Here's my reply to Seamus Malone regarding an enquiry he made about a piston for an M21 on the 'parts wanted' section...

It could be of interest and there might be others who may have something to input....Ian

Re: bsa m21 piston


The fact is that despite advances in materials, casting techniques and machining, the best PRODUCTION pistons out there for a BSA single are still Hepolite, Hepworth and original BSA...

I exclude specialist manufacturers from that statement such as Omega in the UK and JP Pistons and CP Pistons in the U.S., to name a few...

GPN pistons seem to be quite serviceable but, depending on the model, are frequently over weight...

Note that a difference of more than 1 1/2oz. between the original and the replacement means the crank should be rebalanced.....Some reduction in weight can be achieved by careful machining and handwork but I can't say how the M21 version measures up

J&S Pistons from Oz are all over the place as well...However, even some Australians aren't to complimentary about those...I've managed to avoid using them to date so can't quote from personal experience..

Far eastern replicas which can be found on e bay are variable...I have run them more than once without too much of a problem though I ALWAYS replace the ring set with originals...Weight wise they are OK but I have heard stories of examples that seem to have an infinite capacity to expand when they get warm...
I haven't had that problem myself...

British Only Austria is run by an ex pat and from the point of view of spares are basically a dealer similar to most others...They do buy in original NOS when it comes along but they sell other stuff too...

With all dealers make sure you clarify exactly what you are getting...

Without doubt the best chance for an original piston in the UK is definitely 'Bantam John'...Some people don't like him, personally I'm not to bothered if I can get what I want and have never really found him problematical if you approach him with all the relevant information...He has around 10,000 original pistons in stock...

Don't expect an original to be cheap though..There is a dwindling supply and no replacements...Just think of the thousands of miles of reliable service you will get from it as you give your card details.. ..Ian

email (option): ian@wright52.plus.com

Thank you for your reply Ian,
Lots of good advice there,i may have what I,m looking for nearer to home,
Will keep you posted

email (option): Seamusmalone15@gmail.com

Me think Ian has some names a little wrong.
JE are the pistons from the USA
JP are the pistons from Australia.
JP are quite good quality pistons but the rings are rubbish.

As far as metallurgy goes during WWII 12.75 to 13.25% Si aluminium was discoverd to have the same expansion as cast iron due to phase changes at operations temperatures.
These were originally called names like "no spand" , "Low Spand" "spandex" etc.
There have been massive changes to pistons but most of it was orientated to reduction of casting defects, greated dimensional stability and substantially faster mould strip increasing productivity and keeping costs lower. Hydrogen scouring now means that the days of growing pistons are long gone and we can run engines with absurdly low piston clearences.
However no one riding M20's is going to pay the price that a double vaccuum melted, virgin alloy Niobium inoculated , dendriticly modified piston blanks would cost.
People who make helicopter engines will.
It is all about the dollars

email (option): bsansw1@tpg.com.au

['Me thinks Ian has some names a little wrong.
JE are the pistons from the USA
JP are the pistons from Australia.
JP are quite good quality pistons but the rings are rubbish.']

OOPS!... ...Posting error...I should know what's what, I've been dealing with some of it for long enough and I get pistons made by JE in the States..

I agree to an extent on the price comments...Most people wouldn't want to, or need to, buy a high spec. top of the range piston for an M20...

However, it isn't beyond the bounds of possibility to produce a serviceable pattern piston at a reasonable price...They are made, for example, for Triumph twins..I've used plenty of those and in terms of specification and performance they are to all intents and purposes compatible with the originals...

I'm sure GPN could do something about the weight of their offering and not have too much of an effect, if any, on the price..

JP, for there part, shouldn't be offering a defective product..There are plenty of ring manufacturers in the world who could supply JP if they can't do it themselves and again the effect on the price would be minimal...
One of the manufacturers of pattern Triumph pistons buys in American made Hastings rings for example...

When I see the prices being paid on e bay for NOS original Hepolite or BSA stock it is clear that the day is close, or maybe here, when it will be possible to have quality, higher spec. pistons manufactured for the same money.....Ian

email (option): ian@wright52.plus.com

I buy a lot of pistons from JP and always take that up with them.
The rings are bought in and they would be better off selling them bare.
They will make small runs as low as 20 pistons , but like all things volume discounts apply.
The world market for M 20 pistons would be lucky to exceed 100 in any one year.
And that would be over the range of 4 oversizes.
Economic production runs start at around 1500.
So who do you know that would be willing to stick $ 60,000 / pa for the next 5 years to do a minimum economic run of each size realizing that then stock will be sitting on your shelf for the next 10 to 50 years ?

We have already come to the conclusion that the market is diminishing over time as the bikes get less & less road time.
I have only used 3 pistons since 1996 and done over 150,000 on my M20
OTOH I have gone through 5 pairs of pistons for the A 65 since 1989 for some where around the same mileage .
Thus for me A65 pistons would have 3 times the demand.
Come to think of it I have used 3 times as many friction discs in the fork dampers than I have pistons.
The I do regular compression checks and as soon as the compression decrase starts it increase I whip in a new set of rings so I do get excellent life from all my pistons.

When I used to ride daily and to rallys then the B40 or B44 were the bikes of choice being faster better braked and a lot more comfortable.
If SWMBO was coming as pillion then the A 65 got rolled out
If I was going interstate then the A 65 was the weapon of choice as those would have been near 1000 miles over 2 or 3 days which is pushing the M20 way too hard.

Same story with Triumph twins.
No one would think twice about riding their Trumpets 1000- 2000 mile round trips but that is somthing of an epic ride on an M20.
I am sure some on this list are planning to take their M20's to the international in Italy this year but it would be a fairly safe bet none will ride all the way

OTOH I could invest the same $ 60,000 buying novilty biros from China and sell them all at a 500% profit in less than 6 months.

email (option): bsansw1@tpg.com.au

JE will do small batches of less than 20...They are able to do this as they have built up a large range of forging blanks that cover the standard dimensions of many different pistons and they can be machined to a given pattern as needed...

They also offer choices of circlip sizes and design and ring set types and specifications (some, or all of which they buy in)...

I had a batch of 50 main bearings manufactured..and I have had many other small batches of components manufactured including pistons...

These days virtually any enthusiast can commission small batches of components at reasonable prices and sell them on to others as well as satisfying their own requirements..(and possibly covering them with the profits)...

The investment at this level isn't huge and as long as the demand can be identified it can be done for less than some spend on beer per annum...

The component I am currently having manufactured consists of four parts and these can all be manufactured/obtained in a batch qty. of 25 without difficulty and at reasonable prices...

The existence of a demand was identified 'upfront' through a posting on this forum, so not a risky or overly expensive exercise I would say...

The secret is to see what can be done out there and then get it moving..

This type of 'enthusiast driven' manufacture has proven to be a good way of supplying small batches of parts...Just look at what has been made available by various members of this forum at different times..Ian

email (option): ian@wright52.plus.com

And there is nothing wrong with that.
However if you were working for some one so your time got added into the pricing.
It would not be economic unless made in significantly bigger batches to bring the unit cost down then there is the dead money sitting on the shelf till it is sold.

I just did a pre-tax stocktake to find I now have $ 82,000 worth of parts in stock and that is to support a $ 35,000 annual turnover.
I could easily quadruple that amount of parts and still be ordering every day.
so I can see why keeping a complete inventory of M 20 or M 21 parts on hand is not economically viable

email (option): bsansw1@tpg.com.au