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Considering transmission overhaul myself - terrible idea, or awesome idea?

Discussion in 'XJ Technical Chat' started by Phil B, Aug 3, 2019.

  1. Phil B

    Phil B New Member

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    My names Phil. I'm the proud owner of an 81 xs-400 which I love, and ive been a (relatively) active member over at the XS400 forum, which is fantastic. I just picked up an 85 FJ600. Bought it non-running. I cleaned out the carbs and got all 4 cylinders firing. I thought everything was perfect until i put it in first and got nice cyclical click coming from the transmission.

    After doing some research (links below) it sounds like I have a tooth missing on the transmission. I believe the chain came off the rear sprocket similar to the guy in the first post, as there is some damage around the front sprocket. In-fact, the force was enough to break off the section of shielding (part of the case) directly above the sprocket, and also to chip off part of the cap of the starter (black plastic cap at the end where the bolts go through to attach it).

    Cant link it, but google:
    TTR125 First Gear clicking - TTR - ThumperTalk
    TTR125 Broken tooth on first gear? - TTR - ThumperTalk


    Once i put the bike into first gear I get a rhythmic click that corresponds to the amount of throttle, more throttle faster click. But, when i go into second the sound is gone. If i kill the motor and walk the bike forward in first gear I can also hear the click, but much more quietly. However, if i put the bike on the centre stand and give it throttle in first the sound is not really noticeable if at all....but, when the bike idles there also appears to be a kind rhythmic of knock coming from the transmission area.

    So........this leads to the question i have for the people here who are more knowledgeable than my self. And, i should also say my mechanical ability is so far no more advance than: cleaning crabs, calipers, changing for oil, and a drum break. I have no engine experience.

    1) Can I just replace the first gear cog or do i need a whole new transmission set? (assuming this is the only issue I find.
    2) Am i crazy for even considering undertaking this repair by my-self? I'm in no rush as I have a bike to ride, and will have all of winter to do the work.
    3) Can someone give me a basic idea what will be involved? I know the motor will have to come out and then ill have to drain it, flip it and crack open the bottom portion of crank case.
    4) Will repairing the transmission gears require special calibration, tuning, and tools? Or will it essentially drop in where the old transmission gear set is?
    5) Are there any obvious/specific pitfalls I might face? Or specialized tools I will need

    Oh, I should mention that I have the Haynes service manual which will guide me. And also, that i understand that this will be an exercise in organization and planning, lots of bagging, labelling, pictures, and maybe video will be used to help me get it back together. I'm not a mechanic, but my job involves problem solving and patience, so maybe this is the right kind of challenge for me, even though I'm low on mechanical experience.

    My ultimate plan is to convert my FJ600 it to a street fighter or cafe style mod. Basically one way or another the front cowling is coming off! As you can see at some point it received a rather horrendous paint job.

    Okay, thanks for reading. Ill appreciate any advice, wisdom, or information. Looking forward to hearing your thoughts!
     

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    Last edited: Aug 3, 2019
  2. mlew

    mlew Well-Known Member

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    I do believe you will have to split the case in order to access the trans gears. that's a pain. The cost of parts, materials and gaskets to fix it well exceedes the cost of a used engine. I have seen them from 200 to 300$.
     
  3. XJ550H

    XJ550H Well-Known Member Premium Member

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    Franz and k-moe like this.
  4. Polock

    Polock Well-Known Member

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    1) you can just replace what you find bad/broken
    2)no your not crazy, it isn't technical just intimidating
    3)that about sums it up
    4)no special tools, maybe a torx driver and a torque wrench for sure
    5)there might be some other small parts in there you should replace while your in there
    you most likely will get another motor just because it will be easier to find than the specific parts you need. especially since you don't know exactly what you need
    don't overthink this it isn't that hard
     
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  5. Phil B

    Phil B New Member

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    Hey Guys,

    Thanks for the info! That is encourging and its helping me convince myself to do the the work.

    XJ550H: That thread was definitley helpful to get an idea of the process of splitting the case.

    Polock: Thanks that clears up a number of my questions. Much apreciated.

    Ill definitely make a post as i get started. Probably not untill summer starts to wind-down. I may have some questions so i hope you guys will stay tuned.

    On that note, Im curious ive seen people working on motors using a wood box-brance that apears to just be 2x4's, to place the motor inside of. Can someone explain the idea behind that to me?
     
  6. k-moe

    k-moe Pie, Bacon, Bourbon. Moderator Premium Member

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    It keeps the engine from rolling over when applying force to a fastener and the like.
    Personally I just use blocking as needed and hold the blocks to my bench with clamps. More versitile that way.
     
  7. Ryengoth

    Ryengoth Active Member Premium Member

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    Cradles are handy for moving the thing around but they get in the way more than they help IMHO for any major disassembly. An engine stand can be helpful, but then again even the narrow supports can still get in the way when you need to access something. Get some rubber door wedges from the big box store.
     
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