The International Cessna 170 Association

Im putting on a Sportsman STOL, and also painting my engine mount and doing some general tidying up under the cowl. I went to put my spinner back on today and found a large crack in the backing plate. It was actually quite hard to see until I flexed it.

I like this style, and would like to keep it. Its got nice matching paint on it also. Does anyone have a source for a backing plate that is reasonable? Or have one to sell? It is 9 1/2" in dia.

Thanks Charlie

Aircraft spruce has back plates. They come from Univair but they are direct replacements.

I have one EXACTLY like that! (Including the identical crack.)

canav8 wrote:Aircraft spruce has back plates. They come from Univair but they are direct replacements.

I am just not sure I can justify the $474 for the backplate.

I have one that isn't cracked but it is shimmed .016" on the od. the modification was because the Spinner kit I bought from Wag Aero wasn't the exsact size as my original spinner. This backing plate ran on '93D for years. Fast forward to 2015. One of my over zealous airport geezers appeared at my door one day, nearly in tears., He had an Aircraft Spruce catalog in his hands open to the page of the Cessna 170 parts. He said "Gary please don't kill me yet! I just got a new Kubota ZTR and was mowing right in front of your hangar and accidentally hit the spinner on your plane! Here in Aircraft Spruce is the list price of a new one. Please take this check and replace the one I damaged". Needless to say I was pissed but took his money. A few months later Duane Shockey called me and said he had a spinner for me! So for you I have this slightly modified back plate. PM me if you think it will work. BTW the first spinner on my plane was damaged by the hangar door at Atchison KS being blowing in against the nose and that is when I bought the one from Wag Aero. To say that was way below what a polished spinner needed to be was an understatement. I gave that to another project builder who has painted his bird.

Well, just pulled the spinner off my 170 and found another cracked back plate. It was replaced less than 70 hours ago and the whole thing was dynamically balanced after installing the new back plate. All I can figure is the weight required to balance everything is causing undue stress on the spinner. It was about 3 fender type washers and an AN-3 screw/nut combo to get everything balanced up. Thoughts?

rschreiber wrote:Well, just pulled the spinner off my 170 and found another cracked back plate. It was replaced less than 70 hours ago and the whole thing was dynamically balanced after installing the new back plate. All I can figure is the weight required to balance everything is causing undue stress on the spinner. It was about 3 fender type washers and an AN-3 screw/nut combo to get everything balanced up. Thoughts?

Got a picture of it? Were the weights placed under the flange of the backplate..?? or placed on the backplate/vertically..? if the latter… Were they placed equally on boght sides of the bulkhed..?? Was the hole drilled siighlty undersized and then reamed to size..??

There are ad hoc methods…and there are recommended methods of weight placement.

See pgs 13/14: