An airhead tells you how it is doing through its valve gear. The tick that turns into a tap, the exhaust note that goes flat on one side, the oil smoke that appears only on overrun — all of it starts up here, under two aluminium covers a spanner can have off in a minute.
Which is the good news: this is the most accessible serious maintenance on the bike, and the most rewarding. A cold engine, two feeler blades and twenty minutes buys you the difference between an engine that runs and one that runs right.
Clearances changed by model and by year, and the /7 figures are tighter than the /5 numbers most people quote from memory. Find your bike in the first table before you touch anything.
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| Spec | Metric | Inch | Wear limit | Applies | Notes |
|---|---|---|---|---|---|
| In / Ex — /5, /6 | 0.15 / 0.20 mm | .006 / .008" | /5, /6 | ||
| In / Ex — /7 and 800 cc, through 1984 | 0.10 / 0.15 mm | .004 / .006" | R60/7 · R75/7 · R80/7 · R80 G/S · R80 ST · 1000 cc to 1980 | First 600 mi use 0.15 / 0.20 until stable. Recheck ~100, 600, 5000 mi after top-end work; keep records. This row no longer covers the 1981-on 1000 cc — see the row below. | |
| In / Ex — 1000 cc from 1981 | 0.10 / 0.20 mm | .004 / .008" | R100 · CS · RT · RS from 1981, and every later 1000 cc | BMW 3.82 Modelle-81 sheet. The 0.20 mm exhaust clearance begins with these engines, not in 1985. The 0.10 / 0.15 figure in wide circulation is the ’79–’80 specification carried forward in error, and earlier revisions of this guide carried it too. If you set a 1981-on exhaust valve to 0.15 mm, it is 0.05 mm too tight — and airhead exhaust clearances close up in service. First 600 mi: 0.15 / 0.25. | |
| In / Ex — R45/R65, and R80 from 1985 | 0.10 / 0.20 mm | .004 / .008" | R45 · R65 all · R80 & R80RT ’85+ · R80 GS · R80 R | First 600 mi: 0.15 / 0.25. R45/R65 by year not verified — BMW superseded the small-twin figures more than once by service information, and this guide does not yet hold the dated supersession table. See the open-questions register. |
| Spec | Metric | Inch | Wear limit | Applies | Notes |
|---|---|---|---|---|---|
| Head Ø In/Ex — R90, R100/7 | 42 / 40 mm | 1.65 / 1.58" | R90, R100/7 | All other 1000cc (incl. '81 R100): 44 / 40 mm. | |
| Valve head rim thickness — /5–/7 | 1.0 mm min | .0394" | below = replace | /5–/7 | Thin margin risks burned/dropped valve. |
| Valve head runout — max | 0.025 mm | .0010" | /5–/7 |
| Spec | Metric | Inch | Wear limit | Applies | Notes |
|---|---|---|---|---|---|
| Guide OD / bore in head | 14.050–14.061 / 14 mm | .5532–.5536" | /5–/7 | Interference 0.032–0.061 mm. Oversizes +0.1, +0.2. Length /7: 48 mm. | |
| Stem/guide clearance In & Ex | 0.050–0.080 mm | .0020–.0032" | 0.15 mm max @ top of guide | most incl. R100 | Worn guides → oil burn, unstable valves, seat wear. |
| Seat angles / widths | 45° / 15° / 75° · In 1.5, Ex 2.0 mm | .059 / .079" | All | Main / chamber / port. Seat OD 1000cc (non-/7): 45.175–45.200 mm. |
| Spec | Metric | Inch | Wear limit | Applies | Notes |
|---|---|---|---|---|---|
| Spring free length | ≈43.5 mm (blue/green) | 1.713" | All | Brown code ≈46.0. Test: 61–66 lb @ 37.6 mm · 154–160 lb @ 28.5 mm. | |
| Rocker end play — pre-'85 | Nil, but free | oil-film movement | incl. 1981 | Set with adjuster fully loose; rocker must rotate with zero binding. Most "noisy valves" = excess end play. '85+ shim type: 0.03–0.07 mm; retrofit kit 11-33-9-057-699. |