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Hi just purchased a 1993 R100R with about 45K miles. The seller put on new tires, changed the crank and final drive oil.
I've been doing a lot of online reading, looking for BMW specific problems.
Steering head bearings get mentioned a lot.
So does the "diode board" . (Presumably something to do with the alternator. Actually, is it an alternator or a generator?)
Final drive spline lubrication.

I will of course, check filters, lube cables, check the brake pads, bleed the brakes.

Other suggestions?

Steering bearings do wear but not really more than any other bike. They use taper rollers which are very good bearings but required adjustment (or at least checking) fairly regularly. If they are allowed to become loose, they do wear a lot more quickly. The other 'gotcha' is that if they are overtightened, like all adjustable bearings, they are susceptible to a process referred to as brinelling which is where, on overtightening, the rollers can distort the bearing races permanently. It only takes one overtightening to ruin the bearings so care when adjusting is a good thing. On some earlier models, there was an also an issue with corrosion in the head bearings cause by inefficient eathing of some of the lights but this was pretty much solved long before the 'R/mystic' series was conceived.

Worn bearings are easy enough the detect... with the bike on it's main stand, move the steering from lock to lock. If the bearings are worn beyond use, you will feel a slight change in the freeness of the movement going though 2 or three 'tight spots' between the two locks. If that happens, you need to take action. At the very least, you will need to dismantle the head and visually check the bearing races. worn bearings will be evident because there will be a series of heavily polished radial areas seperated by less polished areas. If you see these, then replacement of the bearings is essential. But... the same symptoms can be caused by old dried up grease so examine the bearings before replacing.

While you're about it, you should check the swing arm bearings which are subject to the same issues...

All of the BMW airhead series use an alternator ( a 3 phase star wound alternator to be technical). This produces AC (alternating current) electricity which is no good for electronics and batteries so it has to be rectified, that is to say converted to DC (Direct Current) electricity. This is the job of the diode board (AKA rectifier). If it fails then it will effect the ability of the charging circuiy to keep the battery charged. It should be noted that the rectifier can partially fail leaving some charging capacity but not the full amount. The simple test of all of the charge circuit components is to monitor the voltage at the battery (preferably using an accurate multimeter rather than a dashboard voltmeter... these can be horrendously inaccurate...) You should be looking for a voltage of at least 11.5 volts with the bike at idle, rising rapidly to around 14 volts at any engine speed over - say - 3000rpm.

If you wish to test the rectifier for function, here is a description of how the board works and how to go about testing it https://robfrankham.com/diode-board-test .

Forgive me for jumping to conclusions but your post suggests you have little knowledge of electricity so, unless you wish to embark on a 'learning experience' (which isn't a bad idea actually), I think you'd be well advised to seek expert help if you think the charge circuit is playing up. The airhead charging system is pretty good and fairly resilient but it's care and attention does require an element of 'arcane' knowledge and acquiring that by experimentation can be a frustrating and expensive experience

The 'R/Mystic' series don't suffer from final drive spline issues since they don't have final drive splines (which is a pretty good reason ). They do, however suffer from issues with the splines in the centre of the clutch disc. Not something to cause loss of sleep but, if the clutch action becomes heavy and you've checked all of the other causes (cable, handlebar lever pivot, gearbox end lever pivot) it's well worth pulling the transmission to examine the splines which are on the gearbox input shaft.

You can point to any bike (or vehicle... or any type of machinery for that matter) and say this component fails or that area is weak but the airhead series are no worse than any (and a lot better than some). While the bike is going well and handling well, there's no need to worry. When things start to feel wrong, then they are normally pretty easy to diagnose and put right. The important thing is to enjoy your bike.

Rob

Thanks to Rob and Steve for the long and detailed advice.

I should have stated in the beginning that I am experienced at car and motorcycle repair and restoration. I've owned everything from a Bonneville record-holding Cagiva 125cc to a Honda CBX, with Guzi LeMans, Yamaha RD400, Ducati 750GT and others in between. I have a fully equipped shop and can fab most of what I need. I am also a retired electrical engineer with a shop full of electronics tools, too, so anything electrical doesn't phase me. Bottom line is that I'm not in the least afraid of tackling any work. (Well, except painting. I leave that to pros.)

My current ride is a 1971 Triumph Bonneville 650, which I've owned almost since new. But at 68 years old (today!) I was looking for a bike with electric start, reliability, relaxed cruising, reliability, good brakes, reliability, and something that didn't numb my hands with vibration after 20 minutes. And reliability.

BTW, I now have to relearn braking and shifting, since they are on opposite sides on my Bonneville!

The splined clutch disk issue sounds like a problem common to 1980-era Guzis. In that case, the splines would wear and the clutch throw-out bearing would hang up. A fairly complicated job to repair that required dropping the engine and tranny.

What I am looking for is problems that are specific the Beemers of this era and what might be worn out at 45K miles.

I suspect that I am going to want to put on bars that are a bit wider, and find a flat seat that will fit. But not until I've put on a few summer months of riding to learn it.

Welcome! Something that is specific to the 1993 bikes, up until late 1994/into 1995, is the issue of a removed circlip in the transmission. In the mid 1980s, it would seem that some bean counter at BMW felt eliminating the circlip would save money in the long run. The problem now appears that the bearing can walk on the shaft which creates pressure and eventually begins to create money problems. Issue is here:

http://largiader.com/articles/circlip/

It's not a stick of dynamite to go off at any moment, but there will be warnings...early signs of swarf on the magnetic drain plug. The fix is simple...put the circlip back on. You might have the skills/equipment to do it yourself. But it's likely only something to consider if/when the transmission has to come out of the bike for some other repairs. At only 45K miles, that day is likely far down the road.

Kurt in S.A.

Good idea about the carb needles. I've never worked on Bings, but have experience with lots of different carbs over the years, so I doubt they will be a problem.

Cam chain: Another good one. Is this an interference engine, i.e., if the cam chain breaks the do the valves hit the pistons?

Regarding the circlip: Any obvious symptoms besides drain plug swarf?

I've download the factory manual. I see that Haynes and Clymers both have books. They both claim to cover "2 valve twins, 70-96", which is a rather large spread. Worth buying?

I haven't found an owner's manual yet, free or otherwise. Anyone have a link to one?

Thanks again to all! I have to wait about 2 weeks yet for delivery, so I have time to read everything I can.

Bings are quite strightforward and very reliable. They do have a propensity for leaking fuel a bit and, by the nature of the beast it tends to end up on your boots but that's something to tackle when it happens. If the bike is running poorly, it's worth looking at the carb diaphragms. A tiny pinhole can make a big difference to the engine running.

The circlip issue is a source of some contention. Some people seem to think that a box without a circlip is a time bomb waiting to go off, some think it's blown up out of proportion. Try as I might, I can only find two attested cases of gearbox damage attributed to the bearing moving on the shaft and I find it hard to see how that attribution was made... on the other hand, BMW did reintroduce the circlip later which indicates that they thought there might be something in it. What is for certain is that thousands of airheads have lived fairly stressful lives without any problem in this quarter.

Haynes and Clymer are both worth having but neither is entirely reliable. It has to be said that the BMW repair manual has it's issues as well. Part of the issue is that both Haynes and Clymer get most of their information from the BMW material and, if that is in error, so are the others... with additional typos.

Forums like this are a very valuable asset for information... all of it well meaning and most of it good as long as you remember that a lot of it is personal opinion.

Rob

Hi focusrsh,
You are fortunate to have received the excellent, DETAILED, responses from Rob, SteveD, and Kurt in S.A......
There is a lot of other specific information here and elsewhere.
Good luck with your new bike!
Have FUN.
I am only back here for a quick look, as I have not been around lately.

Ride Fast and Safe,
spo