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ALL DIMENSIONS IN mm

ALL DIMENSIONS IN mm

Fig. 87 In this intermediate stage, all dimmensions have been converted to metric but to three places of decimals.

increase Dt, as a little, as we decreased D.) This brings the reference dimension, originally 44.45mm, to 45mm. Again, a convenient round figure. Turn to the crankshaft. The outer faces of the two webs determine the shaft location, D3. Make this 64mm for trial. Then, if the crankpins are made 16mm wide (the big end bearing can be machined to suit) and the webs made 5mm thick the centre distance of the two crankpins works out at 38mm, exactly as required for the cylinder bores. It only remains to adjust the length of the location boss on the right-hand end plate to match up (D2) and this works out at 13mm. To summarise, we find D at 38, Dr at 26, D2 at 13, D3at 64, and crankpin width at 16mm. The only remaining dimension of this group is D5, the boss on the left-hand end cover. This has been set at 28mm (not 27) to allow the overall length of the block to be rounded to 112mm. Some adjustment will be needed at erection in any case, to allow for setting the meshing of the bevel gears.

Apart from details of rule dimensions the only remaining items to be settled are, first, the crankpin diameter and secondly, the dimensions marked E and F. The crankpins can be either 10mm or 11mm, both standard reamer sizes. If 10mm, the stress will go up by about 9% - well within the safe limit for drop-forged steel - and I would use that figure, if only to avoid yet another reamer size. However, those who have an eye to increasing bearing life would certainly plump for 11mm dia here. The lengths of the various steps in the shaft are not at all critical, and would be simply rounded from the exact figures.

Now for E and F. The figure at E can

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