Vespa Super VBC 150 fitting Pinasco 177 Kit, small end bearing movement.

Hi, Wonder if anyone good give me some advice, Will be fitting a Pinasco 177 kit soon and have recently cut/removed the small end brass bushing out of the con rod. On fitting the new small end needle bearing i noticed if fits the gudgeon pin fine but when inserted in the con rod the bearing seems to slide through fairly easy. I thought the inner piston sides would stop the bearing creeping out of the con rod but it does'nt and the amount of travel can make the bearing creep out the con rod nearly half way.

So my question is do i need a wider needle bearing to take up the slack ? Using a 15x19x20 bearing at the moment.

or will an oversize standard bearing be tight in the con rod enough so it can't creep out of the con rod along gudgeon pin ? 

How much movement / play is allowed ?  



if you have a bushing crank you have to change the whole crank in a bearing one...otherwise it will not work!






Thanks Pierre for your reply,

Bit of a novice myself  ,can i ask the reason why it would not work even if i used an 1 or 2 oversize bearing ? afterall a hole is a hole , i am guessing myself its because the con rod material is different from the material used by the small end bearing race with friction ? reason i am asking is i have seen some con rods with brass bushing one end and roller bearing the other. 

Trying to avoid splitting case open to change crank really , may be back to a new brass bush being fitted.  [;)]