Bertha's Box - What Can Go Wrong in an Airhead Gearbox

[Sunny Jim]

Quote:
Originally Posted by Sunny Jim
Tell me, as a numpty at this depth, is the 'damage' the result of harsh gear changing, lack of oil changing or just good old wear & tear?
The box seems to have been apart a couple of times.

It appears to have had a catastrophic bearing failure which has resulted in the front bearing on the output shaft seizing and spinning on the shaft. Then either the front or rear (or both) output shaft bearings have broken up.

There are teeth marks on the inside of the case near the front of the output shaft and the output drive flange has moved around, distorting the alloy sleeve that surrounds it.

I'd hazard a guess that it ran out of oil in some far distant place and was badly repaired.

The bad repair caused the wear on the selectors and gear pinions.

I don't think harsh gear changes would damage it.

Hopefully its now good for another 100,000 miles .

Bob.

Ah yes - of course explains it all now Thanks again Bob - top man!

Kenny - don't worry about your flange - it gets slacker with age

 

[Posh Pete]

Really great to read about such skill and attention to detail. That pic of the notebook with all the readings says it all really.

 

[Grosvenor 61]

Neutral selection

The box seems to have been apart a couple of times.

It appears to have had a catastrophic bearing failure which has resulted in the front bearing on the output shaft seizing and spinning on the shaft. Then either the front or rear (or both) output shaft bearings have broken up.

There are teeth marks on the inside of the case near the front of the output shaft and the output drive flange has moved around, distorting the alloy sleeve that surrounds it.

I'd hazard a guess that it ran out of oil in some far distant place and was badly repaired.

The bad repair caused the wear on the selectors and gear pinions.

I don't think harsh gear changes would damage it.

Hopefully its now good for another 100,000 miles .

Bob.

Very interesting article, well put together & clear photos. Perhaps you can shed some light on a recent problem I have encountered:

Over the last few weeks I have found it is sometimes difficult to select neutral when the gearbox on my '91 R100 GS is warmed up (say 30+ miles), which is most annoying at traffic lights!
Checked gearbox oil level, which was full (I use Morris GL5 spec gear oil). Selection of other gears seems unaffected, so mystified as to cause of problem, particularly as it is intermittent & no unusual noises from box, which has done approx 7k miles.

It may be worth noting that she had lain idle for 18 years before I acquired her, though I did 4500 miles last year without any major problems. Various seals & gaskets have required replacement over that time, but par for course with a 21 year old bike.

Any ideas?

 

[Richard A]

A thread like this really makes the work come alive. I feel a lot less fearful about having a go at one now, and that despite having various manuals etc. Thanks for taking the time and trouble, Bob the Voyager!

 

[Voyager]

Over the last few weeks I have found it is sometimes difficult to select neutral when the gearbox on my '91 R100 GS is warmed up (say 30+ miles), which is most annoying at traffic lights!

Not uncommon and I get the same problem occasionally.

The gear lever works an escapement mechanism that pushes or pulls on a drum cage on the underside of the upper cam plate.

The upper selector plate has notches that a sprung 'Indexing Roller' drops into to hold the mechanism in gear.

The problem is that Neutral is half-way between first & second, it isn't a positive position. This allows us to change from first to second or second to first without engaging neutral.

The roller indent for neutral is smaller than the others and any drag in the system will try to make the change go 'full travel' rather than stop in neutral.

A dragging clutch will put a constant load on the gears and as three of the gears are also the sliding selector dogs they will tend to jump past neutral.

Check the clutch lever at the box and at the bar. There is a process for this and from memory its . .

Take up the free play on the gearbox operating arm and adjust it until the front edge of the arm is 203mm from the rear of the casting that holds the cable outer.

Adjust the bar lever so that there is 2mm of play at the pivot.

See how you get on after that.


Bob.

 

[andyfrizzle]

Adjust as below

Andy Frizzle

 

[Voyager]

Thanks Andy

While you're here . . . .

How was the gearchange on your 100R . . Upward changes a bit light ??

I hadn't noticed this until I came to strip the gearchange mechanism, but whoever was in there before put the Pawl Return Spring (the strong hairpin spring under the pawl mechanism) in upside down .

The ends of the hairpin straddle a peg under the shift quadrant and hold it central. With the spring upside down the peg misses the spring on upward changes.

And on downward changes the spring is trapped between the bottom of the peg and the base plate.

You can see where the end of the spring has been ground into the baseplate:

There are some flats worn on the spring as a result.

The new spring, mounted the correct way up, sits well clear of the baseplate and properly engages the peg.

You should notice a better feel to the gearchange in future


Bob.

 

[Padmei]

Thankyou gentlemen. You have answered a question I had bouncing around for a while re the neutral shift.

 

[Rugged Path]

An excellant feature on the gearbox. I have a spare that I would like to strip down as a learning excercise / curve.
But, when I tried to cut and paste that long stripdown to a word doc, it would not work. It may be because of its size.

It would be a nice feature in a pdf format for the archives.

Steve in Saudi

 

[andyfrizzle]

Downloadsome some free 'print to PDF' software, there's loads listed here

Once installed you just need to print the page(s) that are showing in your web browser, and select the PDF printer.

You will be asked to give the PDF file a name, then save it.

Hope this helps RP

 

[andyfrizzle]

Thanks Andy

While you're here . . . .

How was the gearchange on your 100R . . Upward changes a bit light ??

I hadn't noticed this until I came to strip the gearchange mechanism, but whoever was in there before put the Pawl Return Spring (the strong hairpin spring under the pawl mechanism) in upside down .


[You should notice a better feel to the gearchange in future


Bob.

Bob,

I have to be honest, my left foot is not the most sensitive or delicate, but I am sure that I will notice the difference.

Many thanks

Andy Frizzle

 

[Aidan1150]

Thank you Bob.

An interesting and informative thread on what for many of us, me included, is a black art. Cracking stuff indeed.

 

[Kenny]

Kenny,

The brown seal is for a Paralever - it is fitted open side inwards (and needs conditioning as you say). It keeps all the oil in the gearbox and the small triangular vent has to be sealed.

The blue seal is for a Monolever and is fitted open side outwards. It lets the gearbox breath oil into the leg - which has oil in it anyway.

I take it you acquired a flange puller (as I couldn't find your request when I looked a second time ).

I have just stripped Andy Frizzel's gearbox . . .

Its from a 1992 R100R (the one with the 'K-Series' forks & brembo four-pot calipers). Its a Paralever (naturally). It has 50K miles on the clock.

So; why is the gearbox apparently dated 1981, has a Monolever rear oil seal yet has the late 17.5 degree gear cluster with the 'X' marks

Wonderful things airheads .

Good luck getting the flange off Kenny

Bob.

Thanks to Bob and Rob, I have now completed this task....and found/sorted a suspension problem as well

Things needed.. ( plus four new stretch bolts for the output flange )

Flange off and old output seal now out

and flange and new seal in....

Generic view

+++++++++++++++++++++++++++++++

Maybe should be in a new thread but whilst we removed the final drive/shaft in one piece it was discovered that the bushes top and bottom had seized ( and I mean seized )...Copious heat and penetrating oil and a little rat file/swearing and the bushes came free ( you can see the bottom bush still on the final drive )...just for the info of other owners who have a Hagon shock fitted. Made a big difference on the ride home, not nearly as harsh !!

Happy days

 

[B Murr]

I can remember reading this thread when it was fresh, and the pictures that were on it I can vaguely remember. Clicked on it again when it came up while searching for something else would have been a great read second time around but the photos all seem to have disappeared, no doubt the result of a free photo hosting site deciding to charge for their services and the poster of the photos not buying in to that service, such a shame that this often happens in a forum which can often be a source of useful reference material.

 

[Kenny]

Yup, good old photobucket has ruined many a postings

Just have a few left.......

 

[Voyager]

I was paying £96 per year to put photos on Photobucket and then they increased it to $400 per year. I deleted thousands of pictures and ruined many posts here and elsewhere!
Bob

 

[(RIP) Arkwright]

I put my photos on SmugMug which is about £45/annum