The International Cessna 170 Association

I’m replacing the failing cork floats on my fuel gauge and I just discovered that the lock washers under each of the four screws that mount the gauge are a special size. The C-170B parts catalog identifies them as 1114-5 “Washer - Shakeproof (attach fuel gage)”. (It’s under item 37 of Fig 7.) Mine that I’ve removed are star lock washers, but what’s special is that the OD of the washer is smaller than usual so that it matches the OD of the screw heads and fits within the recess for the screw on the gauge. Anyone have a source for these lock washers? Or did you just use a split lock washer?

By the way, the parts catalog lists the screws as AN502-416-10 (5/8” long) fillister head screws. But mine that I just removed are 3/4” long (AN502-416-12) and appear to be original to my plane. Why this matters is that the -10 (5/8” long) ones are harder to find and about twice the price as the -12 (3/4” long) ones, which A/C Spruce and others carry. The -12 ones fit perfectly well. I thought I’d mention this in case anyone else wants or needs to replace the screws.

Gene,
Page 2-404 / Fig. 126-12 in the L-19 IPC lists that as a split washer, p/n MS35337-44. Thanks for submitting that L-19 IPC. It's an invaluable cross-reference for stuff like this.

Gary,
I didn’t think to cross reference the L-19 catalog. Great idea. Somehow I knew you would come up with an answer. A split washer it is.

Well, it turns out that MS35337-44 split washers, at least the current ones, also don’t work. The heads of the screws are 3/8” dia and the recesses for them in the Scott gauge are slightly more than 3/8”. But the MS split washers, and star washers (both external and internal tooth), have an OD of 5/8”, so don’t fit. I’m puzzled why the L-19 IPC calls out the MS split washers.

Gene,
Sorry about the bum steer. With an ID of 6.4 mm (0.252”) and an OD of 11.0 mm (0.433”) it looks like these metric sized lock washers from McMaster-Carr might fit. The screws are 0.247” and the screw wells on my gauge measure 0.435”. I’d choose the internal-tooth style.

Thanks Gary. No worries. Not your fault. I’ll check out those metric lock washers.