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Thread: 650 rebuild

  1. #1

    650 rebuild

    here are some pics of what i'm doing.

    The good stuff





    as you can see i've collected a few bits for this build, in the forth picture you can see the arrow cast proud of the crown of the piston should i grind this away so that the crown is flush just like in the wiesco and pro-x pistons, what about weight balancing these, should it be done?

    In the next few pics you can see the engine cases i have. the inlets are polished some bit with the ugly casting marks taken off the edges, will this effect my port timing, the sizes of these ports have not been changes only polished. i put a 45 degree chamfer on the exhaust port in the cylinder as seen in the sbt videos on this site, should i also do this on the inlet ports of the cylinder sleeve. the cylinders are yet to be oversized for my new pistons.






    the last picture is my cylinder head i think its a bit [email protected], anyone have a standard one that they can can send to the republic of ireland. What can i skim off the standard head to get a few more psi in each hole, i read some where 30 thou off standard is a good start. i want some more poke out of this build i even got myself one of these.



    thanks again lads


  2. #2
    CJ's gpr's Avatar
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    I'm about to start the same rebuild.

    i'm just doing a top end kit and the carb (mikuni sbn). the bottom end hasn't failed me yet so i'll just leave that be. my head looks similar, maybe even a bit worse, definitely need a new one.

  3. #3
    steve45's Avatar
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    Quote Originally Posted by bweengmachine View Post
    In the next few pics you can see the engine cases i have. the inlets are polished some bit with the ugly casting marks taken off the edges, will this effect my port timing, the sizes of these ports have not been changes only polished.


    I'm trying to figure out how you'd think that polishing the crankcase would affect port timing.

  4. #4
    Quote Originally Posted by steve45 View Post
    Quote Originally Posted by bweengmachine View Post
    In the next few pics you can see the engine cases i have. the inlets are polished some bit with the ugly casting marks taken off the edges, will this effect my port timing, the sizes of these ports have not been changes only polished.


    I'm trying to figure out how you'd think that polishing the crankcase would affect port timing.
    thanks for the replies, just taught increased air flow would effect the port timing some what, as you can see in the photos the lips on the castings have also been rounded, would this effect the port timing?

    New head is on the cards alright though, Anyone got one?

  5. #5
    DavidR's Avatar
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    Ports are in the sides of the cylinder and their timing ,in relation to the crank stroke, can only be effected by raising or lowering them, either by grinding or by changing the cylinder sleeve itself.

  6. #6
    Quote Originally Posted by DavidR View Post
    Ports are in the sides of the cylinder and their timing ,in relation to the crank stroke, can only be effected by raising or lowering them, either by grinding or by changing the cylinder sleeve itself.

    Well thats one thing cleared up for me,

    Again good info, so i can in theary increase the airflow too my ports by polishing and not effect the port timing.

    What about the chamfering of the edges of the ports?

    is this a good or bad idea.

  7. #7
    DavidR's Avatar
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    Chamfering is done so that the edges of the ports don't hang on the rings.

  8. #8
    Quote Originally Posted by DavidR View Post
    Chamfering is done so that the edges of the ports don't hang on the rings.
    sounds like a good idea to me

  9. #9
    steve45's Avatar
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    Just don't get carried away with chamfering or you WILL affect the timing.

  10. #10
    CJ's gpr's Avatar
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    Quote Originally Posted by bweengmachine View Post
    Quote Originally Posted by steve45 View Post
    Quote Originally Posted by bweengmachine View Post
    In the next few pics you can see the engine cases i have. the inlets are polished some bit with the ugly casting marks taken off the edges, will this effect my port timing, the sizes of these ports have not been changes only polished.


    I'm trying to figure out how you'd think that polishing the crankcase would affect port timing.
    thanks for the replies, just taught increased air flow would effect the port timing some what, as you can see in the photos the lips on the castings have also been rounded, would this effect the port timing?

    New head is on the cards alright though, Anyone got one?

    you probably wont find a 650 head on greenhulk, not a popular ski on the forum. heres a link with an ebay search.
    http://www.ebay.com/sch/i.html?_trks...at=0&_from=R40

    my west coast one was great for a while.

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