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1970 1971 1972 1973 Lower Triple Tree steering stem differences & identification

Discussion in 'The Garage' started by DogBunny, Apr 21, 2021.

  1. DogBunny

    DogBunny Motorcychologist Top Contributor

    Distinguishing 1970-1973 fork underbrackets can be tricky. I've mis-identified them in the past. 1972 and 1973 are one-year-only, and are particularly hard to differentiate. eBay sellers often list them incorrectly.

    DSC01148a.jpg
    It's easy to tell 70-71 lower triples from 72-73, because 1972 and 1973 marked a change to disc front brakes, and they added two threaded holes to the lower triple to hold a brake hose stay (green arrows).
    That area was completely smooth on the early 70-71 triples. Later 70-71 triples had two cast-in, but un-drilled bungs (red arrows). I have tried to figure out what those castings are for. I thought that maybe Yamaha was re-using a lower triple from a different model, but that does not seem to be the case. My best guess is that Yamaha was anticipating the change to disc brakes, and that the original plan was to have the brake hose stay bolt on from the side, rather than the bottom, which is what they ultimately went with.

    DSC01149.jpg
    There are more differences between the early 70-71 steering stem and the later 70-71 ones, but they are completely interchangeable. In general, the early lower triple was a bit on the weak side, with a 27mm stem. This was changed to 30mm, which remained the diameter throughout the rest of production, all the way up to 1983.

    DSC01151.jpg
    In order to accommodate the lower bearing race, a sleeve was added to the 27mm stem. The bearing races are identical.

    DSC01150.jpg
    The steering lock socket is an added, welded piece on the early stems.

    DSC01152.jpg
    The steering damper mating surface was also a separate, welded-on piece on the early stems. Changed to a cast-in surface on later 70-71 stems.

    DSC01153.jpg
    Another view of the steering damper differences.

    s-l1600w.jpg
    Onward to 1972 and 1973 differences. This is the tricky one. The only way to reliably tell a 1972 yoke from a 1973 yoke is to measure the distance between the fork tube holes. The 1972 spacing is 175mm, the same as 1970-1971. In 1973, that spacing was increased to 185mm, and that spacing remained for the rest of the run, up through 1983.

    The 1970 and 1971 lower triples used a single 10mm pinch bolt on each side. 1972 and 1973 used a single 12mm pinch bolt on each leg. 1974 and all later models used a pair of 8mm pinch bolts on each side.
     
  2. Mailman

    Mailman Hardly a Guru Top Contributor

    That’s very interesting to see the engineering progression through the years, thanks for posting!
     
    DogBunny and Jim like this.
  3. That’s a good and very informative post. Thanks for posting that.
     
    DogBunny likes this.
  4. DogBunny

    DogBunny Motorcychologist Top Contributor

    I believe that the early 70-71 stems are fairly rare. All you have to do to tell if you have one is to just do a visual check for that welded-on damper plate -- it's very easy to see if it's there or not. If I had a bike with the early 70-71 stem, I'd seriously consider upgrading to the stouter later 70-71 30mm stem. You could even swap in an XS2 stem, with the more robust 12mm pinch bolts, if you don't mind the two added threaded holes for the 72 brake hose stay.
     
  5. Excellent info. I've been tinkering with my 72 to possibly change to a 73 tree or a 75. This thread is very new, so I would imagine that smarter guys than me will chime in soon. Therefore, I will add some assumptions and questions for others and YOU to maybe help straighten out some myths.

    1. I can only assume that the upper tree on the 70/71 will fit on a 72, the only differnce I see is polished and painted.
    2. The 73 upper has a single pinch bolt that seems to be a betterway to to stiffen up the forks. Also on all models 73 and up.

    Uh, oh! Loosing battery power and no charger. Will continue later.
     
  6. DogBunny

    DogBunny Motorcychologist Top Contributor

    Yes to questions #1 and #2.
    Considerations: 1972 is a one-year only front wheel, and it will only work with 1972 triples, and it only works with 1972 forks. You are going to have to swap in a whole front end if you upgrade.
    Swapping in 1973 triples is an upgrade that makes sense because the bike will still have the steering damper, and it will look almost exactly the same.
    I don't see a whole lot of advantage going to 1975 triples. Instead, I'd go to a 1977 or later front end -- you be upgrading to 35mm forks. The problem is that you loose the look of the early fenders.
     
    Marlin72xs likes this.
  7. I'm back! boooooooo!
    Thanks, Dogbunny, you cleared up point #1.

    3. The 73 was wider to accommodate the wider axle due to the different disc brake arrangement. And the 73 could handle dual discs. I'm sure that the 72 forks will not work in the 73 tree.
    4. I wonder if the early 70/71 lock hole splashed out like the later 70/71 and every thing else on up?
    5. The 73 and my 75 have a rubber washer under the bottom race. The 72 doesn't have that. That should reduce some vibration.
    6. The 75 tree neck is slightly longer, as is probably the 74. Someday I will take the 72 apart and figure out how to adapt the 75 on me 72.
    7. The 75 tree tube placements are set back, changing the geometry somewhat. I wonder if that would noticeably affect the handling?
    Also dreaming about using a 75 swingarm on my 72, along with the 75 front end. I'm hesitating because my 75 wheels have some rusty spokes.
    8. My 72 gauges should bolt onto the 75 tree.

    Gotta go! Will add more later. Ride safely! :bike:
     
    GLJ likes this.
  8. Well, Dogbunny, I own a complete 75, now in pieces. A 77 or later front end would be much better, but I'm on a budget. Gonna stick with what I got unless a good deal comes along. Fenders are not a problem because I am presently using 79 fenders on the 72. Saving the 72 fenders for when I ever sell the bike. Yes, you're right, the 73 will be a simpler swap and I get the top pinch bolts. Still only dreaming! What did Bugs Bunny say, "I can dream, can't I?"
     
    GLJ likes this.
  9. DogBunny

    DogBunny Motorcychologist Top Contributor

    3. The 72 forks WILL fit in the 73 trees. The problem is the 72 axle holes. The left side hole is the same. The right side isn't, different diameter. I forget if it's bigger or smaller, but it could be adapted by either boring larger or sleeving, then you could use 73 and later axles and wheels.
    4. Don't understand the question. "Spashed out"?
    5. No. That is just a "dust seal", designed to keep the steering bearing grease from leaking out all over everything. It goes outside the bottom race, not under it.
    6. I currently have a 35mm front end on a 71 frame that I am building. I forget what I had to do, but it wasn't much. I think you just use the original 70-73 stem with whatever later year triples you choose.
    7. Don't know about the handling yet, have to wait till I finish the 71. I do know that you have to address the steering stops -- you'll have to figure out something there if you go with 74 or later triples.
    8. I think you're right, but I also think a 70-73 gauge bracket would work on any year upper triple tree.

    Regarding your budget. Saving your 72 parts for when you sell the bike is a noble thought. However, your 72 wheel, forks, and triples are rare, and hence valuable. You could sell them and finance a 77 or later front end and come out way ahead. Eventually someone on the Forum will want that stuff.
     
    Marlin72xs likes this.
  10. 650Skull

    650Skull SSSSSSSSSlither Top Contributor

    good in depth DB.

    The 73 trees being wider than the 72, i can understand the 72 being narrower due to the brake rotor setup. The question that pops into my head is .........if the rotor side is narrower, that must mean the speedo drive side is to. If so then is there a difference in the 72 speedo drive compared to all the later models or is does the hub, on that side,have a difference to take up the 5mm.

    Being 10mm there has to be 5mm each side or the wheel wont be centered.
     
    gggGary and Marlin72xs like this.
  11. DogBunny

    DogBunny Motorcychologist Top Contributor

    Looking at the parts diagrams, it appears that the 72 speedo drive is also a one-year only part. I don't have one to measure, but yes, either the 72 speedo drive is a different width from later years, and/or the hub is somehow different.
     
    gggGary and Marlin72xs like this.
  12. 650Skull

    650Skull SSSSSSSSSlither Top Contributor

    Didn't look before asking......

    Here are the Pats files for reference in your thread
    XS2 front hub
    70- 71B-F -72 Parts ist 166.jpg 70- 71B-F -72 Parts ist 167.jpg 70- 71B-F -72 Parts ist 169.jpg

    73TX
    74 TXA - parts  Manualt22 22.jpg 74 TXA - parts  Manualt23 23.jpg 74 TXA - parts  Manualt25 25.jpg
     
  13. Look at your pictures. See how the lock has buggered the slot in the stem. That's splash.

    Basically, I have all the original 72 parts except the mufflers. So I guessing it will be worth something all together someday.

    You can get just about any year of triple trees on ebay. But you, (and you obviously know the differences), need a careful eye because most sellers don't know what year they have.
     
    gggGary and DogBunny like this.
  14. jetmechmarty

    jetmechmarty What should I put here? XS650.com Supporter Top Contributor

    Once those of us who remember them new are gone, they will return to worthless. A couple will survive in museums.... maybe.
     
    gggGary, lakeview and DogBunny like this.
  15. Well, my future's so bright, I gotta wear shades! Don't be so glumb!
     
    gggGary, GLJ, lakeview and 1 other person like this.

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