Hi. I have an extra 300 With a Saito 100.
When I try to start it sometime the metal spinner spins and not the engine part.
The back part of the spinner is metal and the engine is metal.
Am I missing a pice in between them or it's just not tight enough?
Thank you very much.

If you can post photos of how you have it set up that would be A big help. It should be the back plate first, the prop, prop washer, prop nut, spinner adapter nut, spinner and then the spinner screw that runs through the center of the spinner and screws into the adapter. Hope that helps you. The screw holding the spinner doesn't need to be torqued down very tight or you can break out the center of the spinner.

The prop shaft and nut are hardened steel, so you can really tighten 'em down without fear of stripping them. You want to have it good and tight on a 4 stroke...sometimes they kick, and the prop can loosen or even get thrown right off.

I don't know about Saito, but OS 4 strokes use a woodruf key on the shaft. If Saito uses a 'key', it might be missing to cause your problem.

...just a thought.

There are a number of things that can cause this to happen.
Some are:

1. If the spinner / prop nut is one that the prop nut screws onto the shaft while going into the prop hole, sometimes the nut runs out of thread and will not tighten adequately. An extra washer or two between nut head and prop usually corrects.
EDITED to add: In some cases I have had a regular propnut run out of shaft thread prior to getting tight. Usually happens when using thin base LOW pitch props. Again another washer/s will fix.

2. Not tight enough, but check for #1 above.

3. THE BIGGIE!. Aluminum spinner backplates just don't like thrust washers getting all cozied up. Take a small square or round of wet/dry sandpaper, 150-320 grit or about. Cut a whole about the size of the propshaft. Slide it over the propshaft and place between the thrust washer and the spinner backplate with grit against the backplate.
You will be very surprised with the results. No more slipping backplate.


BTW this can be done rather sloppy or fine tooled. Sloppy works well. No big deal.

Thanks a lot!
Good ideas here. I love this site.
Thanks.