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I rotated the engine with the top plug removed on #1 cylinder plugging the hole with my thumb. When I could feel the pressure building up from the piston coming up on the compression stroke I kept rotating the prop until the TDC mark on the flywheel lined up with the mark on the starter housing. At that point my prop was horizontal. My engine is sitting this way now until I get my prop back from overhaul so I can put it back on the same way. I checked with my mechanic and he agreed this would be the correct procedure.
The timing mark that lines up with the starter is not TDC It is the 25 degrees BTDC for mag timing - that being the case the prop would be fairly close to horizontal - but true TDC the prop is another 25 degrees past that point. That clears up the confusion- thanks
Mine is set the same way. Regards the impulse coupling firing, it will fire at TDC, which in my case is prop going thru horizontal. Generally speaking, when you are propping
it, you will likely have it at about it's top speed about the time it goes thru horizontal. The prop will usually stop before TDC and it is usually in that 100-80 degrees before because that is when pressure is begining to build in the cylinder and there is usually not enough momentum to carry it further. About one in a couple hundred flight will
mine stop horizontal at top dead center. With a four cylinder with #1 cylinder at TDC, the other pistons are TDC or BDC only. It's the way the crank is made.
The timing mark that lines up with the starter is not TDC It is the 25 degrees BTDC for mag timing - that being the case the prop would be fairly close to horizontal - but true TDC the prop is another 25 degrees past that point. That clears up the confusion- thanks
On the "engine side" of the flywheel I have both marks. I'm not sure on the "prop side" (which is the only side useful with respect to using the starter for indexing). I'm going to have to look when I go back out.
I wanted to make sure rather than going by memory, so I went by the airport yesterday on my way home. My flywheel has both marks on the front of it. The 25 BTDC and the TDC mark. When I took the prop off I rotated the engine to the TDC mark when the #1 cylinder came up on the compression stroke and the prop is horizontal.
Pictures are worth a lot of words.
Photo showing the starter ring with prop removed and Cyl 1 on TDC. (Prop Studs Near Horizontal but Not Exactly)
Photo showing the OEM Bendex Starter relationship to the Starter Ring Cyl 1 TDC Mark.
Photo showing the Prop Indexed with Steve's recommended 1oclock - 7oclock Index. (Pilots Seat Perspective)
From this I see Pacer 24 is correct that there is no true horizontal option although close enough for arguments sake.
Brian: In the last photo, your engine is still at #1 TDC? Or this is after you ran the engine and it stopped in "mid-compression stroke"?
Best regards, Todd
Still at TDC. Avatar photo of me holding the prop is how the prop stops after shutdown.