Pretiss Waber M1942 Stove Rebuild

I mentioned some weeks ago that I may have a new hobby. What began as a curiosity based on some old military stoves my father owned when I was a kid has turned into regular searches on ebay for trashed-out stoves and lanterns and many evenings tinkering with my purchases in the garage. But, if I’m not building boats at the moment this seems like an interesting thing to do.

The Prentiss Waber M-1942-MOD “Mountain” Stove

A month ago I purchased two Prentiss Wabers M-1942-MOD(ified) “Mountain” Stoves. Both are dated, PW-1-45 (PW = Prentiss Wabers). These stoves were made collectively, I believe, by Coleman, Prentiss Wabers (a.k.a Preway) and Aladdin. When I received the first one, I was working on two other stoves, so I didn’t  take a close look at it, but by the time I received the second one, and compared the two, it was obvious that someone had tinkered with it before. So, I completely disassembled it. In my opinion, as long as you don’t break anything, this is a good way to learn about its operation and helps identify where things can go wrong. I’ve always enjoyed this. One time, back in my early twenties, I bought a two-cylinder, two-cycle, model airplane engine just so I could take it apart to see first-hand how the fuel delivery worked with only one carburetor, and no poppet valves, etc. That was pretty neat. Anyway, I disassembled the stove and got to work on cleaning it up.

Update for July 2017:

For some history about this stove, see my blog entry, The Mountain Stove

For a description of the features of this stove, see my blog entry,  Buying an M-1942 Stove

For a description of fettling this stove, see my blog entry, Minimal Effort to Blue Flame

This blog post updated 27 November 2016 and 22 July 2019

For information about interchangeability of burner bowls, vaporizers and tip cleaners, please see my blog post on M1942 Vaporizers.

Valve Removal (Added 22JUL2019)

The M-1942 MOD stove is not an instant lighting stove, so it isn’t typically necessary to remove the valve from the tank (a.k.a fount). It merely has a straight brass tube below the valve in the fount. However, most of the time I remove them anyway because I’m cleaning them up due to a lot of dirt (and sometimes gravel) in the fount or the fuel tube is clogged, etc. I’ve removed the valve on approximately 15, M-1942 MOD stoves.

Warning: One guy emailed me looking for a new valve assembly because he broke his valve body while attempting to disassemble his stove. Proceed with caution! I’m explaining what I do to remove the valve, however, you must use your own judgement and if you are uncertain of anything, please ask more questions. Old stoves are in all states of disrepair (or someone else’s repair) and I cannot be responsible for damage to your old stove.

There is a lock ring at the base of the valve assembly. It has a series of notches in it. This must be loosened before attempting to remove the valve. Using a punch and a hammer, strike the ring in one the notches to rotate it counter-clockwise. This will eliminate the friction between the pot-support/windscreen and the valve.

M-1942 MOD valve. Note the slotted lock ring at the bottom

Next, remove the valve stem. I do this by removing the valve wheel (plastic knob), and then the 9/16″ packing nut. Using the valve knob, I open the valve all the way and keep going to a point where the valve stem still turns but it doesn’t come out any further. If necessary, I re-install the screw to hold the knob in place and pull out the valve stem. Be careful not to break the valve stem.

Next, I re-install the 9/16″ packing nut. I do this to give more strength to the valve (for the next step) and to reduce the chance of damaging the threads during valve removal.

Finally, I use a 9/16″ deep-well mechanics socket and an extension and slip the socket over the 9/16″ valve stem packing nut so that it touches the main body of the valve. Do not use a standard shallow socket. I think this is how that one guy’s valve was broken. I think you can use a larger socket, inch or mm (15mm seems about right). Then, using a strap wrench around the base of the fount rotate the socket/extension counter-clockwise to remove the valve (see photo). If you have questions, please ask.

These are the tools I’ve used to remove the M-1942 MOD valve from the fount

Identification (Added 27NOV16)

Sometimes I ask ebay sellers for the year or manufacturer of a stove they’re selling and they reply that there isn’t one on the stove. Though Aladdin’s stamping is generally lighter that the others, I haven’t see one yet that doesn’t have it. These are all on the windscreen/pot support.

Identifying an M1942-MOD, Aladdin, Prentiss Wabers, Coleman

Another identification feature is the fold-out feet. Each manufacturer made the feet slightly different. I bought a pair of stoves where someone swapped out the parts, but since the manufacturer is stamped in the windscreen/pot support and not in the frame I looked at lots of photos online to get the proper tank with the other parts.

M-1942-MOD feet; Aladdin (l), Coleman (m), Prentiss Wabers (r)

Pumps

First, the pump. The pumps on these stoves are different than most other gas type stoves in that check valve (a.k.a. NRV) is built into the end to the removable pump tube, which also happens to be the same place you fill the tank with fuel. There are two styles of the NRV, which I didn’t know at the time. My first thought upon noticing this was that someone put in a homemade version of their own. But, I searched around the web and saw both styles on various forums. These little valves can be problematic if you don’t replace the rubber insert, as it dries out over time and allows fuel to back-up into the pump. Some people reported their stove catching fire because of this so I was certain to replace it right away. Another curious feature is that the pump itself is a storage tube for spare parts.

Addded 27NOV2016 – With more experience I know now that the two NRVs in the photo below are the M-1942 style (upper) and the M-1950 style (lower). I’ve been using both, so if you cannot find a suitable replacement spring for the M-1942 type, you can substitute an M-1950 spring/cup/gasket successfully. See my blog post on M1942 and M1950 NRV gaskets for more information.

The M1942 Pump. Note the Hollow Tube Can Hold Spare Parts

The Two Styles of M-1942-MOD NRV

Pump Tube Tolerances (Added 22JAN2022)

Recently, I was involved in a discussion on the Coleman Collectors Forum in which one member stated that not all of the pumps fit in any stove. I did some measurements and discovered that the tolerances can be very tight and that some pumps may not fit in some stoves. Below is a table of pump tube diameters and pump tube/filler openings for the 6 different variations of the M-1942 MOD. As you can see the Coleman (C-A) pump tube is roughly the same size as the 1944 Preway (PW) pump tube/filler opening. It barely fits and I can see where some dried fuel residue or slightly different diameter pump could prevent the C-A pump from being used in the PW stove. So, be cautious when swapping parts.

I replaced the main On/Off valve graphite packing as it was also hard and they are relatively inexpensive and easy to replace, so why not change it now?

I reassembled the valve and installed it in the tank (see Assembly Note below before installation). Then I gave it a pressure check to see if fuel leaked anywhere and it did. I do this by installing the valve assembly without the burner bowl and pot support, pressurize the tank, press my finger over the vaporizer and then open the valve. It appears that the compression ring (the silver disk) was not mating properly to the brass valve body. I tightened it plenty, but it just wouldn’t seal. I spent a lot of time looking for solutions and because I have two stoves was able to swap parts. If appears to be the mating surface of the valve body itself. The valve bodies do not have replacement parts available so I can’t just swap this part out with a new one. Meanwhile, I found that a little Permatex #2 will seal it for now (Note: since this time, I’ve purchased additional stoves, swapped parts between them and both sealed without needing any sealer 19MAR2016).

One question I’ve been asked is whether or not a sealer can be used on the spirit cup-to-valve body threads. None of my stoves use sealer when fitted properly and I’m not sure how well the sealer will perform under heat, pressure and liquid fuel. The seal should be made on two metal-to-metal mating surfaces. The three parts involved are the 1) vaporizer, 2) the steel disk and 3) the valve body. I would not recommend using any sealer on these parts. The beveled edge of the steel disk should seal to the valve body. If it doesn’t, look for damage along the edge of the steel disk. The steel disk is a relatively simple part and I’ve turned some of these on my metal lathe for spares. The vaporizer should seal to the steel disk. Sometimes you can see the wear ring in the vaporizer from tightening the nut/spirit cup which compresses the parts together. If this doesn’t seal, examine the vaporizer for wear where it would contact the steel disk. Additionally, look to see if the vaporizer bottoms out on the steel disk. It could mean that the groove in the vaporizer is too worn or the vaporize might not fit this stove. See my blog post on M-1942 vaporizers for some examples of the vaporizers for this stove and problems you might encounter. Regardless, getting the vaporizer to seat in the exact same spot could be difficult. (Paragraph added, 23DEC19)

Valve body to vaporizer mating surfaces

M-1942-MOD valve assembly fully disassembled

Installing valve stem, with bushings and packing (see note before doing this)

Assembly Note: If you’ve removed the entire valve assembly, like I’ve done here, do not install the packing and valve stem/bushings before you install it in the stove. Here’s what to do: 1) install the valve stem/packing nut on the valve assembly and install the valve assembly using a deep-well socket and extension. The nut will help prevent damaging the threads and prevent bending the valve stem opening. I use Aviation Form-A-Gasket Sealant liquid (Item# 765-1210) on the tank threads as it was recommended by a Coleman repairman. Recall that proper clocking positions the valve stem opposite of the fuel fill opening. See photos later in this blog post if you’re not sure. And, remember to position the mounting post for the wrench on the pot-support/windscreen/frame above the main valve stem.When satisfied with the positioning, remove the nut. 2) place the small bushing on the valve stem with the beveled inside edge towards the wire which wraps around the valve stem. 3) install the packing, 4) install the large bushing, 5) insert into valve body, 6) thread the valve stem all the way closed, 6) install the valve stem/packing nut and tighten.

M-1942 MOD valve stem with wire for bushing stop

Installing the tip cleaner parts, assuming you removed them. Typically, I wouldn’t remove these, however this stove’s tip cleaner packing was gone (as in, missing!), so I needed to make one. Don’t remove it if it isn’t leaking. As far as I know, nobody has made them in 70 years! Well . . . except me, and I’ve made only a half-dozen and am still testing them.

Drop in the tip-cleaner mount

Install the tip-cleaner lever, packing and retainer-washer

Note the direction of the retaining washer

Here is what the full assembly looks like, though you cannot install it in the stove this way. I’m only showing it this way for clarity.

M-1942-MOD, Fully assembled valve assembly

The vaporizer/generator has a little screen which goes inside. These are almost always loaded with carbon and can be difficult to remove. I found a few places where I can get replacement screens and installed a new one. The tip cleaner needle goes through the middle of the screen so you need to be careful not to snag it when installing the vaporizer.

The Vaporizer with New Brass Screen Installed

M-1942-MOD with Tip Cleaner Installed

I finished re-assembling the stove and filled it with fuel, then gave it one more leak test. All good. I re-installed the burner bowl, pumped it up and opened the fuel valve long enough to fill the pre-heat cup. A side thought. I always thought that MSR invented the preheat cup as this is a common feature on the Whisperlite and other MSR stoves, but apparently it was invented during World War II or possibly earlier. It is present on this stove, some Coleman 520s, the American (AGM) M-1941, and the M-1950 stove (which was manufactured up into the 1980s, I believe). Anyway, I lit the pre-heat cup, watched it burn, checking for any flames where they don’t belong, and with everything going properly, opened the main valve and got a nice blue flame.

The M-1942-MOD with the Pre-heat Cup Lit

And Then . . . a Nice Blue Flame

The second stove works without any maintenance other than a tank cleaning, new fuel cap gasket and new seal in the NRV valve. Now, I’ve got two working M-1942-MOD stoves and may just take one on a backpacking trip as these are very light little stoves. And, with that pre-heat cup, I’ll bet it lights-up nicely, high up, in the cool air of the mountains.

Location of instruction labels (added 27NOV2016) – It seems that the three manufacturers didn’t place the labels in the same place on the stove (see photo of stoves with original instruction labels).

Label locations are different; Aladdin (l), Coleman (m) and Prentiss Wabers (r)

 

Update for 19MAR2016: If you have questions about assembly or what something looks like which I’ve omitted, please add a comment. I’ve rebuilt 6 of these stoves (four PWs, one Coleman C-A and one Aladdin) to date and have lots of photos.

Update for 22JUL2019: To date, I’ve rebuilt 17 of these stoves and two M-1942 wheel stoves, and have even more photos. My sons love to use them for backpacking trips as these are all-weather stoves and work really well in the mountains and all temperatures so far. Check out my other posts on this stove and other stoves and lanterns and lamps and irons.

Thanks for visiting my blog.