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Old 11-01-2012, 03:42 AM   #1
ME 109 OP
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Taller 5th in a 33/11

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.
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Old 11-01-2012, 05:02 AM   #2
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Quote:
Originally Posted by ME 109 View Post
Anyone got some first hand advice on what to expect re rpm or other issues?
I have that combo in my bike.
If you want to know how rpm will change try this:
http://www.coerdt.de/rechner/rechner...00&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.
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Old 11-01-2012, 05:35 AM   #3
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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?
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Old 11-01-2012, 08:15 AM   #4
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I'm not smart enough to work out the rpm reduction @ 160 kph (currently app. 6,000 @ 160 kph)
We know it's a linear relationship (0 rpm = 0 kph, 6000 rpm = 169 kph) So...

(160/169) X 6000 rpm = 5680 rpm
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Old 11-01-2012, 08:17 AM   #5
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Quote:
Originally Posted by ME 109 View Post
I'm not smart enough to work out the rpm reduction @ 160 kph (currently app. 6,000 @ 160 kph)
Playing with rpm values delivers this:
http://www.coerdt.de/rechner/rechner...10&btxt=R100RS

You'll gain ~300rpm

Quote:
Originally Posted by ME 109 View Post
Are there any negative aspects associated with installing the taller 5th besides insufficient engine power?
Don't know any.
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Old 11-01-2012, 08:49 AM   #6
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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.
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Old 11-01-2012, 12:52 PM   #7
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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.
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Old 11-01-2012, 01:33 PM   #8
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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.......

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Old 11-01-2012, 02:11 PM   #9
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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.
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Old 11-01-2012, 02:23 PM   #10
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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)
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Old 11-01-2012, 11:40 PM   #11
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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.
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Old 11-02-2012, 01:06 AM   #12
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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.
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Old 11-02-2012, 01:42 AM   #13
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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.
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Old 11-02-2012, 01:52 AM   #14
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Originally Posted by Bulldust View Post
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.
Gidday Bulldust, I knew where you were from even before I looked

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.....?
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Old 11-02-2012, 02:29 AM   #15
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Always replace the pawl spring #7 and check the roller #14. Usually replace the roller too.

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