In the last Yowl, I was delighted to see George Silk contributing, but the only item that caused me some pause for thought, was his belief that I made my cranks out of case hardening steel. Most of you have heard the story enough times, but I wondered about new owners who might take this as true.
I decided to set the matter straight and give Eddie a little fodder for Yowl. I could tell a simplified story telling the involvement of Brian Lilley and Clive Waye in the saga. Late in the evening, prancing away one fingered on the keyboard, I finished that section and then decided to write a bit on big ends.
At this point, a rather hazy notion came into my head concerning the distance the rolling surface of a roller must travel to complete the traverse of the inside circumference of the big end ring, compared with the distance the rolling surface of a roller must travel to complete the traverse of the crankpin bush. I made a complete dogs breakfast of it, sent it to Eddie and forgot it. When I decided to recheck it, it was too late to withdraw and edit it.
May I here confess that I am deeply ashamed. I have plenty of ashes, but have yet to find some genuine sackcloth. All the clever folks can look forward to a good laugh, but then, I never claimed to be perfect.
The best I can do is try and make the best of what I was given when I was born! Otherwise, things go on quite well here. I am entered for Mallory on April 5th and have entered 3 Sisters 8&9 May plus the Beezumph in Anglesey this year on 16/17 July Ted Parkin is bringing his newly built Scott solo racer to 3 Sisters (Near Wigan)
Ted Hills is drawing out the manifolds for the 4 cylinder Scott based Phased Transfer Engine of Rob Collet. The club wish to buy some blind head iron barrels and I am helping with this as I have patterns, in fact I have both blind and detchable types in stock in Alloy. More undertrays are in manufacture, I have just made some heads. Next a few Super head stems for stock and the cranks are still in manufacture with a few Tungsten slug balenced sets to be made for those who might want to go the extra mile. One new engine using Holder cases and block went to Ken Stevens in Aberdeen before Christmas and another is nearly finished for Mark Scott in Texas. A new Moss competition engine is on order for Reinhold Sprenger who uses his Scott in Vintage Races in Austria and finally a couple of engines where the metal has sunk in use, so that the cup main bearings become loose when the case is warm. It was a choice between new oversize cups but send out the cups for grinding in situ, or put a high tensile cup in with ball race mains and synthetic seals. I have done this before and so decided on this option. I said finally, but you know me, I never shut up. This is a really long shot, but you never know.
I have acquired a rather clever jig grinding attachment made by a company called Stokvis in Paris in about 1974. Unfortunately it was stored badly and has some corrosion so far, not in critical areas. I can not see how it comes apart and do not want to damage it. Agents were Automation Engineering of Handsworth Birmingham. If this rings a bell with anyone, I will be very appreciative. If I could get this sorted out, I may be able to regrind cups in situ myself to high accuracy, as doing them in situ is how Scotts did it and is the only safe way. At the moment, David Holder does them for me on a big Heald that Matt used when the Birmingham Scotts were made in Bromford Lane. OK I will stop now, I promise! Live Long and be happy! Roger
i wouldnt bother about it at least you put yout pound in keep it up
@Roger Moss wrote:
I have acquired a rather clever jig grinding attachment made by a company called Stokvis in Paris in about 1974.
I just knew there was some Dutch influence somewhere! Stokvis was a well known company in the 50’s and 60’s selling lots of mopeds over here!
I have plenty of ashes, but have yet to find some genuine sackcloth. All the clever folks can look forward to a good laugh, but then, I never claimed to be perfect.
That is if they have stopped laughing at me mixing up feet and inches from the last issue. I blame my (lack of) imperial education!
But, it shows the human side and I’m sure everyone appreciates the time authors spend writing for Yowl which is after all entirely volutary.
Looking forward to getting my Moss cranks soon, I’m just making some bearing bushes and readying a nice crankcase for them.
Main bore in case as produced was 2.625″ +/- 0.0005″
Standard cup OD was 2.630″ +/- 0.0005″
Shrink ring is 0.009″ less than groove inner surface (I can not remember original figure.
Due to cases being made from aluminium less capable that we are now used to, the metal collapses over time.
Example. I warmed up a case with cup and shrink ring in situ to a fairly normal operating temperature.
When the cups are ground, the 3 security screws usually have their heads ground flush with the edge face of the cup.
They grind this face, so that when the case is turned round, it is located in the cup bore and clamped back to this face, so as to grind the opposite cup.
I use a bit of brass bar and gently tapped the back of the cup by going through the bore of the opposite cup.
The cup moved slightly in relation to the heads of the screws.
I drill a hole in the shrink ring to break it and remove it.
I warmed the case slightly and the cup dropped out
I measured the cup. It was standard at 2.630″
I let the case cool and measured the cup bore that had originally been 2.625″ It was 2.6298″. The metal had collapsed 0.0048″
The shrink ring had impressed itself into the groove face.
There was no longer the interference to control the cup at working temperature.
Scotts use to remove cups when they reconditioned engines and fit oversize cups and undersize shrink rings.
They obviously had many early development problems with this steel / aluminium interface.
I confess that I did not discover the extent of this problem till recent times.
I had an engine from Italy to rebuild.
Ressurection more like
It would have been cheaper to build a new one.
The cups fell out and with them strips of brass shim someone had used to try and give some security as the hole had stretched so much.
So. If you are going to rebuild yourself, do warm the case up and tap the rear of the cups to be sure that at something approching operating temperature, the cups are still secure.
Otherwise, some remedial action is called for if you want a good engine
Very deceptive these “Simple” Scott engines!
All very true words and I just wish I had more time at the moment to dedicate to the cause.
On the engine with the loose cup, had it bashed the bore in the crankcase into an oval? It would seem that as soon as a small amount of clearance is available then the engine forces will quickly ensure the clearance grows rapidly. The worst example I’ve got is a two speeder that was so loose on one side it broke off the retaining ring lip in small parts due to the impacts. The hole was over 20 thou larger than the cup in the vertical, and around 10 horizontally.
I’m building up two at the moment actually, one for the Moss cranks and one for the Silk ones. I’ll be installing new cups in both so I’ll make them to size. I took the old cups out to vapour blast the cases.
I have to admit I had to read that passage in the Yowl twice; ‘did he just say what I thought he did?!’ I was going to write a response, but figure, naw, it just had to be an oversight. But if you have not already done so, you should send in a clarification identifying (most important) and correcting (less important) the wrong bit, as there probably are a lot of folk that do not know any different and are going to accept the whole as gospel based on your excellent reputation with Scotts. To err is human, but to ‘fess-up is manly (an point fingers is politic!) You have sort of hinted about it here, but for those reading this that are wondering what bit is the fuss about, specifically it has to do with the rollers needing to skid to equalize the difference in circumference between the inner and outer race of the big end. At first this may seem like an profound anomaly, but in reality the rollers can maintain contact without sliding by the effect called precession. The difference between the distance traveled by the roller, rolling against the outer race compared to the inner race is made up by the rollers advancing – or proceeding – around the crank pin. This can be easily be demonstrated to non-believers with a caged ball bearing (before seals hid the action.) Holding the outer race and rotating the inner the cage rotates with, but at about half the speed, as the inner. For those that still insist some small amount of skidding must be going on, silence them by give the analogy of a planetary gear train. The teeth do not allow any slippage. There is a lot of thought provoking ideas in what you contribute, so I would hate to see the less technical folk left to wonder what was the wheat and what was the chaff. Though they do say a little bran is good for the diet!
Of course rollers can skid under certain circumstances. Snapping the throttle open in neutral or ‘blipping’ was always said to be unkind to the rollers.
I do have some other thoughts to toss into the fray on the subject of eccentric crank oil grooves, but there is another post specifically on that subject so I will place them there for debate. I would be interested to see if anyone thinks they have any merit.
Douglas Kephart is quite correct about the precession factor, I once had a 3rd year Bsc. student doing his mandatory ½ course unit practical by attempting to create a reduction gear using just that property of a rolling element bearing.
The sad thing was that he tried it with a deep groove ball bearing. “Every time I put any load on it just stops.” He wailed. “What did you do about the clearance?” said I. “What’s clearance?” was his puzzled reply. This from a 3rd year engineering student! There is just no help for some people!!!
I read somewhere that polaris submarines use this property for main engine reduction gearing, it seems it is much quieter than normal gearing. Unlike the above-mentioned student they apply what must be a significant axial thrust to the assembly so that it can transmit that amount of power. Must be an awesome bit of kit and I’d love to know what they use as a lubricant.
Must be an awesome bit of kit and I’d love to know what they use as a lubricant.
Probably something high-tech like Sperm whale oil! 🙂
No matter, being military they probably just replaced the gearbox every two hundred service hours!
Nah! 200 hours? They’d be back in port every eight days, hardly worth going out at all but at least the pink gins wouldn’t get spilt. 😯
They probably use Roger’s ‘fancy-dan’ crankshaft steel — maybe it’s him wot makes ’em!
Which raises two more vital questions:-
(a) does Roger glow in the dark and
(b) is his larder full of tins of spinach?
Where is the News of the World when you need ‘em? The Scotting public have a right to know!!!! 8) 😆 😈
does Roger glow in the dark
I believe this only happens if he drinks castrol R too close to bed time… 😆