Good evening! I'm getting my head above water work- and home-wise and have recently had more time spend tinkering with my packstoves. One of them is an Optimus 8R that is in good cosmetic condition that seems to run fairly well but may not have the power that it should have. It also has an annoying habit of shutting down with a very small little candle flame that is easy to blow out but requires depressurizing the stove to avoid fuel weepage from the jet. Although I'd normally depressurize after use, I don't care for the potential weepage if the tank gets slightly pressurized during storage or transport, so I'm trying to get the spindle to seal as well as I possibly can. Here is where it gets interesting...the go-to advice, which make sense, is to either use fine sandpaper to remove burrs from the spindle or use grinding paste to lap both the spindle and the seat so that they match. Make sense. However, I've tried using fine sandpaper to clean both the spindle (I can get that very smooth) and the seat (I can reach it with fine piece of sandpaper shaped onto a cone around a cotton swab, but I can't see the seat well enough to tell whether its doing any good. After taking the pricker out, polishing with sandpaper didn't give me a complete shutoff. Replacing the spindle with a replacement spindle worked even less well, but that probably has to do with the fact that the new spindle doesn't quite fit the old seat. That left me with the grinding paste option, which I've tried and also doesn't seem to produce a complete shutoff. It leaves me wondering if either my technique or my paste is to blame. Two questions: 1) since the spindle is threaded, it obviously can't be spun continuously to mate the surfaces - I have to close and slightly open the valve repeatedly, which means that the grinding compound is only making contact in the last little bit of the rotation (hopefully that makes sense). I'm doing that at least 50 times. Is there something else I should be doing, or should that be enough? I'm only applying the paste to the conical tip of the spindle, but is there anything else obvious I'm missing? 2) Maybe more importantly, what should I look for in a grinding paste? I think I may be using the wrong paste. I'm using Permatex Valve Grinding Compound (80036). It actually seemed to burr the spindle. When I read the back of the tube, I realized that it claims to be a combination of 4 grits ranging from 120 grit to 220 grit, and that with use it grinds down from 120 to 220 grit. I now think that is much too coarse, especially at the coarsest grit but maybe even at the 220 grit level. Any thoughts on what to look for in a grinding paste, or should I just try to keep using this paste with many, many more turns? I'm even thinking about just using toothpaste but I suspect that is softer than brass. I know tradenames are probably country specific, but if anyone in the US has a particular brand/type they like recommendations are appreciated...but I suspect that the characteristics to look for are universal. Thanks for reading!
I had no luck using a paste on a union for a plumbers lead melter, ended up soldering the union. I usually use 0000 brass or bronze wool if available. Can't find the original stuff I was using. Duane
@Peregrinans I have had some success by cleaning up just the spindle I placing it in an electric drills chuck mounted in a vice, then turn on the drill and carefully using some very fine wet and dry paper on a piece of wood to resurface the cone. (As if it was in a lathe) Very often there is a groove round the cone where repeated contact with the seat and over tightening has damaged it. I try to keep the same angle on the cone but proceed with caution just to remove the groove. Good luck Nick
There are many websites advocating using toothpaste to polish plastic car headlights. The abrasive is normally pumice so it would probably work. However once you have used your grinding paste maybe use a polish like autosol to finish. In my fibre optic course several decades ago we used an abrasive paper to polish the end of the fibre. The course one was 1200 grit from which we worked up to a final paper of 3000 grit. That looked mirror smooth.
This works very well, I use it a lot on regulated silent burners which have a groove worn from years of use. The abrasive does need to be flat- wet and dry backed with a hard, flat material as mentioned above works fine. I use a diamond plate. Done with care, it's so quick and easy it isn't work chucking the part in a lathe to do the job. Here's a spindle part way through the process. The dark band on the taper is the worn groove, in the process of being removed: Once the taper is refaced, the sealing area of the spindle which the packing acts upon can be polished under power for good measure.
I'd do the same as nmp, chuck in a lathe or drill and slowly turn it down, coarsest I'd use is probably 600grit and I'd coat the tip with a sharpie marker which may or may not show you some low spots.
