Stihl MS390 locked piston
- Thread starter southland1
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Get some fine grit sandpaper, it will buff right out!
southland1
ArboristSite Member
Man, that is good news, was trying to decide if I wanted to spent $300 plus on OEM parts or $26 on China parts. Since I don't have to buy a cylinder, I will most likely go with OEM. Any idea what grit sandpaper to use? Do I just sand until the marks are gone. What about using an honing tool, have used one on motorcycles in the past. What is the beat gasket maker brand to use or will most any of it work, have some already, not sure of brand.
Still have every most of the saws I have ever owned. Was wondering how difficult there are to work on compared to the 390.
Stihl o41 Farm Boss, carb kept going out of adjustment, bought new carb and still didn't fix problem, piston is free.
Hasqvarna 262XP, got real hard to start, piston is free.
Stihl 251c Easy2Start, a couple of weeks old, bought when the 390 locked up.
Still have every most of the saws I have ever owned. Was wondering how difficult there are to work on compared to the 390.
Stihl o41 Farm Boss, carb kept going out of adjustment, bought new carb and still didn't fix problem, piston is free.
Hasqvarna 262XP, got real hard to start, piston is free.
Stihl 251c Easy2Start, a couple of weeks old, bought when the 390 locked up.
southland1
ArboristSite Member
As for the cause of the problem on the 390, about 95% sure there was oil ion the gas when it blew but there is a small chance there wasn't. Had been cutting down sweetgum trees at my fathers house for a couple days and the saw ran fine. The next day my brother in law got the saw to finish cutting them up. He said he went to use the saw and it never ran for more than a few seconds, never cut a tree with it. My father says he did start the saw and was cutting with it when it blew. My father said he put some gas in it when it wouldn't start which I didn't know about. So the gas I poured out of the saw after it blew was not totally the gas in it when it blew. So there is a chance one of them put some unmixed gas in it, I'm not 100% sure.
I use Dirko sealant or Permatex Motoseal to seal them back. I think the factory uses Dirko. You'll probably get different opinions on that cylinder. Pics don't always tell the story but it looks kinda bad to me, I replaced one last week that probably looked better than that one. It's not a great idea to hone or sand one of those chrome cylinders other than to de-glaze them which would be real light sanding. I've gotten by with it on occasion however..
southland1
ArboristSite Member
Used one of these(one at top) http://www.vargus.com/shaviv/template/default.aspx?pCatId=25&pageId=52
The marks on the cylinder were a buildup, not gouges except for two small places, one on each side. Used a machinists tool called a scraper to get rid of the buildup. Looks like a screwdriver with the shaft having three sides and coming to a point. Scraped one of the edges on the cylinder wall. There was two small scrapes into the cylinder wall left, very shallow but I could feel them. The friend who had the tool couldn't even feel one but could feel the other a little.
The marks on the cylinder were a buildup, not gouges except for two small places, one on each side. Used a machinists tool called a scraper to get rid of the buildup. Looks like a screwdriver with the shaft having three sides and coming to a point. Scraped one of the edges on the cylinder wall. There was two small scrapes into the cylinder wall left, very shallow but I could feel them. The friend who had the tool couldn't even feel one but could feel the other a little.
southland1
ArboristSite Member
southland1
ArboristSite Member
All the parts are cleaned and ready to go.
southland1
ArboristSite Member
Any special trick to getting the gasket rubber off?
smokey7
jack of a lot ace of a few
3m eraser wheel if it's oil free or a soft wire wheel on a die grinder. There is some aluminum transfer on the jug still so it needs some sanding to finish it up. Light grooves will not cause any I'll effects. The flap wheels from dremel work well or wrap some 220 grit paper on a small nail or dowel rod and use a grinders or drill to get the last bit of transfer off before you run it. Should run fine but oil in gas is required lol.
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Yes, keep buffing!
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A bunch more!
A wire brush works well if you don't have all kinds of power tools.
southland1
ArboristSite Member
Just want to made sure do I won't ruin the cylinder. Do I need to sand until no makes are visible on the cylinder wall. Even though the marks are visible to the eye, they can't be felt except for the two minute grooves I mentioned. The friend with the tool I used is a machinist and he said the cylinder was good to go. Not doubting what you guys are saying, just want to be sure and not ruin the cylinder.
fearofpavement
Trying them all
The vertical streaks in the cylinder should be gone. Until they are, you're not "good to go". Keep cleaning it up.
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Yes, keep buffing. Or you will ruin your new piston.
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That is pasted on aluminum, you won't hurt the cylinder.
southland1
ArboristSite Member
OK. will sand more.
southland1
ArboristSite Member
Spent another 3 hours on the cylinder, sanding and buffing. For some reason I couldn't get a decent picture after about 50 tries.
southland1
ArboristSite Member
Called three local dealers to check on the piston kit.
Dealer 1 piston kit $101.18 bearing $8.72
Dealer 2 piston kit $93.00 bearing $$10.00
Dealer 3 piston kit $42.95 bearing $7.95
None had the part in stock which I understand so it's not like they had money tied up in inventory. Don't mind someone making a fair profit but the first two dealers are more than double the cost of the third dealer. All three are power equipment dealers only, not big box stores.
Dealer 1 piston kit $101.18 bearing $8.72
Dealer 2 piston kit $93.00 bearing $$10.00
Dealer 3 piston kit $42.95 bearing $7.95
None had the part in stock which I understand so it's not like they had money tied up in inventory. Don't mind someone making a fair profit but the first two dealers are more than double the cost of the third dealer. All three are power equipment dealers only, not big box stores.
