122 v’s 149 teeth

R

redfin

FRIEND

• Mar 7, 2022

• #1

From what I have read, 122 tooth applied to ‘older’ installations and 149 newer ones. Is there any other advantage of one over the other in a 0-320 install?

ie. I now have a common starter with a Scout?

Any disadvantages changing the 122 0-320 to 149 on starter changeover?

 

wireweinie

FOUNDER

Palmer, AK

• Mar 7, 2022

• #2

122 tooth ring gears were originally used on aircraft with tighter cowling like twins. 149 tooth starters are more common around smaller stuff like Cubs. Other than commonality there is no advantage to one over the other.

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skywagon8a

MEMBER

SE Mass MA6

• Mar 8, 2022

• #3

redfin said:

From what I have read, 122 tooth applied to ‘older’ installations and 149 newer ones. Is there any other advantage of one over the other in a 0-320 install?

ie. I now have a common starter with a Scout?

Any disadvantages changing the 122 0-320 to 149 on starter changeover?

Click to expand...

The teeth on the flywheel must match the teeth on the starter. If you change one, you must change the other.

 

C

CharlieN

Registered User

Down low in the hills of Vermont USA

• Mar 8, 2022

• #4

The diameter of the ring gear is the same, one has a 10/12 tooth pitch, the other is a 12/14 pitch.

 

wireweinie

FOUNDER

Palmer, AK

• Mar 8, 2022

• #5

I hate when I'm wrong! Lol. But I should be used to it by now.

I've attached an old and a newer page from a Lycoming service instruction that explains some of this.

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Attachments

• SI 1121.pdf

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• SI-Lycoming_n.1121.pdf

  822.9 KB · Views: 95

C

CharlieN

Registered User

Down low in the hills of Vermont USA

• Mar 8, 2022

• #6

I changed the RG to the fine pitch to work with the change to a compact starter, they swap on the same flywheel.