Primus 981 madness

Discussion in 'Fettling Forum' started by Alex74, Jul 5, 2020.

  1. Alex74

    Alex74 United Kingdom Subscriber

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    Great, thanks Nils. I’ll buy a few tonight. Just realised I made a mistake in one of my previous messages. The top recess of the cleaning rod has been re-threaded with a HSS Hand Threading Tap Metric Bottom - M2.6 X 0.45.
     
  2. Alex74

    Alex74 United Kingdom Subscriber

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    Does anyone know the operating principle of the small manometer? Is it an aneroid capsule? What’s the purpose of the metal coil? The dial shows ‘1-2‘ with units of kg/cm2. ( centimetres squared). What’s the optimum operating pressure and how accurate is the gauge?
     
  3. ROBBO55

    ROBBO55 Subscriber

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    @Alex74

    The coil is hollow. As the pressure increases the coil inflates and tries to straighten. The expansion moves the meter needle.
    I can't say how accurate they are as I haven't measured one.

    Nice work on the lantern. :thumbup:
     
  4. Nils Stephenson

    Nils Stephenson Founder Member

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    Manometers on most lamps are not that accurate. They are usually used on lamps with a quick starter so you know that there is enough pressure in the tank to use them. Not really necessary as you just pump until your thumb hurts. :) It's a Primus so you can't over pressurise it with the built in pump.
     
  5. MYN

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    It takes quite a lot for my thumb to get hurt:lol:.
    I'd say, mine doesn't till the pressure's about 4bar(60psi), which is twice the optimum. Tested with a real manometer, not the one on the filler cap.
    @Alex74
    Anyway, the manometer on the filler cap on most lanterns are not quite accurate.
    The initial tension(pressureless) of the hollow flat spring could determine its accuracy and these could be altered to shift the zero and span of the manometer.
     
  6. isfuzzy

    isfuzzy Subscriber

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    I would think that those bespoke filler caps with SMC gauges on the bay will do some good for these old goodies? :-k
     
  7. Alex74

    Alex74 United Kingdom Subscriber

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    Ahh thanks guys. Interesting comments. The thing is, the ‘coil’ in this gauge is completely flat and thin like a small piece of kitchen foil. I’m fairly sure it is not hollow and can’t be ‘inflated’ to bend it. The coil is, however’ soldered onto a central cylindrical part which also rotates. I’ll try and send some photos tonight.
     
  8. Henry Plews

    Henry Plews Subscriber

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  9. MYN

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    @Alex74
    The hollow spring is really as flat ss iit is. Might appear just like a flat piece of metal as you described, but it isn't.
    Its inflatable if its not blocked by dirt.
     
  10. Alex74

    Alex74 United Kingdom Subscriber

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    Ahhh, that makes sense then MYN. Here’s a photo of the coil:

    BE962D0A-A269-48B5-993E-72E387BBAD54.jpeg
     
  11. Alex74

    Alex74 United Kingdom Subscriber

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    I have ‘repaired’ the mid collar. Some experiments revealed that brazing rods required too high a temperature to flow and thin brass could be damaged. I decided to solder instead. It does the job for now but I’ll be after a replacement collar to finish the lamp in glory.

    D1940120-A0B8-4176-AE15-F9B465DF7FCE.jpeg F22EAF0D-882B-4B55-BC03-E0EF0DA49696.jpeg F8557907-83F5-4D3B-B0F8-27CDA3EAC087.jpeg CE153324-AC92-4686-8269-BD1BF5BB6B03.jpeg
     
  12. Alex74

    Alex74 United Kingdom Subscriber

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    And then I flushed the tank out with a bit of fuel, filled it up, tested the jet and cleaning rod under pressure, and tried to light it. And it works!! The lighter roars away with a nice bluish flame. After 10 seconds or so I opened the control cock and the burner nozzle ignited with a yellow flame which soon turned into the nicest collections of blu flamelets. I fitted a cheap Chinese mantle (now waiting for Coleman’s), reassembled with a Suprax replacement glass globe (scavenged from an Anchor lamp) and it’s ready for tonight. The neighbours are coming to see the light up with a few beers...

    9C4CEB6D-BD0A-49B1-8F06-CF6E7F69E638.jpeg EBAC9FCA-5F70-405E-8173-9286A43CD576.jpeg B0B4BD6D-E9C7-479C-816A-58C6416617E2.jpeg B0A5A3D4-9FAE-4E9E-BF1A-9685541C4E16.jpeg 6E57FB58-9991-4EA3-A060-75A7664CFAFE.jpeg
     
  13. Nils Stephenson

    Nils Stephenson Founder Member

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    Can't wait to see the real light up, but the blue flame looks almost perfect.
     
  14. MYN

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    The flat hollow spring looks just like what its supposed to be.
    And really great repairs done.
    The blue flamelets are about as good as I could see them in the pictures, well simply picture-perfect.:)
    Are you waiting for the neighbours to see the mantle burn-in as well?
    Why not pre-burn them first? Sometimes this step could be tricky with some mantles. They could turn either way, if you might guess. Even when everything seems right up to this stage.[-o<
     
  15. george

    george United States Subscriber

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    Nice! :D/:thumbup:
     
  16. Alex74

    Alex74 United Kingdom Subscriber

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    Ok, so we lit it up and all went to plan with the exception of the crappy Chinese mantle which developed a hole after only 10 min. I didn’t want to crack the glass so I turned it off. Neighbours loved it! I think I’ll wait for decent mantles to arrive and I’ll send another photo. But in the meantime have a look below. I really enjoyed this fettle and learnt a lot in the process. Thanks to all of you for your help, but to Nils in particular. If you spot a derelict 981 with a decent collar, please let me know!

    06A86960-5EE2-440F-8C2D-5A9176EE5854.jpeg C0F9CB2C-1364-4B5E-B2C8-267EE51106C6.jpeg
     
  17. ROBBO55

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    Excellent outcome Alex. :thumbup::clap:
     
  18. paul m

    paul m Subscriber

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    IMG_0450.JPG Ohh Adnams ...brewed in Southwold
     
  19. Alex Smith

    Alex Smith United Kingdom Subscriber

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    @Alex74 Great outcome, glad to see it lit. Perfect. A cracking thread, appreciate you sharing the project. Hope you enjoyed your evening.
     
  20. Alex74

    Alex74 United Kingdom Subscriber

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    Thanks guys. Yes, Adnams is a fine brew. Better be at 6.3 % ABV...just don’t have more than two bottles before or during fettling! Nice lamp you’ve got there Paul!

    Erm...disaster struck yesterday. I was fiddling with the lamp again and suddenly noticed I couldn’t shut it down properly with the control wheel. Flames were issuing from the mantle and also noticed the inverted mixing U tube in the hood was glowing a dull red (as if burning was occurring inside it). When cold, on inspection of the burner and jet assembri, the needle had bent inside the jet and could no longer prick through the orifice. Despite my best efforts to straighten it , it snapped off. :rage::shock:

    So, should the needle ever leave the jet hole when the control cock is fully turned on? Was I burning ‘too fat’ in the absence of a needle partially obstructing the jet? It looks as if I have to regulate the travel of the makeshift rod by marking ‘max and min’ signs on the control wheel (a red mark is already there- I assume this is ‘closed’ or needle fully in?)

    I’m going to order another few needles but it may be possible to make my own with acupuncture needles, like Nils did. This fettle is obviously not quite finished yet! 76D0DDE9-C196-4145-9513-5EBD4DBB2697.jpeg
     
  21. MYN

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    It was a great outcome earlier. Too bad, the bent needle and that broke off too.
    These things happen now and every often, Alex.
    Yeah, the needle's supposed to lower sufficiently in the fully 'open' position to be 'clear off' the jet orifice/hole. Its not for regulating the fuel in any sense.
    Bent needles are usually due to the pricker rod and needle not being centred while its poking through the jet. Once fully lowered, it might be below the level of a stepped profile inside the jet. And when you move it up again, it did not enter the conical guidance before reaching the orifice. That would bend the needle instantly. I don't know how the internal profile of the jet in this lantern looks like. Perhaps Nils might have a drawing of it. Its not like the ones for the Petromax.
     
  22. Alex74

    Alex74 United Kingdom Subscriber

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    That’s a good explanation I guess! In theory it should just glide up to the orifice then? I wonder if the needle I got from Fogas was somehow faulty, Perhaps a pitted surface inside the cone.
     
  23. MYN

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    I don't know which jet you're using on the 981 but here's the dwg of the Primus 6145 jet that Nils sent me awhile ago:-
    Its easy to visualize how an off-centred needle could get stuck and bent since the internal conical guidance has a limited 'coverage' and might not accomodate too much deviation.
     

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  24. Nils Stephenson

    Nils Stephenson Founder Member

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    The inside of the jet is the same for all sizes. It is only the actual jet hole that is different (and the number of threads). I believe some of the newer replacement jets have an inside profile that is more like the Px style jets. The end on the cleaning rod is supposed to enter the opening in the jet before the needle reaches the hole. That way the needle is nearly centred and close enough for the conical part to guide the needle the last part of the way.
     
  25. Henrik

    Henrik Sweden Subscriber

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    Great thread! I fettled my 1081. Always a bad sign when you have parts over after assembling... Any ideas where this disc should fit? It is about 10mm in size.

    1074DF82-45FB-4E03-8432-88049319B994.jpeg D02B7360-87DF-4D9C-8EAD-C7C4577E38D9.jpeg
     
    Last edited by a moderator: Aug 21, 2020
  26. Alex74

    Alex74 United Kingdom Subscriber

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    Myn, Nils,

    thanks again for clear explanations. Apologies for the ‘press silence’ but life and work took over again. Meanwhile I ordered two needles (4137) from base camp and another two from Fogas to compare any difference, if I can spot any with the naked eye. The base camp ones have arrived yesterday and am still waiting for the Swedish ones to arrive. I still have the old, original brass jet that was supplied with the 981. I wonder if that’s a better match for my ‘1081-cut-and-shunt’ cleaning rod job? The rod might have the correct length (154.5 mm) and the rack and pinion device work well, but perhaps there are still sub-millimetric imperfections with my bodged repair that somehow prevent that needle from being guided exactly into the jet hole. There is a slight ‘play’ of the upper part of the Adapted shunted rod into the threaded copper coupler. I’m going to replace this with a tighter brass tubing Section this afternoon.... and the fettle continues....:-({|=
     
  27. Alex74

    Alex74 United Kingdom Subscriber

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    Hi Henrik,

    is that a lead washer you have there perhaps? I can’t make out the colour in that photograph.
     
  28. David Shouksmith

    David Shouksmith United Kingdom Founder Member

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    It looks like brass to me with black oxide in places. Circular wear marks suggest some sort of rotary movement.

    No idea... ](*,) :lol:
     
  29. Nils Stephenson

    Nils Stephenson Founder Member

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    @Henrik
    I dont recognise that washer from anywhere on a 1081.

    @Alex74
    With the jet and cleaning needle rod out, you can always try seeing how well it slides into the jet hole. If it catches anywhere or doesn't seem straight should be obvious. Also, when holding it in your hands you can feel if it's not right and avoid bending the needle.
     
  30. Henrik

    Henrik Sweden Subscriber

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    Alex, David, Nils- thanks. Its brass alright. I found a mark just under the silvery washer so I placed it there. Not sure if it is original but without it the hood does not have a snug fit.
    upload_2020-8-22_11-37-32.jpeg
     

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