Prop Spinner on early 170B

[pschmeltz]

My 170B (s/n 20289, C-145-2) has a spinner and backplate installed instead of a scullcap. It is a pain to perform engine maintenance due to the four fasteners that are behind the backplate and inaccessible without pulling the prop. I have seen other early B's with the same arrangement and I am wondering if there is a way to modify the backplate in order to gain access to those four scews.

[Bruce Fenstermacher]

Without seeing your exact cowl and spinner and the space between them I can only say that most of these installations one can remove the screws using a 90 degree bent screw driver, a small ratcheting screw driver or just a driver bit held and turned in a 5/16 box end wrench.

The ease which the fasteners come out is directly related to the type of head the fastener has and the shape it is in. I've found that many but not all of the screws I have holding my cowling one can easily be removed with just my fingers after they are loosened a bit with one of the previously mentioned tools. The screws all look the same but are not the same. I usually keep the front cowl fasteners separate from all the rest so they can be returned to the same place.

Some spinners have holes in the back plate. You don't have to remove the prop just the spinner nose. Then line up the hole with the screw your trying to remove. If I didn't have a hole in the back plate I wouldn't drill one however.

[jrenwick]

Without seeing your exact cowl and spinner and the space between them I can only say that most of these installations one can remove the screws using a 90 degree bent screw driver, a small ratcheting screw driver or just a driver bit held and turned in a 5/16 box end wrench....

My first 170 had the old-style cowling with the newer spinner, and I was always able to undo the screws behind the spinner using a Stanley 90-degree ratchet screwdriver. I think what would be really nice would be an article with good photographs of this setup, both here and in the 170 News. I'd do it myself, but I don't have that configuration any more. Does anybody else have it, who could take some helpful photos and publish them?

[blueldr]

I had that screw access problem on my '52 B model with a spinner back plate. I chose to drill a hole in the back plate, directly over one of the screws, large enough to accomodate the shank of a phillips screw driver. The prop when rotated 180 deg. placed the hole for accessing the screw on the other side of the nose bowl. I then drilled a second hole over the other of the two inaccessable screws which also accessed the screw on the other side.
I found that there was not enough clearance between those screw heads and the backing plate to allow the use of an offset ratchet screwdriver to back the screws out more than a couple of threads. Of course, there was still the PITA of removing the spinner dome to get the cowling off.
Thats probably why Cessna put a skull cap on that earlier model of cowlings before the pressure cowl. That problem alone ought to be enough for any reasonable AI to figure out why a skull cap belongs on an early model cowling.

[Abe]

This maybe a bit off topic, but in the close category, after a few bloody knuckles you'll learn to get those pesky screws out with a modified ratchet with a ground down phillips head and just a moderate amount of talking about the engineers that designed it that way. But my question is concerning the spinner itself, I've got a 52 170B with the spinner and I have never been able to get it put on right to not have some "wobble" in it when she spins. I just put some nylon washers on before the screws as I was told this might help it set itself, but with no luck. Any tricks to finding a solution to this problem short of a new backing plate and spinner...ouch at nearly $900...

[FredMa]

It sounds like you have the newer style spinner that has the plug that fits into the hole in the prop. It is supposed to be tight enough to center itself. Sounds like it might have become worn due to operating with loose screws. I would try using self adhesive teflon tape on the plug to make up for any wear that has occured.

[GAHorn]

With the airplane out of the wind (preferably inside a hangar with a level floor), locate the center/tip of the spinner bullet with a crayon. Mark it with a dot or an X.

Mount it loosely upon the backplate/bulkhead with the insert firmly taped as previously mentioned.
Using a long stick, measure, or other device resting vertically upon the hangar floor directly beneath the spinner, extending from the floor to the front of the spinner/bullet (note the exact spot resting on the floor and the length of stick/device reaching the spinner) ...slowly rotate the prop and watch the "dot/X" as it moves in relation to another spot on the measuring-device/stick. By noting the elliptical/relative motion...you can more accurately center the spinner upon it's backing plate. Now tighten the screws firmly.

Rotate the prop again to confirm.

VOILA!

[Abe]

Thanks for the good info fellows, I will try those techniques and maybe my vision will self correct itself also, as little wobble as it is, it sure draws your eyes to it when your cruising along.

Thanks again...

[redneck]

I replaced the bullet spinner on my '52 B with a Spruce skullcap spinner for about the best $60 I've spent. Replaced the cowl fasteners at the same time. Now that I've chased down most of the oil leaks and don't need to r/r the cowling after every flight, it's not as big a deal, but I got tired of dealing with the 90-degree screwdrivers and mini-ratchets and the awkwardness of working behind the backplate. Besides, I think the skullcap gives the "Green Thang" a certain panache that it lacked with the bullet spinner, and we could all use a bit more panache.

[Abe]

I wanted to follow-up on my wobbly spinner. We were going to try several things mentioned here, but we first turned it 180-degrees and reattached it using the tightning the lug nut theory and it came out as true as can be. It's funny, but now when flying, my eyes don't even see the spinner unless I purposely look at it, whereas before, just that slight wobble really pulled your eyes to it.

[GAHorn]

I wanted to follow-up on my wobbly spinner. We were going to try several things mentioned here, but we first turned it 180-degrees and reattached it using the tightning the lug nut theory and it came out as true as can be. It's funny, but now when flying, my eyes don't even see the spinner unless I purposely look at it, whereas before, just that slight wobble really pulled your eyes to it.

Using a permanent marker, I mark (internaly so as to remain invisible) my backplate and "bullet" spinner to orient them to the No. 1 blade marked on the prop hub.

[Abe]

Great idea George, that will happen in the next couple of days. My eyes will appreciate that preventative maintenance too!
Thanks,
Bill