Cowel Screws

[fshaw]

I have a '56 square tail C172 need some help on cowel screws. A couple have vibrated out and I'm trying to determine the correct replacements. From what I can see the correct replacement is S-1021Z-8-8 which I believe is a type B, size 8, .5' length screw. A few of the tinnerman nut plates have stripped over the years and I'd like to replace them. Aircraft Spruce has NAS 444 anchor nuts in size 8 part number A6195-8Z-1D. Would this be the correct replacement, and if not, where should I look? Also, will the "U" type NAS 395 Tinnermans hold type "B" sheet metal screws of the same size? I'm a little embarrassed to ask such a simple question and appreciate your help.

Also, my right tank gas gage reads empty regardless of gas in the tank. The person who owned the plane before me painted over all the screws in the access cover for the tank. I'm not crazy about using a wire wheel on a Dremel or a drill near the filler cap and was considering a spot application of paint stripper on each screw to get rid of the paint so I can get the screws out. They won't budge as is. Is there a better option than paint stripper? I've tried valve compound on the screw driver to get a better grip on the screw slot. No go. Once I get the cover off how do I determine whether it's the gage or the sender. I expect I should see either 0 volts or 14 volts at the gage when full. What would be the correct screw to replace the screws for the access cover? Are they considered structural? I have an A&P who will supervise the work but want to be as prepared as possible with parts and materials before the work begins. I tried to search the data base to prevent a redundant post.

Thanks.

Frank

[fshaw]

Looks like I should have researched the fuel gage as well as I did the cowel screws. From what I see I don't have to remove the top access cover to access and gage parts, just unscrew the gage and remove it into the cabin. I also see that Aircraft Spruce has a replacement mechanical gage. Does anyone know the correct length to cur the Spruce gage arm to to get accurate readings for my tank? Can I just match the length of the original gage?

Thanks.

Frank

[Ryan Smith]

Looks like I should have researched the fuel gage as well as I did the cowel screws. From what I see I don't have to remove the top access cover to access and gage parts, just unscrew the gage and remove it into the cabin. I also see that Aircraft Spruce has a replacement mechanical gage. Does anyone know the correct length to cur the Spruce gage arm to to get accurate readings for my tank? Can I just match the length of the original gage?

Thanks.

Frank

Frank,

Do you have a copy of the Illustrated Parts Catalog for your airplane? They're available for free from Cessna if you sign up for a (free) account on www.support.cessna.com. I would advise looking at the IPC to determine the cowl screw situation, because as I'm sure you've found out, what's on a 60 year-old airplane isn't always what it left the factory with.

I'm sorry I can't help you with regard to the fuel float arm length...you likely simply need to replace the cork floats with composite replacements, or new varnished cork floats. My family's airplane had a similar issue by the time my grandfather purchased the airplane in 1986. My father simply replaced the floats, or at least re-varnished them. The varnish eroded away as a result of using auto fuel by the use of auto fuel by previous owners.

[Bruce Fenstermacher]

Frank, you are correct. You do not have to remove the wing tank cover, in fact you can't get the gage out that way. As stated about the only thing that goes wrong with these gages from an operational stand point, is the float cork fails. New neoprene style corks are the replacement of choice. You will also need gaskets which you can buy or cut your own. I have instructions available here to cut your own but you will need member access to get to it. Are you a dues paying member of TIC170A? Your forum account does not indicate you are.

As for crew paint removal. There is a nifty little tool available that is a round cutting die. The die fits snugly around the outside of the screw head. Placing it over the screw and turning it cuts the paint perfectly around the head. The screw is then free to turn out without messing the paint around the head. If you need to you would then use an sharp awl to dig the paint out of the screw head so the bit will bite. There are different size cutters for different size screw heads.

http://www.aircraftspruce.com/catalog/t ... cutter.php

Snap-on Phillips bits have little barbs ground into the bit that help it grab when they are fresh. I don't know if they are any better than the valve grinding compound trick.

SDM221IRB.jpg

[170C]

Frank, as Bruce told you, you don't have to remove the fuel tank to do gauge repairs. You mentioned a "sender" in your post. Your gauges, unless there has been a modification, are mechanical--no electrical involved. Once you are a member you should be able to access the procedure for making the repair to your non functioning gauge in our forums. Member Steve Grimsley did a good article on this in one of our Cessna Quarterly magazines. I have removed both of my fuel tank covers, one twice, and if you ever have the occasion to perform this task I strongly recommend you obtain the procedure that member Jim Wildharber prepared. It works! It takes a lot of patience, blood-sweat & tears to remove those covers and the tanks themselves. You will likely find some screws that you will not be able to remove via a phillips screw driver. At some point you will wallow a screw head up and the only practical means that I know of to remove those problem screws is to use a Dremal and cut a slot in the screw head. In most cases that will allow you to remove the screw (just keep the fuel cap on to prevent fumes around where you are cutting the slot). The other option, and one that may have to be used if the slot fails, is to drill out the screw.
Regarding the screws for your cowling. I experienced some screws backing out from time to time and some of the tinnerman's breaking. My IA and I replaced all of them with #8 machine thread screws. That eliminates the issues you describe. Wished I had done it years before I did so.

Frank S

[fshaw]

I will be joining, but it will be in February. January is tax month in my county/school district of NY! I do sincerely appreciate the knowledge and help I get on this site. Though my plane is technically a 172 it has more in common with 170s than with most 172s. Also a bit different outlook about tackling problems here than on 172 sites. So, thanks for your help. I do sincerely appreciate it.

Frank

[Bruce Fenstermacher]

This is what the fuel gauge looks like after being removed.

See the cork on the left. Yours is probably gone or fuel soaked. We just talked about replacing it in another thread. See the black gasket on the left. It is round like but not the same as a fuel or oil cap gasket. It can be cut from neoprene, Buna N or cork gasket material. Thought I had the dimensions but can't put my finger on them at the moment. Maybe I didn't bother to measure as it pretty easy to copy.

Fuel gauge1.jpg

[fshaw]

Bruce,

Aircraft Spruce offers a gasket For a gage that's supposed to be a direct replacement. Do you know if it fits properly. It was mentioned in another thread here.

Thanks.

Frank

[Bruce Fenstermacher]

The gage they sell is the same as far as fitment in the tank and so it would follow the gasket would work as well. But I cut my own.

[fshaw]

Thanks Bruce.

[bagarre]

Be sure to drain the fuel before removing that gauge

[blueldr]

fshaw,
The "A" or "B" on the nomenclature of the sheet metal screws indicate a pointed (A) or a (B) blunt screw tip.