1971 CB350 K3 Motor Rebuild - Page 6
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Thread: 1971 CB350 K3 Motor Rebuild

  1. #51
    Senior Member Boomer343's Avatar
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    1971 CB350 K3 Motor Rebuild-dsc02918.jpg1971 CB350 K3 Motor Rebuild-dsc02916.jpg



    Very Technical and can be baffling ..... this one has much better factory packing than the previous ones I've done but I would still add some additional or as I usually do, replace the factory fibreglass with a better product. Packing is cheap.

    Put some high temp anti-seize on the threads and go make some noise.

  2. #52
    Junior Member COPPERHEAD20's Avatar
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    My 68 CL 350 has 85 LBS and 90 LBS it will star easy and idle but it feels a little weak I don't have anything to compare it too as this is the first 4 stroke I ever owned. I'm thinking rebuild is in its future.

  3. #53
    Supporting Member Yendor's Avatar
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    Spec for a 350 twin compression is 165- 170 PSI and below 150 a rebuild is the recommended solution.
    More than 10% varation between cylinders same thing

    BUT... before you get drastic:
    - Was the Throttle WIDE OPEN ? (Actuall it's best to just remove the carbs altogether.
    - Were you using the KICK Stater or Electric ?
    - Did you remove BOTH Spark PLUGS to get the motor to free wheel with as little resistane as possible?
    - Are you sure your Valves are adjusted properly? (a slight bit too tight and they will leak compression)
    - Did you try a Table Sppon of Oil in each cylinder to see if the compression jumps up? (usually indicates a ring problem as the oil settles against the rings and provides additional sealling)
    1970 CB 350 CAFE - Current Project on the bench,
    1972 CB 350 K4 Red - Now a Happy Rider ! !
    1972 CB 350 K4 Green (My Sons) DONE - YES !,
    1st Bike 1970 SL 350 (Brought home in Parts - Trailer/Trunk/Back Seat - I miss that bike),
    2nd - Bike Kawasaki 750
    3rd - '73 XLCH 1000

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  5. #54
    Senior Member drydreamer's Avatar
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    Did you try a Table Sppon of Oil in each cylinder to see if the compression jumps up? (usually indicates a ring problem as the oil settles against the rings and provides additional sealling)


    Table spoon?? how many cc is that? and whats the compression ratio?

    table sppon should read tea spoon me thinks......

  6. #55
    Senior Member doctorruckus's Avatar
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    Anyone else have a panic attack while your bike is in 100 pieces and you can’t get in contact with the people you sent parts to? Haha. I just want this back together before it freezes because I don’t have a heated garage.

  7. #56
    Super Moderator longdistancerider's Avatar
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    I'm in the same condition with the unheated garage. I'm using this https://www.homedepot.com/p/Dyna-Glo...60BK/303228792 to take the chill off. There is a larger version https://www.homedepot.com/p/Dyna-Glo...60BK/303228790.
    Nice thing about this particular heater is it's UL listed, has a low oxygen cutoff as well as a tip over cutoff. I'm using a 20# propane tank with a hose. For safety I turn the tank valve off until the heater dies, then turn the heater off. That way there's no residual gas in the hose to possibly leak out.
    While you wait for the parts to return work on the little sub-assemblies, cleaning, polishing, etc.
    Jim O'Brien
    1979 CM400T "road bike" modified for travelling
    1978 CB400T1 restored
    1972 CL350 nuts and bolts restore in progress


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  8. #57
    Senior Member doctorruckus's Avatar
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    Should have most stuff in soon so I'm finishing up gasket removing. This stuff seems like it was welded on, it's terrible. I'm using a combo of carb cleaner and gasket remover and peeling it off slowly while letting it sit on for a day usually. There are definitely scrape and scratch marks. Final cleaning I've been using some white roloc bristle discs in a dremel and it's cleaning up nice and flat it seems. Does anyone have a suggestion for a flat file I can use? I'd be nice to check for flatness since I can't remove the studs easily.

  9. #58
    Super Moderator longdistancerider's Avatar
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    Never ever use a file on a gasket surface! They are for removing metal which is not what is wanted here.
    I use a red sharpening stone similar to this one https://www.amazon.com/Norton-547-61.../dp/B00820NSMC It gives you a smooth surface while removing a bare minimum of material. Use a light oil while working in as close to a figure 8 motion as possible, I know the studs present a problem there.
    This straight edge will suffice for what you're doing https://www.amazon.com/Anodized-Alum...QC45HG2D9EHY36 NOTE: straight edges must be stored hanging, never laid flat.
    Jim O'Brien
    1979 CM400T "road bike" modified for travelling
    1978 CB400T1 restored
    1972 CL350 nuts and bolts restore in progress


    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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  10. #59
    Senior Member doctorruckus's Avatar
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    Thanks. I’ll pick those up. It looks looks the bristle discs on the dremel are doing great on the flat surfaces for a nice polish as long as I keep the speed low. I just turned in notice for my job to be done December 6 and won’t start back up until January 6 so I’ll have a full month to get this back together right.

    I thought about polishing it up and making it new but I sort of like the tarnished dirty look for the bike.
    longdistancerider likes this.

  11. #60
    Senior Member doctorruckus's Avatar
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    Got my cylinder back and went to put the rings on by putting in one edge in and rotating it around. Tried it twice and they shattered. I’ve heard the pliers are unnecessary but now I’m not so sure.

    Do I need to get rings from the same place I got the pistons or are any +1.0mm rings ok? The oil rings went on fine, it was the middle ring.


    Edit: bought more from cruzin. I'm so annoyed with myself. I'm also buying pliers this time.
    Last edited by doctorruckus; 12-03-2019 at 07:20 PM.

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