Four separate oil compartments, each with its own fluid, its own interval and its own drain plug hiding somewhere unhelpful. Get familiar with all four and the bike will outlive you.
The specification most often quoted wrongly is fork oil. The older 235 cc figure is still repeated everywhere, but 1981 and later forks take less, are measured by a rod-drop level rather than by volume alone, and are notably fussy about foaming — which means the fluid you choose matters more on a later bike than an early one.
One habit worth adopting from this chapter: airheads dislike long idling. At a hot idle, oil delivery to the timing chain is marginal and bearing films thin out. Ride it or shut it off.
Every figure on this page resolves to one model and year in the book. Pick your bike and the rows that apply to it come forward, with the rest marked.
Open this chapter in the book| Unit | Capacity | Fluid | Applies | Notes |
|---|---|---|---|---|
| Engine (oil change) | 2.0 L | quality motorcycle oil, 20W-50 typ. | large twins — see note | 2.25 L with filter change. Dipstick governs — check on centre stand. Not verified for R45/R65. The small-twin factory literature gives its own fill quantity; do not carry this figure across to them. Deep-sump bikes hold more again. Avoid plain car oils: flat-tappet cam & followers want motorcycle/high-ZDDP oil. |
| Transmission | 800 cc | 80W-90 GL-5 hypoid | All | Fill to lower edge of filler port, bike level. |
| Driveshaft housing | 150 cc | 80W-90 GL-5 | /5 LWB & later large twin-shock | 100 cc on the short-wheelbase /5 and the 1979–80 short-wheelbase R65. R45 / R65-family quantities not verified here — the 248-series literature lists them separately; check the manual for the small twins rather than using this row. Paralever: no oil in shaft housing. Oil migrates shaft→trans on some bikes — annoyance, not danger. BMW-WSM7 §33 Swinging-arm fill 0.15 L on every sheet, 12.77 through 1981. |
| Rear drive (final) | 250 cc | 80W-90 GL-5 hypoid | Twin-shock to 1980 | Fill to port lip. |
| Rear drive (final) | 350 cc max | 80W-90 GL-5 hypoid | Twin-shock from 1981 | BMW-WSM7 §33 1981 sheet: “0.35 L max., up to level check plug.” These have an oil-level inspection port on the rear of the drive — fill to it. Using the pre-'81 250 cc figure underfills by 100 cc. |
| Rear drive (final) | 320 cc | 80W-90 GL-5 hypoid | Monolever | Practical fill. Fill to port lip. |
| Rear drive (final) | 230 cc | 80W-90 GL-5 hypoid | Paralever | Fill to port lip. Verify by exact model. Late GS, R and R100R final drives are not all the same design, and BMW's late literature does not use one capacity across the family — 230 cc is the commonly published figure, not a universal one. |
BMW-WSM7 The filter changed design twice, and the failure mode is the same both times: a filter that carries its own seals dropped into a housing that still has the old loose ones. Double-sealed, the element does not sit where it should, and oil finds a way past the filter instead of through it. BMW's instructions on this are one line long and easy to miss.
| Assembly | What it has | Era | What to do | ||
|---|---|---|---|---|---|
| Old version | paper gasket + steel washer | separate sealing rings in the housing and cover | early | The housing carries the seals; the element does not. | |
| New version | no paper gasket, no steel washer | crimped end to the outer tube | later | Interim design. | |
| New filter with square-section rings | rings bonded to the element with adhesive | element carries its own seals | remove the old rings | 3.82 onward | “If the new oil filter is installed in place of the old type, remove the sealing rings in the base of the filter housing and on the cover for the oil filter.” Leave them in and you have two seals doing one job. |
| Hinged element (RS / RT fairings) | easier to fit past a fairing | O-ring seals at the filter head | remove the housing ring | oil-cooler bikes | On oil-cooler machines either the old or the hinged element may be fitted, and the existing O-ring seals at the filter head. “Important: if using the hinged filter element, remove the sealing ring from inside the filter housing.” |
| Model | Drain & refill | After rebuild | Level check | Notes | |
|---|---|---|---|---|---|
| /5, /6, /7 to 1980 | 235 cc | 250 cc | conflict recorded — see note | 50 mm above damper, forks extended | BMW's own documents disagree with each other. The /7 owner booklet says 0.28 L (280 cc) per leg BMW-TD77; the workshop manual's 12.77 front-fork sheet says capacity 0.25 L (250 cc) per fork column BMW-WSM7 §31 — which is the figure this row's overhaul column has carried all along. 235 cc remains the drain-and-refill quantity, where oil stays behind in the damper and lowers. Set the level, not the volume — 50 mm above the damper with the forks extended governs either way. Pre-'77 alternative: 437 mm rod depth from the top-nut face. |
| /7 1981–84, R80G/S, R100 models '81+ | 220 cc | 225 cc | 300 mm rod-drop method | '81+ forks are foam-sensitive — use a real fork/suspension fluid, ~SAE 5–7.5, never over SAE 10. BMW-WSM7 §31 1981 sheet: “oil content per fork leg 0.22 L.” | |
| R45, R65 to '85, R65LS, R80ST | 190 cc | 195 cc | 35 mm above damper ±15 | ||
| R80 '85+, R65 '86+ | 300 cc | 300 cc | monolever road models | Later long-travel fork — markedly more than the twin-shock figures above. | |
| R80RT '85+, R100RS/RT '87+ | 320 cc | 320 cc | monolever tourers | ||
| R80GS, R100GS, R100GS PD — left leg | 410 cc | 470 cc overhaul | SAE 15 | Paralever GS | The two legs differ in both quantity and weight. Left is rebound damping. Filling both the same is a common and consequential error. |
| R80GS, R100GS, R100GS PD — right leg | 440 cc | 470 cc overhaul | SAE 10 | Paralever GS | Right is compression damping. |
| R80R, R100R (Showa) | 410 cc | 420 cc | Paralever roadsters |
| Rule | Value | Applies | Notes | |
|---|---|---|---|---|
| Gear oil grade | GL-5 80W-90 — BMW factory | GL-4 is community practice, not factory | trans / shaft / final | What BMW actually printed is “brand-name hypoid gear oil, SAE 90 above 5 °C / SAE 80 below” — a type-and-viscosity specification for all three compartments, with no API GL number anywhere in the booklet. BMW-TD77 An earlier revision of this guide said “BMW specifies GL-5”. That over-stated the source and is corrected here. Hypoid gear oil of that era is what the API later codified as GL-5, so GL-5 remains the correct modern reading of the requirement — but BMW specified the duty, not the API class, and the distinction matters when you are weighing the GL-4 argument. The GL-4 argument — that GL-5's sulphur/phosphorus EP additives can attack yellow metals in the gearbox — comes from respected airhead specialists, not from BMW; run it as an informed owner decision if you choose to, but do not mistake it for the factory specification. If synthetic gear oil weeps at seals, return to petroleum — seals often recover. BMW-WSM7 §33 The 1981 sheet prints it in so many words: “hypoid gear oil, SAE 90, API class GL 5.” The owner-booklet era never named a class; from 1981 the workshop sheet does. |
| Fork oil viscosity ceiling | SAE 10 max | stock ≈ SAE 4 (MIL-H-5606) | non-GS | Never raise viscosity to mask stiction — fix assembly alignment instead. BMW-WSM7 §31 The 12.77 sheet names the factory fills: shock-absorber oil — Shell 4001, Shell Aero Fluid 4, BP Aero Hydraulic 1, Castrol DB Hydraulic Fluid, Castrol Shock Absorber 1–318 — all thin hydraulic stock, consistent with the ≈ SAE 4 figure. |
| Idle discipline | avoid long / low idling | All airheads | At hot idle, little-to-no oil reaches the timing chain area and bearing films thin. Keep idle 800–1100 and don't let it sit burbling. | |
| Fork oil interval | Yearly, or 10,000 mi | whichever falls first | All | BMW's schedule calls for fork oil at every Inspection and at least once a year. The “two years maximum” figure in wide circulation is less frequent than the factory interval, not more conservative than it. |