Lycoming O-360 ring gear

[[email protected]]

Hey all. Now that my holiday travels are over, I'm planning to do some
maintenance to my Cherokee. The ring gear has gotten chewed up over time, and now
will sometimes not disengage while the starter is rolling it over. Worn/broken teeth,
etc. I was pretty sure it was a 122-tooth model, but when I looked at it yesterday,
it had the rounded tooth bottoms like the 149. I've got a Skytec starter on it (I'll
have to look up the model number to be sure which one).

Anyway, I think it's quite possible that the wrong ring gear is on the engine.
What's the deal with the two models? I've heard conflicting reports that the older
Lycoming had 122 and then changed to 149. I've also heard that only the O-235 and
O-360's have 149s. I suspect it's probably the former and a mish-mash of
disinformation and ill-fitting ring gears. Since I need to replace the old one, I'm
confronted with the choice of which to get (at least until I verify which starter I've
got)

Questions:
- What's *supposed* to be on an O-360-A3A in a PA-28?
- Is one better than the other?
- How many people have the wrong starter/ring gear combo? I suspect it mostly works,
but probably wears quickly... probably what I've got going on.

Cheers,
-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

[Mike Spera]

> Questions:
> - What's *supposed* to be on an O-360-A3A in a PA-28?

When we removed the air conditioning on our Cherokee, I got my wake up
call as to how little Lycoming and Piper knew about what they installed
on these airplanes. The parts manuals conflicted with the microfiche at
the dealer which conflicted with what was actually installed on our
airplane. So, finding out which part was "right" was a challenge.

I used a method that seems to work well "PIDBWA" (Parts identification
by walking around). I checked the part numbers on other models I saw on
the ramp and at other airports. When I see what was ACTUALLY INSTALLED
on similar airplanes of the same year (and it agrees with one parts
listing or another), that is what I go out and try to find. I had this
problem with the pulley bulkhead/ring gear. 2 different ring gear
pitches, 2 different pulley diameters, and several different belt
widths. Throw in the ones for air conditioned models and... GAAAAAA! I
just checked out the Cherokees on the ramp and instantly got the
consensus. Oddly, the parts installed on all the beasts matched NOTHING
of what the parts places were finding in their documentation.

One place to find this particular part is a little place in Texas called
"Bobby's Planes and Parts". O.K. quit laughing. This guy had every
conceivable pulley bulkhead/ring gear assembly in stock and actually
KNEW what he was talking about. His comment, "yeah the parts manuals are
all wrong". If you get in a jam finding one, I can scrounge up the phone
number and you can see if he is still in business.

Good Luck,
Mike

[Aaron Coolidge]

wrote:
: Hey all. Now that my holiday travels are over, I'm planning to do some
: maintenance to my Cherokee. The ring gear has gotten chewed up over time, and now
: will sometimes not disengage while the starter is rolling it over. Worn/broken teeth,
: etc. I was pretty sure it was a 122-tooth model, but when I looked at it yesterday,
: it had the rounded tooth bottoms like the 149. I've got a Skytec starter on it (I'll
: have to look up the model number to be sure which one).

Cory, every O-360 Cherokee that I've ever seen has a 149 tooth ring gear.
In the end it doens't matter; just make sure the starter & the ring gear
match.
BTW, someone at 1B9 just replaced a ring gear on a Cherokee 180 (not me!),
the ring gear is >$800.
--
Aaron C.

[[email protected]]

On Sun, 8 Jan 2006 14:11:59 +0000 (UTC),
wrote:

snip
>Questions:
>- What's *supposed* to be on an O-360-A3A in a PA-28?
>- Is one better than the other?
>- How many people have the wrong starter/ring gear combo? I suspect it mostly works,
>but probably wears quickly... probably what I've got going on.

Am pretty sure that all the OEM gear-reduction starters used one gear
pitch (fine-149), and that the other was used only on the OEM
direct-drive starters (coarse-122).

Sorry, but it's been too long since I messed with 'em to remember for
sure which was which. With regard to one being "better" than the
other, it would be better if it matched the pitch of the starter drive
installed ; )

I'm sure you are aware that only the outer portion (the "gear") needs
to be replaced, not the entire support assembly.

Part of the confusion comes from the fact that Piper/Lycoming
installations are about 50/50 for who provides the alternator/ring
gear support.

About 90% of the "factory" engines we installed used the original ring
gear support with a new gear fitted. Mainly because the support
supplied with the engine would be the wrong one.

TC

[[email protected]]

Hello guys. I've been browsing this forum for awhile, thinking about
taking up piloting. Just wanted to introduce myself.

[[email protected]]

: Am pretty sure that all the OEM gear-reduction starters used one gear
: pitch (fine-149), and that the other was used only on the OEM
: direct-drive starters (coarse-122).

I don't know about the OEM gear-reduced ones, but Skytech makes their PM in
both flavors. I checked my paperwork last night and it looks like the starter that's
in it is the 149-12LS. I think I need to visually verify this, though. The gap
between the ring gear and starter seems a bit wider than it should be... maybe the
starter is actually a 122-12LS.... or maybe the ring gear teeth are all just worn down
too much.

: I'm sure you are aware that only the outer portion (the "gear") needs
: to be replaced, not the entire support assembly.

Yes... looks like the price on it tends to run about $130-$150

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

[[email protected]]

>The ring gear has gotten chewed up over time, and now
>will sometimes not disengage while the starter is rolling it >over.

The Lycoming starter drive is supposed to lock in the engaged
position until the engine starts and the RPM comes up somewhat. There
are centrifugally-released locks in the drive itself. Some pilots get
all concerned about the drive "sticking" in the engaged position, which
can cause grinding and ratcheting noises when the prop is moved, but
it's normal. Anytime a start has been attempted without the engine
catching will result in this engagement.
The chewed-up gear teeth often coincide with the prop's stopping
position. Check and see if the teeth in the two prop-stop places are
the worn ones. Moving the prop a little (backwards!) before startup
will place less-worn ones in the engaging position.

Dan

[Montblack]

wrote)
> Hello guys. I've been browsing this forum for awhile, thinking about
> taking up piloting. Just wanted to introduce myself.


Welcome. Stick around. Also, check out rec.aviation.student.


Montblack

[[email protected]]

On Mon, 9 Jan 2006 12:25:44 +0000 (UTC),
wrote:

> I don't know about the OEM gear-reduced ones, but Skytech makes their PM in
>both flavors. I checked my paperwork last night and it looks like the starter that's
>in it is the 149-12LS. I think I need to visually verify this, though. The gap
>between the ring gear and starter seems a bit wider than it should be... maybe the
>starter is actually a 122-12LS.... or maybe the ring gear teeth are all just worn down
>too much.

did you count your ring gear teeth? I think the direct-drive starter
gears were a little larger in diameter.

sorry I don't have ready access to prestolite starter drives any more,
the stuff I allegedly maintain nowadays read RPM in % N1 & N2.

>: I'm sure you are aware that only the outer portion (the "gear") needs
>: to be replaced, not the entire support assembly.
>
> Yes... looks like the price on it tends to run about $130-$150

heh. or twice that if you drop in on the support upside down, or fail
to get it seated all the way. BTDT

TC

[[email protected]]

: did you count your ring gear teeth? I think the direct-drive starter
: gears were a little larger in diameter.

: sorry I don't have ready access to prestolite starter drives any more,
: the stuff I allegedly maintain nowadays read RPM in % N1 & N2.

I did this weekend and verified it's 149. The paperwork in the logbook says
the Skytec starter is a 149-12LS. Guess that means I put a 149 back on... just wish I
knew why it wore out in the first place. Maybe the old Prestolite was the wrong one
and wore it out prematurely... it *did* have a cracked mounting flange.

: >: I'm sure you are aware that only the outer portion (the "gear") needs
: >: to be replaced, not the entire support assembly.
: >
: > Yes... looks like the price on it tends to run about $130-$150

: heh. or twice that if you drop in on the support upside down, or fail
: to get it seated all the way. BTDT

Ooops. Guess I'll need to be extra-careful putting it on. How hot of an oven
is necessary? I dont' want to kill any heat treating on it, but I don't what to have
troubles (or lack of time) getting it on either.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

[George Patterson]

wrote:

> Ooops. Guess I'll need to be extra-careful putting it on. How hot of an oven
> is necessary?

When re-sleeving cylinders on motorcycles, we used to stick the sleeve in the
freezer overnight and heat the cylinder to 400 degrees.

George Patterson
Coffee is only a way of stealing time that should by rights belong to
your slightly older self.

[[email protected]]

George Patterson wrote:
snip

> When re-sleeving cylinders on motorcycles, we used to stick the sleeve in the
> freezer overnight and heat the cylinder to 400 degrees.
>
snip

Yup.

Didn't have an oven in the shop, so ring gear supports went into the
freezer and the gears got heated on a steel worktop with a rosebud
torch tip until saliva sizzled on your finger like a hot iron used on
cotton/linen.

Just enuff of the ring gear hanging over the edge of the bench to grab
it with a pair of pliers and plop it on the support. Helpful if you've
got someone standing by with a couple more pairs to hold the ring gear
firmly down against the flange while it's cooling.

TC