I was getting ready to start a rebuilt saw, so I poured in a little mix, put the old flippy cap on and turned the saw right side up. There was a dribble of mix coming out of the bottom of the cap. I took off the O-ring and slipped on a new one that I had bought on Ebay and no leak. Here's what they looked like side-by-side:
The readings on the calipers are where the rings fell off. Four mm difference in inner diameter. The old ring was 3.3mm thick, the new one 3.5mm.
The old ring also had grooves worn into it.
The lot of 50 Buna rubber O-rings of the specified size for Stihl fuel caps (3.5mm x 25mm I.D.) came to $0.21 each, shipped. Worth a try for those leaky flippy caps that look OK otherwise. Might want to carry a few with you into the woods.
The readings on the calipers are where the rings fell off. Four mm difference in inner diameter. The old ring was 3.3mm thick, the new one 3.5mm.
The old ring also had grooves worn into it.
The lot of 50 Buna rubber O-rings of the specified size for Stihl fuel caps (3.5mm x 25mm I.D.) came to $0.21 each, shipped. Worth a try for those leaky flippy caps that look OK otherwise. Might want to carry a few with you into the woods.