HOME and how to join Forum Open Area General Scott topics Wooden crankcase lining ! Re: Re: Wooden crankcase lining !

#13208
Richard Moss
Participant

It’s a long story actually.Too long maybe but I guess you’ll make your own minds up.
Following the design of the long-stroke crank on 1st April 1928, the drawing office realised that they needed to find a way of making sure that you didn’t lose the chunk of crankcase displaced by the rod when the crank let go. Although the crankcase deck was obviously designed to collect the aforementioned piece, occasionally the velocity (and vector) was such that it evaded this designed catchment platform. The timber insert, designed for this application, obviously had to be hard enough to resist complete destruction, whilst not so hard that it caused the dreaded ricochet. African Mahogany was chosen because it had been thought to exhibit the appropriate properties as established using the standard ‘Janka’ test.
The Janka hardness test measures the resistance of a sample of wood to denting and wear. It measures the force required to embed an 11.28mm (.444 in) steel ball into wood to half the ball’s diameter. Although this measurement can be stated in kN or lbf, the normal method is to use the ‘Janka number’.
It was rumored that Harry Shackleton himself spend months testing to find the correct grade for this purpose, eventually settling for the African Mahogany which as you may know has a Janka number of 830. It was so close but a costly mistake. The insert was fractionally too hard and the rider of the test machine, a single downtube frame model with biscuit tin tanks, never sang baritone again.
The drawing office knew they were close to an answer; firstly they decided that they must make sure that they never used biscuit tin tanks again and secondly they must stop at nothing to find the correct hardness of wood.
I won’t go into details, as the travels of Edward Arthur Wickes, the junior draftsman charged with this work, are well documented. His foray into the dark heart of the Congo was reckless but he was convinced that this was where he would find the tree that would bring him recognition back in Saltaire. He was lost for years in that place, losing the heart of Edith who worked in accounts but gaining the experience of the forest, the timber within it and the ingenious construction methods of the people native to that place. All that sustained him throughout that desperate time was the faint hope he held onto that one day he would be able to return to the country of his birth and start his life again with a small chain of builders merchants.
Fortunately for the drawing office, three days after Edward had left on his trip, someone had accidentally dropped a 0.444″ steel ball onto the cafeteria’s doorstop and had realised that it was a perfect indentation. Yes it was mahogany, but Honduran mahogany with a Janka number of 800. Those 30 Jankas were everything and all tests were subsequently performed with repeated perfect capture of the crankcase chunks.
Why don’t you see them any more? It’s very simple. Honduran mahogany was susceptible to common woodworm and all such examples of this fine piece of developmental engineering crumbled away.
Strangely, the original African mahogany prototype was not susceptible but was thought lost after the closure of the factory and the only thing I can think is that this long lost and unique piece of Scott history has somehow found its way to you, Brian.
Life is indeed stranger than fiction.
Let us know how the test ride goes.