Yet Another 76 YZ400 Project Build

Discussion in '2 smokers' started by Scootern29, Mar 18, 2013.

  1. craydds

    craydds Long timer

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    I hope my forks (and Scott's, too) don't GRENADE on us! I wonder why they only made them on the '76 model??? Seems like a good concept. Did they have EXPLOSION issues? :muutt
  2. Valleyrider

    Valleyrider I Survived The '60s

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    No, no explosion issues. They were just very difficult to dial in. You had to have that "Low Loss" gauge to check the top and bottom pressures. The bottom was not so much an issue. The top on the other hand would vary greatly due to the small volume of air in the top chamber. If you used a conventional pressure gauge, the pressure could be off by 5 pounds or more from one side to the other. Of course with today's modern suspension, that has been used with some forks having dampers in only one side....???
    One year was enough of that none sense!
    Dennis Kanegae and I referred to them as "Hand Grnades" cause that's what they looked like.
  3. ADK

    ADK master of the casual pace

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    they look sorta like a tach and speedo. :lol3:1drink
  4. JeffS77

    JeffS77 cheap bastard

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    FMF has a universal Turbine Core 2 that comes in 1 1/4 ... I think they even send a length of mid pipe with it for about $100.


    I usually just pick up new take offs at the long beach motorcycle swapmeet for like $5 ... But that is a little bit if a ways from you.
  5. craydds

    craydds Long timer

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    We want to make a single schrader valve tapped into a splitter, then 2 hoses that goes to both upper chambers, joining the chambers by a common hose so that pressure is equal between them. Something similar to - http://www.motorcycleforksairequalizer.com/ .
    We can do the same on the lower fork tubes, one schrader valve goes into a splitter to both fork tubes via a common hose and both fork tubes have the same pressure. Scott is going to design and machine the parts (yes, I am volunteering you, Scott). I will supply the money for the schrader valves, various parts, hoses, etc. I found a good example of this set-up, simple and easy. I will search for it and post a link when and if I find it again.
  6. Scootern29

    Scootern29 Been here awhile

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    Actually back in them olden days when the canisters wouldn't work, the guys around here would put different fork caps on them and put fitting to be compatible with a centerally located schraeder valve to make sure the air pressure was balanced. The only down fall with the air forks was when you bottomed real hard you could blow the seals and then you got to ride the bike in with no front forks.

    I am doing this bike not so much as a rider, but more of somehting I can ride every once and a while. I have plenty of modern bikes to ride. This one is going to go next to my 76 MX 125C so I can look at it. The wife likes it all ready. That is a big bonus. :clap
  7. craydds

    craydds Long timer

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    I do plan on riding my YZ, but my riding is really just cruising around the desert. Occasionally I might catch some BIG AIR (one-to-two feet off the ground). Hope the forks can take the IMPACT.
  8. ADK

    ADK master of the casual pace

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    Why not just put springs in them? then you know it's balanced and reliable.
  9. Scootern29

    Scootern29 Been here awhile

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    That was also an option. In those days it was te "new" thing. Obviously it only lasted about a year. I dont' really care either way as mine will not be really put through its paces as there really isn't a class it is competitive in. It is more for my own entertainment on my back porch. People can see it and go WOW, thats a cool bike and I can say yeah it is..............I allways wanted one. LMAO :rofl
  10. craydds

    craydds Long timer

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    I suppose one could swap for a set off another model such as a YZ250. I've seen a few pairs of YZ250 forks and complete front ends on eBay. I will give my air forks a try but if they cause too many problems I will swap 'em for a set of REAL forks.
  11. Valleyrider

    Valleyrider I Survived The '60s

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    The reason that these fork didn't work back then... too complicated.
    The special tool offered by YIC to adjust air pressure was expensive.
    I've scoured the web, but have failed to find any photos of it.
    It had a fiiting that would screw on to the shrader valve, but would not depress the core/stem of the valve. There was a small "T" shaped screw that was then twisted to open the shrader valve and allow the air pressure to be read. When the "T" shaped screw was backed out after reading/adjusting the pressure, there was no loss of Upper chamber pressure. This was the "Low Loss" tool that was necessary to properly set the air pressure... Specifically, the top chamber due to it's very small volume of air. I you set the top pressure with a stick or dial gauge, most of that pressure would be lost when the gauge was pull off the shrader valve. Blah, Blah Blah....
    Clear as mud?
  12. Scootern29

    Scootern29 Been here awhile

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    valley rider, If you look at about page 2 of this, I used a Fox pump to set the air pressure's. It doesn't let the air out during adjustment. Kinda like the tool you were talking about.
  13. Valleyrider

    Valleyrider I Survived The '60s

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    Guess I missed that... Great build!!
  14. craydds

    craydds Long timer

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    Cool pump, I want one. But, would it be better to have one schrader valve into a splitter to both chambers? Same on the lower fork tubes. I saw a good set-up for this and now I cannot find it... :kboom . I will keep trying.
  15. Scootern29

    Scootern29 Been here awhile

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    Ray, I have no idea what you are talking about on the lower tubes. These forks did not work that way. They were controled by the canisters and back pressure. Kinda like a pop off valve. You are thinking way too deep into this.
  16. craydds

    craydds Long timer

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    I have never been accused nor convicted of thinking. :huh
    Two separate upper chambers are pressurized by schrader valves on top:
    [​IMG]

    Lower "chambers" - the fork tubes - are pressurized by the schrader valves at the bottom of the cannisters:
    [​IMG]

    There are four separate "chambers" to pressurize. Can we tie the two upper chambers together with a common tube and one schrader? Same for the lower fork? Something similar to this:
    http://www.motorcycleforksairequalizer.com/honda_models.php . Sorry, don't know how to copy and paste a pic here.
    Or, something like this:
    https://www.denniskirk.com/air-fork-balance-kit.p58318.prd/58318.sku
    It seems like it would be fairly easy to make a set-up like this for both the upper chamber and the fork air pressure. I swear I saw a schrader/hose kit that was simple, probably easy to adapt to our suspension, but I CANNOT find it again.
  17. Scootern29

    Scootern29 Been here awhile

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    The only way I know to balance out the air pressure would be to find another set of fork caps that will fit the forks. Put some brass fittings in them and plumb them to a tee with a schraeder valve. The canisters would have to go.
  18. Scootern29

    Scootern29 Been here awhile

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    This week was a little slow for me physically. In the first photo you can see tape on a couple of toes. One is broken. Yes........ it hurt. I did this on Monday morning about 3 am when I walked into a corner of a wall in the dark middle of the night. OUCH!!!!!

    So last night I figured what the hell lets do the rear tire.

    [​IMG]

    Got it to this point in about 5 minutes.

    [​IMG]

    Had a couple of sips on an adult beverage and had it done in about 15 minuts total.

    [​IMG]
  19. Scootern29

    Scootern29 Been here awhile

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    Since I was on a roll, this part has been bugging me for a couple of weeks.

    [​IMG]


    When I disassembled the motor I found this Oring on the floor where I was working on the motor. I tried to put it on every shaft and clutch part I could think of. It didn't fit anywhere. So I figured it didn't go to this motor. Then I was surfing around on the Yamaha Enduro site and some member was having a problem with oil being used from the tranny. One of the guys on there asked if he had put the oring behind the crank gear on the clutch side. LIGHT BULB goes off over my head. That is where the Oring came from. So off comes the side case again. And of course you have to take off the footpeg and the rear brake lever to even get to it. Boy is this fun.

    Clutch pulled off again. Third times the charm.

    [​IMG]

    Stripped down.

    [​IMG]


    Yep............that's where it goes.

    [​IMG]

    I get it all back together and get ready to put the side cover back on. The gasket was trashed so I had the local bike shop make me a new one as they have the plotter to do it. Wrong gasket so I am dead in the water till they can make a new one. I picked it up today.

    More to come.
  20. Scootern29

    Scootern29 Been here awhile

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    I had been waiting to do this teardown till I received the side cover bolts I had on order from one of my salesmen at work. They also showed up this week. I had also forgotten to install the kick start shaft seal the last time I had the cover off. All the parts ready to go.

    [​IMG]

    Even received this in the mail this week. I picked this up on the bay for $12.95, brandy new NOS cable. The other guy who sent me the wrong cable for $25 wanted $44 bucks for a cable. I guess he wanted me to pay a pretty good price for his screw up.

    [​IMG]

    Putting it back together.

    [​IMG]

    All done, third time is the charm. I could just about do this blindfolded at this point.

    [​IMG]