Dears, So I am fixing yet another WWII military Petromax 200cp size lantern. As usual it’s packing nut has stress crack. I am getting better at silver soldering (a bit), so I fixed it. As I am still not good at all at soldering the threading had to be corrected. New tap bough (the right size available only in China). I am done with that, proud and happy. And I am going back to @Martin K. suggestion that this was not a stress crack but factory-made precise cut/slit... from the thread below: Aladdin Petromax 828 I have these “stress cracks” in every WWII 200cp size lantern – 2827, 2821, 827, 821. All with green enamelled hoods, because I do not own other of that size. Before, I thought that these were stress cracks, but now I start to believe that Martin is right. What do you think and what are your experiences with these nuts from old (WWII and older) 200cp size Petromax lamps? In 300/500cp there are bigger/longer nuts and I have not noted (or at least I do not remember) similar stress cracks in several lamps that I own from that period. Of course, apart from these regular slits, there are also common stress cracks in these nuts, but farther away – as a continuation of the regular slit which reaches always to the half of the nut. There is a quite clear difference as to where slit ends and crack starts. Attached four of subject nuts, additional two (not included here) were successfully “repaired” by me. Nuts are of the same size - these just looks different because of my camera quality limitations. Interesting that I was not able find a die to have a set for the M8x0,8 tap. All the best, Piotrek
I just would like o correct myself - I do not consider all Petromax 2827 as a WWII production. INHO most of them are post WWII and available docs confirm that these lamps were made even in 1950s. I see that sensational "military", "Wehrmaht", "wartime", "nazi" descriptions all the time in almost every 2827 sell offer and do not want to multiply it myself. Sorry for off-topic. Piotrek
I’m no expert on Petromax, but the slits in those packing nuts look very much like they were cut deliberately (except for the side crack on the one with the widest slit). Tony
I would have to agree they look like cuts and are on the thickest therefore stronger part of the nut. It does look like the cut can lead to a stress fracture as the nut will splay out if over tightened. Repeated tightening would also “work” the brass possibly leading to fatigue and or hardening, making a stress fracture more likely.
I would not know if those slits on the packing nuts were deliberate, precise cuts or stress-induced cracks from over-torque on the work-hardened brass. I've not known of other Petromax with such cuts on their packing nuts. Wonder why would that be necessary on the 282X series. Not sure if that would help prevent any over-tightening. The threads on the pricker control assembly are straight, not tapered. Therefore the counter-forces from 'over-tightening' would act mostly in the axial direction instead of radially outwards to split the nut. Perhaps some torsional stress from the wrench as well?? *** Anyhow, the M8 x 0,8 thread would not be a standard size. The standard coarse and fine metric for M8 are only available in these pitches:- - 1,25mm - 1,00mm - 0,75mm - 0,50mm - 0,35mm - 0,25mm and - 0,20mm.
The graphite packing inside the nut presses more and more on the nut from inside when the nut is tightened and may cause cracks. But INHO there are quite visible differences between the "crack" and the "slit" even on the same nut (nut in the middle as an example). And cracked is part of the nut where there is no graphite packing but brass... OK, maybe the other end is much stronger but still weird that these slits were in every lamp from that period. Not only 28xx, but 821 and 827 with green tops as well). I do not own them to many, but 6 is still a quite representative number. Maybe some other owners of old Petromax can share their observations. I really do not know, but feel quite stupid soldering something that looks like designed and manufactured part of the lamp Tap with M8 x 0,8 thread - as I mentioned I got it only in China and I could not find a die anywhere.
I think that the "standard" definitions of M8 "fine" threads are .75 or 1. the pitch of 1.25 in the normal or standard M8 thread. When searching online the , or the . can make a difference. Over a short thread the change in pitch from .75 to .8 may be negligible.
They wanted to do something or change something. Then the project was scrapped again and the sawn-in union nuts were allowed to go into production. Back then it was dangerous to admit to wrong developments and waste of materials. That's my theory
