Design of the crankshaft and, in particular, the calculations for crankshaft balance, requires the weights of various reciprocating and rotating components. Part of the input to these calculations is the weight of the connecting rod small ends but before these could be measured some work was needed to make them fit the pistons. Apart from the smallend diameters being different the connecting rod was too wide to even fit between the smallend bosses of the piston, illustrated below.
As can be seen, the connecting rod smallend width is 0 .027” wider than the available space.
The connecting rods were reduced in width to 0.896” by
removing equal amounts of metal from both sides to give a total clearance of
0.14”. The smallend bushes were pressed out before machining.
New phosphorbronze smallend bushes were made to replace the HD bushes and to fit the Ducati piston gudgeon pin – the new ones and originals shown below
These were then pressed into the HD connecting rod smallends and which now fitted properly to the pistons.
Weighing could now begin….
Weights are required for the piston(s) (which are identical), the crankpin and both small and bigends of both connecting rods. A couple of pictures below illustrate this.
The question arises as to how accurate are the scales? I don’t have any precise weights to calibrate them and so I machined a short length of EN24T round bar as a test piece and measured the weight of that. The weight (more strictly, the mass) can also be calculated from the product of the volume and the density, which is quoted as 7.84 g/cm^{3}. It turned out that the 2 values of mass – ie that measured on the scales and the calculated value, were identical. It could, of course, be possible that both are wrong and have compensated exactly to give the correct result but that is highly unlikely.
After making a number of repeat measurements, the following table gives a summary of the results. All masses are in grams (g)

“Knife” Rod + Bearing BigEng SmallEnd 

“Fork” Rod + Bearing BigEnd SmallEnd 


396.6 
205 

557.8 
213 
TOTAL 
601.6 

770 

Additionally, the connecting rods + bearings were weighed individually and the masses compared. These were: “Knife” Rod + Bearing = 603 g; “Fork” Rod + Bearing = 758 g. The correcting differences (+ and ) were distributed in the ratio 0.6 to bigend and 0.4 to smallend.
Other masses are:
BigEnd pin = 515.7 g
Nuts (both) = 97.6 g
Piston + rings + circlips = 373.2 g
All of the information was now available to start detailed design of the crankshaft.
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