Bottom End

You will open the bottom end perhaps once in your ownership, and when you do, everything depends on numbers you cannot judge by feel. Bearing clearance, end float, rod side play — these are dial-indicator and micrometer territory, and the difference between right and wrong is measured in hundredths of a millimetre.

Two figures here earn special attention. Crankshaft end float is the quiet cause of a dozen symptoms owners misdiagnose for years: the grabby clutch, the awkward shift when hot, the idle that changes when you pull the lever. And on 1981-and-later engines, main bearings became a selective colour-coded fit — a genuine trap for anyone working from an older manual.

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

Crankshaft

Spec	Metric	Inch	Wear limit	Applies	Notes
Crank end float	0.08–0.15 mm	.0032–.0059"		All	Set by coloured thrust washers. Grabby clutch, hard shifting, idle change w/ clutch pull when hot = re-shim. Differs oily vs dry.
Thrust washers r/b/g/y	2.483 → 2.673 mm range	.0978–.1052"	−0.20 mm worn	All	red 2.483–2.530 · blue 2.530–2.578 · green 2.578–2.626 · yellow 2.626–2.673. Rear spacer swap ≫ easier than front washer.
Main bearing clearance	0.035–0.065 mm	.0014–.0025"		thru '80	'81+: selective colour fit — red 0.017–0.066, blue 0.019–0.067 mm. Match codes per factory manual.
Regrinds / runout	−0.25/−0.50/−0.75 mm	runout .0008" front journal		All	Flywheel lateral runout max 0.10 mm.

Film · in the book

Rear main seal and flywheel.
The back of the case on the stand, seal in, then the flywheel goes onto the crank flange. The flywheel-bolt torque is in the Torque chapter; look it up every time. Silent, 0:27. Watch it in the book →

Connecting Rods

Spec	Metric	Inch	Wear limit	Applies	Notes
Crankpin OD	47.975–47.991 mm	1.8888–1.8894"		All	Regrind stages as crank.
Rod radial clearance	0.023–0.069 mm	.0009–.0027"		All	Beyond = shells / regrind.
Rod axial float	0.130–0.266 mm	.0051–.0105"	0.320 mm max	All	Weight match: 3 g max diff (/7).
Small-end bush ID	22.015–22.020 mm	.8667–.8669"	22.040 mm max	All	Pin clearance '81+: 0.015–0.024 mm. Pin code (W/S) stamped in crown thru '80.

Film · in the book

The oil pump, out and going back.
On the bench, the O-ring onto the cover, oil on everything before it goes back in. The cover-bolt torque is in the Torque chapter. Silent, 0:28. Watch it in the book →

Camshaft & Followers

Spec	Metric	Inch	Wear limit	Applies	Notes
Cam radial clearance F / R	0.020–0.046 / 0.020–0.054 mm	.0008–.0021"		All	End float 0.080–0.120 mm.
Lobe lift / rocker ratio	308° cam: 6.756 mm · ×1.39	284° cam (R45 20 kW): 6.198 mm		by camshaft · 3.82 / 5.82	BMW-RA382 Lift follows the camshaft, not the displacement — a 450 cc R45 26 kW lifts the same 6.756 mm as an R100, because it runs the same grind. This guide previously labelled the row “750cc+”, which the revision workbook flagged as the wrong divider (item M-04) and which could not be fixed without this source. Valve lift = lobe × 1.39. Timing datum 2.0 mm clearance ±2.5°. Chain: 3/8×7/32", 50 links, single-row from '79.
Follower clearance	0.010–0.051 mm	.0004–.0020"	0.075 mm service limit	All	Pushrod length 274.7–275.3 mm.

Bottom End

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