MS 241 Issue

I feel sorry for this saw, it lives in a truck box and gets the snot beaten out of it. Well it has been acting up the last couple of weeks. It had a hesitation on startup and didn't sound like it was hitting peak RPMs. So I took it out of the box and the tach was showing it didn't want to spool up. So I hit it with the compression tester and I got 132. Hmmm... So I pulled the spark plug and muffler expecting to not like what I saw. But things didn't look too bad so I pulled the jug.

And the cylinder looks ok.



The piston on the other hand.





I was wondering what the heck caused all this? Then I looked at the bottom ring. This is a pic of it where it lines up with the exhaust port. The ring feels beveled on the bottom edge at that point.



Then look back at the pic of the cyl..

Am I correct in thinking that there is a high area (shinny) of Nikasil around the exhaust port that has been causing excessive wear to the rings. That has caused decreased compression and blow by?

 

I was running Belray @ 32-1 till recently, and have been running Maxima K2 for a short time. Non-ethanol 93.

 

I guess I will just get a set of Caber rings from Greece and see how she goes. Meanwhile an 026 is going in the box.

 

Check with definitive dave, he sells cabers at great prices.

 

O.K. here's the heresy... That's too much oil for an M-tronic, especially with Belray. FWIW, my ported MS261CM did not like 32:1 Belray, so I went to 40:1 Yamalube and all is hunky dory. Just my experience, your mileage may vary. (P.S. I'm not trying to turn this into an oil thread) Oh yeah, get some Cabers from Dave, he's good people.

 

I run 32:1 in my 661 no issues. I've been running 2r also.

 

Hence the switch to Maxima and I am running 36:1. Belray is like gear oil compared to Maxima. But in this case the switch didn't affect the initial startup hesitation and slow spool up to peak rpms @ WOT; I just switched last week but have already run about a gallon of mix through the saw. Just not as snappy as it once was.

Rings are already ordered. When I searched the only supplier showing MS 241 Cabers online was the Greek. $10.38 with shipping.

 

Is the muffler stock, or has it been modded with a larger or more openings ?

 

The saw is stock.

 

I have seen similar to this on several motors that run cats in their mufflers, or have really choked up exhausts ................

Too much heat is cooking the oil on the exhaust side of the piston and causes the lower ring to expand more than it normally would. The upper ring is cooled better by the incoming air/fuel charge and isnt as effected, however, if you keep running it with the stock muffler in stock condition, the upper ring will start to wallow as well ............... if the lower ring doesnt fail first

IMHO, put in a set of new rings and modify that muffler, re-tune and run it for the rest of its life like you stole it, she will be just fine !!

 

Mtronic so no need to retune. I have kept it stock since employees run the saw as well and just didn't see the need but your post changes my thinking. There is quite a bit of wear on the exhaust side of the top ring as well just not a bevel, but a burr on the bottom edge.

 

Can you get a pic of the muffler inside and its outlet ?

 

I agree MM ............. however, something got a little hot on the exhaust side. I understand and have seen H1R dirty up areas of the piston, but not like this.


The saw is stock, so no larger ports to contend with and she didnt snag a ring

H1R makes my M-tronics run crappy - especially at 32:1. She could have been real lean from that alone

I would love to see the piston crown, along with the exhaust side between the top ring and crown.

Better to ask for pics and rule out things one at a time, especially since I have seen ring wear like this before when the exhaust was white and the machine ran hot

 

Anyway, I will just update this to say that the saw is running better. The initial start hesitation is gone. The top end isn't as snappy as when it was new though, but better visually from a before and after with the tach.

 

I have finally put 5 tanks through my 241 bought 5/14. I've run 4 tanks of "Ultra" in it, plus one tank of some "pink" colored stuff I bummed off MM or Dexter at the 5/14 GTG. The saw definitely has a start up hesitation when cold. It will start up with 3-4 pulls choked, but then die when clicked up to "fast" setting. No problem, you just go to pull on it again a time or two on fast as you would any other stihl, it fires but won't sustain. You have to re-choke and do it all again. Then when she will finally runs, it won't take any throttle for the first few seconds. Finally it revs on up and runs like a demon from then on. Subsequent starts while warm after that are one pull on idle speed.

I've found the best way to start it is to continue to let it run for several seconds on "choke" before flipping it up. The saw will run there on choke and not quit. When finally flipped to fast it will run, it might still balk at the first throttle attempt a bit, but its a screamer after that. Seems to be the norm for this saw with M-tronics ......................... you have to work through its starting ritual. On the other hand my 026 starts ................................ well, you all know how those run!

 

I'm not sure if the 241 is the same as a 362, but I set the lever all the way down on a cold start...3-4 pulls and it will pop...then 1 more pull and it fires. I let it idle without touching the throttle for 10-15 seconds...you can tell when it is ready because it seems to really load up on fuel....rev to clear the smoke then its off to the races.

 

Thanks guys but this 241 has HUNDREDS of tanks through it not 5.
We have been clearing fence rows with it since it got new rings. Maybe 5-10 tanks worth.