While sitting in my office in the evening and about ready to finish for the day, I thought I would share some thoughts and observations.
It is quite understandable that the technology of aluminium alloys had not progressed far in the early 1900’s when compared with cast iron. It is then no surprise to find aluminium cases that are rather soft and porous. It is interesting to give cases a tap with a small steel bar and compare the sound made. Some are heavy and give a dead sound, whilst others ring like a bell. In the last couple of days I attended to a case which had all the appearance of having been left in a pond for a few years. The cranks and rods were horribly corroded, as were the cups. The case had been protected by a thick layer of thickened oil mixed with road grime. In truth, I was not grateful to receive components in this condition, but I suppose if the customer wants to pay my full engineers hourly rate for time spent cleaning his case, that is his affair. Getting round to the case, it was an LFY case and both the pattern details and the quality of the aluminium was excellent. I had to remove the shrink rings and cups and was surprised to find there were already two drill dimples in the shrink ring groove. This indicated that this case was now going to be on its fourth set of cups. Given how long lasting the Scott main bearing system is, I have to wonder why this should be. I need to check the truth of the tapers in the flywheel, as it may be that these are deformed and so that the problem might be ripped gland faces in previous cups.
I have an alternative end float control design that gets round this problem if this is the case. I knew that as the case had been re cupped a few times already, I should only take out a minimum amount in skimming the main bearing bores for the cups. It is quite a pleasure to work a good machine, especially when the metal you are cutting cuts well. The case was set up on my Kearns S Type horizontal Toolroom Boring and Facing machine and the metal cut like silk. I had first worked one of these versatile machines when I was 17, back in the last century and have a great affection for such a noble machine. One nice feature is the ability that once you have re qualified the main bore, you can use the facing head facility to face up both end cup flange abutment faces at the same setting with the absolute security that they are square to the main bore. The shrink ring grooves are also skimmed to ensure a good undamaged surface for the new shrink ring. Measure the new bore, grind the outside of a new cup to the bore size plus 0.005″ and clean up the underside of the lip of the cup, so it lies exactly in axis to the bore when installed. A good deal of heating, install the cups with alignment correct for the oil feed position. Make shrink rings size minus 0.009″ inside diameter. Put then in our old Rayburn kitchen stove till red hot and drop them in. Tomorrow retap some anti rotation holes M3.5 and fit safety screws. Then it only needs a final grind to the main bearing cup bores, as due to the need to fit them with interference and with the shrink ring, then the semi finish ground main bearing surface will no longer be round and acceptable for use. The owner just wants a bottom end as the bike is apparently in good original condition. This will need cranks and rods. As regards cranks, then where, as is most usual, an owner decides to have new high strength cranks fitted in a rebuild, I ask if he has no further use for the original cranks, can I retain then in case this helps another owner who is not so financially fortunate.
This is such a case and I am able to supply such a set of cranks at no charge. This is both fair and prudent, as if I were to charge for second hand cranks, then I would be liable for restitution of any damage caused if a crank failed and the rod went through the case. If anyone has any second hand cranks that can help another owner, I would be please to know. If a person wishes payment for them, then if you tell me what you have and how much you want, I can refer an owner in need directly to purchase from you so I will not be involved in any liability under fitness for purpose legislation.
I ask myself why I am writing this, as maybe it is of absolutely no interest to the majority of owners, but then I suppose it is my way of keeping in touch.
I am intending to continue with an amended form of the old newsletter. It had been intended as a Q&A form of dialogue, but ended up as a monologue and so lost much of its reason for existing. If anyone has any thoughts or suggestions then all input will be gratefully received. Kindest Regards to all Roger
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