Cardellino 65 Spec help

[Grand Prix Classics]

Hi, I'm building a Cardellino 65 with the cast iron cylinder.
I have purchased a piston that is 1mm over,
but the machine shop needs cylinder to piston clearances.
I only can find rebuild specs for a cardellino 73 and they are in Italian!
Not sure if the clearances would be the same as I believe that the 73 has an aluminum cylinder with
a steel liner. Any body able to help with this?

 

[Chris R]

I am a little bit amazed your machine shop can't give you some advice - it is not going to be a lot different than any lopo two stroke air-cooled cast motor of the same bore which any old machine shop has encountered thousands of times. I'd find an old guy who has rebuilt a lot of small two strokes. Really an old lawn boy and a Cardellino are not that different - both are air-cooled, cast liners and run at full throttle pretty much all day.

I looked through the original users manual (in italian) and it doesn't mention a clearance that I can see. If you have a link to the rebuild specs I can translate.

The rule of thumb when I was building two strokes was 1 thou per inch was generous - inmost cases I used .8 of a thou unless someone who knew told me otherwise. There are a few variables specific to the bike here such as whether the piston was cam ground or not - maybe not given the vintage which would mean a touch more clearance, the wall thickness of the liner and how and where you are running it -ie high ambient temps, high/low alt, city traffic. The rule of thumb work fine with H2s, RD400 , RD350LCs and TZ750s

My guess would be given a bore of 42mm, 1.6 thou would be generous and a little over a thou would be optimal.

In my experience machine shops usually go overboard in their clearances as they get more customer complaints from seizures than engines that wear out prematurely due to overly generous tolerances. I usually had to bend the arm of the machine shop to get the tolerance as tight as I wanted.

I've never actually had a seizure with a two stroke - scoring due to wide clearances yes.
I always assembled dry after I found the rings bedded in a lot more quickly and the cylinder tends not to glaze.

I also mix the leanest mix recommended by the oil manufacturer as detonation is promoted by oil which itself produces overheating and then seizure in a racing two stroke.

You have a tiddler so you can ignore this and just enjoy it for what it is. I'd love a Cardellino.