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When doing a bore, what does the head need.

Discussion in 'The Garage' started by joebgd, Dec 19, 2019.

  1. joebgd

    joebgd XS650 Addict

    Just curious when doing a 750 cylinder the old head goes on as is. Like it seems like the combustion chamber would need enlargement.
    Paul Sutton and mrtwowheel like this.
  2. jay760

    jay760 XS650 Junkie

    No that's why there's a flat ridge around the edge of the pistons
  3. XSLeo

    XSLeo XS650 Guru Top Contributor

    You might want to do some clean up in the ports. Don't make them larger, just smooth out the casting ridges.
    You should do the valves, Lap them in to get a good seal. New valve seals. Possibly valve guides. Check clearances to be sure.
    On my 75 that's what I did when I went 2 nd over. After riding a 750 kitted bike I just had to add that to my 75.
    You don't even have to retune the carbs. If they ran well as a 65o they will run the 750 just as well.
  4. joebgd

    joebgd XS650 Addict

    Is there such a thing as a 750 head. As in if the bore and piston are bigger I just picture the original head as a combustion chamber and it seems that's where the power would be, in a bigger combustion chamber. I don't see how power is increase is, I am trying to picture it. Idk if I'm thinking about this correctly. Just trying to get an idea. I would like more hp and torque, I did decrease my rear sprocket and would even go to an 18 on the front, I like the smoother cruise and the power to play. Looking at the port work being done it seems I'd be just as good to increase the in and out of the fuel mix and exhaust.
  5. gggGary

    gggGary Stop that! XS650.com Supporter Top Contributor

    Wait for Jack to reply. ;) In the meantime look into squish band and combustion. It helps to think how short of a time the piston is at TDC, the rest of the time the combustion chamber shape is changing at a rapid rate.
    grizld1 and Jack like this.
  6. halfmile

    halfmile XS Builder XS650.com Supporter Top Contributor

    It doesn`t work at all like that. If you enlarge the chamber you`ll loose compression. You will need a camshaft that has a little more lift and duration. The more fuel you can ignite efficiently the more power you produce. Jack will tell the whole story.:thumbsup: (I hope)
    grizld1, Jack and gggGary like this.
  7. Jack

    Jack XS650 Junkie Top Contributor

    No 750 head. Power and torque will come from big bore, porting the head, free flowing exhaust, ignition,cam and carbs
    grizld1 and gggGary like this.

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