Bok228c Is Lost.

[b40rt]

Ross

Alloy will expand much faster than steel/iron.

With shrunk in liners it's about getting the fit correct. I must of relined over 100 Bultaco hubs throughout the 90's as far as I know none of the liners slipped or came loose and that was a thin insert (1.5mm Wall). The interference fit I used was severe though.

Wayne.....

Thanks Wayne

Never had any problems with my original cub hub which was on the "wrong" side. Mind you the brake was so bad excess heat was never an issue !

[charlie prescott]

Hi Guy's

Hi B40rt.

Cub /Bantam hubs were never round when they left the factory, and never matched to any shoes, But they do become a good brake as I have stated before. If you skim the braking surface of the hub and then centralise the pivots on the brake plate through the central spindle hole, then fit oversize brake shoes to the plate and skim this on the lathe until it is a good fit in the hub. A better brake arm with more serrations for adjustment also helps. Don't forget to widen the back hub an inch or so for better spoke adjustment, and also Bantam hubs are slightly wider than Cub hubs. PS, always fit double rubber sealed bearings now they are available, seems silly not too?

Regards Charlie

[wayne_weedon]

Cub /Bantam hubs were never round when they left the factory,

Possibly they were knocking em out so fast the raw castings were not aged properly? A local firm to me does disc brake rotors for the automotive industry, the castings sit outside in all weathers for years it seems.

Wayne....

[big john]

Possibly they were knocking em out so fast the raw castings were not aged properly? A local firm to me does disc brake rotors for the automotive industry, the castings sit outside in all weathers for years it seems.

Wayne....

I think that is like seasoning?

I have heard of this technique before

Big John

[wayne_weedon]

I think that is like seasoning?

I have heard of this technique before

Big John

Always been known to me as aging. Interesting was the BMW F1 engines in the 80's based on the 1500cc car engine, it was said they used blocks from cars that had already done high milages as the basis for each F1 engine. Said to be stronger and more stable than fresh blocks.

Metals can be artificially aged and stress relieved through heat treatments, but probably the slow natural process gives better results in some cases.

Wayne...

[jack_the_lad]

Hi

Thanks for the reply I must still be thick. I have been riding my bike with shrunk in liners for 18 months and they are still tight in the drum. If aluminium expands like you say, why does the liner in an aluminium barrel and valve seats in a head not come loose. With most replica hubs I would say it does not mater which way round you mount them.

Jack

[wayne_weedon]

Hi

Thanks for the reply I must still be thick. I have been riding my bike with shrunk in liners for 18 months and they are still tight in the drum. If aluminium expands like you say, why does the liner in an aluminium barrel and valve seats in a head not come loose. With most replica hubs I would say it does not mater which way round you mount them.

Jack

Jack

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 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....

Edited January 1, 2010 by wayne_weedon

[charlie prescott]

Hi Guy's

Happy New Year.

Talking of the Liners in alloy barrels not coming loose, Well the first BSA B25 barrels did not have a lip at the top and were very prone to slipping down into the crankcase. So they were soon changed to ones with a lip. Why BSA did not do this in the first place amazes me. I bet the ones used in the Comp shop always had lips fitted to the top? Pat!! But then these were made in the USA. and not in the cheapest foundry BSA group could source? Probably their own.

Ah the good old British Motorcycle Industry. They always built down to a price,and not up to a standard.

Regards Charlie.

[alan]

Jack

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

Edited January 1, 2010 by alan

[charlie prescott]

Hi Guy's

Hi Alan.

You Are right "An Engineer"!!! should be someone who is also a good mathematician, Know materials he is working with inside out ,have a vast amount of common sense, and the ability to put into practice the task in hand, and the most important ability is to be a perfectionist, and only turn out the very best item that you can create.

So I fail in some of these counts, but do my best. But I have a guy at my shoulder who has all of these abilities, so am very lucky.

I also have a son who is quite talented (so he says) at doing all the CAD modelling ETC, and has a program that can show all the weak points,etc on a model , to the forces of destruction, material thickness etc, so it would be foolish not to use this facility as well don't you think? Sixty odd years, of progress, I know!!!

Long live British Engineers. OLD and New.

Regards Charlie.

[pat slinn]

Wellsaid Charlie, happy new year.

Pat.

[alan]

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.......

[charlie prescott]

Hi Guy's.

Just a Update, on progress,with the project.

Well the Bottom end of the motor now seems fine.But with all this talk this week about casting alloy,shrinkage, ETC. I am sat here with the TR 25 barrel and a 1/4 inch spacer, thinking shall I proceed to cut the fins round and fit this,or go another route. Then I looked at the Triumph piston, 69mm, and checked the bottom of the liner, It is going to be too thin if I bore it out,I thought I will need another liner. Well I have found just the one on the Westwood site, and have used them before.

So do I now go the whole hog and either hand make, a wooden casting pattern. or go the fast CAD prototyping route for a alloy barrel, or use the TR25, and make half a job of it?

Well you know what I have said earlier about an "Engineer". So it looks like I have got to create a new one. And have checked the web and cant find a BSA C15 alloy barrel. So looks like the woodworking tools are coming out this week. PS,I think I will incorporate the pushrod tunnel into the design like the B44.

Regards Charlie.

[alan]

hey up charlie

why not go the whole hog.. rather than fitting a steel liner, why not have the alumuminium bore nikasil coated ?

Nikasil is a trademarked electrodeposited lipophilic nickel matrix silicon carbide coating for engine components, mainly piston engine cylinder liners. It was introduced by Mahle in 1967, initially developed to allow rotary engine apex seals (NSU Ro80 and C111) to work directly against the aluminum housing. This coating allowed aluminum cylinders and pistons to work directly against each other with low wear and friction. Unlike other methods, including cast iron cylinder liners, Nikasil allowed very large cylinder bores with tight tolerances and thus allowed existing engine designs to be expanded easily, the aluminium cylinders also gave a much better heat conductivity than cast iron liners, which is an important factor for a high output engine. The coating was further developed by US Chrome Corporation in the USA in the early 1990s (under the trade name of "Nicom"), as a replacement for hard-chrome plated cylinder bores for Mecury Marine Racing, Kohler Engines, and as a repair replacement for factory-chromed snowmobiles, dirt bikes, ATVs, watercraft and automotive V8 liners/bores.

Porsche started using this on the 1970 917 race car, and later on the 1973 911 RS. Porsche also used it on production cars, but for a short time switched to Alusil due to cost savings for their base 911. Nikasil cylinders were always used for the 911 Turbo and RS models. Nikasil coated aluminum cylinders allowed Porsche to build air-cooled engines that had the highest specific output of any engine of their time. Nikasil is still used in today's 911s with great success.

Nikasil was very popular in the 1990s. It was used by companies such as BMW, Ferrari and Jaguar Cars in their new engine families. However, the sulfur found in much of the world's low quality gasoline caused some Nikasil cylinders to break down over time [1], causing costly engine failures.

Nikasil or similar coatings under other trademarks are also still widely used in racing engines, including those used in Formula One and ChampCar. Suzuki currently uses a race-proven nickel phosphorus-silicon-carbide proprietary coating trademarked SCEM (Suzuki Composite Electro-chemical Material) to maximize cylinder size and improve heat dissipation, e.g., on the engine of the Suzuki_TL1000S and Suzuki DL650 V-Strom and Hayabusa motorcycles [1].

Engines using Nikasil:

Aprilia RS125 And Aprilia SX/RX 125

Armstrong MT500 - Rotax engine cylinder lining

Chevrolet LT5 engine, designed by Lotus and used exclusively in the Corvette ZR-1

Chevrolet Vega 2.3l, and 2.0l Cosworth fours

Citro

Edited January 3, 2010 by alan

[pat slinn]

Hi Charlie & Alan,

I saw a C15 barrel during the 60's that had the pushrod tunnel cast in. It was from the states. Cant remember if it had a liner or a Nikasil bore. The 441cc Victor GP had a Nikasil bore and that was in the early 60's. The F1 & F2 Ducati engines that I built for Tony Rutter in the 80's had NiKasil bores and were trouble free. I never had to change a barrel on the 600 or 750 in 3 years, and that they were used in the TT and all the F1 & F2 championship races in the UK & Europe. There is something really satisfiying about making your own patterns, and casting something. Go for it Charlie.

Pat.