BMW R80

When you buy a cheap bike on eBay there’s al­ways a chance that one of its mi­nor prob­lems might be some­thing ma­jor. Stephen Her­bert is not a man to be dis­cour­aged by such tri­fles, how­ever…

Real Classic - - Contents - Pho­tos by Stephen Her­bert

When you buy a cheap bike on eBay there’s al­ways a chance that one of its mi­nor prob­lems might be some­thing ma­jor. Stephen Her­bert is not a man to be dis­cour­aged by such tri­fles, how­ever…

Ihave a dis­ease. An in­cur­able dis­ease. Maybe you have it too; the main symp­tom is that I can’t stop buy­ing old bikes and re­build­ing them. Most of mine have been Royal En­fields and some would say that is a sep­a­rate, ter­mi­nal dis­ease in it­self! The first one was a Cru­sader Su­per 5, fol­lowed closely by an­other Cru­sader, an In­dian Bul­let, a Con­stel­la­tion and then an­other In­dian Bul­let. Some of th­ese have graced th­ese pages in ear­lier edi­tions. Since re­tir­ing, the in­ten­sity of the dis­ease has in­creased. Some­thing to do with ex­tra play­time, or so my wife tells me. So the time be­tween start­ing re­builds has short­ened, and the shed has be­come more full of old iron.

But this one is a slightly dif­fer­ent. In be­tween Royal En­field re­builds, I’ve had a few BMWs and I’ve come to re­spect the qual­ity of en­gi­neer­ing, the de­sign and the way they look and ride, par­tic­u­larly the air­heads. Most air­heads are VMCC-el­i­gi­ble now too, which is an added bonus. My first one was an R45, which I loved but sold to fund a big oil­head, an R1150R. That was a su­perb bike on the move but proved to be too big and heavy when ma­noeu­vring and I dropped it twice on the drive at 0mph. I swapped it for an F800GT which was great… but slightly bor­ing. I’d been han­ker­ing after an­other air­head, prob­a­bly big­ger in ca­pac­ity than the R45 with­out be­ing too big. One thing I liked about the oil­head was the sin­gle-sided rear end, so I re­solved to find an R80 mono. Which is ex­actly how I came to find ‘Hi-Yo’ (so called be­cause he’s sil­ver), an R80 mono of 1985 vintage (ac­cord­ing to the VIN) but with a 1987 reg­is­tra­tion and less than 40,000 miles on the clock.

As with most of my pro­jects, this was found on eBay com­par­a­tively lo­cally and the seller was hon­est about the de­scrip­tion. Ap­par­ently it was a great bike apart from the horrible clat­ter­ing noise that had re­cently de­vel­oped from the clutch area. More about that later. He even re­fused to take my money un­til I’d come to see it and heard the noise. What a gent!

The R80 was col­lected in a van, mainly be­cause of the clat­ter­ing noise, in Au­gust 2016. Apart from the ob­vi­ous trans­mis­sion prob­lem it had a few cos­metic is­sues to ad­dress, but was in over­all good nick and rep­re­sented good value. The seller was gen­uinely sad to see it go, but had no time or ca­pa­bil­ity to fix the trans­mis­sion. We agreed that we would keep in touch dur­ing the re­build. Be­cause the BM was in rea­son­able con­di­tion (un­like some of my other pro­jects) I de­cided to just fix the ob­vi­ous prob­lems and to do a light-touch cos­metic smartenup. You can def­i­nitely overdo things and this bike had clearly been looked after. It ob­vi­ously needed a bit of a tart-up but to have done a show­room re­fit would have de­stroyed its good char­ac­ter.

First things first, that ‘clutch clat­ter’ needed to be sorted, fol­lowed by a list of other mi­nor jobs:

Lo­calised frame rust needed rub­bing­down and paint­ing The front brake was a bit spongey ac­cord­ing to the PO The fork stan­chions were ex­posed and needed re­place­ment gaiters (not to be con­fused with ‘gators’ which is how some peo­ple write it – that’s a com­pletely dif­fer­ent an­i­mal!) The front tyre wasn’t hold­ing pres­sure The ex­haust head­ers had sur­face rust (but the stain­less si­lencers were OK The engine cas­ings, bevel box and gear­box were cov­ered with white ally ox­ide The fuel tank was not the orig­i­nal one, al­though was the right size, shape and colour. Ap­par­ently the orig­i­nal one had de­vel­oped pin-holes and had been re­placed with an­other one of the right colour from an RT which dis­played typ­i­cal fair­ing fret­ting/witness marks, so looked tatty Some mi­nor elec­tri­cal is­sues: oil/neu­tral lights not work­ing, OEM heated grips had a loose wire, etc

First to the ‘clutch clat­ter’. The as­tute and/ or sub-ed­i­tors among you will have no­ticed that I re­fer to the clutch clat­ter as the ‘clutch clat­ter’. There is a rea­son for this! Be­fore load­ing Hi-Yo into the van, PO started up the bike to demon­strate that all was well with the engine and to let me hear the ‘clutch clat­ter’ for my­self in case I de­cided not to pro­ceed. Very fair. The ‘clutch clat­ter’ was in­deed a clat­ter but I had my doubts at this stage that it was the clutch. It seemed to clat­ter more when the clutch was en­gaged which MIGHT have meant some­thing more sin­is­ter down­stream in the trans­mis­sion. Need­less to say I bought the bike any­way, be­cause the rest was so good.

Find­ing out whether it was clutch or some­thing else ne­ces­si­tated re­mov­ing the gear­box. Those of you fa­mil­iar with th­ese bikes will know that air­head Beemers have a flat-twin engine with an in­line crank ori­en­ta­tion, be­hind which is a car-type di­aphragm clutch, be­hind which is a gear­boxg and then a drive shaft. For me, this is one of the ap­peals of this de­sign – there’s some­thing in­her­ently ‘wrong’ about clutches run­ning in oil on the side of the gear­box, but hav­ing worked on many bikes with this de­sign I sup­pose I’ve just ar­gued against my­self…

One of the well-known man­u­als sug­gests that re­mov­ing the gear­box in­volves re­mov­ing the engine too, or at least tak­ing out the engine mounts and mov­ing it all for­wards. In fact this is not the only way to do it. I al­ready knew an­other way,y, hav­ingg worked on my R45 in the past. In sim­ple terms, you just take off the back wheel and swing­ing arm, un­bolt the gear­box and there’s your clutch – seem­ples!

In prac­tice it’s a bit more in­volved, of course. The process goes like this:

Re­move the bat­tery and its car­rier Drain all trans­mis­sion flu­ids Dis­con­nect the clutch ca­ble, speedo ca­ble and bat­tery earth lead Re­move the air­box sit­ting on top of the gear­box and the carbs. You can leave the ca­bles at­tached and ‘park’ the carbs against the ex­haust head­ers, not for­get­ting to plug the in­takes Re­move both si­lencers Re­move a clip and peel back the gaiter at the swing­ing arm end of the drive­shaft univer­sal joint

Re­move the four stretch bolts that hold the UJ onto the gear­box out­put flange (tricky job as there’s lit­tle space to do this). Throw away the bolts – they need to be re­placed cos they stretch Re­move the rear wheel and dis­con­nect the brake rod Pop the plas­tic cov­ers off the swing­ing arm piv­ots, undo the big lock­ing nuts and un­wind the big studs that screw into the swing­ing arm (tricky again as the big nuts need a special socket with the outer di­am­e­ter ground down, or a suitable box span­ner, as there’s lit­tle room in­side the hous­ing, and the studs need ei­ther a big allen key or a male hex socket) The swing­ing arm, bevel box and drive­shaft can then be re­moved as one Undo the gear­box-to-engine bolts With a bit of a jig­gle and a twist, the gear­box can then be ma­noeu­vred out of the clutch cen­tre (splines) and out of the space be­tween frame mem­bers. At this stage don’t for­get to pull the wire off the neu­tral switch mounted un­der­neath the gear­box, and re­mem­ber when re­plac­ing the gear­box to re­con­nect it (this can­not be done with the gear­box in place) And there’s the clutch, all ex­posed!

I dis­man­tled the clutch from the fly­wheel and had a look at ev­ery­thing to as­sess what was mak­ing that horrible clat­ter. The clutch looked fine. Bit worn, but ser­vice­able. No ob­vi­ous bro­ken bits or witness marks in­side the bell­hous­ing to sug­gest that any­thing was loose in­side. Maybe not the clutch then…

So I turned my at­ten­tion to the gear­box. Firstly the splines on the in­put shaft looked quite worn and sharp. It’s good prac­tice to take the box out ev­ery few years and re-grease th­ese splines with a light smear of your choice of ap­pro­pri­ate lu­bri­ca­tion (fo­rum threads on this sub­ject are miles long). This one looked like it had never had this treat­ment, but it still didn’t ex­plain the clat­ter as the splines were still able to drive the gear­box shaft… which seemed stiff to turn… ac­tu­ally very stiff to turn. Some­thing amiss there!

To test my grow­ing the­ory that the gear­box was the cause of the clat­ter, I mounted it in a be­spoke jig on the bench (OK, in the vice) and drove it with a socket and hand-brace. Not only was it very stiff, it clat­tered in the same way as it did with the engine driv­ing it. Not the clutch then. It was the gear­box!

This was po­ten­tially bad news, as (a) parts are ex­pen­sive, (b) I can’t work on th­ese (I don’t do special tools and in­dus­trial blowlamps), and (c) re­place­ment / ex­change gear­boxes are even more ex­pen­sive. For­tu­nately I’d en­coun­tered a sim­i­lar prob­lem with my R45. It wasn’t a clat­ter, more of a graunch when chang­ing into sec­ond. I’d found a guy in Hud­der­s­field who re­builds th­ese for a liv­ing and is sym­pa­thetic to hard-up re­tired old clas­sic mo­tor­cy­cling gen­tle­folk so doesn’t charge an arm and a leg. I’m talk­ing about Roger Ben­nett of Ben­nett En­gi­neer­ing (01484 536126). His work­shop is a joy to be­hold, be­ing full of air­head bits, and Roger him­self is a char­ac­ter too – plenty to chat about. So I took SWMBO on a day out to Hud­der­s­field (I know how to treat a girl) and sought Roger’s ad­vice.

The news on the phone a few days later was worse. Ev­ery sin­gle bear­ing, in­clud­ing the big, ex­pen­sive BMW-ex­clu­sive one, needed re­place­ment, to­gether with the in­put shaft (be­cause of the worn splines) and a cou­ple of coggy-shaped things. Roger did me a deal us­ing a good used in­put shaft and cogs plus a set of new bear­ings and I col­lected the re­built box a cou­ple of weeks later. Strange re­ally, as there was no out­ward sign of a prob­lem – and the drained oil con­tained no nasty metal­lic lumps.

In the mean­time I re­placed the clutch fric­tion plate in an­tic­i­pa­tion of the re­paired gear­box. That’s a sim­ple un­bolt and re­place job, tak­ing care to re­new the bolts. When buy­ing parts, don’t for­get to buy re­place­ment stretch bolts for the drive­shaft. Did I say that al­ready?

PART ONE

Left: This is Hi-Yo the BMW as col­lected. Looks pretty good, huh?

Above: Bike on the bench. It pays to take a lit­tle time to as­sess the needs be­fore set­ting to with the span­ners…

Left: Engine ‘fuzz’. Plenty of ally ox­ide present, which is what hap­pens if there are no oil leaks

Fa­mil­iar BMW trademark en­gi­neer­ing. The Bings al­ways look vul­ner­a­ble… but are not. Not re­ally

The tank’s not the orig­i­nal item. You may be able to make out the RT fair­ing marks

No fork gaiters, just ex­posed chrome tubes. Bet­ter change those ‘gators’ pretty damn snappy!

Above: Th­ese are the bits that need to come off be­fore the gear­box can be lifted out, de­spite what the manual will tell you

The clutch. Very like a car clutch, for those who are fa­mil­iar with such things

Left: Clutch re­moved. That’s the ‘fly­wheel’ on the end of the crank­shaft. In fact, the clutch it­self adds greatly to the weight of the ‘fly­wheel’

Right: One clutch fric­tion plate. Plenty of life left in the lin­ings, time to stare a lot at the drive splines

Right: Gear­box test­ing. Ev­ery RealMe­chanic knows that you need a highly so­phis­ti­cated, state of the art gear­box di­ag­no­sis kit

Above: One BMW clutch ex­posed. Bit rusty, bit worn, but OK

More old bikes on­line: Real-Clas­sic.co.uk

Above: What Roger re­placed to re­move the wear and cure the rat­tle. All the bear­ings, in­put shaft and a cou­ple of coggy things…

Be­low: A view of the in­put shaft splines. Care­ful… care­ful… they’re sharp!

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