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:  

Pistons aren’t round

An article that explains why pistons aren’t round. Click on piston to open it:

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

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.

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 3.00”    

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.

Leaking carburetor screw caps

When the screw caps on the underside of the carburetor keep leaking (after having installed new gasket rings), then the probable cause is the condition of the seat of the carburetor gasket. If you look closely, you will probably notice that the surface is rough, damaged or scratched. The solution is NOT to further tighten the screw cap: the gasket ring is not flexible enough to fill these small damages. The seats of the gasket rings can be machined, but if the damages are not too deep they can be removed by sanding the seat with a very fine grit
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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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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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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.

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 of piston rings (KS)

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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Bearing prefix & suffix codes

Some of the prefixes and suffixes found on bearings in the webshop: Prefixes: NJ = these bearings have two integral flanges on the outer ring and one on the inner ring. These bearings are used to locate the shaft axially in one direction. They can accommodate axial displacement of the shaft relative to the housing in one direction only. Example: NJ204 bearing on the rear side of the gearbox input shaft (R51/2 – R68) Suffixes: ECP = bearing with polyamide plastic cage M = brass cage MA = brass cage, outer ring centred C2 = bearing with internal clearance smaller than normal
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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