BMW R51 / R61 / R66 / R71 (plunger) — Example photo: Lothar Spurzem, CC BY-SA 2.0 de, Wikimedia Commons

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BMW · BMW pre-war / wartime flat twin (R32-R75, 1923-1945)

R51 / R61 / R66 / R71 (plunger)

Library entry covers 1938-1941

13 factory 57 guideline

Published source

Manual for the BMW Two-Cylinder Motor Cycles R51/R61/R66/R71 (English ed., lubrication chart p.25)

Factory owner's handbook. Covers 1938-1941.

70 items for a 1941 model, grouped by interval the way a factory chart is laid out.

How this bike is built (what the schedule is based on)

Engine cycle: Four-stroke
Engine lubrication: Wet sump (oil in crankcase)
Oil filtration: None (no filter)
Valve gear: Side valve (flathead)
Ignition: Magneto (incl. magdyno, flywheel magneto)
Charging: DC generator with regulator
Battery: Wet cell (flooded lead-acid, needs topping up)
Fuel system: Two or more carburetors
Cooling: Air / oil cooled
Primary drive: Gear or chain inside engine, shares engine oil
Gearbox oil: Separate gearbox oil
Clutch control: Hand lever, cable
Final drive: Shaft
Front suspension: Telescopic fork
Rear suspension: Plunger
Front brake: Drum (or band / stirrup)
Rear brake: Drum (or band / belt rim)
Wheels: Spoked, tubed
Sidecar: No sidecar

Maintenance schedule

1941 BMW R51 / R61 / R66 / R71 (plunger)

On the road: every 250 mi

1 item

Check engine oil level

Pre-ride / on the road

Factory

Factory: Push dipstick in, do not screw in

On the road: every 300 mi

2 items

Check lights, horn, brake light switches

Pre-ride / on the road

Guideline
Check tire pressures

Pre-ride / on the road

Guideline

On the road: every 500 mi

1 item

Walk-around: check nuts and bolts for vibration loosening

Pre-ride / on the road

Guideline

Old machines shake things loose: exhaust nuts, mudguard stays, footrests, tank mounts, battery strap.

On the road: every 1,000 mi

1 item

Check road kit: plugs, points file, master link, tube patches, wire, tape

Pre-ride / on the road

Guideline

Every 250 mi

1 item

Lubricate control cables and lever pivots

Controls and cables

Factory

Manual: Lubricate brake joints and clutch lever. Factory: Engine oil

Every 650 mi

2 items

Rear axle casing oil level

Engine

Factory
Check gearbox oil level

Primary and gearbox

Factory

Manual: Transmission oil level. Factory: To lower thread of filler hole

Every 1,000 mi or 1 month

1 item

Check battery electrolyte, top up with distilled water

Ignition and electrics

Guideline

Wet-cell batteries on old machines need regular topping up, more in hot weather.

Every 1,000 mi or 6 months

6 items

Inspect, clean and gap spark plugs

Engine

Guideline
Lubricate manual advance / retard control and cable

Ignition and electrics

Guideline
Adjust front drum brake

Brakes

Guideline
Adjust rear drum brake and rod / cable linkage

Brakes

Guideline
Check spoke tension and wheel true

Wheels and tires

Guideline
Inspect tire tread, sidewalls and date codes

Wheels and tires

Guideline

Every 1,000 mi or 12 months

1 item

Grease saddle pivot, check saddle springs / seat post

Rear suspension and frame

Guideline

Every 1,300 mi

3 items

Change engine oil

Engine

Factory

Manual: Drain engine oil, fill fresh.
Check footrests, pegs, rear brake and gear lever pivots

Rear suspension and frame

Factory

Manual: Grease gear change pedal.
Grease plunger rear suspension, check springs and bushes

Rear suspension and frame

Factory

Manual: Grease rear wheel spring suspension.

Every 1,500 mi or 6 months

1 item

Clean / inspect air filter

Fuel and air

Guideline

Mesh or oiled foam: clean and re-oil. Paper: blow out or replace. Some very early machines have no filter at all.

Every 1,500 mi or 12 months

2 items

Check and adjust valve clearances

Engine

Guideline
Adjust clutch free play, lubricate cable and lever pivot

Primary and gearbox

Guideline

Every 3,000 mi or 12 months

14 items

Check engine mounting bolts and plates

Engine

Guideline
Check throttle cable(s) free play and return

Fuel and air

Guideline
Clean fuel tap filter / sediment bowl

Fuel and air

Guideline
Synchronize carburetors

Fuel and air

Guideline
Check / set ignition timing

Ignition and electrics

Guideline
Check generator drive belt or chain

Ignition and electrics

Guideline
Clean and gap contact breaker points, oil cam felt

Ignition and electrics

Guideline
Oil / check generator bearings (where an oiler is fitted)

Ignition and electrics

Guideline
Adjust clutch pushrod / clutch adjuster

Primary and gearbox

Guideline
Check steering damper (friction or hydraulic)

Front end

Guideline
Check steering head bearing adjustment

Front end

Guideline
Inspect fork seals, stanchions and fork boots

Front end

Guideline
Grease and check center / side stand and springs

Rear suspension and frame

Guideline
Check wheel bearings for play

Wheels and tires

Guideline

Every 3,000 mi

1 item

Inspect generator brushes and commutator

Ignition and electrics

Factory

Every 4,000 mi or 12 months

2 items

Replace spark plugs

Engine

Guideline
Lubricate brake cam spindles, check linings and drums

Brakes

Guideline

Every 5,000 mi or 2 years

1 item

Check cylinder head bolt torque

Engine

Guideline

Air-cooled iron and alloy engines can lose head bolt tension; follow your manual's sequence and whether it is done hot or cold.

Every 6,000 mi or 12 months

4 items

Clean carburetor float bowl(s), check float level and jets

Fuel and air

Guideline

Ethanol fuel varnishes old carbs quickly in storage.
Check charging voltage and regulator / cut-out

Ignition and electrics

Guideline
Check final drive for leaks and bearing play

Final drive

Guideline
Lubricate speedometer / tachometer cables, check drive

Controls and cables

Guideline

A dry speedo cable whips the needle and eventually kills the instrument.

Every 6,000 mi or 2 years

4 items

Check engine breather and oil return

Engine

Guideline
Lubricate and check automatic advance unit

Ignition and electrics

Guideline
Magneto: clean slip ring and pickup brush, check HT lead

Ignition and electrics

Guideline
Repack / replace wheel bearings

Wheels and tires

Guideline

Cup-and-cone and taper roller hubs need periodic repacking and adjustment.

Every 8,000 mi or 3 years

1 item

Decarbonize head, grind / lap valves (top-end decoke)

Engine

Guideline

Period practice. Leaded-era valve seats may need hardened seats for unleaded fuel.

Every 10,000 mi or 2 years

1 item

Compression test (or leak-down)

Engine

Guideline

Every 10,000 mi or 3 years

1 item

Repack / replace steering head bearings

Front end

Guideline

Many old machines use loose balls in cups and cones. Taper roller conversions are common.

Every 10,000 mi

4 items

Universal joint: fill with grease gun (Mobil Grease No. 4)

Engine

Factory

Factory: Lubrication chart p.25 (ManualsLib viewer p.25, re-read from the page image): item 11, every 10,000 miles
Change gearbox oil

Primary and gearbox

Factory

Manual: Transmission drain and refill. Factory: Scan OCR is poor; figure read consistently but verify against scan
Change final drive (rear drive) oil

Final drive

Factory

Manual: Rear axle casing drain and refill. Factory: Scan OCR is poor; verify against scan
Grease front and rear wheel hubs (grease gun)

Wheels and tires

Factory

Factory: Scan OCR is poor; verify against scan

Every 12,000 mi or 3 years

1 item

Replace points and condenser

Ignition and electrics

Guideline

Every 15,000 mi or 5 years

1 item

Inspect clutch plates and springs

Primary and gearbox

Guideline

Every 15,000 mi

1 item

Replace brake linings / skim drums (wear based)

Brakes

Guideline

Every 20,000 mi or 4 years

1 item

Lubricate drive shaft splines / check U-joint

Final drive

Guideline

Every 25,000 mi or 10 years

1 item

Magneto overhaul / re-magnetize, replace capacitor

Ignition and electrics

Guideline

Weak spark when hot is the classic symptom. Old capacitors fail with age, not miles.

Every 30,000 mi or 6 years

1 item

Rebuild forks: seals, bushes, springs

Front end

Guideline

Every 6 months

1 item

Clean battery terminals, check charge and strap

Ignition and electrics

Guideline

Every 12 months

1 item

Check speedometer / odometer against a known distance

Controls and cables

Guideline

Old speedos drift with tire size and drive wear. Use phone GPS over a measured 10 miles / km.

Every 2 years

3 items

Inspect fuel tank for rust, sealer failure, leaks

Fuel and air

Guideline
Inspect wiring, bullet connectors and ground points

Ignition and electrics

Guideline
Inspect frame, welds and lugs for cracks

Rear suspension and frame

Guideline

Every 4 years

1 item

Replace fuel lines

Fuel and air

Guideline

Old rubber and modern ethanol fuel do not mix well.

Every 6 years

2 items

Replace inner tubes and rim tape with tires

Wheels and tires

Guideline
Replace tires on age (regardless of tread)

Wheels and tires

Guideline

No interval set

1 item

Change fork oil

Front end

Factory

Manual: Front wheel fork: fill in about 1/5 pint Arctic. Factory: Lubrication chart p.25 (ManualsLib viewer p.25, re-read from the page image): item 10, occasionally

Guideline lines: Intervals here are general guidelines for the machine's era and layout, compiled for this app. They are not factory manual figures. Check your workshop manual, and edit any interval in the bike's Schedule tab.

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Other 1941 BMW models

All 1941 BMW

1935-1942

R12 (side valve, telescopic)

Guideline

1941-1944

R75 (sidecar, driven wheel)

Guideline