Finally got to get into some doug fir that made my 28" bar feel small. Stock HD rental saw with skip chain. I traded my MS290 for this saw a couple of years ago and really like it for bucking. It's awfully heavy when you have to limb a tree or work in a pile of slash though. I pack along the OEM 20" bar and a few chains for backup. Saw still has cat muffler and I've never touched the carb screws. I sure do like the huge fuel/oil tanks.
Glad you enjoy your saw . Don't be afraid to MM that baby and give it a good tune . I promise it will put a smile on your face .
That's a nice looking saw. I'd like to think that I will be spending less and less time in the tops and slash. Can pop the 20" little bar back on the 6421 if the 28" bar becomes a problem. Do the 6421 saws, mine is stamped 2012MY, have epoxied carb adjustment screws? The idea was always to make this a 7900 but I want to put a couple of dozen cords through the 64 cc set.
Do the 79cc conversion!!! I hate running mine with the 28" bar, way too unbalanced for my tastes so I only pull it out when the 20" bar won't make it through logs in 2 passes. But with the larger top end, a 20" bar and a larger sprocket (8 pin I think) it's an absolute screamer!!
I just killed the cat in my doll a couple of weeks back. Had to pull the carb and take a propane torch to it to get the epoxy out. Have not had time to retune it yet. But as soon as this job is over it on the top of my list.
Dolmar guys, beware of this problem. It may be my fault since I've only ever ran Stihl saws and their nuts are bigger (haha). I was noodling the big fir rounds in the photo and the saw spit out the chain. Weird, I thought. It wasn't loose when I started. Then I noticed that the cause of the spittage was that I had loose bar nuts and one was GONE. Hell. I'm a long ways from home and need to load a lot of wood. Since I had cut in this same place yesterday I started looking through the piles of noodles and got majorly lucky. Like lottery lucky and found it. I did bugger up the drive teeth on the chain so I need to un-mushroom them before I can reuse it but since I found that nut I was back in business with a new chain. How tight do these little dolmar nuts need to be? I'm just using a scrench. Oh and I'm not fat, my hands are just very meaty. Looks like I'm the marshmallow man in these pics.
I've never tightened them any tighter than with any other saw and haven't had any problems. Well, I did lose one of the nuts once, but that was completely my fault as I know I didn't tighten them after adjusting the chain tension. Since they're sold in pairs I have an extra somewhere now.
Hmmmm.... never had a problem with the 7910. I just noodled the chit out of some big white oak too. Is it possible you only snuged them and forgot to tighten them completely. I've done that in the past, with Stihls no less, and it's a surefire way to have them loosen and fall off
Is that bar stud sheared off? Or is the cover just loose? Doesn't look like there's much there for those little nuts to hang on to... I've thrown a chain before too - same thing that happened to you basically. First time running my MS460R - the threads on one of the studs were boogered up, and it wasn't tightened all the way. Cover fell off while I was cutting and it pitched the chain about 25'. I never did find that nut. I was lucky that I was cutting with the bottom of the bar at the time; so it pitched the chain away from me. If I had been cutting with the top of the bar, I probably would have been looking for a different set of nuts!
The stud and the threads looked good. I wiped them off before reinstallation of the new chain. The cover must have loosened just enough to disengage the tensioner but not so much that the cover fell off. Too bad about the chain damage. I hope to clean up those drive teeth with a die grinder so that they will ride in the bar nicely. Been looking: CYLINDER AND PISTON KIT, PS-7900 038130910 Probably just get a better tune on the 64 kit and maybe decat the muff.
Just an FYI tip I keep a little parts kit in a zip lock container. I usually have a bar nut or two, spark plug, fuel filter, some an extra air filter and the one for my 056 of keep a few extra fasteners/ screws and bolts. I have a kit for each saw and if I have a big day planed I grab the kit with the saw.
I have pretty tight nuts I haven't had mine very long but, I tighten them about the same as any other saw, no loosening so far. Maybe you just forgot to tighten them. Top of the nuts are just about flush with the studs.
I think you're right. I noodled a cord of rounds last night, a full fuel tank, and no loosening was detected. I'll just keep checking until I become confident again. I carry extra chains, screnches, extra fuel and oil, and an extra bar but I do not intend to start packing an extra spark plug. But that's it. If I had some extra bar nuts, I would throw them in. Everything else had better hold together or I'd be getting a different saw! I have spent many years racing dirtbikes way way off road and carry spark plugs but have never ever needed to replace one in the field. Modern plugs in all engines last surprisingly long.
Bar nuts have to be torqued on pretty we'll. Also make sure to lift up the tip of the bar as you're tightening the chain to remove the slack. Sent from my HTC One_M8 using Tapatalk
