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alpinelakespilot2000

Well Known Member
Here's a picture of my Saber extension over my Aerosport Power-installed starter ring. From what I understand from earlier threads, a two-blade fixed-pitch prop is generally clocked at the 2:00/8:00 position with 12:00 being the marking of TC#1 on the forward face of the starter ring. (There's another TC#1 on the aft face of the starter ring at about the 6:00 or 7:00 position. But I understand that's not for prop purposes.) Does this picture correctly show the approximately angle at which I want to install my Catto 2-blade prop?

EDIT: This clock numerals on this picture are incorrect... see posts further below for some clarification...

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Or 1:00/7:00... or 3:00/9:00

OK, actually I changed my search terms and found that 1:00 and 7:00 is best (from Mahlon) and 3:00 and 9:00 (is what Mel suggested). My 2:00 and 8:00 came from another set of threads. There seems to be no consensus.

To add to the mix, I just went out to the hanger and found that my prop won't attach in the 2:00/8:00 position (if I've correctly located 12:00 as being the hole closest to TC#1.) It only fits at 1/7 or 3/9.

Thus, given the fact that everyone seems to argue 1/7, 3/9, or 2/8, the only thing I really need to know is whether I've correctly located 12:00 in the picture. Then I'll just have to make a decision for myself about where to clock the prop. Is 12:00 where TC#1 is engraved on the forward face of the starter ring?

Thanks for the help.
 
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I could be wrong but I think one of the things you want to think about is where you want the prop to be in case you ever have to hand prop it. At least that's what my Tech Counselor said when we attached my Catto a couple weeks ago.
 
ArVeeNiner said:
I could be wrong but I think one of the things you want to think about is where you want the prop to be in case you ever have to hand prop it. At least that's what my Tech Counselor said when we attached my Catto a couple weeks ago.
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I agree, Kelly. That's why I need to figure out (a) where 12:00 is for sure, and (b) whether 1/7, 2/8, or 3/9 is the best position for handpropping.
 
I'm confused by the "clock" positions in the picture. 12 o'clock is straight up on my clock.
Prop position should be at 10/4 when the cylinder is coming up on compression.
This should relate to approximately 9/3 at TDC.
 
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Mel said:
I'm confused by the "clock" positions in the picture. 12 o'clock is straight up on my clock.
Prop position should be at 10/4 when the cylinder is coming up on compression.
This should relate to approximately 9/3 at TDC.
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I'm probably confused too. I just got done reading 24 Years of the RVator and found that the T/C mark I should have been paying attention to was the one on the aft side of the starter ring (not the one on the forward face that I have marked TC#1 in the picture above):

"When the T/C mark on the back of a correctly installed ring gear is at 12 o'clock, aligned with the split line of the case, a 2-blade prop should be mounted at the 2/8 o'clock position, viewed facing the airplane.... when the engine stops, the prop will come to a rest at the 10/4 o'clock position, making it possible to hand prop if necessary." (p. 252)

Indeed, the TC#1 mark on the aft face of my starter ring came from Aerosport at the top, right on the case split line. Thus, it looks like 12:00 is at the top of the starter ring as it's currently positioned on my engine. 2/8 should work fine for the prop.
 
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The picture is correct (1 and 7 o'clock) when a cylinder is at or near TDC. Put the prop on the yellow line.
The prop will be at 10-4 when the engine stops running. Just where you need it for hand propping.
 
Indeed, the TC#1 mark on the aft face of my starter ring came from Aerosport at the top, right on the case split line. Thus, it looks like 12:00 is at the top of the starter ring as it's currently positioned on my engine. 2/8 should work fine for the prop.
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When the aft TC lines up with the top case seam, the forward side TC will also be lined up with the "center punch" hole on the starter nose. The rear marks were installed to facilitate timing on aircraft with a one piece nosebowl or other difficult access to the starter/gear.
 
Yes your clock position is correct for the case I think you're talking about. You seem to be translating the TDC position to a prop mounting position. There seem to be some varying opinions about this and I'm not above sharing mine. Your 12 o clock is where # 1 or #3 will fire if you ever have to hand prop. 12 O'clock meaning top dead center of the compression stroke of the respective pistons. It's here that you will be able to more naturally step back or away from the propeller ark The motion of your arms in this position if your engines fires is to be pushing the prop AWAY from you. However, your Yellow line is incorrect. It should (if that line indicates your prop) run along the 12-6 position. Your engine should stop with the cylinders in a non compressed state in other words it'll stop turning and come to rest approximately on your yellow line. If you were to be hand propping with the prop running along your yellow line as it is right now your tendency would be to follow the prop into the ark or if you were stretched out with your arms pulling the prop down from the 8 position you could easily fall into your prop. Wherever the prop gets mounted it should be the preference for you to be able to spin around quickly and naturally and move away from the front of your plane. It's my understanding that other than hand propping there is no reason to mount the prop in any particular orientation.



I just read your post #2. You should take a plug out and locate TDC visually. In this case it wont make any difference whether it's an exhaust stroke or a firing stroke it'll be TDC.
 
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aerhed said:
When the aft TC lines up with the top case seam, the forward side TC will also be lined up with the "center punch" hole on the starter nose. The rear marks were installed to facilitate timing on aircraft with a one piece nosebowl or other difficult access to the starter/gear.
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Makes sense. I think I knew one was for the starter and the other for clocking the prop, but I had the two mixed up. I had mistakenly thought the aft TC was for the starter and fwd TC for the prop.
 
Rivethead said:
I just read your post #2. You should take a plug out and locate TDC visually. In this case it wont make any difference whether it's an exhaust stroke or a firing stroke it'll be TDC.
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As is probably obvious, I'm still on a steep learning curve re: what's happening inside the engine. Thus, I was hoping that the marks on the starter ring would make understanding what's inside unnecessary.:rolleyes: That said, I'll try to get someone who knows what they're doing around engines to show me what you're talking about. Thanks.
 
You guys may not like what I have to add, but Mel. is right. The trick I for my uses have adoped is. Take the spark plugs out of the top hole. Roll the engine over slowly. The is the crank not the hole thing, in the direction of normal running rotation. When the mag. snaps the coupling, stop. The is the spot the engine will fire first on a hand crank. Now look at the prop and it;s monting holes. Try to get it somewere close to 1 to 3 O clock on the down side with your best blade for pulling though. When you have to this will put your arms coming down and away from the mill when it fires. "You hope". That is if this kind of thing was done any more, as I don't think we are to do these kid of things as per State Farm kind of guys and all.
Yours as alway. R.E.A. III #80888
 
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