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Techno 250 advice


DAICROCKet
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Hi guys, 

 

After much deliberation, I managed to purchase a new cylinder kit from molinari in Italy..  on looking to fit, I have found that the piston is a type B of 72.451. I've measured the cylinder and get 72.48/9. On working the tolerance 

, I get near 0.030mm ... which is around 1 thou.. Will this seize ? 

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Possibly the piston, being the smaller metal object will expand more due to heat that the cylinder, which also benefits from its cooling.

Id say the tolerances were too close, and you'd need a bit more. Have you contacted John Lampkins for proper advice, they'd know for sure!

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On 12/4/2020 at 9:45 AM, DAICROCKet said:

Does anyone know offhand, what a new cylinder measures? I'm getting 72.48 with telescopic guages and calipers... 

Will will never measure it correctly with a Caliper

You need a bore gauge and micrometer to get the correct measurement (a mic that measures 0.001mm) 

Good quality feeler gauges would probably give a better clearance measurement, if you cannot use the above :thumbup: 

250cc bores normally need between 0.04 to 0.05mm clearance

Edited by suzuki250
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Thanks for the info guys... I've read many threads stating 1 thou per inch = 0.0028 for a 72.48mm bore. So If the piston is 72.457mm leaving a tolerance of 0.023mm equating to .0009 of a thou!! So if I put a standard 72.451mm equating to 0.029mm or 0.00114 I'm confused as that would also be tight!!

Does anyone know where I can access beta tolerance data? Am I measuring the bore wrong as it is stated as 72.5?? 

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5 hours ago, DAICROCKet said:

Thanks for the info guys... I've read many threads stating 1 thou per inch = 0.0028 for a 72.48mm bore. So If the piston is 72.457mm leaving a tolerance of 0.023mm equating to .0009 of a thou!! So if I put a standard 72.451mm equating to 0.029mm or 0.00114 I'm confused as that would also be tight!!

Does anyone know where I can access beta tolerance data? Am I measuring the bore wrong as it is stated as 72.5?? 

The bore is 72.5mm + or - whatever the tolerance is for the plating, (that's why they have size graded pistons)

the clearance depends on the piston material, if its hypereutectic then 0.023 would be fine 

Measuring it with a caliper you cannot get the accuracy required, therefore if the seller says they are paired, then its probably correct. 

Build it and ride it ;)

 

Edited by suzuki250
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