What happened to my MS390?

[lone wolf]

Not my saw...owner doesn't want to pay a Stihl price to get it fixed.

That puts you in a real ****** position. The China cylinders and pistons are no good. Better off with used OEM . Now what can you do?

 

[pioneerguy600]

That puts you in a real ****** position. The China cylinders and pistons are no good. Better off with used OEM . Now what can you do?

Buying another will be no guarantee that it will last.

 

[lone wolf]

Buying another will be no guarantee that it will last.

Right and people expect him to be a miracle worker and get it running right cheap. Turn down that stuff.

 

[pioneerguy600]

Right and people expect him to be a miracle worker and get it running right cheap. Turn down that stuff.

That is what I do, but that`s just the way I roll.

 

[lone wolf]

That is what I do, but that`s just the way I roll.

Its definitely the way to go.

 

[BuckthornBonnie]

Check the flywheel key ?
Spark plug threads decent enough to seal?
Broken ring... common with cheap AM rings.

 

[lone wolf]

Check the compression.

 

[a. palmer jr.]

When I worked in a factory we made stuff for other brands other than our own and I didn't notice anyone looking over my shoulder....

 

[a. palmer jr.]

I'm wondering if maybe the oil I used to assemble the piston/cylinder didn't get used up or leaked down while I was starting it resulting in a somewhat lower compression. I might try putting a few drops of 2 stroke oil down the spark plug hole and see how much that raises the comp..

 

[a. palmer jr.]

You guys will have to admit that this has turned out to be a fairly lively thread...

 

[lone wolf]

I'm wondering if maybe the oil I used to assemble the piston/cylinder didn't get used up or leaked down while I was starting it resulting in a somewhat lower compression. I might try putting a few drops of 2 stroke oil down the spark plug hole and see how much that raises the comp..

Might be the piston just dont make the compression due to being improperly made to tolerance.

 

[a. palmer jr.]

Might be the piston just dont make the compression due to being improperly made to tolerance.

I never noticed it when I installed the piston into the cylinder, seemed like all the others, but I might have been daydreaming while I was working..The first time I pulled the starter rope after putting it together it seemed like it had gobs of compression then it kinda faded away. This may be a saw that gets put back until Spring before it gets fixed, kinda cold in that semi-heated garage of mine...

 

[Vintage Engine Repairs]

Sorry you’re getting a bit of a hard time for this one matey. You asked a simple question and got some unnecessary heat.

Doesn’t matter what you choose to use, you just want some help.

I don’t know very much, I am fairly new, and you will have far more experience than me, hut I’d start logically, and do a compression test and look at 150 psi as where you’ll want to be and do a pressure and vacuum test to make sure it holds between 6-7 psi. Look through the exhaust port for damage. When you pull the rope does it make any strange engine noises? Clinking, knocking etc? If everything seems to be straight, then take off the flywheel and check for a sheared key. If not then take the cylinder off and have a look.

 

[pioneerguy600]

Even easier to pull the muffler first and take a look, maybe see if there is scratches and if the rings are free.

 

[jltrent]

Is the carb AM? No start might check it.

 

[a. palmer jr.]

Sorry you’re getting a bit of a hard time for this one matey. You asked a simple question and got some unnecessary heat.

Doesn’t matter what you choose to use, you just want some help.

I don’t know very much, I am fairly new, and you will have far more experience than me, hut I’d start logically, and do a compression test and look at 150 psi as where you’ll want to be and do a pressure and vacuum test to make sure it holds between 6-7 psi. Look through the exhaust port for damage. When you pull the rope does it make any strange engine noises? Clinking, knocking etc? If everything seems to be straight, then take off the flywheel and check for a sheared key. If not then take the cylinder off and have a look.

Not to worry about the heat, I'm used to that, but thanks. I mainly wrote this thread to get people awake. I've put several of these together and pretty well know where to look for the problem. I probably don't have to check the compression because I pretty well know it's around 110 or thereabouts, I'll confirm it in a day or two when it warms up around here. Doubt the rings are stuck because the saw didn't actually run, just hit a few times getting the prime burned out, less than a couple of seconds. The engine went together fairly easily so I'm pretty sure the piston has too much clearance but I'll check that to be sure. Again, thanks

 

[a. palmer jr.]

Is the carb AM? No start might check it.

No, it's the standard carb with the H & L limiters removed...muffler modded of course..

 

[Vintage Engine Repairs]

Not to worry about the heat, I'm used to that, but thanks. I mainly wrote this thread to get people awake. I've put several of these together and pretty well know where to look for the problem. I probably don't have to check the compression because I pretty well know it's around 110 or thereabouts, I'll confirm it in a day or two when it warms up around here. Doubt the rings are stuck because the saw didn't actually run, just hit a few times getting the prime burned out, less than a couple of seconds. The engine went together fairly easily so I'm pretty sure the piston has too much clearance but I'll check that to be sure. Again, thanks

All good I didn’t want to patronise you or anything, clearly you have done this way longer than me, but never hurts to go over a few things good luck!

 

[Mad Professor]

Huummmm....quality Chinesium

 

[BuckthornBonnie]

Flywheel ok?