a high wear item and should be replaced as a matter of course when rebuilding a fresh engine or if it has worn.
    I've just done a full rebuild on my nephews engine and the piston seems to be hitting the PV,it isn't because of the rebore or size of new piston etc as it's only on 0.5 OS.
    The valve has sideways play (can move valve in and out) and a little up n down play too.
    Just thought I would bring this to other people's attention 😉
    Hope this stops someone ruining a new engine or helps keep an old engine running.

    https://youtu.be/REPjGEhrZKQ



  • Modify the powervalve when the engine has been rebored is common practice.

    The seals should be replaced when building a fresh engine, they come with the Athena top end rebuild kit, so no excuse for not replacing it.

    Fairly common stuff for engine building, still good post for people new to building engines.



  • Yh all new o-rings and oil seals in the PV but the bushes wear and let the PV move causing it to rub on the piston,it's not about shaving down your PV for rebore as even if it had lots of clearance when in correct position it is still able to move sideways and the rounded part of PV is then not inline with centre of piston and will catch the piston,not in the middle like when PV isn't shaved down after large rebore size but more like the side of exhaust port, also standard bore size is still susceptible.
    Anyone had this ?



  • @castrolsniffer Never heard of the bushes failing.

    They are not under any load so not sure what to make of that.



  • Their not failing,they wear out and allow too much movement as in the vid,I've been building 2strokes for over 20 years and have only just come across this problem and thought it might help others out 😉





  • @castrolsniffer Yeah poor choice of words. I did watch the video.

    Yeah, I've never seen one wear out before, but I don't work on bikes enough to have seen it all. I'm sure anything is possible.



  • Been on the RD sites and they are full of info on these bushes ????
    Shocked as I've done a lot of Dt's over the years and never had this problem.
    A firm called tss make billet power valves and bushes and there is talk of boring out old bushes and having a sleeve pressed in.


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