BMW Airhead Circlip Modification Explained

[@lastairhead]

Man, I have just put back together my transmission. I examined only the output part and looked great. Now I’ll have nightmares with this shaft I have not taken out. ...and I was so happy everything was perfect inside. Damn circlip!

[@rsnesbocaj]

Now I understand 'why'. Thanks for posting!

[@pstef8936]

A machinist friend had the same problem so he machined and sleeved the shaft then honed the gear to fit. Still fine after 100K.

[@louisrauzi3872]

It's the bmw mantra. We do no wrong, we know best. Unrelated to this post, my 78 RS hit a pot hole (front of course). At night. Immediately went wonkey. At home discovered not just bent, cracked! God bless tube tires. New rim cost me $320. Only to find a 'silent recall' on the said rims. This occurred in '92, with 50k miles.

[@achristian7015]

But if a circlip keeps the shaft components "together" and since the outer race of that bearing is captive in the transmission case and since an axial load is placed on the output shaft when in 5th gear, does that not put a side load on the ball bearing which is a no-no. Ball bearings are not meant to be subjected to a side load. Also if the shaft is pushed rearward in 5th gear, how does that happen when you have a bearing at the output flange end? Is the output shaft not stepped where that bearing is installed at the output flange end?

[@2on2off1]

Good questions. Call Beemer Shop for the answers.

[@erikmotoman9190]

If you didn't know this... now you do. Porsche did a similar $ 0.10 circlip delete which in turn resulted in thrust bearing failures on 1987 and up Porsche 928's equipped with automatic transmissions. . destroying the motors. UGLY! Thanks TED !

[@RB-xj4fg]

I have a Last Edition R100CS, 1984. It had the groove for the circlip but no circlip. So I'd say 1986 is a misnomer and it was wearing my 5th gear and making noise while decelerating in neutral with the clutch out. BMW is NLA for 5th gears so you'll need an aftermarket part, likely the 6% taller one.

[@nickwildsmith6537]

Perfect explanation

[@-C.T.-]

What's the typical cost one would expect in 2021 to have this repair completed by a dealership or certified BMW mechanic?

[@2on2off1]

I'm guessing it will be expensive. The transmission needs to be pulled and then inspected for parts that are worn and need replacing. When mine was pulled, one of the gears was damaged and needed to be replaced.

[@AndrewTheCelt]

I have a 1984 r100rt which has developed a small whine and I’m wondering if it has the circlip or not is there a way to tell without taking the transmission out?

[@vespasandengines]

So the issue is on airheads during the 86-94 period? This doesn’t happen pre-86?

[@2on2off1]

That is the way I understand it but there are many others out there that know much more about this than I do.

[@tnth9099]

my 94 r100gspd gearbox output bearing started to fail at 52,000 km replaced the bearing (was tight on the shaft and hadn't moved) and has been running fine since without a circlip. to check put the bike on the centre stand and turn the back wheel to hear any bearing noise. also when opened gearbox there were small metal bits on the bottom of the case. if was ridden until the bearing collapsed then there is more trouble eg bearing moves on shaft making people think this is the cause of the bearing failure. the real cause is gearbox was designed for a much smaller engine. (r80gs doesn't seem to have this trouble)

[@noteasilyoffended4649]

How much does this usually cost to have done?

[@2on2off1]

Depends. I took my whole bike to their shop and they did the disassembly, repair and reassembly. I believe they only do this mod when you send them the transmission. They closed their service shop a few years ago. I have talked with them lately so things may have changed.

[@DARisse-ji1yw]

and the cost to pull a transmission and correct this is ????? assuming it hasn't yet failed....

[@59panelvan]

Is there a serial number changeover from circlip to no circlip. I have a 1985 R80RT. How would I know I have it without opening up the transmission?

[@2on2off1]

Call Beemer Shop in Scotts Valley, California.

[@DARisse-ji1yw]

For the price of machining a groove & a .20 cent circlip... I think buyers would have gladly paid the small added cost !

[@Thekrpntr]

So that's the clunking sound in my '92 R100 RT. Thanks. I'll get right on it.

[@stephensaunders4668]

Seems that straight cut gears would solve this issue. Imagine that, a more reliable BMW. Look at modern ones and it would be hard to convince yourself that they have learned anything.