The International Cessna 170 Association

I am servicing both of my Fuel Gauges in my '48 Cessna 170. The gauges have cork's for the floatation device and I was told that it is best to seal them with varnish. Do any fellow pilot's know how thick I should apply this varnish? I don't want to put it on too light and risk not filling all the holes in the cork/not sealing it well enough, but I also don't want to put on too many coats of varnish and risk making the bobbers too heavy so that they don't float in the gas. Any thoughts?!

Thank you!

Chris H
'48 Cessna 170

Chris, if they were mine I'd coat them with as thin a coat as I would dare think completely sealed the cork and no more. A method model airplane folks used for years resin coating wings was to apply the resin thick enough to assure complete seal or fill of the weave of the cloth then use paper towels to blot or wick off the excess leaving a film. You could apply the varnish and do the same. BTW I'm sure someone might suggest a two part epoxy impervious to fuel to the varnish but applied just as sparingly.

Also you should know there are neoprene float available which could replace the cork. However this requires slight mods to get the cork of and the new float on and then something to replace the flat on the shaft that held on the float that had to be removed in the process. There have been writeups in the past how others did this. Perhaps someone could point to an article.

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

Here is a picture of this float on a similar gas gauge from Spruce. The page also has a PDF with drawings showing the washers used to hold it on.
http://www.aircraftspruce.com/catalog/i ... cfer=24050

Please check the 170 News second quarter 2012 page 10. My write up with illustrations. For a few dollars you can save a bunch of time and have a better solution. Steve Grimsley

Is there a simple way (other than pulling the gauge) to ID whether it's the float versus the magnets causing erratic readings?

Would the gauge always show empty if the cork was gas logged while if it's the magnets it is erratic possibly?

Kyle Wolfe wrote:Is there a simple way (other than pulling the gauge) to ID whether it's the float versus the magnets causing erratic readings?

Would the gauge always show empty if the cork was gas logged while if it's the magnets it is erratic possibly?

Can't think of any and I doubt you will see any sloop between the needle and the magnet. The sloop and erratic needle is from crude, loose gear mesh.

Kyle Wolfe wrote:
Is there a simple way (other than pulling the gauge) to ID whether it's the float versus the magnets causing erratic readings?

Would the gauge always show empty if the cork was gas logged while if it's the magnets it is erratic possibly?


Can't think of any and I doubt you will see any sloop between the needle and the magnet. The sloop and erratic needle is from crude, loose gear mesh.

Kyle and Bruce
Erratic readings can be caused by slipping between the rod and the magnet at the head of the gauge. I have used epoxy to secure the joints. Has worked for many years.
Just need to make sure empty reads empty and allow the epoxy to cure.

When removing the cork from the end of the rod, you can put the rod end, that has been broadened/flattened to keep the washer on the rod, on a vise and carefully use a hammer to unflatten the rod end. After putting the new cork on the rod, use a hammer to flatten the end of the rod again. This has worked for mine for 10+ yrs ( following Steve Grimsley's guidance).

DWood wrote:Just need to make sure empty reads empty and allow the epoxy to cure.

Cessna expands on what Dan writes in SEB99-18. There they call for the gauge to read empty with unusable fuel in the tanks.