MS250, need expert advice?

[Okie]

A friend gave me a MS250 chainsaw with 18 inch bar and chain for parts knowing that I have one that's running. It was given to him also in this condition. He said it don't turn over easy and he started into it and quit because when he got the clutch off and recoil it still did not turn over easily with the spark plug out so he just set it back in corner as a lost cause.
I removed the recoil, muffler and the clutch side centrifugal clutch so as I could see all and could see that the chain brake was not involved and it was still snug turning, not rough turning just took some additional hand force on the flywheel to turn the engine over similiar to if the magneto was rubbing on the flywheel but no noise ar scubbing noise and the air gap on the flywheel is .011 with no flywheel or bearing slack play. The oil pump gear is acting normal and not trying to engauge The piston and cylinder looked real good looking into the exhaust port and the spark plug hole with a flashlite.. I turned the flywheel backwards and it turned normally. When I turned it the normal crank run direction the flywheel came back to a friction place again. Now this is the strange part. I marked the flywheel and counted two turns in reverse and it took EXACTLY two turns to reach the friction feel again when I turned the flywheel in the normal run direction. (strange to me) I counted 3 turns on the flywheel and reversed and three turns back to the friction feel place again. All at once it started turning normally in forward direction. I checked the compression at 135-145 pounds on two compression testers and the saw cranking normally. I checked and ignition fire as ok. I reluctantly added little bit of primer mixed fuel in the carb throat and the saw started and was idling on the first pull with the muffler off. I immediately killed the saw. It's still turning over ok.

Any ideas. I do not mind taking the saw apart for inspection but have never split the case on a Stihl MS025.
I could not find anything externally scrubbing or rubbing. Would a crankshaft bearing or rod bearing cause such or ??? Really strange that it would get back to the same snug spot the same number of turns that engine was rotated????

I did not pull the flywheel off an check underneath.

???????????

 

[neely]

A friend gave me a MS250 chainsaw with 18 inch bar and chain for parts knowing that I have one that's running. It was given to him also. He said it don't turn over easy and he started into it and quit because when he got the clutch off and recoil it still did not turn over easily with the spark plug out.
I removed the recoil, muffler and the clutch side centrifugal clutch so as I could see all and it was still snug turning, not rough turning just took some additional hand force on the flywheel to turn the engine over similiar to if the magneto was rubbing on the flywheel but no noise ar scubbing noise and the air gap on the flywheel is .011 with no flywheel or bearing slack play. The piston and cylinder looked real good looking into the exhaust port and the spark plug hole with a flashlite.. I turned the flywheel backwards and it turned normally. When I turned it the normal crank run direction the flywheel came back to a friction place again. Now this is the strange part. I marked the flywheel and counted two turns in reverse and it took two turns in the normal opposite direction to reach the friction feel again. I counted 3 turns on the flywheel and reversed and three turns back to the friction feel place again. All at once it started turning normally in forward direction. I checked the compression at 135-145 pounds on two compression testers and the saw cranking normally. I checked and ignition fire as ok. I reluctantly added little bit of primer mixed fuel in the carb throat and the saw started and was idling on the first pull with the muffler off. I immediately killed the saw. It's still turning over ok.

Any ideas. I do not mind taking the saw apart for inspection but have never split the case on a Stihl MS025
I could not find anything externally scrubbing or rubbing. Would a bearing cause such or ???

I did not pull the flywheel off an check underneath.

???????????

Could of been some carbon oil slag , depending on how rich it was run , take a couple oz of diesel and dump down the plug hole turn it over a few times and pour it out , then take some light wt oil and do the same thing, put it back together and run like it’s yours, run a 32-40:1 mix

 

[Okie]

neely:

Kinda strange that it was like it was being wound up was why I did not think slag is/was in the cylinder. The piston would go up and down the same number of turns when I reversed the flywheel before it got snug again. (that throwed me for a loop, brain teaser)
I've been into a MS250 down to the engine block, I just have never opened up or split a case on one. I do all my own chainsaw piddling work, try to stay out of the high dollar shops.
The previous owners have lost the throttle wire so I can only run it at idle or fast idle for now. I have some diesel and light weight oil.
I might get it ready for a start with muffler on, etc and let my bro in law do the high speed test. That guy would go stick his head in a fire if I told him too. Cannot believe he still trusts me. (just kidding)

 

[Philbert]

have never split the case on a Stihl MS025.
I could not find anything externally scrubbing or rubbing. Would a crankshaft bearing or rod bearing cause such or ??????????????

Clamshell engine - no case to split: easy to take apart. Might be a damaged crank or bearing?

Philbert

 

[Okie]

is it as easy as a clamshell strato Poulan engine to get apart? (clamshell is up and down)

I was thinking that maybe a special tool would be needed to split open sideways the MS250 plastic case? (so as to get too the crank bearings and rod throw area)

 

[Philbert]

@Okie - Send me a PM with your email address and I will send you the service manual, with an exploded parts drawing, etc.

Philbert

 

[Okie]

@Okie - Send me a PM with your email address and I will send you the service manual, with an exploded parts drawing, etc.

Philbert

PM sent

Thanks

 

[Thommo]

It sounds like something was stuck in one of the main bearings. I would run it for a while and then check the bearings for play because a bearing cage could be starting to break up.

 

[jackjcc]

I’ve had bearings do what you describe. Spin them in your hand and get a little grinding here and there. For it to be as you describe you might have a failed bearing where one ball has got something on it or is damaged and it takes two revolutions for the spot to come in contact agains. That’s my guess, usually if there is debris in bearings it’s in multiple spots giving more constant friction.


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[Okie]

I’ve had bearings do what you describe. Spin them in your hand and get a little grinding here and there. For it to be as you describe you might have a failed bearing where one ball has got something on it or is damaged and it takes two revolutions for the spot to come in contact agains. That’s my guess, usually if there is debris in bearings it’s in multiple spots giving more constant friction.


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There was never any roughness at all. It was sorta as you describe, maybe even ball bearing with a flat place in just one spot and when it got back to the bad place the bearing race may have previously spun in the plastic housing or the ball bearing or two locked together and sliding instead of rolling inside the race. When counting the turns on the flywheel the piston would make rotations up and down before the snug place re-appeared. 2 turns rev of flywheel and 2 turns forward and snug, 3 turns back 3 turns forward and snug turning. Then all at once just freed up. Not symptoms of small crank throw rod needle bearing, and not symptom of carbon on top of piston, more symptoms of a crankshaft ball bearing with a flat spot and sliding and maybe the bearing race spinning in the plastic case. ?????

I'll take it apart for inspection in few days and get back with the results. What ever is happening is most likely not going to cure itself with MY type of LUCK. (Murphy's Law seems to be right at home on my workbench)

 

[Okie]

I flogged the MS250 late this evening and got the clamshell opened up and found the intermittent erratic snug turning of the crankshaft problem. The plastic roller bearing separator that keeps the roller individual roller bearing separated and in place around the inside of the race on the clutch side bearing was busted up in small pieces and about 1/2 of the bearing were not separated and small pieces were lodging in the bearings race causing some of the bearings to slide and hang on the broken pieces and few plastic pieces were in the bottom of the clam shell. The bearing race had not spun in the housing. The piston/cylinder/rings looked great.

Plastic bearing separators looks like a weak/wimpy design for a high rpm engine? (appears the plastic cage could chip or break at almost any time in the life of this type bearing even a new bearing)

I'm thinking about replacing the following. Both crank bearings, both crank seals, the intake manifold boot, pulse line and maybe fuel line and since the saw had a good strong 140-150 compression just leave the existing rings?

Is their a better bearing design replacement or should I just go back with the OEM plastic cage type bearings?

Anyone have any other recommendations about replacement parts, to install when going back together, etc????

 

[hotshot]

Seriously? Don’t go back with plastic separator type bearings, buy the steel ones. Nachi or Koyo 6202C3 have the riveted steel type ribbons.

Those were a cost saver to the manufacturer, but it didn’t save your friend a dam thing!

 

[Okie]

MS250: Now running and oiling/cutting good.

New Nachi all metal bearings, new seals, Yamaha bond and pressure tested the crankcase BEFORE re-installing.

Thanks for the info.

 

[Wood Doctor]

I ran into this with an 025 also awhile back. Some thought it was the impulse hose but that was OK. Engine had good compression. New bearings and seals fixed it all. Good job, Okie.

 

[Okie]

Anyone have any ideas as to about what Model's of Stihls had the crankshaft bearings plastic bearing separators and about what years they came out with the plastic bearings and do they still come out new with such? etc???

 

[hotshot]

Good job there, okie dokie!

 

[MannyO]

Seriously? Don’t go back with plastic separator type bearings, buy the steel ones. Nachi or Koyo 6202C3 have the riveted steel type ribbons.

Those were a cost saver to the manufacturer, but it didn’t save your friend a dam thing!

Do you know the full part number for the nachi bearings? Having trouble identifying the correct type, any help would be appreciated. Or maybe there’s a size spec I should be looking for?

 

[Okie]

This is a old thread. You might think about starting a new post.

I used Yamaha bond as a sealer when re-installing the case halves.
I used a homemade type clamp to hold the case halves toget until the yamaha bond dried for 12 hrs before doing the complete re-assembly. Do not remember the exact steps but you will get the idea, I wanted to made sure that the new wet Yamaha bond sealer was not wiggled and worried as I was re-assembling all is why I did the about

 

[KASH]

Okie did you use the Nachi bearings?
Kash

 

[stihltech]

Plastic bearing separators make small marks on a piston when they fail. The piston is reusable. Metal cages take out the piston and cylinder. And metal cages do fail. The plastic cages usually fail from a dull chain heat. I would use the standard Stihl bearings. Take care of the saw and you may never do it again.