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To Bore or not to Bore?

Discussion in 'XJ Technical Chat' started by ingie1062005, Aug 1, 2013.

  1. ingie1062005

    ingie1062005 New Member

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    I have a 1983 xj750 it has 84000 kilometers on it. Doesn't burn oil but I have it all apart now as I had a base gasket oil leak. Should I go with the big bore kit (818cc) or just replace the standard rings with new ones?
    Is it a hassel to get it running right after?
     
    ingie1062005, Aug 1, 2013
    #1
  2. RickCoMatic

    RickCoMatic Well-Known Member

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    The Big Bore Kit will require Machining and New Pistons.

    The present condition of your Cylinders dictates what you need to do or not.

    Press a Standard Compression Ring half-way down the Hole with a Piston with removed Rings.
    Measure the Ring Gap.
    Compare your Measurement to the Spec Limits for your Bike.

    You might only need New Standard Rings.
    -or-
    Over-sized Rings ( 1st or 2nd Over )
    -or-
    Over-sized Pistons ( Big-bore Time )
     
    RickCoMatic, Aug 1, 2013
    #2
  3. adrian1

    adrian1 Active Member

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    Often its just the case the old rings have lost tension...have you done a compression test. IMHO you are probably overcapitalising with a rebore unless a regularly used keeper...
     
    adrian1, Aug 1, 2013
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  4. bigfitz52

    bigfitz52 Well-Known Member Premium Member

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    Think about this for a minute.

    The bottom end and the rest of the drivetrain have 84K kliks on it. (52,000 miles for us Yanks.)

    So you do an overbore to an 818 and then let's say you do somehow figure out how to properly re-jet and get the carbs tuned so you can actually ride the bike.

    Now you have a hot-rod top end on a sorry arsed old well-worn bottom end.

    How long before something goes (in the words of David Hobbs) KABLAMMIE!!! ???

    Unless you plan to go whole hog hot rod, I wouldn't do it. There wasn't much of an aftermarket for these bikes because shaft-driven bikes just weren't taken seriously as "performance bikes" back in the day. The XJ series make excellent street bikes and are pretty much bullet-proof and capable of some really amazing service lives if properly maintained. Not so much for hot rodding. It could get expensive fast.

    I'd keep it as stock as possible, and with some TLC you could double those kilometers. Hot-rod only the top end and it probably won't last nearly as long.
     
    bigfitz52, Aug 1, 2013
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  5. ingie1062005

    ingie1062005 New Member

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    Thanks Guys, Yes I have new Timing, Primary, & Oil Pump chains & oil pump. I have the new stock rings. I've deglazed the cylinders but haven't had time to check the clearance on the rings yet, but it's the long weekend and I'll be doing that tomorrow.
    Thanks again!
    Mark
     
    ingie1062005, Aug 2, 2013
    #5
  6. adrian1

    adrian1 Active Member

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    Please add your location and type of XJ so we can assist in the future...
     
    adrian1, Aug 2, 2013
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