Low compression 596 short-stroke pistons

This topic has 4 replies, 3 voices, and was last updated 5 years, 8 months ago by BRIAN MARSHALL.

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21st May 2017 at 9:38 pm #4622

BRIAN MARSHALL
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Hi all, some years ago Ken Lack rebuilt an engine for me, a 596cc short-stroke Flying Squirrel, and it had low-compression pistons. It was an absolute delight to ride, being incredibly tractable. It would pull smoothly down to a walking pace in top gear and then accelerate briskly away without a trace of four-stroking. Once rolling there was virtually no need to change gear ! I rarely used bottom gear at all, and this was with a 21 tooth final drive sprocket and a 21″ back wheel. I am hankering after an engine with the same characteristics and I need a pair of pistons, 596cc short-stroke, and preferably plus .040″. They are readily identifiable by the letter ‘T’ stamped on the crown, as opposed to the usual ‘R’. My contact details are as listed in Yowl in Section Information, or send me a PM.
Brian

22nd May 2017 at 5:27 pm #15665

ERIC BAYLISS
Participant

Brian ,if you can not get any +40 as a last resort I have got a pair of +60 with a big letter T on them. eric

22nd May 2017 at 5:50 pm #15666

BRIAN MARSHALL
Participant

Many thanks Eric. If my appeal doesn’t turn up a pair a bit smaller I will get back to you.
Brian

23rd May 2017 at 9:59 am #15667

efr215
Participant

I am not expert enough on Scott pistons to know the subtle differences between “T” and “R” stamped specimins but if it is a matter of the height of the crown would it not be possible to reshape the “R” type piston crown?

A long time ago I had to make my own pistons and rings for the Scott’s little brother, a 125cc Moto Rumi ‘Tipo Sport’.

At 62cc per pot I’ll admit the Rumi pistons are quite a bit smaller than the Scott ones but on the other hand the deflector crown shape is rather more complicated.

Back then I had access to an Alexander 3 axis die sinking machine, I scaled up a pattern of the piston crown made from wood and body filler and went to work. If a die sinker will not serve for the larger Scott pistons then these days there is always CNC.

Nowadays new pistons and cylinders are available for the Rumi, I have a set by me, but those home-brewed ones are still working and if it ‘aint busted don’t fix it!

23rd May 2017 at 11:51 am #15668

BRIAN MARSHALL
Participant

I will need to carefully measure the difference in crown height and also check that the gudgeon pin is in the same position. I wouldn’t want to have perilously thin piston crowns…
Brian
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