@presscall Hi John, Great catch with noticing another O-Ring. It's nice to know I wasn't hallucinating about the fuel leak. John, if you do source out all of the O-Rings for the Soto Muka pump it would be nice to know the sizes of each. Who knows maybe someone else will get brave enough to dissmantle and recondition their Soto Muka pump. If Soto would make their pump far more user friendly for servicing most likely these types of problems would never occur. Cheers, Norman
It's kind of interesting that they have swapped out the black plastic on the "control dial" for what appears from photos to be aluminum. I wonder if they had problems with the lettering fading on the black plastic or something. HJ
@hikin_jim Unless lettering is undercut/engraved in the surface (like the LOCK position on the plastic knob is) and not just painted on there's potential for it to wear off whatever the material. Yet another update! @teckguy_58 I might have known that once an O-ring's got leaky just lubing it up won't cure it. Sure enough, though it doesn't leak during firing with the control knob at 'Run' (the O-ring on the end of the spindle provides secondary sealing in that position), there's still some seepage after shut-down. In fact, it's washing out the silicone lubricant I smeared inside the fuel/air metering barrel core. Oh well, a third strip-down is on the cards! Incidentally, there's no apparent dismantling possible to remove/replace the O-ring and removal/insertion through the hole for the spindle seems the only way ... John
They knew they didn't want the pump back. Beta testing by consumers. I wonder if the replacement pump has the same inaccessible feature.
@presscall Hi John, Thanks for the update. I was truly hoping you wouldn't have the same problem with leaking I had. Most likely they have some sort of a machine placing the O-Rings onto and into the pump. To figure out the ID of the O-Ring you will need to measure the OD of the control barrel. I used one of your pictures. Figure out the ID, OD and cross section. Again most likely the O-Ring material is Buna N 70. While you're replacing one you should go ahead and replace all of the O-Rings. I'm sorry you have to dismantle the pump again, but I'm sure it is getting easier and faster. As usual you tutorials are always very interesting and educational. Cheers, Norman
That is one complex pump. E-gads. I like the Muka, but I don't know if I could recommend one to someone or not. I assumed that it would be more complex due to it's air mixing capabilities, but I didn't realize it would be quite, well, this. And that one "O" ring that has to be replaced through the hole? Yipes. I suppose it can be done, but it isn't necessarily going to be straightforward. No doubt Soto has some type of jig or something set up for that purpose. HJ
In re-reading all that's been written here, I think this stove might be just fine on a group trip where it's not the only stove, or by itself if a spare pump can be procured and carried. The pump is really over-engineered, and unlikely to fail. Even with this particular pump that did leak, it looks like John figured out an operational work-around. Weigh this against the (slim) chances of an MSR pump melting down, and I think we have a wash. Either way, I would want to have another pump (or another stove) available if I was on a trip that justified carrying a stove such as this one. On the other hand, I recall a trip where there was a lot of fine blowing grit that seemed to get into everything. I would want to be able to access all of the o-rings after usage in that environment. Rare case, though. ....Arch
Another day another dollar Soto Muka pump dismantling. The O-ring came out pretty easily using the tip of a jeweller's screwdriver. Tiny O-ring it is too. Indeed, Norman. A measure of the sealing inadequacy of this O-ring is the sloppiness of fit visible here, where it's not only not a 'snug' fit that grips the spindle but it can be nudged askew and doesn't spring back. I find it hard to believe that wear is responsible for that (spindle rotates through a limited arc to click stops, moves in and out axially a couple of times on each stove firing) and wonder how good a fit it could have been to begin with. I'll take a look online for a replacement.
Hi John, You'll get it firgured out very soon. I'm looking forward to the final fix and repair. I know quite few people that have the Soto Muka stove and they have not had the problem with their pump I had with this one you are working on. The pump is well engineered and there shouldn't be very many problems but I guess there is a lemon every once in a while Cheers, Norman
@teckguy_58 @hikin_jim @ArchMc Celebratory fanfare ... ! Got it sorted. I decided not to search for a replacement O-ring but instead to make my own seal out of viton sheet. You'll see a few test holes and one that resulted in the final seal made from the disc of viton left in the punch head after punching the hole. The viton I had was too thick for the application and I took a Dremel sanding drum to the centre portion of the strip of viton I cut from my stock sheet. After a few tries I managed to get the small hole for the spindle central in the disc. Original O-ring on the right of course. As you'll see, I made the hole in my replacement seal smaller to compensate for the known oversize of the O-ring. I reasoned that since the replacement was of a square cross-section section rather than the circular cross-section of the O-ring I'd be installing a greater sealing surface. I jockeyed it into place in the brass component without too much difficulty. Pump reassembled, I took it outdoors for a test firing ... ... peering intently with the aid of a torch for any tell-tale fuel leaks. There were none, and with the pump detached from the stove and indoors now I pushed and pulled and twisted the control dial to attempt to reproduce the seepage that had arisen before. Fuel tight. My conclusions? Mostly it's already been said in our discussion in this thread and I'm grateful to you and others who've joined in for your comments. What I would add though is to point out the irony that for all the high-tech precision of the stove pump, it took a home-made replacement for what I consider to be a weak link of an O-ring seal (too flimsy) to achieve a fuel-tight solution. The replacement is a durable viton seal of a more robust cross-section and I'm pretty confident that it will last better than the one it replaced, hopefully indefinitely. Speaking for myself, it's been satisfying to have explored a device I anticipated (correctly as it turns out) would throw up complexity issues in dismantling and making sense of function. That 'hidden' O-ring was a curve ball I hadn't seen (literally). The exercise has certainly removed the 'fear factor' the pump represented for me and though I wouldn't envisage making all the replacement seals myself should any more seals fail, that crucial one was better for it and the repair is reproduce-able should my other Muka pump - or a pump belonging to a CCS pal such as yourselves - develop the same symptoms. Again, I'm very grateful to you Norman for giving me the opportunity to work on the failed pump. John
It's been said in this thread that the customer may unfortunately have found themselves in that role and paid for the privilege.
Well, done @presscall. Hat tip in your direction. Or two. Very well done. Their pump is an impressive exercise in engineering at one level -- and a disaster if it goes awry in the field at another level. That is odd that when there was care in every detail throughout the rest of the pump that this one "O" ring was mis-sized. I wonder if it was an assembly error. I suppose one would have to disassemble multiple pumps to answer that question, and you've probably had quite enough of that for now! Thank you for your fantastic dissection (and discussion), @presscall. HJ
@presscall Well done John, well done indeed. I had no doubts you would be able to sort all of the problems out with the Soto Muka pump. Also this gives you a backup pump and if anything goes wrong you now have the expertise to repair any other problems that may occur. The Soto Muka pump is a very well engineered, but with anything dealing with being over engineered there comes the possibility of problems. For me I'm very pleased to have my Soto Muka stove. The stove works very well and does a fine job of cooking and one can get a very decent simmer out of this stove. I know several people who have the Soto Muka stove and have never had any problems. Personally I think the problem with the pump I sent to John is due to operator error. If you want to know if I would recommend this stove I can tell you yes I do recommend this stove. John, I'm with Jim on tipping my hat in your direction. This is truly the work of a Master Fettler. Cheers, Norman
