The International Cessna^® 170 Association

Thanks George. I'll see what I can work up for the 170 News. As an enticement to get all you freeloaders--oops, I mean future C-170 association members--to join up I will say that there are a number of ways to screw up (no pun intended) the actuator when rebuilding it. I'll include REVEALING full color photos in my TELL ALL report! And yes, I'll even EXPOSE all my sources! What do you say we entitle it, "The Turn of the Screw: Part II"? If you think that's frightening you should see the grade I got in technical righting at LouEasyAnna Tech.

As far as the grease goes there are a couple of things to consider. One, like I mentioned above, is compatibility with o-rings. The o-ring in the actuator is the only o-ring on the whole airframe that is in contact with grease. Interestingly, the parts manual doesn't even show the o-ring. One has to go to the Service Letter or a later C-172 parts manual to see the parts within the actuator. Another consideration is compatibility with other greases. Mixing greases made with different thickener types may cause a breakdown of the thickener structure. Grease is thickened with either clay or soap (lithium complex). Normally this is not an issue on things like wheel bearings because we clean off all the grease to inspect the bearings before regreasing them. But in the trim actuator grease compatibilty might be something to think about. Placing a note adjacent to the actuator indicating the type of grease used would be a good idea for the next guy who greases it years later. Be sure and use a grease pencil! Seriously though, don't use a regular pencil--the graphite will cause corrosion on aluminum.

As a side note, I was under the impression that the reason the jackscrew failed on Alaska Airlines 261 was because they mixed Mobilgrease 28 and Aeroshell 33. Aeroshell 33 uses a lithium complex thickener while Mobilgrease 28 uses a clay-based thickener. But in fact it was lack of lubrication that caused the jackscrew to fail. http://seattlepi.nwsource.com/business/ ... ka11.shtml

George you wrote, "Cessna and most other light-plane mfr's allow any good quality grease produced by major refiners that meet automotive standards in similar service." Where did you find that? I happen to agree with you that the marine grease you use is a very good choice for the C-170 including the trim actuator but was wondering about approval basis. The loads and temps. placed on the various C-170 bearings and the actuator are minimal--the real concern when choosing a grease for the 170, in my opinion, should be corrosion resistance. The following pages from the 1962 and prior 100 Series Service Manual are all I could find on Cessna's recommendations:MIL-G-7711 has been superseded by MIL-PRF-81322. Both Mobilgrease 28 and Aeroshell 22 meet this mil-spec.

Gary, look under NOTE on the first page. It states that products of reputable manufacturers of the greases meet or exceed the mil spec and may be used. See I found it and now Geoge will say even a blind hog will find an acorn every once in a while (talking about me-- not you). Ron

Ron, I guess I ought to read what I post. Thanks for finding that! I wonder if Cessna changed it's mind on what grease to use for the trim actuator though. Rather than calling for the general purpose grease (or equivalent) listed in the service manual, service letter SE73-25 is quite specific: "MIL-G-21164C High & Low Temperature Grease (Molybdenum Disulfide Grease)".

I have found that the premier lubricant for just about anything is a good shot of my girl friends cold cream. When I was a telephone lineman, I once used it to jam a crossarm up a bees butt.

Boy, that was a long time ago!

blueldr wrote:I have found that the premier lubricant for just about anything is a good shot of my girl friends cold cream. When I was a telephone lineman, I once used it to jam a crossarm up a bees butt.

blueldr, I was waiting for your reply on this but thought you would recommend KY or Astroglide. Cold cream???

Gary, make certain you include bluEldr's recommendations in your ART-ICKLE!

Everyone: Grease is a mixture of oil (either mineral or synthetic) and soap, usually made of either mineral ash or metal hydroxides. Lithium (a metal), aluminum, and calcium are the most common but others are also possible depending upon the particular characteristics desired. Molybdenum is sometimes added to lubricants to provide "slickness" and sometimes phosphates and sulfur compounds are added to increase extreme-pressure resistance. (The EP additives actually vaporize/re-condense under pressure to create a surface-lubricity against scoring and galling.)
The point is: They are not compatible with each other and they are NOT TO BE MIXED with each other, and that requires GOOD CLEANING when disasembling and re-lubricating. You always want to remove ALL old grease for inspection purposes anyway. NEVER simply smear new grease on old. You never know what the previous guy used, no matter what it looks like, and adding different grease types can be the actual act of destruction! No kidding.

Cessna's subsequent SB regarding actuators probably follows similar practices as other actuators.