BMW R-series Air­heads 1969‡1996

Af­ford­able and easy to work on the R-series was BMW’S move into mod­ern bike build­ing. Bike’s Dealer goes retro…

BIKE (UK) - - THE DEALER -

SPAN­NING 25 YEARS and over 35 mod­els, BMW’S R-series her­alded the Ger­man mar­ques’ ar­rival into mod­ern mo­tor­cy­cling thanks to bril­liant in­no­va­tion and a mod­u­lar con­cept phi­los­o­phy. Pow­ered by an evo­lu­tion of BMW’S tra­di­tional air-cooled 4v boxer mo­tor, the new Type 247-en­gined bikes boasted more per­for­mance and re­li­a­bil­ity. Air­heads have al­ways had a cult fol­low­ing, but these days in­ter­est in the mod­els has peaked thanks to re­newed in­ter­est from cus­tom builders. Parts in­ter­change­abil­ity across the years and mod­els is ex­tremely high, mean­ing own­ers of ear­lier R series bikes can ben­e­fit from the in­no­va­tions of later mod­els, and there’s also a very strong af­ter­mar­ket parts sup­ply. They’re also ex­tremely sim­ple for home me­chan­ics to work on, too. Pick up a bas­ket case for as lit­tle as £1000.

KNOW YOUR AIR­HEADS

The ba­sic model run down goes like this: /5 19691973 in 500cc, 600cc and 750cc; /6 1973’1976 in 600cc, 750cc and 900cc, R90S is the most de­sir­able; /7 1976’1980 500cc, 600cc, 750cc, 800cc and 1000cc. For ’81-’84 BMW dropped the slash sym­bol and these are known as the ‘Brembo brake mod­els’ (due to their Brembo brak­ing sys­tems). R80G/S is the most de­sir­able.

VALVE AD­JUST­MENT

De­spite be­ing noisy, par­tic­u­larly on /5 mod­els, the valve train is re­li­able if well main­tained. BMW rec­om­mend check­ing clear­ances ev­ery 8500 miles, but it’s worth check­ing them at 5000 miles. The top cover gas­ket can be reused if in­tact.

CYLIN­DERS

alu­mini­u­mironAll mod­els in­ter­nal al­loyup boreto bar­rels1981 sleeve. fea­tured­with Lat­era cast model cylin­ders were up­graded to full alu­minium bar­rels with a nikasil plated bore, which were lighter and had bet­ter cool­ing and wear prop­er­ties. This means later and larger bores fit ear­lier bikes, for ex­am­ple many R75/7 own­ers fit R80 bar­rels. How­ever, care needs to be taken to match the cylin­ders to the cases, and also take into ac­count squish bands, pis­ton ring type…

BUILD QUAL­ITY

‘They don’t make them like they used to’ and in terms of BMW bikes I’d agree. We sell loads of mod­ern stuff and the build qual­ity is nowhere near the stan­dard of this older stuff. I bought a 1976 R75/6 from a chap who had it from new. He said it was nearly three times the cost of the Honda equiv­a­lent at the time, so they were ex­pen­sive even then.

TOP END

Pre-1985 bikes were de­signed to run on leaded petrol and so were prone to valve seat wear prob­lems when run on un­leaded fuel which man­i­fested it­self in ex­ces­sive tight­en­ing of ex­haust valve clear­ances. BMW in­tro­duced new seats made from an up­graded ma­te­rial for later mod­els, and these can be retro fit­ted into the early model cylin­der heads. There are also very good af­ter­mar­ket valve seats to buy.

IG­NI­TION

The orig­i­nal ‘bean can’ pointstype ig­ni­tion sys­tem fit­ted to pre-1981 twins can mean poor start­ing and un­re­li­able run­ning. How­ever, there are lots of af­ter­mar­ket al­ter­na­tives in­clud­ing the op­tion to up­grade to an elec­tronic ig­ni­tion, which BMW in­tro­duced on 1981 on­wards mod­els.

SER­VIC­ING

If a high-qual­ity semi-syn­thetic 20/50w oil is used you should be look­ing at chang­ing oil ev­ery 5000 miles, then re­plac­ing the oil fil­ter and its O-rings ev­ery other service with a gen­uine BMW item. When it comes to choos­ing an oil, look out for an ad­di­tive called ZDDP in the in­gre­di­ents list, as this com­pound helps pro­tect camshafts.

TRANS­MIS­SION

It’s nor­mal for an air­head’s gear­box to rat­tle at tick­over, es­pe­cially when warm, but this noise should dis­ap­pear when the clutch is pulled in or the en­gine revs are raised slightly. That said gear­boxes are no­to­ri­ously poor and prone to fail­ure, so reg­u­lar main­te­nance is vi­tal. Early /5 mod­els came with a four-speed gear­box, and bikes from 1974 on­wards came with five-speed ’boxes. Pre-1981 five-speed trans­mis­sions of­ten suf­fered with bro­ken dogs re­sult­ing in a loss of fourth gear. Bikes built be­tween ’85-’94 also suf­fered ex­ces­sive wear on the out­put shaft bear­ing due to BMW omit­ting a cir­clip and groove

from the shaft it­self. This was re­in­stated on late mod­els.

SMOOTHER SHIFT­ING

Shift­ing on early /5s can be en­hanced by fit­ting later model parts such as Te­flon-lined clutch ca­bles, rose-jointed gearshift link­ages, the post-’82 shift de­tent kit and the light­est pos­si­ble fly­wheel/clutch car­rier. BMW also rec­om­mend in­spect­ing and lub­ing the in­put shaft splines ev­ery 10,000 miles, as dust gen­er­ated from the dry clutch can cause the shaft to dry out and grind the splines away.

STARTER

All air­heads from 1969 on­wards fea­tured an elec­tric start, which was backed up with a kick­start. How­ever, the kick­start mech­a­nism on /5 five-speed ’boxes is renowned as be­ing very weak and re­ly­ing on it to start the bike can re­sult in trans­mis­sion prob­lems.

TUBE­LESS SPOKED WHEELS

Cross-laced wheels were in­tro­duced on the 1988 R100 GS, al­low the use of tube­less tyres, and are still used by BMW to­day. These wheels are very strong but need spe­cial­ist care if dam­aged, as they are ex­tremely dif­fi­cult to true. Wheel builders such as Hagon (hagon-shocks.co.uk) of­fer a re­build­ing service for cross-laced wheels.

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