piston dimensions needed (still)

[lingeringstin...]

Been trying for some time to find any kind of reference info giving the actual dimensions of various two stroke pistons and had no luck at all.

I have resorted to looking up pictures of pistons and then enlarging the photos onscreen to measure them but that can't be very accurate.

Basically I'm just looking for a ready source of bog standard non reed valve two stroke pistons. Naturally I'd like to do as little specialist modification to the barrel as possible so I've been looking for pistons that are a close enough match for the standard ones and would require the least faffing about with. A bit of piston modification is easy enough, I've shortened skirts on a grinder to suit con rods before with no problem.

Gudgeon pin size isn't that important as I can use a different or modified con rod, and two stroke heads are easy to alter but piston crown height and the design of the skirts are important and that's the information I'm not finding very easily.

For instance some pistons have weirdly shaped bottom halves to accommodate weird shaped transfer ports and that sort of thing so what I really need is some kind of cross reference info or blueprint type drawings with measurements and so far I've not found anything useful.

Mainly looking at jetski and snowmobile pistons at the moment due to their ready availability and the fact they're designed to go like the clappers.

[Vincent]

I think you've set yourself an impossible task with this one. What capacity is/are the barrel/s?
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Space Is Deep

[lingeringstin...]

Ah well the actual bore size has been easy enough to find. What I was mainly looking at was pistons to shoehorn into MZ barrels. I've got a few barrels so mucking about with one or two is no big deal.

The 250 engine bore size goes from about 69mm to about 72-ish before you run out of liner and the 300cc barrel starts at about 75mm and can be bored out to about 80mm if need be, so there's lots of scope for bore sizes.

Obviously I'd rather not rebore too much initially so I can rebore later as I wear them out but there seems to be a lot of good quality jetski and snowmobile pistons made in exactly those sizes. I don't much care for MZ pistons and they're harder to get nowadays anyway.

[Vincent]

First one that comes to mind is the TS250, that's 72 x 64mm Bore & stroke, early ones were 66 x 72mm:-

"The design of the early motocross machine suffered because of its heritage, having been patterned after the dated Villiers engine, with it’s under square, 66 x 72mm bore and stroke set up. In the early 60’s when work began on the project, this was a perfectly good design, so Suzuki was doing little wrong by copying it. The internal architecture did hold the design back so for the TS model, parts and dimensions from the all new, road going, T500 were implemented, making the TS250 effectively half of this ground breaking twin-cylinder design with a more manageable, and reliable, 72 x 64mm bore and stroke".
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Space Is Deep

[lingeringstin...]

I have been considering a Suzuki TS250 piston because as far as I can tell the only barrel modification I'd have to do id shorten the barrel top or bottom or both by a little bit so the transfer ports matched up. That's not too bad a job for the local wee man in his local wee machine shop so it's not expensive.

The ONLY problem I had with that idea was that as I understand it Suzuki no longer do those pistons and I'm unsure of how much after market support there is. Would be a bugger to alter a barrel to suit a piston only to find the pistons have become rare and thus "vintage" priced expensive. Haven't really delved into that yet.

For simplicity I just figured two stroke snowmobile and jetski pistons are a ready supply of spares and plus sizes for rebores.

I know just bunging in a complete Suzuki TS250 engine (or something completely else) would be a way to go but I've got a lot of spares for MZ like clutches, carbs, cranks and gearboxs already so upkeep is minimal if I stay with mainly MZ shite and I'm not going to get spendy with a 40 year old ratbike.

[Suntan Sid]

I may have misinderstood you, but you can buy a Suzuki TS250 Piston kit, up to 2mm oversize, for just under £36, from wemoto!
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[Kickstart]

Hi

I have been told there is a large book around somewhere listing pistons with their dimensions.

If you find a copy then let me know as I need a piston suitable to go into a Gilera NGR250

All the best

K
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[sickpup]

[Kickstart]