Prop Mounting

[N73087]

I hope to get my C145 back from overhaul soon. With the crank at TDC, is there a "best position" to mount the prop incase I ever have to hand-prop?

[N170BP]

My notes say to place the trailing edge of the #1 blade
on the T/C mark of the crankshaft flange. Part of my
notes are "stolen" from the Swift site/folks, and that
information follows:

Cessna came out with a bulletin dated 7-8-53 which had
an illustration showing the t/c mark aligned vertically with
the split in the crankcase, and the c/l of #1 blade at the
11:00 position (looking at it from the front; the first bolt
hole being 10:30) I think the way I do it (TE of #1 blade on
the T/C mark of the crankshaft) is the same as what they're
saying, except 180 deg different (which should make no
difference)

Another note from the Swift site:

The the crankcase split should be aligned at the Zero on the
bottom of the prop flange, which will place the #1 piston at TDC.
The number one blade of the prop should now be at the 11 o'clock
position (when facing the cockpit as if you are about to "prop" it for
starting) ....or when viewed from the cockpit (like everything
else should be) that #1 blade will be at the 1 o'clock position.

Hope this helps....

[blueldr]

The Cessna 170 book from the TIC170A has an illustration and instructions on how to properly index the propeller when installing it.
If I remember right, the number one blade is positioned at about 10:30 o'clock, facing the prop, with #1 piston on TDC.

[simatos]

OK bone head question for today. How do you designate which prop blade is number one??????????????G

[Bruce Fenstermacher]

The prop should be marked with a 1 and 2 on each blade face near the hub.

[GAHorn]

Bruce's msg does not mean that WE are to mark the blades. He means that if you inspect the blades, you'll see where they will be already so marked near the hub as "1" or "2", in most cases. In cases where the blades are NOT so marked, Blade number ONE is the blade closest to the SERIAL NUMBER marking on the prop hub.

[N3243A]

Aside from blade position for hand propping, it would be Okay to mount the prop in any arbitrary orientation on the hub, right? I can't see how the engine would know or care where the prop blades are.

[N73087]

Aside from hand propping, I remember a crusty old mechanic who had a cure for vibration. He would try the prop in every possible position, and leave it in the one that ran smoothest. All you need is time, gas and safety wire.

[GAHorn]

Aside from hand propping, I remember a crusty old mechanic who had a cure for vibration. He would try the prop in every possible position, and leave it in the one that ran smoothest. All you need is time, gas and safety wire.

I'm going to guess he had no reference materials to determine the recommended position and the prop was already not in that position and/or was not properly balanced. The reason for mounting the prop in the recommended position is because that is not only suitable for propping, but also because it's the position utilized when the crankshaft counterbalance dampers were designed and selected.

[zero.one.victor]

The article in The 170 Book is on page 45 of the 1999 edition, under "engine operations". This article states that the "11 o'clock" prop orientation was used by Cessna starting with s/n 26110,& detailed in a "service information summary" dated 7-8-53. Prior to this, the prop #1 blade was oriented at approximately 1 o'clock. According to the summary,the prop orientation was rotated 45 degrees counterclockwise to get smoother operation.
A friend of mine thought his 170 ran kinda rough, he discovered that he didnd't have the prop oriented to this 11 o'clock position. He did so, & claimed it made a world of difference. Another friend tried all possible prop positions on his 170, and claimed it didn't make any difference at all.
I have another friend who is real big on "prop tracking". Put the prop on,place a chair or something right in front of the airplane with the prop blade "just" touching it. A dial indicator can be substituted for the chair if you're into high-tech.Then rotate the prop 180 degrees without moving the airplane (it helps to have the plugs out). The other blade should be in exactly the same position--if it's not, the prop is not tracking true & it'll cause vibration. It's possible sometimes to correct an out-of-track condition by rotating the prop orientation 180 degrees- the crank flange may be off a hair & the prop off a hair also, so that the two may cancel each other out.
I lucked out, my prop seemed to track OK with the #1 blade at 11 o'clock so that's just how I left it.

Eric

[GAHorn]

According to TCM the letter was issued subsequent to the discovery that props were being installed during aircraft assembly in the eleven o'clock position from the pilot's point of view based upon Cessna's interpretation of TCM instructions. This was corrected at sn 26110. (Eleven o'clock had been interpreted at Cessna to be from the pilot's viewpoint ...while TCM specifications considered it from the mechanic's viewpoint.) Repeated complaints from operators led to an investigation which uncovered the discrepancy.