Stihl MS390 locked piston

[southland1]

OK on the chain break piece, will see where it fits. The plastic piece is identical size on both sides. Seems to be where you can use the saw vented or unvented. Maybe for different types of weather.

 

[HarleyT]

Here...
The tag below the trigger will give you the date of manufacture.

 

[HarleyT]

The break free product I used is Aerokroil by Kano Laboratories. Had to order it through the mail after someone recommended it for a bolt in a car rear end that would not give, it worked on that also. Got the saw back together and tried to start it but the pull rope will only pull out half way or less, maybe a third of the way. My 77 year old father took the saw apart and I put it back together so wasn't sure about all the pieces. The little plastic piece that sits over the spark plug will not go all the way down so the outside cover will fit. Also had the small flat piece of steel left over. Not sure where it goes.

Just flip the black piece around and put it in the other way around.
It sounds like you loaned your saw out, and while they were using it, they engaged the chain brake........
And we are slowly finding out what happened 3rd or f0urth hand...

 

[a. palmer jr.]

The picture of the black plastic piece shows how it would attach to your saw if the saw was pointing up, screen goes up and to the rear, at least that's how mine looked.

OK on the chain break piece, will see where it fits. The plastic piece is identical size on both sides. Seems to be where you can use the saw vented or unvented. Maybe for different types of weather.

IPL calls it a pre-filter, guess it keeps the sawdust out before it can get to the filter..

 

[HarleyT]

 

[a. palmer jr.]

Mine would only go one way. Maybe it's because some of those 290s had a round top and some were flat?. One of my saws also came without that slide that you move with a screwdriver.

 

[HarleyT]

Mine would only go one way. Maybe it's because some of those 290s had a round top and some were flat?. One of my saws also came without that slide that you move with a screwdriver.

Like in diagram 3?
You have to use the right pre-filter, they are different depending on the contour of the top of the saw.

 

[ssm1699]

My saw didn't come with the pre-filter. But I also bought it used.

 

[a. palmer jr.]

Like in diagram 3?
You have to use the right pre-filter, they are different depending on the contour of the top of the saw.

Yeah, I didn't think about that when I ordered a couple of them online. I think I ended up trimming one of them to get it to work.

 

[southland1]

As in the HarleyT picture mine is like that, the black piece works either way, vented for winter, unvented for summer. Still can't get it to go all the way down so the cover fits.

What do you mean by saying the saw was loaned out and the chain break was engaged? I myself have engaged the chain brake while cutting. Is that a bad thing that could have caused the saw to lock up.

 

[a. palmer jr.]

A lot of guys use the chain brake all the time, some seldom use it, count me as the latter..

 

[southland1]

I'm not sure I understand the chain break. What I am talking about is when the guard that protects the your top hand, when cutting if I hit that guard on the tree, it pushed backwards and locks the chain. I don't intentionally use it, just happens while using the saw. Also when the saw is being moved around when not in use I will sometimes hit the hand guard by accident and engage the brake. It's not something I use on purpose.

 

[HarleyT]

Just was trying to guess what is going on with your saw. When I saw that someone had taken apart the chain brake,
I just assumed that was involved in your problem. Take off the muffler and take a peek at the piston.

 

[a. palmer jr.]

I'm not sure I understand the chain break. What I am talking about is when the guard that protects the your top hand, when cutting if I hit that guard on the tree, it pushed backwards and locks the chain. I don't intentionally use it, just happens while using the saw. Also when the saw is being moved around when not in use I will sometimes hit the hand guard by accident and engage the brake. It's not something I use on purpose.

The chain brake is supposed to stop the chain when it is pushed forward, it unlocks when you pull it back. They are supposed to actuate when you have a kickback situation but I never had that happen when I use a saw, maybe I'm more careful than many..

 

[southland1]

Yeah, chain break works that way, I just jiggle the hand guard until it unlocks, I had it backwards. Here are pictures of the tag and piston rings.

 

[Cease232]

That piston is trashed. You'll need a new one at the very least. Possible a new cylinder as well.


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[HarleyT]

D.O.M. is May 2009.
Take a pic of the fuel line before it attaches to the carb.

 

[a. palmer jr.]

Harley T is correct, some fuel lines kink right before they attach to the carb, causing the saw to run lean and trashing the piston. I wouldn't use a Chinese aftermarket fuel line on the 290. If you must use aftermarket get one made by Oregon, I'm thinking Stens has them also, may be the same thing. I tried one and it worked well.

 

[HarleyT]

Actually, Stihl had a major problem with their fuel lines. They would develop cracks between the carb and tank.

 

[a. palmer jr.]

Actually, Stihl had a major problem with their fuel lines. They would develop cracks between the carb and tank.

I've had several different kinds of the 390 lines and the Chinese ones were the worst. I bought an Oregon fuel line from a local shop and it seemed to not kink and I assume Stihl has their problem worked out? I guess an easy way would have been to put a metal or plastic elbow there.