Porting crankcase transfers

Hello !
When i look at the polini explanation on how to modify the transfers i am a little confused… They show a picture from upside view how to mill the transfer, but are the transfers milled all the way down just like the original transfers. Or are they following the cylinder skirt ?? Malossi cylinders dont have the same cylinderskirt so i rekon they should be milled „all“ the way down to the crank just like the original transfers… Is there anyone out there that knows what i am talking about, that can give me an explanation ???



you should follow the cylinder skirt. This area is used to transfer mixture from the crankcase to the cylinder.

With a Polini 177 kit since the crancase porting has a more forward oriented design than Malossi 166 if you mill all the way down even if you do at a very steep angle you would have left less than 1mm of alu on the cranckcase clutch side pratically it means if you are not experienced you will make a hole. And I don’t find it mechanically reasonable having left 0,5mm even in an area that doesn’t have to support too much stress but there are vibrations and heating anyway.
So if it is the first time be conservative and follow the cylinder skirt.
I have a Polini engine kit too, and I opened my one in a more risky a radical way then I did another engine (strictly following the cylinder skirt). With the same carb and exhaust the difference is not relevant. But this is my experience…
Malossi 166 kit I find it easier to open all the way down at a certain angle.


Hello !
Yes i thought they ment to only mill after the cylinder skirt.Anyway
i have had the crankcase welded, but if the performance is not increaced by milling more, i would leave it just following the skirt.
I will use a racing crank,Polini 177cc,si24/24 and a leovince exhaust, so it is problably not so extreme engine.

Thank you for your respond


…this of course apply if not welding same material from the outside of the crank. In that case you can mill more…
[:D]…but it is not necessary exept you are extreme…[H]


the performance is effected but not in a significative way.
With a 24/24 I wouldn’t boder.
You will gain much more with a better exhaust.