The Javelin aux tank approved for Cessna 170's on the TCDS used a Gates 20 cap. While I have not gotten absolute confirmation, I believe the Stant BK 7031220 (that's a Bravo Kilo 7031220 ) is the modern equivalent. (Stant has acquired the Gates fuel cap product line.) You can get this from any NAPA dealer. It is believed to originally fit early 1950's Chevy 1/2 ton trucks. Should cost about $6.
Hope this helps. (Join!)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention. An originality nut (mostly) for the right reasons.
That same cap will fit the wing fuel tanks on B models & early 172's. They are vented caps and cost the $6.00 that George mentioned. I bought mine at O'Rilley,s Auto Parts, but most other retailers also carry them. Just tell them its for an early Chevy or maybe Ford pickup. Don't mention its for an airplane! I used mine for several years without any flack from my IA, but I doubt it is/was legal. Finally resorted to purchasing two of the "proper" ones hoping to stop fuel leakage, but without success. Thus the fuel tank gasket project that is upcoming. One nice thing about the auto parts ones is that they appear to be chrome and don't rust. However, there isn't any provision for the safety chain. An imaginative owner could likely find a way to attach one.
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