Stihl MS250 - Chain Loose then Tight - Won't Run

I have Stihl MS250 that has run well for years. After noodling some big oak rounds into halves, it will no longer run (occasionally will start, but not run for more than 3-5 seconds). As I pull the chain around the bar, it is very loose, then very tight. I figured that I bent something and needed a repair. The local Stihl dealer diagnosed a stretched chain, sold me a new one, and said everything would be fine. However, I am still having the same problem. Thoughts?

 

How does it run with the chain and bar off?

 

Runs fine. Not sure if this matters, but over the last season I have started to experience the pull cord not moving at all at least once every 3-5 pulls.

 

If you hit a nail or had some sudden stoppage, the crankshaft can twist at the crankpin and you will notice possibly both flywheel and clutch ends to wobble. Take the spark plug out where you can spin the crank more freely.

There are people that can realign cranks but it has to be removed from the engine.

 

A guy sold me a right new Husqvarna 350 for $120 because it was doing this.

He had two new .325 chains for it and the presets in the chains were 3/8ths low pro. Everytime the preset would come around either sprocket, the chain would bind. I replace the presets and filed all the burs from the DL's where the chains had come off and it was like a new 350.

 

Check your clutch drum bearing. The EXACT thing happened to my 026.
The bearing had lost several needles and came apart
$10 and 10 minutes fixed the problem.

 

I think that's a good idea too. There must be something binding in the clutch or it would run, at least idle, with our without the bar and chain. A few missing needles could cause the clutch to bind on the drum from it bring misaligned. That's my uneducated guess.

 

The above and also check your bar for wear. make sure it is flat and not tapered.



If it looks like this, it is not good! Either file it down or replace. This wouldn't cause the loose/tight but it will make your saw act like it has no power and bind.

If you still have a spark arrestor screen, have you looked at it or cleaned it?

 

U probly need a new bar.. and chain.. I have an 038 doing that and the sprocket at tip was worn on one side pinchong chain causing friction. Had to replace w a new bar n chain. Cuts like I bought the saw yesterday..

 

Everyone, thanks for the responses. This is my first time attempting a small engine repair, so I will probably get the names of things wrong, and ask some basic questions. I appreciate your patience with me.

Woodchuck, I think you got it. When I turned the sprocket, the clutch drum would turn about 1-2 times before hitting against the side of the housing and stopping. I took off the clutch drum and found nothing except 13 loose needles (5/16" pin-looking pieces of metal) in and on the clutch. It appears that the clutch drum bearing is completely gone. Is it as simple as replacing it and seeing whether the saw works again, or should I remove the clutch and see what else may be going wrong (for example, seeing if any pieces of the clutch drum bearing are in there)?

MasterMech and w8ye, the sprocket does not appear to be worn or out of pitch. I removed the spark plug and the cord pulls easily (first time in a long time that has been the case), the clutch assembly spins easily, and I see no movement of it toward the housing. Does this rule out a bent crankshaft?

Kevin in Ohio, I am using an almost new bar, which appears flat, and a brand new chain. I have not looked at the spark arrestor screen -- how do I get at it?

FYI -- I used to read a different website quite a lot, but got away for a couple of years, and noticed last night that most of the key posters were missing. Just found this site, and signed-up immediately. I look forward to being a part of FHC.

 

This site should be good enough?

 

I meant to include in my last sentence: I found most of those key posters here on this site. I have watched them help a lot of guys like me over the years, and I was really pleased to find them again here at FHC.

 

Your bearing is the culprit, just replace the bearing unless the part it rides on is chewed up real bad. make sure to put a little grease on the new bearing if it doesn't have any on it.

Not sure on your particular saw but look on the muffler. There should "normally" be a single screw , maybe 2, that will hold a little cover. Inside will be a small screen. If the screen is carboned up or dirty, clean it. Most people just remove it and are done with it. Oil residue builds up and effectively chokes the saw down because exhaust can not get out.. I've bought several saws that the owners said were wore out because they had no power anymore and that was all that was wrong.

 

Simple step by step vid to watch. I would bet if the bearings were all loose in there you have found your problem. I would want to make sure you found all the bearings though so they aint floating around in there to do more damage.

 

Stacks,
I cleaned up everything and inspected my clutch and drum. Everything appeared to be in good shape.
A new bearing, a little grease...back in business

 

Drum, clutch (looking at what I can see without removing it), and shaft appear in good shape. Found and inspected the spark arrester screen -- it is clean.

Butcher, thanks for the video. I watched his MS250 teardown and rebuild videos last night, and missed the one you found.

I too am concerned that some pieces of the bearing may be underneath the clutch or the washer beneath it, or may have damaged the wormgear-pin (for the oiler) in some way. However, I am a little hesitant to remove the clutch -- concerned I might screw-up or break something. Based on the YouTube videos I watched, it looks like placing a rope or cloth down the spark plug hole into the cylinder, and then turning the clutch clockwise to unscrew, correct? Anything else that I should be thinking about?

I plan to go tomorrow to the dealer for the bearing -- would it be smarter to let him remove the clutch and inspect everything?

 

Pretty straight forward deal. You can easily pull the clutch you self. Just use a soft nylon or cotton rope to block the piston.
I remember the first time I pulled my Husky 51 apart for oiler problems. Had brain bubbles cuz I never done it before. Out board clutch off, chain sprocket off, now to get the fly wheel off. Back the crank nut off to the end of the threads, clamp a vice grips on a fly wheel fin and wack the nut with a hammer. Popped right of and away we go.

 

A good practice is to remove the recoil first (or pull the rope out to give it some slack) so you do not put undue pressure on it prior to removing the clutch.