Airhead Gearboxes

[Rob Farmer]

I doubt a BMW workshop would know how to rebuilds gearbox. A lack of support for gearbox work is behind a few of us on this site getting geared up for rebuilding them.

To be honest I've seen three circlips and had one myself pop out of the groove so it isn'tthe be all and end all modification.

 

[Voyager]

To be honest I've seen three circlips and had one myself pop out of the groove so it isn'tthe be all and end all modification.

As always, there is more to this than one realises at first

The standard 6403 C3 bearing has the ends of the inner track radiused. This means that if the shaft moves in relation to the bearing the inner track hits the outer part of the circlip causing it to bend and pop out of the groove.

I read somewhere that BMW use 'special' bearings with straight-cut inner track faces to overcome this.

What we mere mortals do is add a small snap ring behind the circlip in order to fill-in the radiused hole and therefore give a straight push on the circlip if the shaft should move - seen here:

And here after assembly - the snap ring can be seen behind the circlip.

I've heard of others (Garry H to be precise ) machining-up a small spacer that fits the radiused hole perfectly.

I guess none of this prevents the circlip from failing under extreme usage, but every little helps .

Bob.

 

[Rob Farmer]

Bob,
Mine had the snap ring in place but still came off.

 

[richie moore]

good job with the circlip Bob, its a shame you put it on the wrong way round.

 

[Voyager]

good job with the circlip Bob, its a shame you put it on the wrong way round.

OK . .The flat face should be against the bearing - DOH !

One to remember for next time.

Bob.

 

[Garry H]

I did make a spacer that fit the bearing rad exactly ( more than 1 till i got it to fit bang on !! )
I have one somewhere i will take a pic

I have machined some shafts to fit the curclip ( not the the easiest of jobs the shaft is well hard )

One mod i would not reccomend is replacing the nylon selector roller with
anythink steel...It seems to shift worse...I now only use nylon

 

[Voyager]

One mod i would not reccomend is replacing the nylon selector roller with anything steel...It seems to shift worse...I now only use nylon

I have stainless bearings in place of the nylon indexing roller in both my boxes. It makes the box rather 'clacky' and sometimes difficult to shift so I know what you mean.

I have wondered if I should re-profile the cam plates to make it change easier as the bearing is very positive. It would probably end-up no better than standard but these thoughts go through my mind .

Re the circlip groove. I have some carbide steel cutters and now have a scrap shaft to practice on - I must find the time to play sometime.

Bob.

 

[Voyager]

OK . .The flat face should be against the bearing - DOH !

I've been thinking about this (which is why I've logged-on at this ungodly hour ).

The circlip is stamped out which gives it a rounded side and a flat side.

The load on the circlip, should the shaft & bearing move, is outwards, away from the bearing.

Having the flat side facing out gives better registry in the groove and lessens the risk of the circlip being spat out of the groove by the bearing.

Which seems to be what I did (co-incidently ).

Or were you joking .

Bob.

 

[Rob Farmer]

1:45 in the morning Bob!! I hope you haven't been up fretting

Flat face should sit away from the bearing to reduce the risk of the circlip riding up the groove. Didn't help mine though. I still can't figure why mine came off. I was running a Wilber's shock that was the same length as a standard shock to reduce any risk of the uj binding and the sliding joints were all greased. The pot hole I hit have the bike a big hit but it wasn't anything that the bike shouldn't have taken in its stride. All quality bearings in there as well. Very strange.

 

[Beemerboff]

Shouldn't the bearing also be a seven ball bearing, which reputedly has a higher capacity?

 

[Voyager]

I still can't figure why mine came off.

All quality bearings in there as well. Very strange.

Rob,

Had the shaft moved and pre-loaded the bearings as well?

I'm wondering whether the shaft can move back and forth under load, something which wouldn't be obvious when the box is stripped if it had moved back into place (apart from a dislodged circlip).

Where do you get your bearings ?? I get good quality (SKF) ones from "Simply Bearings" but I haven't seen any options regarding different numbers of balls or the shape of the inner track (Beemerboff's comment is interesting ).

Bob.

 

[Garry H]

Pic of spacer ring that matches the bearing rad the one side flat the other for the curclip

 

[Padmei]

Couple of quick questions.
My gearbox is whirring/whining (1991 R80 GS). I have recently replaced the timing chain & replaced the valves, seats & set the valves/ endfloat nicely so the engine is a bit quieter now. It also has a new clutch plate (budget motobins one) It may have made this noise for a while but I've not been aware of it.
Is this a sign of impending doom for all mankind or not worry about too much? it changes pretty well in 3-4-5 but 1 & 2nd have always been reasonably notchy & need a firm approach.

I have a spare gearbox off a wrecked 81 R65 twin shocker which I want to get running at some stage as a cafe/ tracker/ Schek mongrel but was wondering if I set it up as a spare paralever box whether I can still use it later when the R65 is up & running. I believe from 81 the boxes were interchangeable.

 

[Voyager]

Hi,

They all whirr/ whine a bit, but have a look at the magnetic drain plug for swarf - if its more granular than silver paint the bearings may be showing their age.

Also, check the output flange for sideways play. The rear bearing may be going and if it is the front one on the output shaft is probably the same.

What sort of mileage has the box done ?? The notchiness in 1st & 2nd may be due to wear in the cam plate grooves around the neutral position. There's not much you can do about that apart from changing the pair of cam plates.

It could also the the Indexing Roller getting worn and hanging-up in the index notches. If that's all that wrong with it I would just live with it .

I'm not sure about the compatibility of the '81 R65 Twin Shock box, we need Rob Farmer here .

If they are compatible then you will need to stop it breathing oil into the Paralever leg. That means a different rear output shaft seal and some sealant in the breather notch. Use a hollow earthing strap / Speedomerer retaining bolt to allow the Paralever box to breath to atmosphere.

Its easy enough to swap it back for use in the R65 (although it will work fine in 'Papalever' mode); the only issue is removing the output flange which requires a substantial puller.

Let us know how you get on .

Bob.

 

[Padmei]

Thanks for that Bob - great info

The only difference I have seen when comparing them is the earlier 65 box has the many piece piston assembly for the clutch whereas the gs has the one piece. I'm hoping I can use the para one on the early box. The output flange looks the same - You think they may be different?

I'm also wondering how much of a prob having the output seal para style & sealed vee would be when back on the mono - the R65 will only end up being a rolling parts bike for the GS anyway.

Is shimming the gearboxes absolutely required when rebuilding?

 

[Voyager]

Hi,

Thinking back, I re-built a box from a 1992 R100R that turned out to have been made in 1980/81:

It was a perfectly normal 'Paralever' box - though I didn't see the clutch pushrod bits. It did have a 'Mono' oil seal in it though (I replaced that with a Paralever one).


I think that proves that your R65 box will be fine.

The output flanges will be the same, they are on a taper that is torqued-up to 162 lbs/ft. It helps to have the pukka puller for the job.

The 'Cycleworks' puller:

The BMW puller:

I don't see any problems in having the Paralever output seal in a Mono - the Mono has oil in the leg anyway so adding a bit from the gearbox was just expediency I guess.

The Para runs dry so oil down the leg is a bad idea.

I have never tried a box without shims, but all the received wisdom is that it is necessary. We shim them to 0.05mm clearance which isn't much of a gap (certainly less than a British Standard Baw' Hair ).

I think it will all be fine .


Bob.

 

[Rob Farmer]

I know diddly squat about 650's. Didn't the 650 have the heavy flywheel gearbox later than the other machines or was it the other way round?

The V above the seal relieves pressure in the drive shaft on Mono bikes to save the gearbox to drive shaft gaitor. The paralever shaft vent through the swinging arm pivot bearings and is the reason you can block the V up. It's also the reason why you don't pump grease into the drive shaft pivots on Paralevers.

 

[Padmei]

Cheers guys. From 81 onwards the bttom end onwards is the same as the 80/100s. My clutch is the same on both bikes.

I will do a swapsie & see if there is any noise from the 65 box or if it the same & report back.

 

[Padmei]

I'm taking my gearbox apart but I'm not having any luck removing the 2 shafts from the case. i've had the missus with a torch & heatgun simultaneously on the back of the case but they just seem to wiggle on the bearing. Any tips?

 

[Rob Farmer]

Put the output flange back on and using a pair of soft jaws in your vice clamp the flange into the vice so the whole lot can sit on the bench with the flange in the vice. Get the end cover really hot and give the casing a few blows with a soft faced mallet. You shouldn't need to hit it very hard at all. It's the shock of the blow that gets it moving. The intermediate shaft will be drawn out with the output shaft. You need to keep any forces in line with the output shaft. If the case is hot enough it should only take a couple of knocks to get it out. I haven't marked a case yet doing it.