Ok, not a conventional 'Stove Reference Gallery' view of a Primus stove (or even a part of one) I'll confess, but let me explain ... The stove is a gift from someone here on CCS who's asked me not to name him. He explained before sending it that it had cost him little or nothing and was surplus to requirements. He'd warned me that it would need fettling, with a suspected leaking burner. It certainly looks well and it's a bonus that it still has its original cast iron flame tube, which could easily have got detached and lost when passing from one custodian's shed/garage/workshop to the next during its 63 year life so far AN (1949) date code in the centre of the base A few things to put right, granted, like an excess of solder on the pump tube to tank joint, which could well leak in spite of all that mass of lead ... One of those endearing (until you come to use the pump) elongated holes in the pump cap, suggesting it's had a lot of use - which is what's endearing about it It also has damage to the spirit cup that suggests it's been cooked by a careless blast from a blow-torch - possibly as a quick and handy alternative to priming with meths. It's in a hefty gauge of brass though, which should be easier to fix than with the thinner stock I'd to deal with in this spirit cup repair Svea spirit cup repair My attention turns to the burner which my CCS chum suggested is holed - in places where it shouldn't be that is From some angles it looks ok ... ... then an old and lumpy attempt at a brazed repair comes into view This scoop in the flame tube support ring points to more injudicious use of a blowtorch, this time the one used to sear those burner tubes during that brazing attempt, most probably Preamble over, I'd best explain what that arrangement in the header photo is all about. It's to make sure that the brazed 'repair' leaks. With a wodge of tissue to prevent drips of water from the jet nipple impinging on the suspect joint and confusing the diagnosis the burner's suspended over a bowl and water's trickled in the burner inlet A certain and substantial leak A word of explanation for the fastidious archivists why a fettling project appears here in the Stove Reference Gallery. I reasoned that it's a project that demands getting up close and personal with some crucial components of the stove - offering plenty of reference photos on this stove type. Mostly, though, I'd like it to go somewhere in the CCS archive where it constitutes a more lasting tribute and 'thank you' to the donor. Of course, that's only going to happen if I don't mess up the repairs ... TO BE CONTINUED John
Hello John A tantalizing teaser to tickle my taste-buds temporarily (sorry, am watching old TV Batman as I type). Not having the equipment or skills, the point at which you have arrived in your tale would have been the point where the burner would have gone in the bin. But I have every faith in you and look forward to the next installment in your saga.
Hi John a very good and interesting read and detective work on the 702. I agree it realy has seen a lot of work, and i would imagine worked at full power and beyond. seeing the elongated pump tube cap realy does show how much use it had. Quite often the 702 stove/burner unit, was used in conjunction with the plumbers furnace, brand name the london furnace. On seeing the amount of use it has had,i am going to say this stove was originaly owned by a plumber, and part of his furnice for melting plumbers metal. As in 1949 lead pipeing was mostly used, and lead pipeing was repaired with out replacing well into the 1960's 70's. But i dont like the look of the solder repair around the pump tube,if it was done by a plumber it is not very neat. Another point i forgot to mention why i beleive this was a plumbers tool,is where you have pointed out, where the spirit cup has been cooked with a blast from a blowlamp, and has started to melt it. As a plumber would want it lit as quick as possible,so he could get on with as much work as possible,and it would be used at full power a lot of the time to melt the lead as quick as possible. I like your way of testing the burner for leaks,by pouring water in it and watching for where it leaks out from. I usualy check my stoves and burners, by putting in a blank jet, and pumping a good amount of air in the tank,and emersing it in water and watching for air bubbles. But the stove etc would need to have a fully working pump and good working seals,your method one could check the burner first. I am looking forward to reading more on the 702 and seeing it fully restored and working
Thanks fellas! A lot of useful information to ponder there Brian, and the voice of authority too (by lineage at least) since you've told us here (Nick's 702 and furnace) that your great uncle was a plumber and an artisan in lead (bit like Billy the Kid was?). Much appreciated, thank you. I'd usually go with that 'spot the air bubbles' approach with a smaller burner, but this larger size made the way I did it feasible, with its (comparatively) cavernous burner inlet and that dodgy brazing on a large enough scale to spot where the water was emerging from. John
Fun-packed evening. First, a robust exchange of views with mate Ian about owning a swastika-emblazoned stove (Juwel 33) then a go at clearing that ghastly mound of brazing metal off the Primus's burner. A session with the Dremel and a few cutting wheels and tips did the trick As I'd suspected, taking time to clear up the debris revealed the source of the leak - a cavity that would make a dentist reach for a bulk supply of amalgam Back to the set-up in the header photo again to confirm that it was the source (and only source it turned out to be) of the leak. Not a problem to put that right - just won't be using silbraze rod like solder like the last person to attempt a repair did John
Winter in the UK and it's dark on getting home from work. I needed daylight to make a proper job of the silbrazing so it's been left until the weekend. Job done. It's just been silbrazed in this photo and I'm about to get rid of the flux residue and oxide Before I can re-unite the burner with the rest of the stove I've some jobs to do - new pump washer, replace NRV pip, take a look at that pump tube soldered joint. I wanted to give the burner a 'hot' testing and not just the water treatment so I mounted it on my Sievert Vapouria (Vapouria - Stove Reference Gallery) No leaks, working as it should and with a healthy roar, punctuated by the lazy, bass-register 'chugging' sound that these big burners put out when they're chucking out the heat Seeing the Vapouria and the fact that I've not yet got around to making up a set of carrying handles for it reminds me that they're lacking on the Primus too - another job to do, modelling them on this example on my Primus 85 John
Hi, John, Excellent thread, and another fine fettle for you! Your skills are outstanding, and your hands steady, to be able to pull off some of the things you do with stoves! I doff my chapeau to you, Mate! Any idea what the BTU output is for your big stove? I believe the official CCS terms is "Gobs of BTU's", right!?! Very nice job, John, and thanks, again, for sharing it with us. Take care, and God Bless! Every Good Wish, Doc (who wishes that he possessed many of your skills, and your absolutely intrepid fettling courage!!) 8)
Hi Rick, Trevor, Doc. Output of the burner, Doc? This burner chart from CCS member Optipri shows the 702's burner isn't the largest in what I think of as the 'furnace' stove line-up recognisable for having tubular flame rings as opposed to the flared flame rings of the large 'domestic' stoves such as the No.2 and No.3. Burner Chart I reckon the 702's burner equates in size/output to that of the No.2 stove's burner. I couldn't but a BTU output figure on that (I bet Kerophile could - he's a mine of information) but that'll give you the general idea. John
Hi John, can you find figures for the tank capacity and burn time for a Pr.702? If so I can give you a theoretical power output. Best Regards, George.
Thanks George. Establishing the tank capacity won't be a problem, but theoretical burn time on a 3/4 tank fill has me stumped. Might not have to be a theoretical burn! Burner charts apart, here's the Primus 702 burner dwarfed by the burner I featured in this post John
Hi John brilliant thread and restoration,the silbrazing job is first class john very neat indeed. All so John your pictures are brilliant and so clear,especialy the close up shots,which show every fine detail clearly IE the crack and cavity on the burner.
Thanks again Brian. A bit more progress. Pump tube solder cleanup and a check for an airtight joint. Here's how it was My technique for getting rid of the excess solder was to take a narrow-flamed hot blowtorch, which for a larger stove such as this one with a lot of brass in the tank (creating a heat sink) I judged would have to be my MAPP gas blowtorch. It seems counter-intuitive, but a fine, searing blast of short duration 'stabs' with the torch flame melts the excess solder away - helped by a wipe from a cotton cloth - and doesn't heat up the surrounding metal of the tank or pump tube sufficiently to disrupt the pump tube/tank solder joint itself The scratches in the brass around the pump tube were already there and I'm not inclined to burnish them out and reduce the thickness of metal to the extent I'd have to. A welcome bonus was that the solder joint itself proved to be airtight. Quite possibly, in melting off the excess solder any imperfections in the joint itself benefited from capilliary flow from the pool of molten solder briefly created as I played the blowtorch flame around the area. As a final night's work I cleaned up the tank filler riser tube area too John
Hi John, I enjoyed the photos of the progress with your Primus 702 furnace. When you get it up and running you might consider a little experiment to assess burner power: 1. Weigh stove just before lighting up. 2. Run at full power for at least half an hour. 3. Allow stove to cool, and re-weigh. 4. Calculate the fuel consumption in grams per minute or second, and we can quickly assess the maximum theoretical burner power. Best Regards, Kerophile.
Hi George. With only some cosmetic tweaks to complete and having replaced non-return valve 'pip' and fuel cap sealing washer, I reunited tank and burner last night and fired it up successfully. I'm keen to give your method to establish a heat output figure a go, most probably tonight. Pictures and results to follow ... Cheers, John
Clear, dry evening. A snag in weighing the stove - with or without fuel. Too heavy for kitchen scales, not heavy enough to register on bathroom scales. An alternative. I filled the tank to 2/3 full and took a fuel level reading, marking it on a dipstick. I fired the stove for half-an-hour, then poured in a measured amount of fuel to take it back up to the dipstick mark. I then calculated the weight of the fuel used from the formula Weight = Volume X Specific Gravity (0.82 for paraffin) I got through 725 cc's of paraffin in the half hour, or 594 grams of fuel. Half-an-hour is 1800 seconds, so I was burning 0.33 grams of paraffin per second. Over to you Kerophile! John
Hi John, a burner using 0.33g/sec has a maximum theoretical heat output of around 15kW or 51000Btu/h. If you look at one of the clearer tables in the later parts of this thread you will see that the figures given by Primus for a No.85 stove are very close at 16.3kW/ 55478Btu/h. https://classiccampstoves.com/threads/9572 Your Pr 702 has a powerful burner with approx. 50% more heat output than a Primus No.3 stove. Best Regards, Kerophile.
