Simplified diagram of the wiring of the battery charging system R24 – R26

Wiring diagram for the system with an electronic voltage regulator P/N 12321354758H

Capacitor testing

The correct functioning of a capacitor can be measured with (for example) a FLUKE multimeter. The value specified by the manufacturer is 0.22 μF (microfarad). Over time, a capacitor’s performance can be expected to decline. The left photo shows a broken capacitor: the measured value is 0.131 nF (nanofarad) = 0.000131 μF The right photo shows a properly functioning capacitor: the measured value is 0.249 μF. This is 13% higher than the specified value, but this does not affect proper operation. The value specified by the manufacturer is a chosen ideal value for the expected average engine rpm. This value is therefore
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Bearing radial play specifications

The table below shows the radial clearance specifications for all bearings used on the R24 – R69S models

Pistons aren’t round

It’s a wide spread misconception that pistons must be round / cylindrical. The opposite is true, This is a new Kolbenschmidt R27 piston 68.50 mm:               From the Internet: Profile: If you roll a piston across a flat surface, you’ll notice it doesn’t roll in a straight line. This characteristic is called profile. Aluminum conducts heat significantly, so pistons are designed with a taper. The top of the piston (near the crown) has a smaller diameter than the bottom (near the skirt). The skirt itself is shaped like a barrel. This taper allows the
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List of bearings in the 1 & 2 cylinder engine, gearbox and final drive

  Click thumbnail to open the list. R24 – R27           R51/3 – R68           R50 – R69S            

Bearing cover R51/3 – R67/2, R50, R60

The front main crankshaft bearing is enclosed in the bearing bushing (P/N 11 11 0 002 156) by the front main bearing flange cover (P/N 11 11 0 002 176) and a spacer ring (P/N 11 21 0 016 244), to prevent axial movement of the crankshaft. If you notice that the 6207 bearing still has some movement in the bushing, it is usually caused by a worn main bearing flange: the edge of the flange has bent back over the years and therefore no longer has enough height (+- 4 mm) to enclose the bearing. With the correct pressing tool, the
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Gearbox problems: shafts do not turn smoothly after assembly.

This is specifically aimed at 1 cylinder and /2 gearboxes. If you’ve tried everything and you can’t figure why the gearbox shafts do not turn freely, you can use following very time consuming method  🙂 to determine the cause: Instead of putting all 3 shafts in at the same time, put in 1 shaft at the time. Remove the input shaft seal from the gearbox: the seal makes it harder to rotate the input shaft, making it difficult to assess whether the shaft is running freely. Remove the idler gear and kickstarter gear segment. Whenever you install (and remove) one
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BMW motorcycle wheel bearings, 1956 through 1969 by Duane Ausherman

Very informative and comprehensive treatise on the tapered wheel bearings. Click on the photo to go to the relevant webpage:    

Seal material property comparison

A “strenght & weakness” overview of the different seal materials available in the market.

Diagnosing clicking sounds as a worn carburetor slide – by Scottie’s Workshop

Very informative video!    

Oil slinger screw

The oil slinger screws are not available from BMW anymore. Most suppliers now offer a general purpose DIN 963 M6 x 10 screw. However, the head of this screw is higher than that of the original screw: the head of the screw protrudes above the oil slinger surface. This may be undesirable in some cases. We now supply oil slinger screws with the same dimensions as the original screw.

Hardy disk installation R26, R27

To ensure the longevity and optimal operation of the Hardy disk, the distance between the output shaft flange and the drive shaft flange must be set at 30 mm + 1.5 mm

Spherical and cylindrical rollers for connecting rods

The BMW specification for the radial clearance of the conrod big end & crankpin is based on the use of slightly spherical rollers in some of the crankshafts. The use of spherical rollers prevents the rollers from “biting” when the crankshaft flexes at high RPM. Today the new FAG Dürkopp conrod sets are equipped with cylindrical rollers. This requires a slightly larger radial clearance to prevent the rollers from getting stuck when the crankshaft flexes at high RPM. Spherical rollers (used) are identified by the wear track in the center of the roller:                
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Ignition keys

These photos show the difference between the Noris keys and the replica keys. This can help to identify the cause of malfunctioning ignition switch.      

Valve adjustment problems – cylinder head sleeve height

If the valve adjusting screws have reached their end and there is still insufficient valve clearance, the cause may be (a combination of): the valves sit too deep in the valve seats the cylinder head sleeves have sunk deeper into the cylinder head over time. In our experience, the sleeves at the exhaust side sit usually deeper than at the intake side. Below an example of 2 R27 cylinder heads. The RHS sleeve at the intake side of cylinder head 1 has a height of 88.47 mm The LHS sleeve at the exhaust side of cylinder head 2 has a
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Parts list – conversion from 6V to 12V for R51/3 – R68, R50 – R69S

This list shows the part numbers for all parts that need to be changed in case of a conversion to 12V  

Crown and pinion gear contact pattern

Staburag is a good alternative for “Prussian Blue” when determining the contact pattern between the crown and pinion gears. By adding a few lines, the contact pattern becomes even easier to read.                  

Flywheel R69

The R69 flywheel differs from the other / 2 flywheels because of the position of the ignition marks:

Smooth shifting R50 – R69S

A comparison of the required shifting force needed, between the old and new style shifting mechanism.                                                                                      

BMW /2 Swing arm leaks – final drive leaks by Scottie Sharp

Link to the original post: BMW /2 Swing arm leaks, final drive leaks During a routine oil change, it was noted that the drive shaft housing was empty.   Could it have been stolen by vagrants?   A guy works hard for his oil just to have vagrants come and steal it. Well, before contemplating a move to a safer neighborhood, BMW riders should remember that oil migration from the drive shaft housing to the rear drive is a common problem. There are three ways that oil can migrate from the driveshaft housing to the final drive and they
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Removing and reinstalling the drive shaft flange

The drive shaft flange has a press fit with the shaft. A workshop press is needed to press the flange off and onto the shaft. When removing the flange, standard press plates can be used to support the flange. However, to press the flange back on, the drive shaft collar must be supported. There are several ways to do this, but this tool works best for us. The tapered shape of the 2 halves and the ring ensures that the shaft is increasingly clamped during pressing. The edge of the hole between the 2 halves follows the radius of the
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Comparison R60 and R60/2 pistons

Piston for R60 with 130 mm conrod and R60/2 with 125 mm conrod  

Testing valve springs

Valve springs can lose a lot of their strength over the years, as seen with this R25/3 valve spring: a new spring measures 16.6 kg, the old spring 10.1 kg, almost 40% lower. Lower spring tension usually causes no or minor problems on low revving engines, but it can lead to loss of power / misfiring on higher revving engines as a result of valve float                 The test device:  

R50 – R69S Old and New style shifter mechanism

Comparison between the “old” and “new” version of the R50 – R69S shifter mechanism. Click following link for a comparison of the cam plates: Gearbox cam plate comparison

Fitting the correct distribution gear set

The number stamped in the crankcase (from -10 to +10) refers to the size of the crankshaft and camshaft gears installed by the BMW factory. After 60 – 70 years of service, the crankcase may have grown, which means that the original gear set may not be the optimal set anymore (0.01 to 0.02 mm play between the 2 gears). One way to determine the correct gear set number is to measure the c-t-c distance between the crankshaft and camshaft. This value must then be compared to the nominal c-t-c distance. This is impossible without very accurate measuring tools. The difference in
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Valve seat inserts (Dura-Bond)

Recommended press fitting for valve seat inserts in aluminum cylinder heads: OD insert 30 – 40 mm: 0.15 mm / 0.0059″ OD insert 40 – 50 mm: 0.18 mm / 0.0071″   Spindle speed for cutting a seat pocket in aluminum cylinder heads: 400 – 600 rpm It’s recommended NOT to freeze (f.i. with liquid nitrogen) the sintered valve seat inserts before installation. The valve seats are to be pressed in with a flat and square seat driver tool. The valve seat is inserted with the radius side down.   Source: DuraBond

Installing atomizer in Bing Carburetor

By Richard Sheckler, Wayne, Ohio A tool that can be used to accurately and squarely install and press fit the atomizer in place without damage. The replacement part has a different size knurling than the original, and therefore has sufficient resistance to remain in place for a long time.    

Side stands for EU and USA models

There is a clear length difference between the side stands for the R50 – R69S models and the R50US, R60US and R69US models (due to different configurations of the front fork) These are therefore not interchangeable.

Puller spindles and lubricants

All Matra tools with spindles such as M355, M499 / 1/2, M422a, M501 and M282 work much better (more smoothly) if a small amount of lubricant (eg Molykote G-n Metal Assembly Paste) is applied to the thread. This prevents galling of the thread under heavy load and reduces, to a certain extent, unwanted rotation of the other part of the tool.

1 and 2 pin Breather plates

If you are working on the overhaul of a 2 cylinder engine block with the old 1 or 2 pin breather plate, it is advisable to replace it with the later version with cast-in pins The pins of the early 1 or 2 pin breather plates are known for loosening or breaking off, causing damage to gear case cover. However, this means that the complete set of gears must be replaced (from 20° to 30° gears) The breather plate of the newer version is also available with larger slots, reducing pressure in the engine block during the downward movement of
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Rim width

The width of rims can be measured in 2 different ways: the inside or the outside. This means that one and the same rim can be indicated both in (for example) 2.15 “and 3.08″ WM2: inside 1.85″ (47 mm) outside 2.72″ (69 mm) WM3: inside 2.15″ (55 mm) outside 3.08” (78.2 mm)      

Timing gear numbers

For the correct set, check the number marked in the crankcase. The number is found near the upper engine mount, see following examples: In some cases, when the engine has had a long service life, it may need a different gear set number to get the required 0.02 mm clearance. However, this can only be determined through an accurate measurement.   The 30° gear set can be used to replace the 20° gear set on all 1950 to 1963 models. This requires following additional parts: › part nr. 11410052156 – oilpump gear 30° Only for crankshaft with 17 mm taper: › part nr. 11310016400 – 1.5
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Mono and Twin throttle assemblies

The R50 – R69S dual cable throttle assembly cannot be simply converted to a R26, R27 single cable throttle assembly by replacing the cam & chain and the cover. The depth of the recess in single cable cam and dual cable cams differs. The mono cam will not sit deep enough to engage with the throttle twist grip. Vice versa: the dual cable cam will not fit in the single throttle cable assembly: it’s too high.

Leaking carburetors

A frequently asked question is how to fix a leakage of the idle mixing screw. Further tightening the nut of the idle mix screw is certainly not the solution: holes have been drilled in the idle mix screw which connects the idle mix chamber to the the outside air. If fuel leaks out through the same bore, it simply means that the fuel level in the float bowl is too high. (assuming that the bike is on the center stand, if the motorcycle is placed on the side stand, there is a greater risk of leakage) If the carbs keep leaking, it’s
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Crankcase surface repair

By Michel Loos, The Netherlands The photos are self-explanatory. Steps:  filing  – sanding – pneumatic hammer – aluminum oxide blasting (Edelkorund) – glass bead blasting  

Instructions for Cylinder black (Einbrennlack)

Cylinder black with part nr. 09122 For temperatures up to 500 °C continuous use and up to 700 °C with impact load 200 ml is sufficient for 2 to 3 large cylinders. Ideal for spraying and painting engine cylinders, exhaust systems and other metal objects subject to high heat. Classic cylinder lacquer is initially thermoplastic; in other words although it is air-drying, it becomes sticky even with moderate heat, expands and hardens again when it cools down. This process is repeated as long as the polymerization temperature is not reached. The lacquer must be heated at least once to 150-180 °C to finally cure. After
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Solving hard-start problems by Craig Vechorik

  Click this link:   In addition: The resistance across the two spark plug leads on the ignition coil is usually 11 – 12 K Ohm (original coils and new “made in Germany” coils). Some after-market coils have a resistance up to 20 K Ohm. When the magnetic field of the rotor is still OK, this higher resistance will not necessarily cause a problem. A weak spark at the spark plug can have different causes: a broken or poor quality ignition coil is one of them. When the insulation (schellac) within the coil is damaged (crazing), the internal windings will short circuit,
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BING jets

BING jets are stamped with numbers, such as 35, 40 (idle jets) and 110, 115, 120 etc (main jets). One would expect that these numbers refer to the diameter of the jet bore, however this is not the case. This is confimed by the company BING in Germany. A few examples of main jets measured with a wire / jet gauge: BING 44-051 main jet 130 = gauge 120 (= 1.2 mm) main jet 125 = gauge 110 (= 1.1 mm) main jet 120 = gauge 105 (= 1.05 mm) main jet 110 = gauge 95 (=0.95 mm)            
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Carburetor flanges

The Bing carburetors used on the R51/3 to R69S models came with 3 different flanges. We sometimes get the question: can I put carburetor X on BMW model Y? In theory you can put an R51/3 carburetor on a R69 engine and even get the engine running, but you will quickly discover that the air pipes won’t fit. These images are self explanatory   Modified carburetors can be found in the market that fit the R68, R69 and R69S cylinder heads. However, there are some differences from the original models, most notably the carburetor flange:              
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Foot brake lever pin repair

By Richard Sheckler, Wayne, Ohio These pins wear out over the years for lack of lubrication, design and abrasives from the road working their way into the mating surfaces. Some early axis pins came equipped with a pre-drilled grease passage and a grease nipple. The procedure for repair can be replacement with a new pin available from Bench Mark Works or one of the outlets in Europe. For those who have access to a lathe and have the time and materials to make the repair and upgrade, please note the following: First step is to remove the axis pin from
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Cylinder heads R50 – R69S: butterheads and LK heads

Very informatieve article by Duane Ausherman on “butterheads” and LK heads:

Checking R27 oil pump

A simple tool to check the working of an R27 oil pump, without starting the engine by G.M. de Kok, The Netherlands Will also work on other mono BMW’s Silver steel rod 8 mm x 22 cm, diameter of square part = 7 mm

Transmission upgrade/rebuild to “S” gearbox ratios

This modification and upgrade, using BMW components, results in a lower-ratio gearing for R26, R27, R50 and R60 gearboxes producing smoother, robust and responsive performance especially in 1st, 2nd and 3rd gear changes while 4th gear is unchanged. The “S” gear ratios allow the rider to accelerate smoothly through gear changes by letting the motor rev freely through an optimum power-torque range. Although the 3rd gear of both gearboxes have the same number of teeth, they are different: The standard gear has a diameter of 65.6 mm and the S-type gear has a diameter of 65.2 mm. They have a
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Carburetor reconditioning

With hardly any new carburetors being produced by BING for the < 1969 BMW mono and twin motorcycles, it’s getting increasingly important to be able to repair and recondition the used original carburetors. Luckily, special parts and tools are available nowadays to restore the carburetors to a good working condition. A. Idle mix screw: very often, the M7 x 0.75 mm screw thread in the carburetor housing is worn out. There are 2 good solutions to this problem. 1. drill the threaded hole to 7.2 mm – cut M8 x 0.75 mm screw thread – install the idle mix screw with
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Installation voltage regulator (Kleiber)

electronic-voltage-regulator-bmw-r24-r26-eng electronic-valtage-regulator-bmw-r51-3-r69s-eng electronic-voltage-regulator-bmw-r27-r50-eng

Installation of piston rings (KS)

By MS Motor Service (Kolbenschmidt) Click here to open as PDF: KS Installation of piston rings


Source: Wikipedia The Lead Acid battery is made up of plates, lead, and lead oxide (various other elements are used to change density, hardness, porosity, etc.) with a 35% sulfuric acid and 65% water solution. This solution is called electrolyte, which causes a chemical reaction that produce electrons. When you test a battery with a hydrometer, you are measuring the amount of sulfuric acid in the electrolyte. If your reading is low, that means the chemistry that makes electrons is lacking. So where did the sulfur go? It is resting on the battery plates and when you recharge the
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Valves types and related components

Overview of the different valve types and related components, used in the BMW 1 and 2-cylinder motorcycles 1948 – 1969


Overview of carburetor nr’s and settings  

Reading spark plug faces (Bosch)

A visual inspection of the spark plugs can serve as a good indicator of the condition and tuning of the engine. This Bosch sheet may help to identify the possible cause in case of trouble. (click to enlarge)

Spark plug tech tips (Bosch)

Guidelines for correct installation of (Bosch) spark plugs  

Overhaul of a 2-cylinder crankshaft

The photos are a compilation of the work done on different crankshafts: R67/2, R60/2 and R69S.