Well I am bummed. I got out the Dremel this evening and only the tiny carbide ball bit was in there. And worse, the chuck piece for that size is missing. Parts all came in for putting the saw back together so it may have to go back without playing with it. Just that little touch probably wouldn't do much anyway. I couldn't find the several carbide bits I had. I must have loaned those bits out sometime and forgot all about it. Well, I'm not gonna spend money on tools to do something I don't really need to do. Darn I was thinking I had all the stuff I needed, but stuff seems to go missing when you're not using it regularly.
I had to wait on a long torx bit set to get here so I could use the torque wrench to assemble it. The torx set came in this morning so I put the saw together this morning since I took the day off work. I started up and runs good, but I have to warm it up and fine tune the carb later. The wife has me for the afternoon so all I was able to do was start it up and make sure it runs. Idles great so far. I'll check it out tonight, hopefully...
After we got back home, I took it over to the area I'm processing a bunch of logs and it ran great this evening. A couple tweaks to get the idle up a tad and I'm back in business. I'm going over to a friends tomorrow evening to drop a few Ash trees in their yard that got "bored". Thanks again to all for the tips and support. The service manual was a big help with all the torques. I really hate putting stuff back together without knowing the torque values. Most stuff I can "feel" and end up fairly close, but all the plastic stuff with the special threads were my biggest concern. You guys Rock!
Extra bummed tonight. Was finishing up at my friend's place when the 391 quit running and I couldn't get it started and I knew something was wrong, bad wrong... I finally got time to tear it down tonight. I could kick myself. I got the bargain basement bearings and seals to repair it. After almost a tank of fuel through it, the flywheel side bearing went wonky and spit chunks, or at least thats all I can figure that happened... I can't imagine anything else getting in there. I cleaned it all really good and blew out the jug and ports before assembly. There was plenty of oil in the crankcase when I tore it apart tonight. Clutch side bearing is fine and rolls free. The flywheel side bearing wobbled and I could turn it by hand a couple times but you could tell there were extra chunks in there and then totally locked up. It was running just fine and when I finished a cut and let off it just stopped running. Piston and cylinder are trash. Not sure if I want to mess with it or not... OEM parts are 'spensive and I'm gun shy of the knock off stuff now. I guess I need to start looking for a saw.
Bearings in that series should only be oem due to their size issue. They’re not conventional 6202, 6203 that other saws use.... right? I asked earlier about that as I haven’t rebuilt that series yet. The AM copy of them was probably quite low in the quality control department. The better quality bearings (Nachi, skf, others) are great. IF the saw uses non-proprietary “normal” bearings.
I went down to the shop this morning and looked in the seals to make sure the springs were still in there, YES they are where they should be. I put some of the metal flecks that came out of the crankcase on a rag and brought a magnet close and they jumped off the rag to the magnet so the chunks are steel. Maybe I'm missing something, but here's the rundown of how I put it together. All parts were cleaned and blown out with the compressor (not in carb, only spray cleaner). Jug got a soapy bath in the sink and a kerosene wash before and after that. Clean rags on bench during all assembly. Crank was clean and new bearings warmed in oven to 300* and slipped right on into place. Mic'ed at .0005 interferance fit prior to putting them in place. 2 stroke oil in all bearings and coated cylinder and piston. Piston rings positioned on pins correctly. Seals installed with grease in the ID groove. Seals pushed on with deep socket so they didn't get stretched by getting wonky crooked during slide on. Bearings / crank assembly went into jug with a "snug fit". I didn't measure the crank assembly or the jug / case opening. There was not any undue force needed to assemble it although it didn't set in as nicely as the original set. The original bearings were not as snug when I had played with the crank assembly prior to removing them. But they also had some play in them. That's why I went ahead and replaced them... regrettably... Did a trial fit prior to applying crankcase sealer. Torqued everything per the shop manual during assembly. Standard 45:1 mix was used and there was plenty of oil in there during dis-assembly. Ran great for almost a tank of fuel, then... No foreign objects where in the intake path during assembly unless I was blind. Again, cleaning everything as it was being assembled. I don't do this very often, but it was probably my fifth or so motor build overall, and I had my blaster apart and ported it myself a few years back. I'm not a pro engine guy, but I'm thinking I did it right (other than the cheapo bearings). I have used lots of aftermarket parts before and never had any issues. The bearings and seals I got were aftermarket, but were specifically marketed as for MS311 / MS291 crank bearings so I didn't cross reference them myself. Please let me know if I did something glaringly stupid so I don't do that again, EVER... but to me it looks like a failed bearing as stupid as that sounds. The carrier cage in the bearing looks ok like nothing is missing from it, but it's hard to tell. It is totally seized now. It never spun in the crankcase or on the shaft. It was still turning roughly when I took it apart. It wobbled pretty good too. I had really hoped that this saw was gonna last for as long as I needed it. Guess NOT...
Are the bearing spacers steel, or plastic? I generally only warm bearings to 225*F...but that all depends on the bearing design too...
I don't mind sharing my "not so great" moments if someone can learn from it and not have to repeat what I am dealing with. Thanks for the support. Just don't tell my wife about the washer I left in the transfer port... I've been eyeing a cute little MS362 that I saw in town the other day... There's a reason the wife always says we don't have time to stop at the Stihl shop when we get to town... If I don't laugh about it, I'd end up crying...
Ok, probably fine at that temp then...I'm usually dealing with greased packed and sealed (rubber seals) bearings, so little different scenario.
Your procedure looks professional from afar. The bearings were probably the issue. These are C3 tolerance and have some “wiggle” to them (hard to describe that, I know). Didn’t the seals just slip on the crank before closing up the clamshell? That’s how 1127 Stihls work (no need to drive them in). I know there are two different seals for the 1127s.
This one (MS311/391) takes the same seal and bearing on both sides, there are two different OEM seals available, the press in when the clamshell isn't split and the larger for when the case is opened. I had my case opened so I didn't need any special tools, I just use a deep well socket to push them onto the shaft so I don't get them whopper jawed and they are nice and strait on the shaft. The original bearings did have a little wiggle to them and not knowing that they are supposed to be a little loose is the reason I replaced them... Great tip to pass on so the next guy doesn't do extra work and use cheapo bearings like I did. They are very hard to get off the shaft also and I pretty much destroyed the original bearings getting them off. Is there a slick trick to that. I used a bearing splitter between the crank counterweight and bearing to support the shaft then used a punch on the inner race to drive them down and off the shaft. I hate pounding on bearings even to get them off. I didn't try heating them since they are right there on the shaft and I figured the shaft would expand also. I didn't replace the piston pin bearing as it felt pretty good. I had cleaned it out and re-oiled it before assembly. Both it and the rod bearing were and still are fine. Only the flywheel side bearing is trashed. All the metal flecks that I checked are magnetic so it is not case or piston material that did the damage. The rings are all one piece and show no signs of damage, and I can't find any other parts showing damage other than that one bearing. Of course the piston and cylinder then took it in the shorts...
Gotcha, yes- I was wondering if you drove the seals in but it sounds like you just stabilized them with the socket. While I have a couple personal saws with AM bearings, I highly recommend oem only unless it’s a common bearing size and isn’t proprietary. I think your original problem was fuel related. Too often people assume the worst without going through the progression of “easy to check” items before digging in. I’ll say it again- the tilt test to determine seal leaks isn’t 100% conclusive... don’t use it.
Bearing removal- lots of ways to do this but anything forceful can bias them and put stresses on cages. For bad bearings on shafts- I make a heat shield out of foil to cover the crank. I use cold oil in the big end bearing as well. Then, I slowly heat the bearing with a heat gun and lift it away from the shaft using screwdrivers and eventually a gloved hand. Heat is your friend for metallic interference fits.
This may very well be the case. My mind tends to go to the worst case scenario. Thinking things through is a good thing, but overthinking stuff can be distracting as well. I have learned some hard lessons because of that over the years and this may have been one of them. But what's done is done and time to move forward with more experience and knowledge. There are times when I wonder if I'm one of those people who shouldn't own tools... Overall I'm way ahead, but I have my blunders also.
Yep, agreed. You learning how to do this will give you skills and confidence for future endeavors. Not many saw geeks want to admit this, but f/ing up rebuilds is part of the journey. Nice thread overall, by the way.
