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Piston interchange

Discussion in 'XJ Technical Chat' started by Maxim700, Nov 3, 2006.

  1. Maxim700

    Maxim700 Member

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    Will pistons and rings from an early 80's xj750 fit my 85 xj700?

    The 700 pistons are not available anywhere but I have found some 750 pistons online.
     
    Maxim700, Nov 3, 2006
    #1
  2. OU812didntU

    OU812didntU Member

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    am not positve on this i know there is a few people in here that owne the same type of bike as we do and they might know for sure but i thinking that the 750 pistons will not fit your 700.
     
    OU812didntU, Nov 3, 2006
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  3. MacMcMacmac

    MacMcMacmac Member

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    Bore is the same. 700 has 4mm less stroke. The rings should fit fine. You could go to BikeBandit and do a prats number search for the piston rings under OEM Parts and see if theyhave the same numbers. 700 has a bit higher compression ratio than the 750: 9.5:1 compared to 9.2:1.
     
    MacMcMacmac, Nov 3, 2006
    #3
  4. Maxim700

    Maxim700 Member

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    Parts numbers are NOT the same but I read somewhere a long time ago that Yamaha took existing parts to make the 700 when the tax was put on bikes over 700cc to protect Harley. I read that they took the 750 pistons and combined them with an existing crank (650?) to make the 700. Since the bore is the same and the 700 pistons are not available, I thought these pistons or rings might fit my bike.
     
    Maxim700, Nov 7, 2006
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  5. Joel07

    Joel07 Member

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    By changing the stroke, they would have had to either change the piston, rods, or both to get the correct deck height. Most time manufacturers change the piston and leave the same rods, but not always. But, since the 700 had higher compression, I'd have to guess that it's a piston change, unless that is they changed the cylinder head also. Only way to know for sure is to have them out and measure them.
     
    Joel07, Nov 8, 2006
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