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Holy Grail of XS400 Big Bore Pistons

Discussion in 'The Garage' started by aaronxs400, Dec 24, 2012.

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  1. BBS360

    BBS360 XS400 Guru Top Contributor

  2. drewpy

    drewpy Excess twin Top Contributor

    I bought new xjr1300 rods for £120 from yamaha
    got the GS500 liners machined and just awaiting my machinst to do another job before I can collect.
     
  3. Myke Nytemare

    Myke Nytemare XS400 Enthusiast

    It may take me all year, but if I go ahead with my plan to mod the bike (going to take me a few weeks to get it all back together and cleaned up), I will definitely do this!!!!

    Drewpy, what was the charge for the machining from your guy...just curious?
     
  4. Wolfe_11B

    Wolfe_11B XS400 Guru Top Contributor

    Make sure you add it all up, it will get expensive quick for very little gain. It makes sense for Drewpy since he is cramming more air into the motor, and it makes sense for guys road racing since every little bit helps. But you have top take into account that you are stuck with your intake valve size and that is a huge limiting factor.
    Rods will be $226 here in the states. Pistons will run you about the same. New cam grind to take advantage of it- $375. Head work- $75. Will need slightly bigger carbs- $300-500. Liners are probably a few hundred. What about big end bearings? Are you going to have the shop match them to your crank? Machine shop work- figure a hundred for the liners machined and $250 to set them in, a 'correct' bore and hone to match to the pistons is about $75 a cylinder, and taking the top off the pistons will cost you whatever the hourly rate is most likely.

    Just a thought. For that much money you can buy a beast of a motorcycle. If you still want to do it, go for it :)
     
  5. drewpy

    drewpy Excess twin Top Contributor

    about £40
     
  6. Myke Nytemare

    Myke Nytemare XS400 Enthusiast

    I didn't think of the cam grind and definitely thought I could just rejet and tweak the stock carbs. Maybe I'll put the money elsewhere.
     
  7. Wolfe_11B

    Wolfe_11B XS400 Guru Top Contributor

    A bore/hone with the next oversize pistons/rings will probably be just as beneficial and much cheaper.
     
  8. Myke Nytemare

    Myke Nytemare XS400 Enthusiast

    Thank you wolfe...I'm hoping to finally pick up the bike this weekend and see if I can get it running before the Florida heat really kicks in and I wont be able to work in the garage.
     
  9. Jeff0133

    Jeff0133 XS400 Junkie Top Contributor

    So...After 8 pages...I have a few questions:
    - I have the DOHC would fj 1200-1300r rods fit..?...it would follow that the conrod bearings would fit...but they are not the same part #...:umm:
    - would taking the balancer shaft out give a little extra oumf...?....is it doable/advisable?
    ...kinda lost track...
     
  10. XS400Cup

    XS400Cup XS400 Member

    Yes.
    The difference is the oil hole.
    bearing.jpg
     
  11. Jeff0133

    Jeff0133 XS400 Junkie Top Contributor

    Easily resolved then.
    Thanks
     
  12. Jeff0133

    Jeff0133 XS400 Junkie Top Contributor

    So...would the same apply to the crankshaft bearings?
     
  13. young_gun

    young_gun XS400 New Member

    1
    0
    1
    Germany
    Hey everyone, especially Hey Wolfe! I registered to revive this several year old thread so you could tell us which pistons would fit onto the XJR rods since you kept it a little secret. I'm planning on upping the compression in my '79, already did an indebt head overhaul, the xs360 crank switch, so upgrading to lighter, sturdier rods would be the last thing on my list.

    Much regards from Germany
    Sebastian

     
  14. kuuurrrt

    kuuurrrt XS400 New Member

    Rod 1TX-11631-00-A0 for FJ1200
    Piston 4PU-11631-00-A0 for XJR1200
     
  15. Phoenix

    Phoenix XS400 Member

    Time to resurrect this yet again

    Have my new xs400J dohc waiting for me to bring her back from the brink after buying her for $250... very curious to look inside.
    As I rebuild, and going for a tracker/scrambler type build, I'd like to plan ahead for the internals, and would love your help.

    xs360 crank is waiting in my ebay cart, just curious how much worse the vibrations get? I'd like to use this bike frequently, and be okay with taking it longer distances without losing too many fillings.
    I understand the pistons from the xjr1200 need to be machined down, is that the case?

    Really appreciate your guys' bold dives into modifying these bikes. Very excited to start on this project. Thanks for your inputs!
     
  16. BBS360

    BBS360 XS400 Guru Top Contributor

    The XS360 crank won't be any help on a DOHC bike.
    Not sure how much of the info in this thread applies.
     

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