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

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

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

Very informative video! https://fb.watch/gQycYmmz_h/    

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.

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

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

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.                  

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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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:  

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

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.

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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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)      

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

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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  Click this link: http://www.benchmarkworks.com/articles/tech/hardstart.html   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 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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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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By MS Motor Service (Kolbenschmidt) Click here to open as PDF: KS Installation of piston rings

Source: Wikipedia https://www.batterystuff.com/kb/ 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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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  

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)

Guidelines for correct installation of (Bosch) spark plugs  

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