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  1. #1
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    Default Triumph 500 unit gearbox redneck repair

    Started tinkering with the old trumpets gearbox this weekend, third keeps jumping out so was time to fix it.
    Found out the shift fork was worn down and sloppy so welded the face up with stellite and ground it down on the mill. Straightened with a hammer in the vice grips first!

    Still needs finishing and annealing.
    And the camplate got a new contour, since it was not actually fully engaging 3rd gear dogs. Welding has been done with stellite and bearing bronze.

  2. #2
    SamHain
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    Cool deal on the camplate. I'm shimmed mine to get full engagement after welding up the worn dogs. Next is ditching the circlip and welding a boss on the outside of the inner cover and milling off the one in the inside. They flex and don't help any and rumor is they will even break right out.

    I've got a thread around here somewhere doing it, got the ideas from that British forum. Couldn't keep 3rd engaged in high revs before, good until it breaks up at 8900 now. If only the rest of the bike would stay together.

    http://www.chopcult.com/forum/showthread.php?t=37784&page=2
    Last edited by SamHain; 11-22-2016 at 7:41 PM.

  3. #3
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    How do you shim the camplate?
    Word of caution in welding in a boss to hold the bearing, i did that on another engine, and it shrunk horribly. I needed to grind out the bearing housing. A lot! i think if you weld it carefully a bit at a time it will hold the shape better.

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    Also you have fuckin absolutely huge balls taking an old lump like this with a theoretical safe rpm limit of 7500 up to 9k rpm! 👍👍 mine feels like its gonna kill or at least mutilate me around 7k.. 😀

  5. #5
    SamHain
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    Sorry, Shimmed the main shaft to get full engagement on third. Yeah I shrunk the shit out of the inner cover too, then ground it out too much, then had to sleeve it.

    Eh the ol race bikes ran 10k.....They may have got rebuilt every race, and mine might not even do that good..... but I can't not twist that throttle, it's too fun. on hiatus still with a disintegrated hi-gear bush and broken frame.

    http://britbike.com/forums/ubbthreads.php?ubb=showflat&Number=555366

    There's a few more threads on the subject over there too
    Last edited by SamHain; 11-23-2016 at 7:26 AM.

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    Of course they did, and im not saying you should not ride the fuck out of it!
    Also just read that you have done all the important things to keep the top end up with the revs, so you'll probably have stronger rods in there as well. Im running a mismatched couple of stock rods as well as stockish valve gear so 10k is out of reach for my machine, but someday i would love to hear how that sounds!

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    Disintegrated high gear bush probably happened because of either
    1: poor axle alignment after the bearing mod, or more probable
    2: wrong type of gearbox oil. I think api gl5 or gl4 is aggressive against yellow metals, when corrosion sets in they have a very short service life.

  8. #8
    SamHain
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    Running late stock rods, seems the crank is the weakest link so don't want to run anything heavier.

    Don't recall what I had for oil in the trans, just went with the weight by the book. Don't think I got 1k miles out of the new bush.

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    Then it must be something other than oil quality.. did you need to ream the new bush to fit the axle? Mine looks hardly worn and its probably almost 50 years old. Its an extremely long bush with a very big surface needing full oil film to survive, so i guess things need to be very straight to work as intended there. If mine checks out with the micrometer im leaving it undisturbed, preferably not shimming the main axle either as primary chain is nicely lined up as well.
    Gonna check if 3rd main is shimmed correctly to begin with - i found a small spacer ring on the drive side of third gear, wondering if it would not work better on the other side..

  10. #10
    SamHain
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    Quote Originally Posted by datadavid View Post
    Then it must be something other than oil quality.. did you need to ream the new bush to fit the axle? Mine looks hardly worn and its probably almost 50 years old. Its an extremely long bush with a very big surface needing full oil film to survive, so i guess things need to be very straight to work as intended there. If mine checks out with the micrometer im leaving it undisturbed, preferably not shimming the main axle either as primary chain is nicely lined up as well.
    Gonna check if 3rd main is shimmed correctly to begin with - i found a small spacer ring on the drive side of third gear, wondering if it would not work better on the other side..
    Got it lined up good, had to shim the front after shimming the mainshaft for third and has a newby on it.

    Stock bush was loose/leaks so I ordered another and I think it was even worse, should have just had one turned, do the ol Harley 4spd leak fix.
    Last edited by SamHain; 11-25-2016 at 11:06 AM.

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    Quote Originally Posted by SamHain View Post
    Got it lined up good, had to shim the front after shimming the mainshaft for third and has a newby on it.

    Stock bush was loose/leaks so I ordered another and I think it was even worse, should have just had one turned, do the ol Harley 4spd leak fix.
    Yes some of that aftermarket stuff is really junk.
    So, running a newby clutch, did you have to seal the pushrod as well in some way? I'm guessing most of my leakage is from there so thinking about soldering some brass shim plate on it and turning it down to an oil film tolerance. May be able to seal the bush behind the clutch in some way as well, shouldve been an oil seal with a shoulder to go over the bush there really. Oh well, a bit of gear oil in there wont hurt.

  12. #12
    SamHain
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    Yeah of course I cut plenty of the engine case and primary up, so the oil just makes a mess.

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    Waiting on the 20t sprocket before assembling the box finally so im doing some last fine adjustments to the camplate, turned out i needed to shim the main axle 0.9mm as well for gears to align nicely. Also primary chain probably isnt aligned as well as i thought on closer inspection, may even need to turn down the engine sprocket spacer a bit. Will see when assembled.

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    Cleaned up all the bits to go back in the box last night, bearing in gearbox cover was nice and crunchy so picking another one up today. 49 years is not bad for a bearing thats been partially submerged in water for parts of its life..

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    Bearing dropped right in, now im just gonna grind off 0.1mm on the new layshaft shim, and wait for a 21t front sprocket. Which seems extremely hard to come by for the 500's. If it cant be sourced i can always just weld on a 21t on the 19t center.. should drop rpm's from 5000 at 90kmh to 4000. Damn tiny rear wheel.

  16. #16
    SamHain
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    Nice. That's a whole lotta gearing. I run 17/46, Bnr is 2:1, so primary is taller than stock and I do rev the piss out of it, but they don't do much until 4K.

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    Quote Originally Posted by SamHain View Post
    Nice. That's a whole lotta gearing. I run 17/46, Bnr is 2:1, so primary is taller than stock and I do rev the piss out of it, but they don't do much until 4K.
    Yea, whats strange is engine sprocket is huge as well, 24t i think. Its the largest possible to fit in between the stator studs. Also running a 46t rear sprocket. The 16" rear wheel should not do that big a difference. Mine has good lively pull from 3k, and with a lower gearing i should be able to do some highway riding at more relaxed rpms. And be able to hit the ton.. 😀

  18. #18
    SamHain
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    Oh yeah should be no problem hitting the ton. I couldn't get on the thing without doin it. Except for those shinkos most the 16s aren't much shorter overall. I'm running a 19-3.50

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    So you have 3" taller "gearing" on the wheel 😀 yea, really shouldnt do much difference. Mine feels seriously stressed over 7k so im just looking for a good relaxed 4-5k cruising speed. Also found yesterday that crank was a bit generous on the sliding fit to the drive side roller bearing.. might have to redo the crank to cure the high rpm vibes, timing side bush is worn already as well. Well, next time it will get filtered oil from the start thats for sure.

  20. #20
    SamHain
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    In the wheel yeah, but I think it's 26.5 overall, probably only an inch taller than most 16 tires. I always worried about that timing side bush as that's where all the oil pressure comes from, still I never changed mine, trusty machinist kept insisting it's good.

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