I got tired of problems with bent pricker needles on my Primus 1001 "blue hat". After yet another procedure of straightening pricker's wire I looked closely onto root-cause of the problem. Obviously it is the pricker rod which is "wobbly" in its upwards movement. That causes the pricker to be sometimes off-centre when it should enter the jet. Not much to be done with "wobbliness" - I don't have spare parts to rebuild this assembly. But upon looking closer on Primus jet (modern replacement) I notice that they have a flat area, plateau, which is trapping the needle if not perfectly centred. Below is a close-up of Primus jet's inside: Compared to Optimus jet (left below) one can see the plateau in Primus: Why do they do it like that is beyond me, probably something with saving production costs. I'm not sure if original Primus parts also have this flat surface. To cure the problem one takes the biggest drill bit which can go into the opening. In this case it is D=4mm drill. Below you can see that the plateau is gone: drill's cutting surface is making nice dome inside the jet. What is left is to polish "the dome" to remove burrs. I do it by applying drill at high speed but with just very lightly handheld jet. This takes care of all burrs. Due to wide drill this procedure does not affect the jet opening at all - the drill never reaches the small cavity with jet. I reassembled the lantern and lighted it. All is as normal, light level is the same, no flames etc. Only that now I can safely use the pricker to clean the jet. No more straightening of this tiny wire! I hope that helps you guys.
I've never understood why, but that flat area is the way all original Primus jets are. Not the smartest idea, but with the correct cleaning rod, the needle centers enough to be within the small conical area.
The Primus jet is unique. Its just different from the jets of other makes. You'd likely need an end-mill to make the flat part inside the jet. There must be a particular reason why it was made that way. Its actually more difficult to re-produce the multiple steps as compared to a straight conical end towards the orifice.
I agree: milling flat-bottom cavity at certain depth and then following it by centered drill of small diameter then followed by another tool ”puncturing” jet hole (Primus) - compared to drilling conical opening finished with jet hole puncture (Optimus). So much work! There certainly must be a good reason Primus made it their way. These people were very smart and everything is there for a reason. My modification might not affect performance of my 1001 but may be disastrous for another Primus lantern. So feel free to take my experience but beware of risks. @MYN you turned my head around with this comment - thanks! I’ll dig into that a bit more and make some experiments.
I should think the original was done with something similar to a spade bit, all in one operation. Drill bits for brass are best with near zero rake angle as it stops grabbing and chatter so a spade bit suits that well. Drilling the jet hole would be the last operation of course.
Gentlemen, don’t go my way. I have installed non-modified Primus jet again and tested light output. It is better! There is a good reason they made these jets the way they did. It must have something to do with gas stream forming etc. Even though jet hole was not altered in my experiment it still shows a difference. It is not dramatic though so my modified jet will be used on another lantern but on Primus 1001, which is not the brightest lamp anyway, this subtle difference in light output was noticable. By the way: problem with wobbly pricker and bent needles has solved itself. If one does not use the pricker when the lantern is off (why would one) then there is no problem. Once the lamp is operating the stream of fuel/gas at high pressure, rushing to jet opening, is keeping the pricker in perfectly aligned position. No misses, pricker always finds jet opening. It feels now I was reinventing the wheel but I’ve learnt a bit and my respect to old-time engineering has increased even more.
