I have researched, and contacted Lycoming, re this and am still a bit confused. Have my engine at approx top dead center on the compression stroke based on looking into the spark plug hole and guessing whether I am at the top of the stroke. But, I would like to know for sure where in the stroke I am as there seems to be quite a bit of leeway as I rotate the prop between the time the piston stops moving on the up stroke and the time it starts moving again downward. In other words, lots of degrees of rotation between the place where the piston stops moving and starts moving again as the prop is rotated. I have two sets of timing marks on my starter ring gear. One set on the aft edge which I have shown in the photo lined up with the center of the engine case based on where I think the piston as the top of it's stroke. But, there are marks on the forward edge of the ring gear, as well. These don't seem to line up with anything. I have read that the marks (TP-1) on the rear should line up with the center of the case, which in my case, they kind of are. But, what about the marks on the forward edge? I read the TP-1 on the front should line up with a hole in the starter case. But, I have no such hole and as can be seen from the photo, they don't line up with anything on the starter.
I'm used to timing auto engines with a fixed pointer on the engine block closely aligned with the timing marks on the crank pulley or starter ring gear and would like to get my 390 timed as precisely as possible. And, lining up the TP-1 mark with the center of the engine case seems, well, a bit imprecise and clumsy.
I'm used to timing auto engines with a fixed pointer on the engine block closely aligned with the timing marks on the crank pulley or starter ring gear and would like to get my 390 timed as precisely as possible. And, lining up the TP-1 mark with the center of the engine case seems, well, a bit imprecise and clumsy.
