The International Cessna 170 Association

Except for the "stepped" engine mount the 172XP would be a source, as well as some of the "Mescaleros" and the Senecas (which apparently are also good sources for mounts.) Hurricanes sometimes produce a new source of the things.

I have to admit that it's only a "dream" to have the addt'l horsepower. It only makes sense for me if I find a cheap engine and mount and I'm at TBO on the present engine. I figure a decent ovhl on an O-300 will cost $20K, and for the kind of flying I do, another $20K on top of that for the conversion doesn't really make sense only to cruise 10 kts faster and burn 2 more gph to do it, as I don't typically have any real need for shorter TO distances. (I've got more than 3500' here at home and can always relocate the plane or takeoff lighter elsewhere.)

But, like Tim Allen on "Home Improvement" and "Tool Time"... I'd like to dream about a "Binford 2000" powered by an IO-360.

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Does anyone know offhand the approval basis for installing solid aluminum axles on the '48 170? Thx.

48RagwingPilot wrote:Does anyone know offhand the approval basis for installing solid aluminum axles on the '48 170? Thx.

Yes. Cessna is the approval basis.
(They are known as "ski axles" and are recommended by Cessna Service Letter.)

I've attached S.L.N. 60 in the Maintenance Library to help your A&P with documentation.

Perfect, thanks.

Don't be surprised if your inspector doesn't accept a S.L.N....
The S.L.N.'s were newsletters to dealers, not approved documents, and not even on letterhead. (It was a simpler world back then.)

If you have a set of known quality solid axles, why not just go ahead and install them to keep from worrying about a failure on a hollow set. If the question ever comes up, plead ignorance and just say they have always been there. Probably there isn't one out of a hundred inspectors that would know the difference anyway.

The only thing worse (in the eyes of the administrator) than not performing maintenance.... is not recording the maintenance.

Having the appropriate documentation from Cessna includes having the work description in-hand as you do the work.
One of the things necessary when converting from hollow alum. to solid alum. or hollow steel axles is the need to drill out the lower axle bolt holes to 3/8" and radiussing the new holes to avoid cracks. This should be done on a drill press as it requires precision and pressure to drill those holes....it's very difficult to accomplish accurately by hand.

gahorn wrote:The only thing worse (in the eyes of the administrator) than not performing maintenance.... is not recording the maintenance.

Having the appropriate documentation from Cessna includes having the work description in-hand as you do the work.
One of the things necessary when converting from hollow alum. to solid alum. or hollow steel axles is the need to drill out the lower axle bolt holes to 3/8" and radiussing the new holes to avoid cracks. This should be done on a drill press as it requires precision and pressure to drill those holes....it's very difficult to accomplish accurately by hand.

Are the top axle bolts 3/8ths already?
Reason I ask is because I have solid axles but the upper and lower bolts are different sizes with the lowers being smaller.
I don't have access to the plane or I'd check their sizes.

Relying on memory (I'm not near my library),...the original four holes in early gear were 5/16". Later axles/gears had upper holes the same...but lower holes 3/8".
AN bolts were used and still approved, while NAS bolts are also approved and stronger.

Just checked the IPC.
Lower bolt is an AN6-24A or NAS146-42 optional for skis
Upper bolt is an AN5-23A or NAS145-41 optional for skis

Looking at a grainy photo, my memory was reversed. The upper bolts are smaller as expected.

Why would you need approval to run solid axles vs hollow? The solids are identical in every way except for strength (they are stronger) just like the AN vs NAS bolts.

So, if the S.L.N. is not a valid basis for approval, what is?

48RagwingPilot wrote:So, if the S.L.N. is not a valid basis for approval, what is?

SLN?

According to the experts here, it's Cessna service letter linked above.