Pistons problemo!

[Pylonracer]

21mm piston, completely machined on a Mazak 530, the first photo is prior to turn finishing the OD, at this point the OD is 0.25mm oversized.

Second photo shows the piston being machined on the OD with a PCD tool.

But these are round !!

For Graham (the OP), this is all done within a few miles of Saunders.

I would get the Honda piston and hold it in the orientation of this piston and go around the OD with a decent tool to create that tapered oval, I think there is a machine shop at the Totton end of the road that runs past Saunders that could do this. We have no time to take on sub con work like this, too busy doing the stuff in the photos.

 

[graham-xrf]

21mm piston, completely machined on a Mazak 530, the first photo is prior to turn finishing the OD, at this point the OD is 0.25mm oversized.

Second photo shows the piston being machined on the OD with a PCD tool.

But these are round !!

For Graham (the OP), this is all done within a few miles of Saunders.

I would get the Honda piston and hold it in the orientation of this piston and go around the OD with a decent tool to create that tapered oval, I think there is a machine shop at the Totton end of the road that runs past Saunders that could do this. We have no time to take on sub con work like this, too busy doing the stuff in the photos.

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That is a beautiful thing, and so tiny. I have just realised the association with pylon racing. I guess you would not be into the full-sized version like the Red Bull Air Race. I am into sailplane gliding. Think about 3/4 of a ton of high performance flying machine, able to fly 100s of km, staging from cloud to cloud on thermals. It's a very real kind of flying, not at all like regular flying, which is a bit like getting on a bus in comparison. Arguably, I am getting too old for this kind of thing.

Regarding the pistons, for me, the hunt is on for anything that will fit, or can be adapted. It's a simple, vintage engine of 1940's technology. If I can find a old motorcycle type piston set with 5/8" wrist pin, about 70mm (2+3/4") tall, and OK to suit the bore, with about 56mm (2.2" or 2+13/64") that isn't dome, it might work.

 

[Pylonracer]

No RC pylon racing.

Down in Milford One Sea there was a company called FJ Engineering which was run by Dave Fletcher Jones who was ex Wellworthys development engineer.

It is not there anymore but he had a huge number of patterns for pistons which they then machined. Such things as Austin 7 but loads of R&D stuff as well.

It might be worth trying to see if Dave is still kicking.

 

[graham-xrf]

No RC pylon racing.
Down in Milford on Sea there was a company called FJ Engineering which was run by Dave Fletcher Jones who was ex Wellworthys development engineer.
It is not there anymore but he had a huge number of patterns for pistons which they then machined. Such things as Austin 7 but loads of R&D stuff as well.
It might be worth trying to see if Dave is still kicking.

Thanks much for the suggestion.
It seems the place is still there, with that same name, and in Milford. Apparently it's a top-notch outfit in aluminium and stainless steel fabrications.
I am not sure it is still into anything Dave Jones did, but..
.. it may take a while to even get started. This is what the website yields.



I have had one of those passing crazy ideas that totally deserves what will inevitably come, such that I hesitate to even say it, but what if ..
Plate electroless nickel strike onto the cleaned up original piston, masking out the wrist pin bore, the little skirt holes, and possibly the walls of the ring slots, but leaving the bottom of the slots exposed. Without help from an external current source, (and also a different plating solution), the process runs out of chemistry urge at about 0.127mm (0.005").

Then plate copper, about 0.010", or a much as is needed to get to the +0.020 (in diameter) oversize for the bore, but allowing for the hard final plate.

Finally plate with nickel the last 0.005". That final surface would be very hard, and may not be appropriate for sliding in a bore. Maybe some other metal? Anyway, I just wondered what could be done to to re-work a piston into something "a bit bigger".

OK - consider the thought now perished. I still think we might yet find something near-fit suitable.