Jan

The bearings you are talking about are standard issue in the MVVS #3068 Q-500 engine.
The bearings have the C4 internal clearance and the ball cages are not plastic, but TBH - glass fabric filled phenol resin.

The are for extended high speed and high temperature use.

You can see specifications for these bearing types in the [link=http://www.wib-nsk.com/en/products/standards/index.htm]WIB web site[/link]. Look into 'Cages', 'Internal Clearances' and so on.

The Q-500 bearings do fit all other MVVS .40-.49 engines and some other makes too, but the standard WIB bearings, that come in all 'normal' MVVS engines, also last very long and I have never had to replace, any bearing in any MVVS engine so far.