Can/Should I tackle a top end rebuild?
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  1. #1
    Junior Member Vintage914racer's Avatar
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    Can/Should I tackle a top end rebuild?

    Greetings. Long story short I picked up a Honda Twinstar last winter to build into a fun little neighborhood shooter/pitbike. I picked it up for $150, knowing that one of the cylinders had low compression. At the time I wasn't too interested in tackling an engine rebuild so I picked up a used engine on eBay that was represented in very good condition. Time passed and the project got sidelined. Recently I've learned that the second engine has no-compression in one cylinder so I'm at a turning point, namely do I do a top end on the first engine myself of find another alternative?

    I'm pretty mechanical, have torn down car engines and rebuilt a few manual transmissions. I don't doubt that I can tackle the top-end job, but I really have no idea what the cost might be. My pistons/cylinders are out of spec so I'd have to go oversized. One of the valves is also damaged so I'd have to address that. All told it seems parts and machining could cost several hundred dollars, above of beyond the time. To that end, how much time is involved in a top-end job? Am I foolish to think about just buying another used engine?

    Just for kicks I've included a couple images of the bike as it sits today. Cosmetically it's getting there...if only it ran.

    Can/Should I tackle a top end rebuild?-img_5030.jpg

    Can/Should I tackle a top end rebuild?-img_5031.jpg

  2. #2
    Senior Member Gene's Avatar
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    Do it. You'll be fine with the help of a good manual and this forum.
    *1974 CB360G (sold)
    *1985 Nighthawk 450 (sold)
    *1975 CB550K - O.B.
    *1973 CB750K3 - Bow

  3. #3
    Junior Member Vintage914racer's Avatar
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    I just realized I posted this in the wrong forum, ssing as the bike is a CM185. Could an admin move it? Sorry

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  5. #4
    Super Moderator longdistancerider's Avatar
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    This is in the SOHC section now, possibly it got moved w/o notation of doing so.
    If you've been thru engines and transmissions before there's no reason not to go through either one of these engines. That's far better than buying another used and abused engine if you plan on keeping this one for awhile. Yes, it's going to cost more to rebuild it but at the same time you will end up with a fresh engine assembly that you know is correct.
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    Jim O'Brien
    1979 CM400T "road bike" modified for travelling
    1978 CB400T1 restored
    1972 CL350 survivor restoration


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  6. #5
    Junior Member Vintage914racer's Avatar
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    Quote Originally Posted by longdistancerider View Post
    This is in the SOHC section now, possibly it got moved w/o notation of doing so.
    If you've been thru engines and transmissions before there's no reason not to go through either one of these engines. That's far better than buying another used and abused engine if you plan on keeping this one for awhile. Yes, it's going to cost more to rebuild it but at the same time you will end up with a fresh engine assembly that you know is correct.
    PM sent about the FSM
    Thanks. I've decided to move forward with the rebuild. I was concerned about finding parts, but from what I can tell there are a couple authorized honda parts outlets I can order most everything I need from online. If there's a vendor you'd recommend please PM me any recommendations. Also, thanks for the FSM.

  7. #6
    Member Sconda's Avatar
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    I agree that moving forward in rebuilding the engine is the way to go. The bike looks good, by the way.

  8. #7
    Super Moderator longdistancerider's Avatar
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    I try to use the local dealers if they will accept the posted internet pricing, that way I save of freight charges. If not then I use www.partsfish.com, a dealer out of Nebraska, or Partszilla.com
    Jim O'Brien
    1979 CM400T "road bike" modified for travelling
    1978 CB400T1 restored
    1972 CL350 survivor restoration


    https://www.hondatwins.net/forums/22...d-attempt.html and https://www.hondatwins.net/forums/1-...r-attempt.html
    Road Trip https://www.hondatwins.net/forums/11...here-i-go.html or "where's Jim now?"
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  9. #8
    Junior Member Vintage914racer's Avatar
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    Parts are ordered so there's no turning back now

  10. #9
    Senior Member Rothafella's Avatar
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    Good luck with the project - definately came to the right place for support!
    1973 CL350 "Claudia"
    2006 SV650 "Sylvia"

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