I've been helping a neighbor cut down some trees to make room for a workshop. Today, I had a strange experience. There are (3) 6MM screws that hold the top cover...over the air filter and cylinder head in place, and today 2 of them popped out and got lost somewhere in the dirt and debris. I take the cover off every time I use the saw and clean out the air filter area, etc., real good. I tighten these 3 screws good, but today good apparently wasn't good enough. These screws are "captive" and shouldn't just pop out, even if they come loose. Naturally, I can't find a parts breakdown online, and I doubt the dealer has something like this in stock, but I will be going over there in a couple of days to see. The saw is still under warranty, and if there is a problem with these screws working loose, I may just request a whole new top cover....we'll see what he says. If anyone has a parts list for these saws, could you see if there is a P/N for these screws. Thx, in advance.
Stihl MS391 Cover Screws
- Thread starter deminin
- Start date
Fish
Lawn Pro
- Joined
- Aug 2, 2013
- Threads
- 11
- Messages
- 5,145
New screws won't help much. The saw is not meant to be dismantled daily, and tightening the down real good just destroys the
plastic that they are meant to set in. You can go to the dealer, and they may or may not cover it, so I would leave out all of the details you unfolded here, if you want it covered, and get a lot less anal about cleaning your saw in the future, because they will not cover it twice!
plastic that they are meant to set in. You can go to the dealer, and they may or may not cover it, so I would leave out all of the details you unfolded here, if you want it covered, and get a lot less anal about cleaning your saw in the future, because they will not cover it twice!
Actually, the Threads these screws mount into are Steel inserts...Not Plastic. Even so...if the screws back out, they are supposed to have a retainer in the cover that keeps them from falling out completely. The one remaining screw is "locked" into the cover...as were the others...but something is causing them to back out or breaking the "retainer" that is supposed to keep them in the cover. I sent Stihl a note today, and will check with the dealer in the next couple of days. I was hoping there might be someone on this forum who actually has some experience with a 391.
I firmly believe in cleaning up the "tools" after a days work, and getting them ready for the next day....I operate under premise that the job isn't done until everything is cleaned up and put back in its place. There should be No reason why a simple "user" cover should have any issues. I closely inspected these STEEL threads in the case, and they are in excellent shape...one could torque the screws down quite heavily without damaging anything. I think that once a get the cover screws, or a new cover, I will probably put some thread lock in the case threads...to give the screws a bit more grip if vibration is working them loose.
EngineMan
Lawn Addict
- Joined
- Jun 12, 2012
- Threads
- 9
- Messages
- 2,275
Yup...that's my plan...but, I'll wait until I hear back from Stihl, and talk to the dealer. I can understand these screws working loose during a day of cutting, but falling out of the cover completely, when they are supposed to have a captive washer in the cover indicates a basic flaw in the design. I've had this cover off numerous times to clean the dirt from around the filter and carb. area, and these screws have always stayed in the cover....until yesterday.
gfp55
Well-Known Member
- Joined
- Mar 13, 2014
- Threads
- 23
- Messages
- 860
Also when you unscrew the bolts, don't unscrew the first one all the way out before you move on to the next bolt. Unscrew the first one a little then the same for the next one and so on. If you unscrew the bolt with the others still tight, the bolt that you are unscrewing works its way out of the bolt retainer on the cover. I hope I said that so you can understand me?
I sent Stihl an e-mail yesterday afternoon, and one of their techs replied this morning. According to him, this cover has plastic "retainers" molded into the cover, which are "supposed" to hold the screws in place and keep them from popping out of the cover completely. He said that apparently there was a failure in these retainers, and the dealer should be able to supply a new cover within a few days, if he doesn't have one in stock. I'll be going over there in the next couple of days, and get things rolling. If I can find a couple of 6MM-1 screws, I can get the cover on securely...or with the bar side still intact, I can rig up a couple of cable ties to hold the other side in place. I'm probably going to drop a couple more trees tomorrow morning, before the forecasted rains move in tomorrow night and Tuesday. I've got a Stihl 036 that shucked its crankshaft bearings last fall, which I rebuilt through the Winter...so I think I'll take it tomorrow for a good workout, and keep the 391 as a backup if my 036 rebuild shows any problems.