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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

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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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  8. Phil B

    Phil B New Member

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    Just wanted to say I think it was a success. Thanks for the advice and helping me to not talk myself out of it.

    In the end i got a new transmission set off eBay for 60 bucks or so, which isn't bad for shipping up here to Canada. It came with a change-lever/shift shaft in addition to a perfect condition drive shaft and main shaft. I switched out all 3 as the shift shaft was out of true, the first gear on the main shaft was missing a tooth and the corresponding gear on the drive shaft had a mangled gear.

    It was really fun and super educational and Im definitely glad i did the work myself...

    I'm even cutting the gaskets which i worked out a way to scan and print at 100% scale which worked really well. I already did the oil pan, now just need to do the clutch cover. Funny thing gaskets. If not for all the cleaning and cutting of gaskets this could be a much faster project. And my pride and joy in the work will quickly turn to horror should any of the new gaskets, or god forbid the crank case seam start to leak. I sealed it up with Permatex anaerobic gasket maker based on advice in another thread.

    I'm just rebuilding the clutch and now find that 2 of my metal plates are just a tad out of warp spec, and that my springs are just a bit (2mm) short. Given I didn't have any clutch trouble in my limited testing, Im planning the let the plates ride for now and throw an extra washers on the spring bolt which will almost exactly bring the springs into spec (spring length+washer height=spec).

    Okay, thanks again and ill post a final update when I have er back on the road next spring. After all the rebuilding/styling work is done. :)
     
  9. kerriskandiesinc

    kerriskandiesinc Active Member

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    I used to do my own gaskets too, for 'non critical' items.....hope the sump( oil pan) holds out !!
     
  10. Polock

    Polock Well-Known Member

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    If possible get new springs for the clutch
    Be sure to use blue thread lock on the bolts in that clutch
     
  11. Ryengoth

    Ryengoth Active Member

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    Permatex ultra-grey is a good option for metal mating surfaces that are machined and will not be coming back apart. The same formula is spec'd for most automotive engines for timing covers and such. Permatex ultra-black is a good option for oil and gas-contact areas where a flexible seal is needed on machined mating surfaces that will be periodically removed and cleaned. Again, it is often spec'd for oil pans, valve covers and other "splash zones" that are accessed for maintenance. I've never had a leak when using them properly, without any sort of gasket material.
     
  12. chacal

    chacal Moderator Moderator Supporting Vendor Premium Member

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    I don't think this is a good idea at all...……...a clutch explosion can be a nasty thing even at neighborhood speeds.
     
  13. XJ550H

    XJ550H Well-Known Member Premium Member

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    ^ solid advice. a cheap fix just never is cheap in the end
    there is a few old threads of clutch explosions with photos I think it happened to 2 or 3 members in a very short time. not a pretty sight.
     
  14. Polock

    Polock Well-Known Member

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