I guess i am am saying that in the good old days, the guy that could do the sums to design something that worked as it should was "an engineer"
over the years the technician/mechanic/ fitter that could manufacture/assemble these bits (often using a degree of feel and common sense) has become known as an engineer
now any Tom, Dick or Harry that can only swap entire units proudly call themselves engineers.
I have seen some fantastic developments made that would not have been possible without CAD, but i have also seen some tremendous cock ups that have been corrected by the old boys on the bench..
The real point is they should not come loose if all working parameters are evaluated properly when the parts were toleranced. Al-alloy has about twice the linear coefficient of thermal expansion as steel/iron, so some correctly applied math should give ideal fits for a proposed working temperature range.
As for brakes on a trials bike, well I doubt they would be even significantly warm in the average section.
Hell of a tangent this threads become!
Happy New year all!
Wayne....
At the risk of a complete thread hijack, i think this shows how the term "engineer" has been cheapened in this country. In Germany, for instance, you need to be qualified to at least degree standard before before being accepted as an engineer.
As for shrink fitting components together that have different co-efficients of thermal expansion, as Wayne says "an engineer" would consider the temperature rise in each component, calculate the likely expansion based on its size and cross-section. The cold interference required would then be determined. The engineer would then calculate the realease temperature, ie the temperature at which the interference is lost and then build in a safety factor.
In the good old days this would have been done with a slide rule, and a rule of thumb would have been devised (such as 2 thou interference for every inch of diameter.. or similar)
These days, the parts are designed on computer and then modelled to see what will happen in service. As a result parts are trimmed down to reduce costs and improve efficiency.. hence single cylinder engines happily running to 14,000 rpm and more, producing in excess of 150 hp/litre
as my other half had to work, I took the opportunity to repair my fibreglass tank in the kitchen on boxing day. Despite the best efforts of a 12" extractor fan, the heady cocktail of polyester resin, petrol and cellulose paint aromas ensured a good bollocking and a spell in the dog house..
Still ...hopefully my crotch will be petrol free on new years day...........
quite agree, the heat rise on a trials bike will not cause significant expansion,
However, being further away from the heat source ,exposed to the air and a good conductor, the aluminium hub will be cooler than the steel liner so the differential expansion will have little impact if the correct fit was used to start with.
One other little hint on the new Alloy replica Cub/Bantam hubs is, be carefull which way you fit them because the good ones are designed to be fitted only on the side you spec , and some of the copies of these the braking surface comes away from the alloy hub, because there design is not quite right..
Regards Charlie.
uhhhhhmmm
i can only imagine that you are referring to hubs with threaded braking surface inserts ???
even then wouldn't there be a risk of the insert un-screwing as you roll backwards down the hill with the brake on.
aren't the more expensive hubs metal sprayed so you can fit them either way (i note they use a circlip as a bearing retainer for the same reason, when you fit a cub hub backwards there is a possiblity of unscrewing the lefthanded bearing retaining ring.)
as a side note... i understand that apart from a better cable run, the brake plate is orientated so that the leading edge of the shoe acts on the weight bearing side of the drum for a more positive action..
Well, I don't know about your local rules .....but having ridden a Bantam for a full season let me say this: It would not be my 1st, 2nd or 3rd choice of bikes to ride in any class.
Reasons:
Seriously underpowered
Tough to make a 1st kick starter(requires electronic ignition, which is illegal).
Pogo Stick front forks
Very limited ground clearence
Won't fit "real" Trials tire without illegal modification (need a Cub or C15 rear rim and swing arm).
Requires modifications to the foot pegs (which then requires different brake and shift levers)
I won't boor you with the other 30 items required.
Alan
wow, the rules are no where near as strict here, without opening the old can of worms again (later engines, fiddle forks, frame and wheel mods, electronic ignition.. etc..), the "relaxed rules" means that there are sufficient entries to keep the thing going.
To keep the events commercially viable, unit bikes are allowed to ride non competitively in pre-unit trials and those that have pushed the envelope too far are put in the "specials" class .
There is always going to be several factions, the trophy hunters spending big bucks to gain any competitive advantage, "the clubmen" having a go on a limited budget, and the old boys still plugging away.
The trick is to make sure everyone is having fun and turning out regularly, I fear strict enforcement of the "pre 65" rule would probably kill the class.
Deep down every one knows how much every one else is bending the rules by.. and those with the more legitimate bikes take great pleasure in beating the fiddle bikes.
I for one enjoy a sunday run around on a relatively cheap bike, usually finishing mid-order without damage to bike or rider.. long may it continue..........
Yorkshire classics allow 2 strokes up to 1970, so 4 speed bantams are allowed...... although the latest crop seem closer to beta's rather than anything BSA manufactured.
thanks for your input , much appreciated .... and very good advise .
i do not think it would be a problem to ream out the yokes to take larger diameter fork legs , the problem is the absence of pinch bolts on the top yoke ?
if there is a way round this i do not know .
You are not going to be able to hand ream the yokes out and keep the hole round!, it needs to be machined.
The best way to avoid the need pinch bolts on the top yoke is to machine the taper out but leave a 2mm step on the top side of the yoke. You can then used the fork top nut to pull the fork stantion against the step.........simples..
the "old" serco used to recommend the R cam, low compression but usually in conjunction with a 230 (big bore) or 250 (big bore and longer stroke) conversion. Strangely enough the local club changed the rules to allow "other the british manufactured carburettors " on cubs to try to over come this problem.
Adams was the original Serco owner, As an engineer and trials rider he developed the "trick" trials bits. He emigrated to Austrailia a couple of years ago and sold the Serco business and the house that the business operated from to Ian Roberts.
Could it be that Martin Adams sub-contracted some of his stuff... and perhaps some of these contractors are now finding other outlets for their wares ???
Compared to parallel yolkes, The offset on the cub yolkes reduces the trail (much in the same way as leading axle fork on all modern bikes), parallel yokes will increase the trail and make it want to go in a straight line. to reduce your trail you need to steepen the head angle on the frame.
Now Roger are you sure that your Tigercub sub frame is not part of the missing gold from the Great Train robbery, Cos if it melted it ent from the Triumph factory, unless they were in on the job?
Regards Charlie.
that might explain why they are so heavy.............
Put the top nuts on with the legs fully extended..
What i am saying is that you can use the oil level to fine tune the spring rate of the fork assembly.
Not knowing the forks you are using, i imagine that you will need say 150 ml of oil to get the damping mechanism working, adding more oil will make the spring rate stiffer and therefore reduce sag.
Ignoring the fork springs, If for example you have say 6 inches of air gap with the forks fully extended, compressing the forks by 3 inch would compress the air gap by 50% and double the pressure and therefore force inside the forks.
If you then added more oil to reduce the air gap to four inches, compressing the forks by the same 3 inch would compress the air gap by 75% and triple the pressure and force inside the forks.
This is why some forks have schrader valves built in, to enable the spring rate to be fine tuned by adding air.
For most trials applications a long slow spring rate is preferred, for instance MP forks are vented to prevent the air acting as a spring.
I would reduce the level by say 5 ml at a time until it stops topping out.
One thing I have noticed is the yokes on tlr have smaller offset fork centres to head stock centre line - 15mm approx. 4rt has 35mm offset.Tis pushes forks further away from centre line of steering axis - what effects does this have?? All part of camber, caster and rake etc but don't know the theory
the bigger the offset reduces the trail and makes it easier to steer and more difficult to keep it going straight.
Offset used to be acheived by having a leading axle, this has the advantage that it reduces the inertia caused by offsetting the weight of the forks and wheel.
i guess with modern forks being lighter this is less critical, and sharper head angles means that both fork offset and leading axles are required to reduce the trial.
assuming your current lever pivot is in the foorest mounting plate, drill and bush a corresponding hole in the RH plate, drill out pivot and fit bush in LH plate, fit shaft thro holes in plates, new brake lever mounted on RH end of shaft,
then either new lever arm or existing lever on LH end of shaft (how trick would that be to have a lever on both sides?)
Seriously though you need to find out the towbar weight rating for the Corsa as a bike on the back might be too big.
according to the local traffic cop, towbar rating is a manufacturers recommendation not a legal limit, the only thing the cops will be intererested in is axle weights and that the "load" is secure.
On a practicle note, although i am well within any weight limits, and the car (an A6) looks OK when loaded, there is a definate loss of grip from the front wheels and corners can get interesting in the wet.. watch out in your corsa..
i think you will find that the triumph frame bearing housing is a totally non-standard imperial size.
your options are to fit adapotors into the frame to accept a metric bearing. The bearings will be further apart so you will need a longer spindle than the original triumph one and you need to watch the ride height as the top yoke will be higher than before.
alternatively you could weld the fantic headstock to the triumph frame, losing a couple of degress rake at the same time.
Bok228c Is Lost.
in Pre-65 Bikes
Posted
Hi Charlie,
I guess i am am saying that in the good old days, the guy that could do the sums to design something that worked as it should was "an engineer"
over the years the technician/mechanic/ fitter that could manufacture/assemble these bits (often using a degree of feel and common sense) has become known as an engineer
now any Tom, Dick or Harry that can only swap entire units proudly call themselves engineers.
I have seen some fantastic developments made that would not have been possible without CAD, but i have also seen some tremendous cock ups that have been corrected by the old boys on the bench..
sometimes , you can't bet human experience.......