elevator trim tab horn bearing

[learaviator]

Does any one have a source or another number for the bearing in the elevator trim tab horn? In the 170A parts manual, it is figure 16, item 48 - part number PN-3-A.

[Bruce Fenstermacher]

I think your pointing to the wrong part. Figure 16 item 48 is a rivet. Your looking for bushing figure 16 item 55 in my book anyway.

According to Hill Aircraft (www.cessnaparts.com) a PN-3A (pn3A) was superceded by S2629-1 which is superceded by S3895-1. These are available for $71.28. Wish I could help with the Torrington number maybe someone else can for reference of course.

[learaviator]

My book must be old or something, item 55 is a bolt. Item 48 is a bushing for certain serial numbers and a bearing for later serial numbers. I actually think I found one on the internet for 38.00. We will see when it gets here.

[Bruce Fenstermacher]

When you get it you might be able to post the Torrington number for the rest of us, for reference only of course.

[learaviator]

When you get it you might be able to post the Torrington number for the rest of us, for reference only of course.

I sure will, the guy says it is the PN-3A number, and that is also what is stamped on my bearing. I really looked hard for one also, checked with all the bearing manufacturers and was unable to find any, just got lucky calling these guys. If it is the right one I will post the info, I should have it Thursday.

[learaviator]

Well, I had an exellent weekend working on the plane, got to spend both days on it. Put in new lord engine mounts and all new hardware, replaced the cloth covered wire running from the solenoid to the amp gauge. Built a new alternator harness out of tefzel, including the 6 gauge wire running to the alt. c/b. Removed alternator and tightened mount on engine case. Re-installed alt using all new hardware. Must have cut off 20 old hard tie wraps attaching things to the engine mount. Rerouted most everything and installed adel clamps on all of it. Removed carb air box and scrubbed off years of accumulated dirt and grime. It was amazing how dirty it was inside. Fixed a couple of small cracks. Removed the muffler and tig welded a couple of small cracks, removed the shroud and thoroughly washed the shroud and muffler with soap and water. The muffler is in excellent condition, not sure why it cracked where it did. Pressure tested muffler. Removed intake tubes and all oil drainback lines. Installed new oil drain back hoses,new intake hoses, and new intake gaskets. Put everything back together with all new hardware. Installed a different mag on the right side, Built a new electrical cable for the solenoid to starter out of tefzel. Ordered the bearing for the horn on the elvator trim tab. All in all a good weekend. Got my Dip Davis latches in the mail today, and should have the PPonk kit for the gear in a few days. Come on next weekend. Soon to be in the air!

[GAHorn]

I merged these topics since they pertain to the same aircraft project underway.

So, learaviator.... what is the source and part number for that rudder bellcrank bearing you installed?

[Bruce Fenstermacher]

Come on George he said we have to wait till Thursday to find out what Torrington number is on that PN-3A bearing he ordered.

[GAHorn]

He said he'd ordered it...so I thought perhaps he already knew what PN he ordered. (and the real reason for my post was to merge the topics....)...
I can wait.

[learaviator]

This is where I found the info on the bearing, of course for reference only............I will let you know Thursday how it turns out.

http://www.daltonbearing.com/

[learaviator]

Got the bearing today, it is the correct one, it says Torrington PN-3A on the bearing and box.

[GAHorn]

Got the bearing today, it is the correct one, it says Torrington PN-3A on the bearing and box.

What did they charge you for it? (Cessna also supplies that bearing under PN S3895-1 BEARING $ 71.28 (EA)

[learaviator]

The cost was 38.00. Should have ordered two.

[n2582d]

I found this Torrington PN-3A bearing at http://www.locateballbearings.com for $38.50 each. Talk to Mark Hoffman there at 1-800-409-3632.

I'm in the process of rebuilding my trim actuator as I found it very stiff to turn. In doing some research on this I plan on some minor alterations to the assembly. The 170 parts manual shows the push pull tube between the actuator and the trim tab attached using a standard AN365 nut. Later model Cessnas use MS24665-132 cotter pins with AN320-3 castle nuts on both ends of rod between the actuator and the tab. "Cessna: Wings for the World, Part II" says that Cessna made this change after they lost a C-340 prototype during flight test when this bolt came loose.

Trim Attach.jpg

Cessna single-engine service letter SE73-25 calls for checking the free-play of the trim tab every 100 hrs. (See also AC43.13-1B 4-36 d and Section 9 "Elevator Trim Tab Control Systems" in the Service Related Articles Manual published by the International C-170 Association). The C-170 trim tab should have 0.11" max free-play when measured at the end of the tab adjacent to the tab push-pull horn. It also says, "at each 1000 hours of operation (or every 3 years, whichever occurs first), remove the tab actuator, inspect the components and relubricate according to the procedures given in the attached instructions." The four screws attaching my actuator were rusted in place. I had to drill them off and then drill out and replace the nutplates. A royal pain. After getting the actuator out one has to punch out two 1/16" dia. roll pins. I don't plan on doing this every three years so I installed a grease zerk on the actuator. One still has to remove the jackscrew to lubricate that but there is no good way to grease the forward end of the actuator and the internal collars unless it is disassembled or one installs a grease zerk. Mine was bone dry as it had not been disassembled since it left the factory 57 years ago.

Trim tab actuator.jpg

The service bulletin calls for "MIL-G-21164C High & Low Temperature Grease (Molybdenum Disulfide Grease)". Aeroshell 33MS meets this spec. But this grease is Synthetic Ester based. On a scale of Very Good to Very Poor it ranks "Poor to Good" by Shell as far as compatibility with Acrylonitrile. The AN6227B5 o-ring in the actuator (item #12 above) is made from Acrylonitrile/Nitrile/Buna-N. So the solution is to replace the o-ring with a Viton o-ring which is "Very Good" with whatever type of grease you use. NAS1593-010 is a Viton o-ring of the same size as AN6227B5 with a similar durometer rating (squishiness). According to http://www.callapg.com (pg. 97) Viton has an Age Resistance of up to 20 years compared with Nitrile of 5-10 years.

While it is a chore to rebuild this actuator it beats paying the $1444.50 Cessna wants for a new one. Neglecting the actuator is not a good option either--just ask the relatives of passengers and crew on Alaska Airlines flight 261.

[GAHorn]

An excellent short-article, Gary! Perhaps you could submit it to headquarters for the 170 News? And include part nos? and sources?

(For myself, I used my all-time favorite grease, Lubrimatic Boat-Trailer wheel bearing grease, because it's mineral based and absolutely waterproof. It will be good for such long-term useage, in my opinion.)

Note: Lubrimatic is a brand name. This grease is a Calcium Sulfonate complex grease. Another brand name of this type grease is Pennzoil Marine grease, which may be more readily available.