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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.                  

Contributed by Matthias and Erich Lemmerer Click here for PDF file: Stromlaufplan R51 R67 R68 1951_52 V01_21  

Contributed by Matthias and Erich Lemmerer Click for PDF file: Stromlaufplan R51 R67 R68 1953_54 V01_21

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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For unknown reasons, the supplier of the after-market throttle assemblies for the R51/3 – R68 models (pn 32722072350), has decided the modify the design of the sliding block. The old sliding block used to have recesses to hold the cable ends, the new version does not. While in the new version the cables cannot “escape” either, the cable ends can rub against the inside of the throttle body causing unwanted wear. We therefore remove the new sliding block from the throttle assembly and add the correctly designed older sliding block. This however increases the price of the throttle assembly.  
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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:  

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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  4 versions of the saddle Y-frames are available: P/N 52 51 7 002 164:   R51/2 – R68      with 8 mm holes for saddle bearing bolt 52 51 7 002 125.7 P/N 52 51 7 002 165:   R51/3 – R68      with 10 mm holes for silent block 52 51 7 002 141 P/N 52 51 7 002 115:   R25/2                 with 8 mm holes for saddle bearing bolt 52 51 7 002 125.7 P/N 52 51 7 002 116:   R25/3 – R27      with 10 mm holes for silent block 52
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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

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.    

Some statistics based on last 5 years (2013 – 2018)      

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.