I've never seen one shrink and fall out, but sticking to the rim of the fuel filler riser and pulling out of the cap on unscrewing it from the filler is a common occurrence. Not just on the 71's but on larger stoves (and consequently caps) without an air screw boss to offer an additional edge bond to secure seal to cap it can be an issue too. Unless there's a patent reference somewhere in the literature to establish for sure why, I'd speculate that the fixing screw was a refinement to overcome the seal-sticking-to-filler riser-syndrome. John
I'm new at primus stoves. I just got an older model- I think. I cant see any dates, or markings that help me know the age. The gas fill cap on the tank though is domed, and has an inside screw holding the gasket/seal in place. ("C" cap in the proceeding page.) Also, any great place to get a new gasket/seal? Patrick
@Patrick The Fettlebox will have the washers/seals you need. As to the date, if I isn't stamped (on the underside?), did it come with a tin? Photos? Tony
bump OLD THREAD. My thanks to nmp and all those who contributed. Yun is latest member interested in various Primus 71 filler caps, Primus 71 tank lids. He's already familiar with Ross's excellent image: Yun and others are interested to know MD: filler tube thread, major diameters and ID: filler cap thread, inside diameters: A: MD is 14mm, ID is 12mm. This exact cap was a carry-over from Primus 70. B: MD is 14mm, ID is 12mm. A & B are shown here, B (rare) is same as A with center screw added to underside (late in '37). C: MD is 16mm, ID is 14.5mm. aka dome lid "'... '38 is the debut for that filler cap" source. D: MD is 19mm, ID is 17.5mm It's use began in 1953/54. E: MD is 19mm, ID is 17.5mm. It's use began by 1963 Note same *size cap as D (not same seal). The lead up to, including 1962 (genuine) Primus 71 used "D:". Re E: it is the Optimus *298D filler cap. By 1963, Optimus began producing their PTC Primus 71. They used their Op 80 tank (w/P71 stamped on it) and their 298D filler cap which was in-use on their Optimus 80 (& 8R). *again E is the the same size cap & thread as Primus "D:" (& swappable). Although there are many variations, the P71, Op 80 & 8R and Optimus/Svea 123s continued to use this same size & thread until production ended (all SRV type caps of D & E size are swappable). Among Swedish stoves, there are many swappable parts between makers, the D & E filler cap size & thread is quite common. ------------------------------- There's another, rare, Primus 71 cap btw, it could fall in between C & D. I'll refer to it as a *'52 shorty cap (1952 Primus 71 shorty, filler cap) '52 shorty cap: MD is 16mm, ID is 14.5mm. (cap same size & thread as dome lid "C:") also seen here , scroll down in link and see more of it. IIRC credit Hazet to 1st post it on CCS ('n that secret was out lol). *I called it '52 shorty cap" because , to date it has only been found on that version & year P71. Of note, these examples also have their safety pin . tag @Yun124 @kerophile 2,750 views
Dear @OMC , Thank you for your post, very very helpful and exact details you gave us. Now I clearly understand AB & C cannot be compatible.
