The International Cessna 170 Association

Hollow steel axles vs solid Aluminum ? I'm going to take a WAG and guess the hollow steel is stronger than the solid Aluminum? I assumed my 170b had hollow aluminum & I bought some used solid aluminum axles. After getting 1 side apart I realized my axles are hollow steel... With 4 small bolts. So I will be stepping up the lower holes & installing correct/upgraded hardware.

when I had my first annual done on my 52 170B, they had found the angles of the wheels where off a fair amount. Which explained why the airplane was a really squirrelly on landing. We then made sure the gear legs where good and secure, raised the tail and measured all of the angles. Then had a CNC machine make a custom shim that put the wheels straight. Now the airplane lands much, much better. Thought you might look at things as long as you have the axles off.

I would certainly not drill into the gear legs. Sounds like you have early gear.

For what it's worth SLN 60 gives instructions for drilling the gear legs.

Thanks Gary, I stand corrected. I’ll just say scoring of the hole’s sidewall from the bit in high strength steel is sufficient to create a stress riser, best to finish the holes by reaming to size. Or better yet bring the gear to a machinist.

Dillonz170b wrote:Hollow steel axles vs solid Aluminum ? I'm going to take a WAG and guess the hollow steel is stronger than the solid Aluminum? I assumed my 170b had hollow aluminum & I bought some used solid aluminum axles. After getting 1 side apart I realized my axles are hollow steel... With 4 small bolts. So I will be stepping up the lower holes & installing correct/upgraded hardware.

I had a 1953 170B for over 50 years. When first acquired, it had hollow steel axels. At that time folks were changing out the hollow steel axels for solid aluminum axels because of cracking. Never had problem with the solid aluminum ones in all those years and about 5000 hrs. Solid steel axels are out there also if you can find them… they were used mainly on ski installations I think.

Correction to the above, the cracking problem was to hollow aluminum axels. The fix was hollow steel axels or solid aluminum axels or solid steel axels. Sorry for the mix up… I think I’m getting senile

Back in 2010 Del offered to loan a reamer. See this thread.

n2582d wrote:For what it's worth SLN 60 gives instructions for drilling the gear legs.

Thanks for linking the document. Big help.

edbooth wrote:

Dillonz170b wrote:Hollow steel axles vs solid Aluminum ? I'm going to take a WAG and guess the hollow steel is stronger than the solid Aluminum? I assumed my 170b had hollow aluminum & I bought some used solid aluminum axles. After getting 1 side apart I realized my axles are hollow steel... With 4 small bolts. So I will be stepping up the lower holes & installing correct/upgraded hardware.

I had a 1953 170B for over 50 years. When first acquired, it had hollow steel axels. At that time folks were changing out the hollow steel axels for solid aluminum axels because of cracking. Never had problem with the solid aluminum ones in all those years and about 5000 hrs. Solid steel axels are out there also if you can find them… they were used mainly on ski installations I think.

Correction to the above, the cracking problem was to hollow aluminum axels. The fix was hollow steel axels or solid aluminum axels or solid steel axels. Sorry for the mix up… I think I’m getting senile

I am thinking the hollow steel axles are going to be stronger than the Solid Aluminum, bearing no defects. I don't plan on Skis (which according to 337's it once had them installed... Maybe 8:00x 6's in the future... Thanks for the info.

Some things still have me scratching my head, not unusual…but the date of the snl letter is 49. ish The change in production to reflect larger diameter bolts didn’t take place until mid 51. Some where, some time, someone must have changed out the legs from a mid 1951 170A or earlier model if it has 4 5/16 holes in the gear on a B.

The first axles on 170s were hollow aluminum with four 5/16” holes in them for AN5 bolts. The hollow aluminum axles would sometimes develop cracks at the interior machined steps of the axle…so Cessna modified the hollow aluminum axles to a more “robust” design… which also developed cracks at the interior machined steps.
The recommended “fix” was to install SOLID aluminum (so-called “Ski-Axles”) which had the 3/8” (AN6) lower bolt holes. This required drilling out the lower landing gear legs to accommodate the AN6 attachment bolts.
Our Assoc’n Historian (and aircraft engineering specialist for Andersen-Greenwood who owned the Bellanca type certifiates) Cleo Bickford was very vocal that he felt anyone who drilled out the lower gear legs to 3/8” should also “bevel” or “radius” the edges of those newly-drilled holes to avoid future cracks at that point.

The solid aluminum “ski” axles, while the “preferred” axle for 170s can be improved-upon…by installing the still-stronger hollow Steel Axles.
(This also was Cleo’s comments on the matter.)

Hope this helps. (And most of this info was included in the SRAM “Service Related Articles Manual” which was once published by our Assoc’n but is now (thankfully) out-of-print (due to many anecdotal and incorrect commentay/articles.)

GAHorn wrote:The first axles on 170s were hollow aluminum with four 5/16” holes in them for AN5 bolts. The hollow aluminum axles would sometimes develop cracks at the interior machined steps of the axle…so Cessna modified the hollow aluminum axles to a more “robust” design… which also developed cracks at the interior machined steps.
The recommended “fix” was to install SOLID aluminum (so-called “Ski-Axles”) which had the 3/8” (AN6) lower bolt holes. This required drilling out the lower landing gear legs to accommodate the AN6 attachment bolts.
Our Assoc’n Historian (and aircraft engineering specialist for Andersen-Greenwood who owned the Bellanca type certifiates) Cleo Bickford was very vocal that he felt anyone who drilled out the lower gear legs to 3/8” should also “bevel” or “radius” the edges of those newly-drilled holes to avoid future cracks at that point.

The solid aluminum “ski” axles, while the “preferred” axle for 170s can be improved-upon…by installing the still-stronger hollow Steel Axles.
(This also was Cleo’s comments on the matter.)

Hope this helps. (And most of this info was included in the SRAM “Service Related Articles Manual” which was once published by our Assoc’n but is now (thankfully) out-of-print (due to many anecdotal and incorrect commentay/articles.)

Thank you so much for the definitive response. I have obtained new hardware & will be reaming the lower leg holes & chamfering those holes as well. Funny thing (SIC) is this airplane has a 337 for skies being on it when In AK but it has -5 bolts in all 4 holes even tho the lower axle holes are -6's... Not the only "strange" thing I've found on this bird.

My recommendation for utilizing a good machinisit was to simplify and ensure the entire process would be done right. Drilling, reaming to size and finishing the edges is just common sense for those types when dealing with a hard material. Helps if you know how and if you know how, it's tends to be done easily.
All sounds good and sounds like Mike knows what he has and knew how to go about it (sorry if I sounded alarmed but I had concerns).
I think the conversion kits from Cleveland come with small bushings to adapt the brake carrier to the axle bolts for various bolt configs as well so likely there could be mixing and matching going on.