I have a new os max .046 ax abl engine that I have installed a dubro 2 1/4" plastic spinner on. The prop nut loosens almost every time I try to start the engine with a power starter. The component parts are added to the prop shaft in this order: Prop drive collar (as supplied with engine), spinner back plate, spinner bushing, propeller, prop washer (supplied with engine), prop nut (supplied with engine) and finally the spinner cone. Is this the proper sequence? Is there a torque specification for the prop nut?

I have tried tightening the prop nut to the point where I am afraid of stripping the thread on the prop shaft and still the prop nut loosens.

Please help,

Terry

Sounds right except the bushing part. On Dubro spinners this generally presses into the spinner back plate from the rear so that the spinner will work with various shaft sizes. Is that how you assembled it or did you slide the back plate on the shaft then the bushing?

Also, I see a lot of people who simply don't torque the prop nut enough. Don't be afraid to put a little force on it. Both the nut and the crank threads are hardened.

Finally, make sure the engine isn't hydro-locked from too much fuel.

I see you are just up the hill from me. Are you a a local club member? Even if you aren't, feel free to head down 41 and stop by. It looks like rain tomorrow but if it clears up, the Wednesday crowd should be out. I'll also likely be there flying on Friday and definitely on Saturday weather permitting. I'd be glad to take a look at it and I'm sure most of the other members would be too.

Lose the plastic spinner and your problem will be solved . Plastic just doesn't have enough friction to stop it slipping on either (or both) the prop driver or the prop. There's a work around fix though by using thin leather washers made from old gardening gloves or washers made from "wet and dry" paper that go against the plastic spinner. These just add friction. With a good setup it's surprising how little force is needed to tighten the prop nut enough to stop it coming loose. Even with a 60 or larger I have no problem just using one of those 4 way wrenches.

nah you're ok with a plastic spinner on this engine....wood props swell and shrink with humidity...are you using a wood prop?...My money is you aren't getting the nut tight enough...go ahead and crank it down until the prop digs in into your hand...second make sure the engine isn't over primed.....causing a hydrolock....
Good Flyin to ya

Gotta agree with jetmech. I've been using plastic spinners for over twenty years, and haven't had a problem with them coming loose yet. Just have to tighten sufficiently. The spinner back plate usually has raised lines radiating out from it's axis on the back and the front, to create friction against the drive washer and the prop respectively. My 2 cents.


Lm

I had the same problem with my OS .46 ax when I changed the way I fueled the plane. By putting a catch tank on one of the lines to save the fuel over sprill, there was just enough back pressure to over prime it. Then it would backfire and spin the prop loose. After removing the catch tank, no more loose props.

Once a spinner slips, it is all over as far as not slipping.

You then have to resort to using wet or dry type sandpaper on the back plate to keep it from slipping.

I dont' use spinners on open cowled engines. They are more trouble than they are worth.

Problem solved thanks to all of you who took the time to respond. Hydro lock was the problem.

Thanks again!

Terry

Easy solution