The Cessna 120-140 Association Forum

I have done Dynamic Propeller Balancing in an AcroSport Biplane that I built. This Biplane had a big aluminum spinner and it was fairly simple to add washers on the outside of the spinner to get it properly balanced.
My 47 C-120 with a C-85-12F has a little spinner with one bolt in the center. I have searched the forum but have not found anything about prop balancing. Do you have any suggestions/ideas on how to add weights to dynamically balance this McCauley aluminum prop? I guess I could use automotive stick-on tire weights but I am concerned that they will fly off!
Thanks,
C. Duenas

I don't remember where I copied these images from. I believe they came from our forums before we switched to the new servers. My apologies to anyone if you feel I have used your photo without permission.

A couple more photos...

Thanks so much Chris for posting those pictures!
That was exactly what I was looking for. I assume that it will take a little longer bolt to accommodate for the thickness of washers / spacer.
Thanks again

Sorry for asking, but this is the first time I see pictures like that and discussion about Dynamic Balancing.
Should we all do this with our prop installation???
What is the procedure to be able to achieve it?
Any special tools or equipment required?

Thanks for clarifying

Dynamic balancing requires some sophisticated equipment. My feeling is that if you have a well balanced prop you won't need it, but it can't hurt anything, either, and it may reduce vibration if your engine internals are not well balanced.

Thank you John for the explanations.

The propeller position is critical to dynamic balancing. With the T/C mark, on the crank flange, lined up with the case halves it should be at the 7 o’clock position.

That is interesting Randy, but standing and looking front what position? Sitting in the cabin or standing in front of the prop?

What I know, is that standing outside the plane on the passenger side, looking towards the propeller, my prop is at the compression phase at 2 o'clock, so it is easy to hand start with my right hand while holding the strut with my left and having by left foot in front of the tire. Very easy and safe.

but if we clarify the 7 o'clock and it is a better position altogether for the prop and the engine to be, I'll surely try that.
Thks!

5115 wrote: ↑Thu Jan 31, 2019 10:58 am That is interesting Randy, but standing and looking front what position? Sitting in the cabin or standing in front of the prop?

What I know, is that standing outside the plane on the passenger side, looking towards the propeller, my prop is at the compression phase at 2 o'clock, so it is easy to hand start with my right hand while holding the strut with my left and having by left foot in front of the tire. Very easy and safe.

but if we clarify the 7 o'clock and it is a better position altogether for the prop and the engine to be, I'll surely try that.
Thks!

I would say that your prop is in the right position. Coming up on compression at 10/4 o'clock is right standing in front of the engine. 2 o'clock standing behind where you prop it is the same. The mags click at the 7 o'clock position on Top Dead Center for start up. That is when the impulse couplings cause it to fire. As the piston is driven down from the combustion the energy is pushing the prop blade.