Ms200 - kaboom!!

[gcsupraman]

Have to vent.

Was using the MS200 today over the in-laws and the bar got pinched under throttle cutting a downed tree. Got it free and fired up the saw to hear a loud fast repeating banging noise. Took the bar/chain off and it's something inside the motor. Any ideas?

Saw is in excellent shape but I think I'm going to sell it for parts and get a new saw.

RIP MS200 11/18/11

 

[MnSam]

Not sure, but that sounds bad. How aggressive were you while "unpinching" it? Almost sounds like a bent crank.

 

[gcsupraman]

Not sure, but that sounds bad. How aggressive were you while "unpinching" it? Almost sounds like a bent crank.

Not very...but it was full throttle when it got pinched so that might have done it.

-Greg

 

[gcsupraman]

Hmmm.....just ripped it apart. Wow - this saw is easy to work on.

Found metal in the top of the cylinder preventing the piston from reaching TDC. The crank spins freely....

Now the mystery - where did the metal come from?

Piston looks good,cylinder isn't scratched at all.....still looking stay tuned. Nothing obvious.

-Greg

 

[Iron man]

If you tear into it deeper you might find what came apart and got sucked in the cylinder originated in the crank case.

 

[gcsupraman]

If you tear into it deeper you might find what came apart and got sucked in the cylinder originated in the crank case.

I must have looked in the crankcase for 20 minutes - looks beautiful! So I decided to clean everything up and re-assemble and I broke a piston ring so game over for today at least

I cannot for the life of me figure out where that metal came from......

-Greg

 

[Ax-man]

That piston has seen better days. Looks rough almost to the point of being worn out.

I don't know where the metal came from without having the saw in my hand but it is possible the metal from a transfer port, shouldn't be too hard to spot on a 200 the transfers are open. The piston itself is a good source for metal fragments or worse case scenario a bearing or a roller from the bearing or from the case halves. You won't know until you get a good look down inside the crankcase. Splitting that case will reveal the true story if you want to go that far with it.

What is up with the plug and that blue stuff???

 

[brokenbudget]

check the crank bearing cages for missing parts.:msp_thumbup:

 

[gink595]

I'm betting low end bearings got a little loose and decided to come up for a visit:eek2:

 

[gcsupraman]

That piston has seen better days. Looks rough almost to the point of being worn out.

I don't know where the metal came from without having the saw in my hand but it is possible the metal from a transfer port, shouldn't be too hard to spot on a 200 the transfers are open. The piston itself is a good source for metal fragments or worse case scenario a bearing or a roller from the bearing or from the case halves. You won't know until you get a good look down inside the crankcase. Splitting that case will reveal the true story if you want to go that far with it.

What is up with the plug and that blue stuff???

The piston looks dirty....but I just did a compression test about 4 weeks ago and it had 165psi so I dont think it's too worn out.

Excuse my ignorance, is the transfer port the passage from the carb?

I'm going to take another look. I was prepared to split the cases but everything looks so perfect I can't imagine something went wrong down there. The crank spins freely and the fragments don't look like the used to be a bearings. Im going to take some pictures of them....maybe that will help

 

[barneyrb]

Are the pieces aluminum? If so piston is only source. Steel pieces would be crank or bearings.

 

[belgian]

check the crank bearing cages for missing parts.:msp_thumbup:

I picked up a nice Jonsered 111S last week and found compression a bit low. Pulled the muffler, and piston was clean as a whistle.
Decided to replace rings and when I pulled the jug, found lots of debries in the case ; the needle cage from the piston rod gave way. Left a very big groove on the piston intake side as well.....grrrrr. But the cylinder was spotless :smile2:

 

[blsnelling]

Leave the bottom ring off. You'll thank yourself later

 

[Ax-man]

The upward stroke for the compression part of the cycle is only one very small part of the complete cycle for a two stroke engine. 165 is good but it is high for a 200. Average is 150. That carbon deposit on the skirt of the piston shouldn't be there. If that is on the intake side which I am assuming it is that is not good. That is telling me that the piston is not mating with the cylinder wall. Way too much clearance and is casing a spit back of fuel from the downward compression stoke after the intake port has closed. This might be the cause of your high compression reading, a little too much fuel getting past the rings with the upward stoke and into the combustion chamber for the compression part of the cycle.

The transfer ports are on the side of the cylinder .

There are other little telltale signs on that piston that tell it is worn. It really shouldn't be that dirty looking.

 

[blsnelling]

The piston looks fine to me. It still has most of the machine lines one it. Just dirty is all.

 

[blsnelling]

Looking at the combustion chamber and piston, it appears to me that the saws has been run with a very rich tune. What kind of oil are you using?

 

[gcsupraman]

The upard stroke for the compression part of the cycle is only one very small part of the complete cycle for a two stroke engine. 165 is good but it is high for a 200. Average is 150. That carbon deposit on the skirt of the piston shouldn't be there. If that is on the intake side which I am assuming it is that is not good. That is telling me that the piston is not mating with the cylinder wall. Way too much clearance and is casing a spit back of fuel from the downward compression stoke after the intake port has closed. This might be the cause of your high compression reading, a little too much fuel getting past the rings with the upward stoke and into the combustion chamber for the compression part of the cycle.

The transfer ports are on the side of the cylinder .

There are other little telltale signs on that piston that tell it is worn. It really shouldn't be that dirty looking.

AX-Man,

Let me take a closer look at the transfer port. I cleaned the piston up and touched it up with an electric sander (just kidding). I lightly touched it with some 400 grit sandpaper so the marks in these pics are not factory.

The pieces are aluminum. The crank spins perfectly, no play, no resistance in a certain spot - certainly no obvious indication of any issues down there. Strange....

 

[Ax-man]

Looks much better. First let's get one thing out in the open. I am not telling you not to use the piston . It does have some life left in it.

This is what I see from your pics. I can see where that skirt has more wear on it than the rest of the piston. The overall appearance of the piston is getting that battleship grey look. This is caused usually by fine dirt ingestion from a not so good air filter. The overall appearance of a good piston in a good cylinder is that it has a shinier look to it.

Also if you look close the skirt on that piston is not even , another sign of wear.

The ring glands are also dirty and show carbon deposits. Most pistons will show wear in this area it is just another sign of rings that are wearing and getting thin. DON'T AND I MEAN DON'T attempt to clean this area of the piston with your broken ring. You remove metal from this area and your piston will be junk. Either leave it alone or use a decarbonizer like Seafoam and a VERY SOFT BRUSH to clean in this area.

 

[MattCrowe]

It doesn't matter how good the piston looks in a digital photo on a forum, the crown has hammered chunks of alloy into the combustion chamber so it quiet simply isn't good at all.

 

[gcsupraman]

Looking at the combustion chamber and piston, it appears to me that the saws has been run with a very rich tune. What kind of oil are you using?

Brad,

I just picked up this saw used four weeks ago - I use the stihl ultra oil but I only used the saw for about 2 hours before this. Here is the new plug with two hours on it and more pics....

Ax-man,

Thanks for the detailed response. I am certainly not the expert on pistons and I appreciate the advise.

I ordered a set of new OEM rings and was going to try and clean everything up (including the carbon on the top) and re-use as-is. Of course I will check the compression later once it breaks in.

My biggest concern right now is where those aluminum chunks came from. Last thing I want to do is get it all back together and have it happen again

-Greg