Taller 5th in a 33/11

Discussion in 'Airheads' started by ME 109, Nov 1, 2012.

  1. ME 109

    ME 109 Long timer

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    I found a few sparkly bits on my tranny magnetic drain bolt and have pulled the tranny apart for repair.
    I found some pitting on the 5th gear. The mating 5th gear on the lay shaft appears to be good.
    Bike is an 81 RS. 33/11
    So my plans are to replace all bearings and maybe some other 'bits'
    As I also need to replace 5th, I'm wondering whether to put the taller gear in.
    There have been plenty of times when touring that I've thought it would be nice to have the slight reduction in rpm associated with the taller gear.
    Anyone got some first hand advice on what to expect re rpm or other issues?

    I tried to search for info but had no luck.

    Thanks in advance.
    #1
  2. RGregor

    RGregor Been here awhile

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    I have that combo in my bike.
    If you want to know how rpm will change try this:
    http://www.coerdt.de/rechner/rechne....67&g5=1.5&g6=1.42&n=7400&nn=6000&btxt=R100RS

    It's in german, but I think you'll understand it. It's calculated with 3% slip (Schlupf) and a 130/80 rear tire.
    I've entered the long 5th as sixth gear so you'll see the difference.

    You have a stock engine?
    For travelling at constant speed this may be really good.
    Acceleration in fifth will suffer, can't say how much.
    My engine pulls it easily.
    #2
  3. ME 109

    ME 109 Long timer

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    Thanks for that RGregor, if I'm correct I would gain about 9kph @6000
    I'm not smart enough to work out the rpm reduction @ 160 kph (currently app. 6,000 @ 160 kph)

    My motor is stock although it has quite acceptable roll on in 5th, I think it would pull the taller gear ok.

    My serious riding in the mountains relies on 2nd, 3rd and 4th so the taller gear will not interfere with my fun.

    I think that knowing the rpm reduction provided by the taller gear will assist me greatly in understanding how suitable it will be.

    Are there any negative aspects associated with installing the taller 5th besides insufficient engine power?
    #3
  4. Airhead Wrangler

    Airhead Wrangler Long timer

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    We know it's a linear relationship (0 rpm = 0 kph, 6000 rpm = 169 kph) So...

    (160/169) X 6000 rpm = 5680 rpm
    #4
  5. RGregor

    RGregor Been here awhile

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    #5
  6. disston

    disston ShadeTreeExpert

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    The taller 5th gear should be a nice move I'm in favor of it but I've never had one. Will someday.

    Just wanted to tell you that a little pitting of the gears is so common it's almost normal. The silvery bits you found were not from any gear teeth. The silvery bits were from bearings and their races. These wear and eventually start falling apart. Gear teeth wear but IMHO not as much until the trans spends too much time with water in it. This is what causes the pits in gear teeth.

    The above is my opinion.
    #6
  7. mark1305

    mark1305 Old Enough To Know Better

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    I agree with Disston about what you are seeing. BUT, since you are already in there and considering the taller 5th option, now is the time. I wish I had done that when I rebuilt and installed a replacement gear box in my ST. Of course the ST has the 37/11 FD and just really doesn't like sustained Interstate speeds when I take it on trips (tends to increase blowby, thus oiling the left carb a lot, fouling that plug after two days of slogging the Interstate in warm weather, and using slightly more oil).

    And the shiny flakes mean its time to do all the bearings - although from what I've read and seen in my own gearboxes, the one roller bearing up at the front may still be good. I didn't disturb that one in my rebuild and continue to have trouble free operation.

    But I do bemoan the fact that I could have installed the higher 5th while I had it all opened up. :cry
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  8. ME 109

    ME 109 Long timer

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    Good information chaps, thank you.
    The chips have occurred in the last twelve months after thirteen years of spirited riding since the last rebuild so I'm impressed with that.
    All the tranny oil changes in that time have produced only a black slime on the magnetic plug.
    I would imagine a rapidly increasing amount of chips would result from all the bearings after the first bearing started to let go.
    300 rpm 'eh? That's just a nice amount I think.
    I have always noticed that fourth and fifth are reasonably close together so the taller fifth may bring the ratio more into line with the rest of the gears.
    Out of interest, I have ridden an 1150 gs and found the ratio between fifth and sixth to be just a little too great. I wonder if I will experience similar with the taller fifth.......

    [​IMG]
    #8
  9. disston

    disston ShadeTreeExpert

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    The pitting I see there on the spiral gear is not what I call pitting. I don't know what to call it exactly but that does seem to be from stress. The gears messing together. It may be the same thing that I call pitting but it certainly doesn't look it from here.

    The few gears I have saved that have pitting have the pits in a very irregular pattern, or no pattern really.

    So that is the gear that gets replaced? Good deal.
    #9
  10. ME 109

    ME 109 Long timer

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    My unqualified thoughts are that the 'marks' on the gear were from an end play issue.... although the mating gear is fine to my eyes.
    Interestingly, the marks are present on about one third of the gears circumference only. The marks are also irregular in size and location on the various teeth.
    The tranny has always been smooth and quick shifting (for our bikes)
    #10
  11. Wirespokes

    Wirespokes Beemerholics Anonymous

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    I've seen that sort of wear when the front output shaft bearing has gone, and the gears don't mesh properly, along with grinding all the swarf floating around in there. It might not hurt to re-use the gear, I don't know. But if another better one was available, I'd certainly change it out!

    It's actually best to use fifth as an over-drive and not put much stress on it because of that front output bearing.
    #11
  12. ME 109

    ME 109 Long timer

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    The front output shaft bearing was the first one that I spun by hand and thought...........oooooh yuk.
    I'm doing another 180 with more people regretting 'not' putting the taller fifth in.

    I'm not sure life is worth living without WOT in fifth Wirespokes.
    #12
  13. Bulldust

    Bulldust Bulldust

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    I get a 250rpm reduction at 100kph with my taller 5th gears in my Hot Rod R100GSPD (1070) and my R100GS (stock displacement but twin plugged). Both pull the gear with ease but both engines run far better than a stock motor.
    #13
  14. ME 109

    ME 109 Long timer

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    Gidday Bulldust, I knew where you were from even before I looked :1drink

    My mind is made up. Taller 5th.

    My ol' gal is stock but pulls like a trooper, just over 8 grand in third the other day.

    So what else 'must' I replace besides taller 5th, all bearings, seals, SKF bearing on the shifter, circlips etc.....?
    #14
  15. disston

    disston ShadeTreeExpert

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    Always replace the pawl spring #7 and check the roller #14. Usually replace the roller too.

    [​IMG]
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  16. ME 109

    ME 109 Long timer

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    Number 14 I'll replace with a bearing. Apparently it's a good improvement.
    The pawl spring has been on my mind to do. Apparently it's a contentious issue to some?
    #16
  17. disston

    disston ShadeTreeExpert

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    Yes, the pawl spring can break on you at almost any time while on the road. A regular happening at the larger gatherings of Airheads is the one or sometimes two people with broken pawl springs. The transmission will not shift and will be stuck in what ever gear it was in when the spring broke. If in 3rd gear you might get to ride it home providing it's highways to your house. If it's in second gear you might get around the neighborhood. It it's stuck in 5th gear you might burn up the clutch getting home.

    To fix is not an impossibility on the road. Need some time, the rear flange puller (for the drive shaft out put flange) and a new spring. Also very helpful to have a propane torch (but you can also buy one of those)

    It is also possible to put your trans in a suitable gear to get home by using a piece of wire stuck in the filler hole to move the shifting cams. I say possible but I've never tried it. Don't know if I would be able to make sense of this method of shifting.

    SOP anytime the trans is opened for any reason is to replace the pawl spring.
    #17
  18. supershaft

    supershaft because I can

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    I never replace them unless they are broken or the customer insists. I have seen too many just installed springs break to think you are better off with a new one.
    #18
  19. ME 109

    ME 109 Long timer

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    That's my point about the spring change being a contentious issue.
    I did have a spring break one time, a fair way from home. But It was in 4th so I managed.

    Consider though, that the spring in my tranny is at least 13 years old.........
    #19
  20. supershaft

    supershaft because I can

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    I have a spring in my R100 that is 20 years old and one in my LS that is 29 years old. I haven't worried about them in the past and I am not going to start worrying about them in the future. Chances are reallly good that they will be just fine as they are.
    #20