OT - BMW RS100

Ive got a R90/6, '75 model. It has 187,000 miles on it.
The clunk is pretty common for Beamers. Its the nature of the beast and may not be final drive wear, particularly with that few miles on it. At 56,000 unless the previous owner was a kid knee dragger (unlikely with that particular ride), its just broke in. Just be aware..that older Boxer rear brakes are....a bit...inadequate, if you have the rear drum.
Put it up on the centerstand, pull the rear wheel and check the final drive "lovejoy" couplers. The gizmo that connects the rear wheel and the final drive. They are replaceable, but spendy if they are badly worn, which they shouldnt be at that mileage. YMMV
Also drive shaft spline, when you have the time.
You will want to either bookmark or print out this site Also, check the 'gaiters" on the front forks. If they are cracked or broken, they WILL need to be replaced. (gaiters are the accordian rubber tubing covering the front fork sliding sections.
Oh..the boxers of that vintage have a surprising amount of kneel..when you cram on the front brakes, they tend to lean far forwards..makes you feel like you are about to do a summersault. But if the previous owner put Bembo brakes on it, he may have modified the suspension.
Good bikes. Ive not had mine on the road since 98. No time, no money. But I fire it up every 6 months and run it till it warms up, and change the oil once a year. Someday when Im rich and famous, Ill change out the point style ignition and put in an electronic one. Shrug
Gunner
Rule #35 "That which does not kill you, has made a huge tactical error"

Can't tell you anything about the RS 100 but... When I got out of the Navy, I bought a used 1965 R60 from a BMW dealer. He said it would be the last motorcycle I would ever really need. 35 years later, I still have it.
Vaughn

Agreed - about the idea they're probably not badly worn at 50-something.
But harder to replace than you think, it means a new spline coupling on the wheel, *and* either a new ring gear (the male spline on that is integral) or a re-work of the existing worn spline. Some folks glop braze on the worn spline, and then remachine the splines. THis supposedly gives 75% wear life from that point on, compared with the original. I'm not sure I believe that.
My R75/6 is high miles and has a fairly worn rear drive coupling. When it gets critical I plan on begging the wire EDM guy here at work to make me a new male spline out of steel, and then machining the old one off, and silver-soldering the replacement on.
A bike of this vintage probably has no gaiters. If he buys it I would suggest he fit them. This is the 'gummikahw' effect. Fitting slightly heavier (7wt) fork oil, and a set of progressive springs, will help on this one. The real trick is a fork brace, this makes an amazing improvement.
You can put a Dyna III in there, but if you want my personal advice - leave the points.
Jim
'59 R50 (ready for powder coating) '60 R60US '75 R75/6 '78 R100RS

Thanks Gunner and Vaughan, (only replies I've seen so far) Gunner, those sites were exactly the sort of thing I need. Had heaps of bikes but know bugger all about BMs. I bought the bike. Rear disk. Bit rough appearance wise but seems mechanically sound. The mechanic that put me on to it knew the bike and told me it was good. The ex-owner seemed like a straight shooter. Has the two panniers and top box. Stainless exhaust. Always wanted a BMW. Paid $Aus4000, which seemed quite reasonable after checking mags etc. I like it! All in all, a good day. Thanks again. Some blokes, when having a mid life crisis get the blonde and Porsche, me, I get the bike and me knee fixed! :-) See ya, Mac.

Thanks again for the info, as you see from previous post, I bought it. It does have the fork brace. I'll generally be riding it on open road and am a fairly sedate rider, but you never know, have been known to get a rush of blood to the head! :-) See ya Mac. >> >>Put it up on the centerstand, pull the rear wheel and check the final >>drive "lovejoy" couplers. The gizmo that connects the rear wheel and >>the final drive. They are replaceable, but spendy if they are badly >>worn, which they shouldnt be at that mileage. YMMV > >Agreed - about the idea they're probably not badly worn at 50-something. > >But harder to replace than you think, it means a new spline >coupling on the wheel, *and* either a new ring gear (the male >spline on that is integral) or a re-work of the existing worn >spline. Some folks glop braze on the worn spline, and then >remachine the splines. THis supposedly gives 75% wear life >from that point on, compared with the original. I'm not >sure I believe that. > >My R75/6 is high miles and has a fairly worn rear drive coupling. >When it gets critical I plan on begging the wire EDM guy here >at work to make me a new male spline out of steel, and then >machining the old one off, and silver-soldering the replacement >on. > >>Also, check the 'gaiters" on the front forks. If they are cracked or >>broken, they WILL need to be replaced. (gaiters are the accordian >>rubber tubing covering the front fork sliding sections. > >A bike of this vintage probably has no gaiters. If he buys it I >would suggest he fit them. >>>Oh..the boxers of that vintage have a surprising amount of kneel..when >>you cram on the front brakes, they tend to lean far forwards..makes >>you feel like you are about to do a summersault. But if the previous >>owner put Bembo brakes on it, he may have modified the suspension. > >This is the 'gummikahw' effect. Fitting slightly heavier (7wt) >fork oil, and a set of progressive springs, will help on this one. >The real trick is a fork brace, this makes an amazing improvement. > >>Good bikes. >>Ive not had mine on the road since 98. No time, no money. But I fire >>it up every 6 months and run it till it warms up, and change the oil >>once a year. Someday when Im rich and famous, Ill change out the >>point style ignition and put in an electronic one. Shrug > >You can put a Dyna III in there, but if you want my personal advice - leave >the points. > >Jim > >'59 R50 (ready for powder coating) >'60 R60US >'75 R75/6 >'78 R100RS

Very fair price. The rear disk is fair. The front duals are pretty good. As suggested, do the increase in fork oil viscosity and progressive springs if this has not already been done. The fork brace's existence implies it has, however.
If this bike has the front master cylinder under the tank, it will be weepy because of the rough casting, and should be sleeved with brass at some point. If the m/c is on the bars, then that's good.
The charging systems are good but not very good. 280 watts is the limit. Get a good manual for maintenence. The stainless headers and mufflers are a nice touch. Those are worth over 500 by themselves.
Keep oil in it, keep some valve clearance in the valves. Put some inline filters in the fuel lines to keep away that 'wet shoe' feeling.
Things that go wrong:
Rear main seal can get weepy Driveshaft boot can get weepy Instrument cluster lights are troublesome, so's the housing
You're good to ride for over 100K miles.
Jim

My '77 BMW R100/7 had that clunk. I'm not aware that it was a problem, just "one of those things".
Ask specifically about carb synchronization if this is the 1000cc boxer engine with bing carbs that I'm thinking. If the owner gives you a vacant stare, then be aware that it's probably not performing up to potential. Unless it changed dramatically between '77 and '82 (I have no idea, sorry), there's not a lot to go wrong. Bosch electricals common to any european car of the era, and so on.
It's well built and designed. I didn't have much experience fixing mine because it didn't break.
Dave Hinz

Not really. The bing cv's are actually pretty easy to synch, and they hold their settings for a long time. The only major known carb bug is a) the CV diaphragms hole after many years (easy fix) and b) if there's no filter upstream of each carb, the float needle will hang open and give one gasoline-soaked footwear.
Jim

It's been a while, so I can't picture that model. I remember R100S (small fairing), and the R100RS (larger fairing with lowers). I had the latter, it was either the first or second year of production. Only major problems I remember were warped front brake rotors (they were pretty thin), and broken gear dogs (third perhaps). Both should have been well cured by '82. I also remember lots of fork stiction, which the factory said could be alleviated somewhat by removing one of the two seals in each leg , which pretty well finished off my impression of the "finely engineered" thing. I did like the light weight and big fuel tank. I took it on a 5000 mile trip once without problems, and I'll give the seat nine stars.... out of a hundred. ;-)
Wayne

Whats the up and down sides of sticking in a pointless ignition?
Gunner
Rule #35 "That which does not kill you, has made a huge tactical error"

Boxers..and boxer owners tend to be something of an unusual bunch. You have the snooty techno riders, who have to have the latest and greatest high tech shit, expensive custom leathers and look like something out of the 22nd century.
Then you have the rest of us. Personally, I like SOME boxers (not K bikes) simply because they are dependable rides that are comfortable over long distances. Wash and detail one? Thats what putty knives are for, once a year, if you cant see the headlight anymore. Or if you got coyote/rabbit guts deeply into the cooling fins of the head(s) and the smell makes you hungry.
I actually had ants swarming my bike once. But that was cool as they only ate the rabbit guts. Saved me from having to use a pressure washer to get Thumper off the engine.
Beemers make great rat bikes. Though they do tend to be tough on rear tires as they seem to wear faster than on any other bike Ive owned.
Oh..and clutch lever adjustment...something Jim might give you a heads up on
Gunner
Rule #35 "That which does not kill you, has made a huge tactical error"

First off you don't get them for free, I think a dyna 3 is a few hundred dollars.
I have a points ignition in my R75, and the new bike had that same setup but was retrofitted by the previous owner with the dyna 3.
When he did it, he hooked the electronics box up wrong to the coils, but it did still run fine.
Comparison shows that both points and the electronic ignition do indeed provide satisfactory spark to run the bike. Granted I've removed the stock BMW wires and resistor plug caps on them, and replaced with straight copper 8mm silicone rubber wires from Taylor Vertex. So the resistor issue is moot.
The think I like about the points is they seem to not require adjustment on that bike hardly at all. I haven't had the front cover off the R75 in about two years, so there's not a lot of tinkering required.
The Dnya 3 uses the stock mechanical ignition advance unit, so whatever unreliability is inherent in that, is still present. And the dnya trigger unit that attaches to the cam seems a bit fidgity, though I've had no troubles with it. Likewise the circuit boards that hold the pickups seem kinda fragile.
The one upside with the Dyna is, I think you can individually move the pickups to get the spark spot on on both jugs. But then, my R75 never had the 'split timing marks' problem.
I think for me the biggest worry is that if something goes wrong inside the potted electronics unit, it's a drop-dead, walk home failure. With points, you can always manage to get 'em working somehow. Of course I carry spare points and condenser in the older bike's toolkit. I know that folks say that electronic parts are so much more reliable than mechanical ones - but this is a vehicle, and the parts are a) built to a price, using b) consumer grade parts, and d) subjected to extremes of temperature and vibration.
I'm either going to start carrying an entire spare dyna unit, or swap back to points on the newer bike.
Jim

Well, that's what I'm saying. If they haven't done it, then there is a huge potential for vast improvements in performance by doing it. If they answer "Yeah, it's a snap, buy a polysynch if you don't have one", then that tells you more about the seller and how they may have kept the bike up.
Maybe the one I bought was more fscked up than normal, but they were _way_ out of tune with each other when I got it. Then again, the clutch was out of adjustment (no free play - 30 second fix), the oil was chunky, the voltage regulator was shot, and one fork was nearly dry. Guy figured the bike was ready to part out, when it just needed about an hour of attention (and a voltage regulator from one of my parts Saabs).
Dave Hinz

I like to just short first one, and then the other, plug to ground. If the sync is right the idle will not change speed at all when this is done. I've found that setting the idle air screw on those carbs seems to be done best with *both* carbs running, unlike the bikes I have with direct slide carbs.
Those are good buys - the bike I bought had the headlight installed upside down. The seller made the comment "I don't like those H4 headlights very much, they don't seem to work very well...."
Jim

G'day, Thanks Jim, it has the front master cylinder on the right bar, has inline fuel filters and he threw in a 'Haynes' manual which seems pretty good. He said he changed engine oil and filter, gearbox oil, drive shaft oil and diff oil every 10000 kms (about 6000 miles) Changed the lot! See no reason to dis-believe him, he seemed the type. It just gets better! :-) Regards, Mac.

G'day, Thanks Dave, the ex-owner volunteered information about the carbys, said easiest way to check was to run on stand to about 3000rpm, pull a plug lead, note rpm drop, replace, pull other plug lead and compare rpm drop and should give indication of how carbies performing. Sounds sort of logical and this bloke maintained it pretty well. Bit like mag check on a/c! Regards, Mac

Good post, and food for thought.
Gunner
Rule #35 "That which does not kill you, has made a huge tactical error"

I haven't had much to do with the Airhead beemers - I have a K100RS (inline flat 4) The Internet has lots of resources for them. There are also a lot of places selling parts online. I have found and to be good. They are generally 30% cheaper than here (New Zealand) and delivery is much the same as getting parts through the official channels from BMW. One example - fork stanchion (gen BMW) for my K - 179euro from Siebenrock, 440euro from BMW NZ and would have to be ordered in - same part, both brand new. What is the value in local support there with that markup?
may be of use: (although for a later model than yours) parts fiche for most BMWs /90 models another parts fiche (incld cars)
Discount Motorcycle Wreckers, 35 Dawson St, North Coburg, Melbourne, Phone 03 9350 4417 specialise in wrecking BMWs
Geoff

Yeeeahhhhh...I can see how an H4 upside-down would be unpleasant. For him, _and_ for passing airplanes. The one I bought was from a cow-orker, so I couldn't gloat _too_ much about it. I just told him that I spent some quality time with the bike for a week. Didn't mention that it totalled a couple hours.
He also didn't know about the hinged oil filter, so the fairing was making oil changes a major ordeal. Wasn't a mechanic type guy. Good at tuning MRI scanners, though...
Dave Hinz