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Tx750 madness.

Discussion in 'The Garage' started by ShaggyMech, Mar 30, 2021.

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  1. ShaggyMech

    ShaggyMech Socal Mechanic.

    I've begun the perilous journey to restore the long lost TX750A. Anyone with knowledge, parts, or just curious about the flagship 74 yamaha contact me please! Mostly I need parts.
     
  2. Jim

    Jim Beyond the edge is the unknown. Here be Dragons XS650.com Supporter Top Contributor

    Pics or it didn't happen.... :sneaky:
     
    Paul Sutton, gggGary, joebgd and 3 others like this.
  3. ShaggyMech

    ShaggyMech Socal Mechanic.

    IMG_20210310_204045_187.jpg IMG_20210310_204045_192.jpg IMG_20210310_204045_193.jpg
    I picked it up non-running. Rebuilt the carbs, put a good battery in the slot, scrubbed the grounds with a wire brush, polished the points with a playing card dipped in wd-40, kicked the ever loving piss out of it for an what felt like an hour and she rumbled to life. I found a NOS air cleaner I epoxied new foam onto, and have my father machining me the BMW type oil filter adapter to replace the goofy can type. The starter chain is slapping around in the housing so I have an NOS chain on the way and I have a tensioner assembly i am making to fix that. If I can find a sprag type bearing that fits in the rotor pocket and rides on the gear correctly, like a fellow named Argo in Holland made in 2015, It'd be literally perfect. Has all the factory pieces to correct the balancer chain issue, deep sump, external oil filter, adjustable chain lobe, etc. It runs beautifully except for the starter issue. Which is mostly caused by the crap 3 bearing one way assembly that Japanese used until i think the early 90's. It is literally a 99% complete example. Minus the factory exhaust silencers.
     
    gggGary, jonesey, nj1639 and 5 others like this.
  4. ShaggyMech

    ShaggyMech Socal Mechanic.

    gggGary, Grimly, Team Junk and 2 others like this.
  5. arcticXS

    arcticXS XS650 Guru Top Contributor

    With a deeper sump and a good balancer chain, two weaknesses are hopefully sorted.
    But I also seem to remember something about that exhaust "flange/balance chamber" arrangement causing it to run hotter than ideal. Is there any way to fix that!?
     
    gggGary and Jim like this.
  6. ShaggyMech

    ShaggyMech Socal Mechanic.

    Yea, you either cut the balancer forging in half and weld it or just fill the thing up and weld it closed. Easy. I've had to make several pieces like the exhaust collars that go in the nut to hold the header on. I used 1 1/2 stainless pipe cut to a 1/4 thick then split the pipe and put them on the tube. Voila, collars.
     
    gggGary, arcticXS and Jim like this.
  7. ShaggyMech

    ShaggyMech Socal Mechanic.

    I have been researching the TX for months now. I even got my hands on a factory service manual to understand it better. When I'm done with the elephant foot mods, oil pump modifications and all the internal changes, Australians have been getting the better part of 50k out of an engine.
     
    gggGary, Mailman, Jim and 1 other person like this.
  8. arcticXS

    arcticXS XS650 Guru Top Contributor

    Having never owned or ridden a TX750, but I know a couple of guys that had them. Both for a short time, without any particular reason I know of.
    But that hollow balance casting really bugs me from a cooling perspective. Even if there is no exhaust flow through it, it will still block the cooling air flow to the head. Or am I totally wrong?
    So a couple of individual flanged and threaded adapters should improve this? Or not? Just ramblin' here.....
     
    gggGary and Jim like this.
  9. Jim

    Jim Beyond the edge is the unknown. Here be Dragons XS650.com Supporter Top Contributor

    Nice bones to start with. You thinkin' full on resto or survivor?
     
    gggGary and arcticXS like this.
  10. ShaggyMech

    ShaggyMech Socal Mechanic.

    16171449065176599432130559541770.jpg
    That black header piece is the unit. To get the best you physically cut the center out and weld the holes closed, or do away with the factory headers and make your own flanges/headpipe that bolts to that location.
     
    gggGary, RustiePyles and arcticXS like this.
  11. ShaggyMech

    ShaggyMech Socal Mechanic.

    Well, Jim it's really in such a nice condition that I don't need to "restore" it. I have to replace the gas tank, on the way, some knob broke the section where the key catch is pinned on. I am re-keying the bike to one key, snagged a set off fleabay, and I am going to correct the wiring disaster since I am OCD about wiring cleanliness. I am an industrial electrician so dirty wiring just drives me nuts.
    I will be modding all the short comings of the tx engine that will make it a true rider. And probably just keep on tinkering with it since it is such an oddity. Yamaha's first in house designed four stroke that when it's working correctly is honestly a dream. German electronic ignition to fix the hard starting, sprag type starter engagement mechanism and starter chain slider/tensioner made from a harley big twin cam chain tensioner block, improve the oiling to the top end and transmission by increasing pressure and increasing the oil gallery port sizes, increase the size of the scavenge pump by 3mm, change the oil filter out to the tried and true BMW R6/5 filter, I will make one small modification that's my own, and bore the triple trees from 36mm to 37mm to take a set of XS850 forks so I can use a motolanna 40mm brembo adapter like I used on my Heritage. I have a modern solid state tyoe A regulator/rectifier to replace the outdated mechanical units, I will remove the lighting reserve unit like on the XS and convert to all LED to just add a minor touch of modern. But besides that, I will be doing the usual replace all cables/ bearings/ tires/ tubes/ and full Inspection of all rubber pieces to ensure a long and happy life for the already impressive 37000 miles it's lived.
     
    gggGary, Mailman, RustiePyles and 2 others like this.
  12. ShaggyMech

    ShaggyMech Socal Mechanic.

    Considering the tx750 website is practically dead I will be chronocalling the adventures of the maroon missile here. So stay tuned for a wild ride into the great unknown TX750 engine. I do plan to do a bottom to top rebuild/refresh while I have it cracked open.
     
  13. Rasputin

    Rasputin XS650 Addict XS650.com Supporter Top Contributor

    ABD1AA06-B3EA-41D0-8B8D-F406C772C0FC.jpeg TX750. Now there is a conundrum in a puzzle wrapped up in an enigma.
    A lot of what you will no doubt read, like me, will fill you full of dread but, a lot of this info stems from experience when the bike was launched onto the American market, and when they were raced in Australia and elsewhere.
    The engines are neither fragile or unreliable when used in the correct manner.
    Certain design flaws were corrected on the 74 model.
    I have one, and have carried out most of the mods on my engine.
    There is a couple of FB sites for this model that are full of useful info.
     
    Paul Sutton, gggGary, Raymond and 5 others like this.
  14. Rasputin

    Rasputin XS650 Addict XS650.com Supporter Top Contributor

    By the way. A good fix for the starter is a Yamaha R6 sprag clutch. I have just fitted one to a friends XS500.
    Mine has a similar set up although not from a R6.
     

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    Paul Sutton, gggGary, Jim and 3 others like this.
  15. ShaggyMech

    ShaggyMech Socal Mechanic.

    How in the world did you do that?
    I found a sprag from a
    One Way Clutch Starter Bearing Sprag for Suzuki LTF 250 300 QuadRunner 88-04 B5
    That is 42mm Id and my understanding is the TX starter sprocket is 42mm. I found an xv250 sprags outer diameter is 94 and so is that one. As far as I can tell since I haven't torn my apart yet, that's what I am doing tomorrow actually, that sprag should be a nearly perfect fit.
    But regardless, where did you get the r6 sprag and do you need to modify the rotor?
     
    gggGary and arcticXS like this.
  16. ShaggyMech

    ShaggyMech Socal Mechanic.

    Also I didn't feel dread from reading about the TX honestly. I find troublesome machines to be my favorites. I am in pursuit of perfection always and the poorly misunderstood TX seemed like the greatest challenge yet. Something just to cool to pass up the chance to fix a venerable giant.
     
    Paul Sutton, gggGary, cra-z1 and 6 others like this.
  17. Mailman

    Mailman Hardly a Guru Top Contributor

    I’ve always had a soft spot for the TX750, a friend of mine bought an orange one , just like Rasputin’s, brand new off the showroom floor. I remember being very impressed with it back then. Still like the looks.
     
  18. ShaggyMech

    ShaggyMech Socal Mechanic.

    Well, unfortunately the orange models are the dog models. Had nothing but problems. They are dry sump and the shallow return would allow the oil to whip into a foam. Numerous amount of issues.
     
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  19. Rasputin

    Rasputin XS650 Addict XS650.com Supporter Top Contributor

    F15FBB66-7563-49C7-9489-10A1E58EEBAA.jpeg This is my actual rotor with modified sprag clutch.
    I can’t claim the honour of this mod, it’s one I bought from a guy in Estonia. I wanted to get it fixed pronto when I first bought the bike. Apart from drilling and tapping six holes it’s a direct fit, whereas the R6 unit requires a spacer ring machining as the OD of the Sprag is smaller than the ID of the step in the rotor.
     
    gggGary, ShaggyMech, arcticXS and 2 others like this.

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