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[ooyah/2]

hi George,


Your memory serves you right, the Borderer pistons are 5/16" and that of the Marcher are 1/4". My trial will hopefully demonstrate the feasibility of fitting an "O" ring.


With respect to the crankshaft; My first thought was to mount two discs, say 5/8" long the necessary distance apart to accommodate the main centre bearing and then machine the crank pins utilising two additional discs at either end having centres that match the crank pin centres. The aim was to reduce amount of machining. That was the plan, until I noticed the throw of 7/16" means that 1/4" crank pins overlap the main journals of 1/4" which prevents such an approach. So before I follow your method I am going to have a go at machine one from solid. I will post the results, if successful.


In the meantime, The photos that I have posted show a shaft for a Stuart Compound Twin that I machined from the 'lump' of material Stuarts provide in their kit.


Photo 1 shows what they provide. When it dawned on me the purpose of the two pieces at either end was to drill centres in order mount the shaft between centres the machining operation proved to be relatively straight forward, if not a little slow. The other photos show the progression to the final finished shaft.


Ian

Hi Ian,


Looking at the way and the finish of the Stuart forging that you have done, it should be a breeze to do the shaft on the Marcher.


Could you mark off the centres on a piece of 3/4" dia EN1A free cutting steel as shown on the drawing and machine between centres.


I have never been successful in machining these forgings, aptly described as "LUMPS" of material, hence I always fabricate them, plus I just don't have the skill to machine them between centres.


Thanks for the reply and the pics and keep us posted on the "O" rings on the piston valves, the Marcher is a fine little engine.
Do you have all of the castings as I have some spare castings for the valve holders, let me know and you can have them.


George

[IanJ]

Hi George,


Thank you for the confidence as to my skills! Forums Like this only work if people participate. So, I am planning to post a build log showing the machining of the crankshaft from a solid bar. As I have A piece of EN1A that is 3/4 dia., it can form basis of the Marcher prior to purchasing any casings etc. Thank you for your kind offer of the spare castings.


My plan is to face and centre drill either end of the bar. Set up the bar on 'V' block and mark out the off-sets with a surface gauge. Drill a further two centres at either and then mount the bar between centre in the lathe. The intension would be first to reduce the main shaft to somewhere near 1/4" leaving a disc at either end that continues to embrace the off-set centres. The next stage would be to turn the crank pins between their respective centres. Then finally taking every thing to finished sizes before reducing the discs at either end to 1/4" That's the plan anyway.


As we are now away on holiday it going to be a little while before I will be able to post any details.


Ian