-325
The oring for the standard cap on the RV-8 is a dash 325. I got these from Mcmastercarr.
https://www.mcmaster.com/5267T362/
Steve
An alternative O-ring to use ...
This alternative flouroelastomer (viton) o-ring may have already been discussed for the Usher cap, but if so - I missed the memo, so ...
I have been using this ring on my new style Usher caps for more than two years now, and find it to be a much better (at least for me) "fit" for this application - where it's operation requires it to be elongated, while it is being compressed to facilitate sealing the cap to the filler neck.
The original o-ring spec'd by Usher is a 75A durometer hardness, which is at the middle of the Medium Hard range on the Durometer "A" scale, and is comparable to a tire tread - this is a fairly dense compound. The o-ring I chose to replace it with, has a 60A durometer hardness rating ("A" scale) , which is at the middle of the Medium Soft range and is comparable to a pencil eraser.
This extra softness has two benefits: It can be expanded more easily with less "break over" effort on the cap lever; and, since it compresses more easily, it can expand to form the seal with less mechanical input. Because it is softer, some additional "take up" may be required on the lever to give the feel you want. But, flying my Rocket (goes fast = lower pressure over top of the wing - think sucking the cap out) has proven a pretty good "test bed" for such an experiment - no issues so far ...
I got mine from McMaster-Carr (doesn't everybody) - P/N 1284N198 Chemical-Resistant Soft Viton Flouroelastomer O-rings, #325 with a Durometer 60A (Soft). They are colored White & are expensive - but they do work ...
YMMV - Just Sayin'
HFS
HR II S/N 002 - Flying now 22+ years
