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flywheel to hub alignment

SgtZim

Well Known Member
Hi, basic question here. Does the 0 on the flywheel match to the (smeared) 0 on the hub?

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Thanks
 
Aren't the some of the holes and studs different sizes also for proper fit / alignment? For some reason I have it in the back of my head they were.
 
Some props have different recesses for the prop flange, but the ring gear will fit any way.
 
Some props have different recesses for the prop flange, but the ring gear will fit any way.

That's odd, I had my ring gear/flywheel marked for many years so I would always return it to the correct position and recently checked and it will only fit in one position, it will not fit down over the one prop thread insert in the 0 position if the flywheel is in the wrong position, and the prop will only go on in two locations 180 degrees so you can't get that wrong either. I bet you find more than one arrangement out there though.
 
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That's odd, I had my ring gear/flywheel marked for many years so I would always return it to the correct position and recently checked and it will only fit in one position, it will not fit down over the one prop thread insert in the 0 position if the flywheel is in the wrong position, and the prop will only go on in two locations 180 degrees so you can't get that wrong either. I bet you find more than one arrangement out there though.

I have unfortunatley seen flywheels that would go on in any direction - not supposed to, but they did. So I am always suspicious now - put #1 at TDC and check the timing mark on teh back of the flywheel to make sure its in teh right spot when installling a new-to-me flywheel on an engine. It doesn?t;t take long to verify that you?ve got it right.
 
That's odd, I had my ring gear/flywheel marked for many years so I would always return it to the correct position and recently checked and it will only fit in one position, it will not fit down over the one prop thread insert in the 0 position if the flywheel is in the wrong position, and the prop will only go on in two locations 180 degrees so you can't get that wrong either. I bet you find more than one arrangement out there though.

It may depend on how far the individual prop drive bushings stick out in your particular configuration.

Looking at the Lycoming SI for the bushings the index bushing fits a hole in the crank that is about .031" larger than the other 5.

http://www.yeeles.com/Lycoming_Reference/service_instructions/SI1098G.pdf

I know that on both of my O-360's ( -A4K and -A1A) the flywheel will only fit when the "O" marks line up.
 
Some props have different recesses for the prop flange, but the ring gear will fit any way.

If that was true, then the timing marks would be wrong more often than right. There "should" be a single drive lug with a slightly larger shoulder diameter that indexes with a single appropriately sized hole in the ring carier. The ring carier "should" only go on one way - and should do so easily by hand. That said, it's a close enough fit that you can smoke it down with the prop bolts, but if misindexed you essentially guarantee a cracked ring carier.
 
I have unfortunatley seen flywheels that would go on in any direction - not supposed to, but they did. So I am always suspicious now - put #1 at TDC and check the timing mark on teh back of the flywheel to make sure its in teh right spot when installling a new-to-me flywheel on an engine. It doesn?t;t take long to verify that you?ve got it right.

This wouldn't surprise me. A lazy or inattentive mechanic could replace the index bushing (the one with the larger OD) with one of the non-index bushings. This would allow the flywheel to be installed in any configuration. I would suggest confirming any flywheel installation on an engine new to you.

Larry
 
I did a condition inspection on a 6-A that had the flywheel mounted one hole off (with constant speed). Rather than pull it off and mount it right, whoever did it just used a felt tip pen to place new timing marks.....ya sure do find a lot of strange things.:rolleyes:
 
This wouldn't surprise me. A lazy or inattentive mechanic could replace the index bushing (the one with the larger OD) with one of the non-index bushings. This would allow the flywheel to be installed in any configuration. I would suggest confirming any flywheel installation on an engine new to you.

Larry

I don't think so, at least not on my O-360's

The hole in the crank flange is 0.031 larger diameter. The non-index bushing would not be a friction fit. See link in post #8.

However, with a big enough hammer I'm sure someone could make the flywheel fit in any orientation. :D
 
I don't think so, at least not on my O-360's

The hole in the crank flange is 0.031 larger diameter. The non-index bushing would not be a friction fit. See link in post #8.

However, with a big enough hammer I'm sure someone could make the flywheel fit in any orientation. :D

Good to know. I thought it was a stepped bushing with the same size hole in the flange.

Larry
 
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