Hello from San Jose

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    My name is victor and I am currently living in San Jose, California. I was drawn here in search of info on big bore setups. I was a member over at the kz twins owners forum before that went down. That was a tragic loss of info over there, I had the big bore thread bookmarked. I’m hoping to get some info on that here (seem to remember using YFM350 pistons?)

    I have been a KZ lover for many years now and last year got my first 750 twin. It was hacked up and not running. My friend bought it and really underestimated what it would take to get it on the rode so I bought it off him. I have been honing my fabrication and machining skills on the project. I have been keeping a thread going over at KZR on my progress if you care to take a look.

    So far;
    KZ650 wheels
    Works shocks
    sub-frame revised and custom shock mounts rotated forward.
    XS650 fender with custom tail-light housing
    customized GS1100E swing arm that has been shorten to the stock length
    stainless motor mount bolts for close tolerance fit
    fiberglass seat pan and seat
    forks rebuilt with progressive fork springs
    fork brace
    engine covers from a “B”
    frame powder coated

    remaining plans are;
    finish stainless 2<1 exhaust
    finish billet footrests
    finish headlight/gauge/fork ears
    Get some nice paint on it. tri-coat candy maybe?

    I also just picked up a junk motor that I want to hot rod, but that will proceed a little slower.

    here are some before and current state photos.





    Hey Doctorot

    Welcome to our forum.

    I have looked at your blog and I love your enthusiasm. The bike in the living room picture is to die for. Who hasn’t wished to do that?

    Chrislwg on our website has done Big Bore to his twin. Took it to 865cc with other mods such as twin spark plugs and oil cooler amongst others. He bought his twin new in 1976 and I believe can now boast over 100,000 miles.

    Michael from the German website z750twin.de is currently in the process of producing an even bigger bore size. I am sure he will be on here shortly to help guide you.

    Enjoy the site and please keep us updated with your progress and feel free to ask away and contribute.




    What’s up Doc? 🙂

    I have been watching your thread on that other forum too. Yes, shame about the old KZ site but, life goes on. Good luck on the build and looking forward to watching another big bore in progress. 😉


    Thanks for the welcome guys.

    I have been in touch with Arias pistons and without sending in my exact requirements they said it would be around $160 USD per piston with a minimum order of 4, discounts for more. That is not bad at all, and I think I may be pursuing this as an option. After reading through Michael’s big bore thread I found the link to LA sleeves, which could be a relatively cheap way to get a new set of sleeves. Hopefully I will have some time in the next month or so to break down the junk motor I have and get some measurements to get a firm quote on the pistons.

    This very well could be a pipe dream, but after reading about people re-phasing their XS650’s I’m wondering how insane I would be to attempt to try it. The 750 has a single piece crank so a custom pressed crank would probably be necessary to facilitate this along with re-phased cam and ignition. At the very least I’m going to have the crank lightened and balanced, but a guy can dream can’t he?


    Hi Victor,

    welcome and good to see you on board.

    Cheers, Michael


    That does seem a good price for the piston Doctorot but what about the rings?

    I would be interested in some pistons at that price.

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