Clocking the prop

6468 · Post by **6468** » Wed Dec 09, 2020 8:30 am

When mounting the prop with Cyl #1 TDC (compression) ,,, should the prop be in the in the 11-5 position for the best hand propping? What is the preferred position in relation to TDC? Thanks

Post by **6643** » Wed Dec 09, 2020 9:54 am

Are you looking for a technical answer, or a practical one?

The engine doesn't stop at tdc; it stops about 90 degrees before (or after) tdc. So, where it stops, install the prop with the blades at about 10:00 a 2:00.

Technically, (IIRC) the #1 blade should be one bolt hole clockwise from vertical (about 1:00) when cylinder #1 is at TDC on the firing stroke.

6298 · Post by **6298** » Wed Dec 09, 2020 1:19 pm

There is a T/C mark (Top Dead Center) on the crankshaft flange. The prop blade goes slightly behind, or counter clockwise to T/C mark. Very close to top dead center but slightly behind it. On compression is will be at the 10/4 position from the front of the airplane.

6468 · Post by **6468** » Wed Dec 09, 2020 3:05 pm

I forgot to mention reference position, when viewed from the front of the plane; Cyl #1 TDC prop at 11-5 (or 10-4). From the pilot seat (the correct way to call out right side/left side of engine); Cyl #1 TDC prop at 1-7 (or 2-8). Sorry for the confusion. John your right, the prop will stop where it wants. I was trying to set it up to be in a good position if & when hand propping is needed. I realize there are other considerations like balancing but I was thinking more about position for hand propping. Thanks

Post by **6643** » Wed Dec 09, 2020 4:39 pm

The prop will always stop in one of two positions 180 degrees apart. Randy is right, and said the same thing I did, except his references the TDC mark on the crank and mine the crank flange when #1 is at TDC. One blade should be at about 10:00 viewed from the front where the engine wants to stop.

5675 · Post by **5675** » Thu Dec 10, 2020 10:54 pm

If you do a compression check, the prop blade should be at the 7 o'clock position looking at the front of the engine when you get TDC on all cylinders, This is when the mag will spark for starting, TDC to 5 degrees after TDC. This should be the correct position for the propeller installation, which will give you a 3 and 9 position for hand propping, straight across blades. Propeller will stop in same position every time, coming up on a compression stroke on one of the cylinders. Good Luck

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Clocking the prop

Clocking the prop

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