Author Topic: MS250 - piston / cylinder need replacing ?  (Read 478 times)

0 Members and 0 Guests are viewing this topic.

Offline KilliansRedLeo

  • Nitro Hotsaw
  • *******
  • Posts: 2361
  • Karma: 80
  • Location: Rochester, NY
    • RoCHusqvarna
Re: MS250 - piston / cylinder need replacing ?
« Reply #10 on: May 05, 2014, 10:16:33 pm »
The saw breathes through the case. Excess air coming in from the outside leans out the fuel/air mixture. Too lean fuel/air mixture creates excess heat causing premature wear/damage to the saw. Lean=more air than necessary.
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

Thomas Jefferson
1743-1826

Offline Fish

  • Piped Saw
  • *****
  • Posts: 309
  • Karma: 39
Re: MS250 - piston / cylinder need replacing ?
« Reply #11 on: May 06, 2014, 11:32:49 am »
Yes, one could melt the piston on a brand new saw just by adjusting the carb incorrectly.  You can sit it on a bench, and slowly turn the high screw in and get it really screaming, say 16,000 to 18,000 rpms for 40 or so seconds.

You need to "richen" the mixture to slow them back down to 13,000 or so, depending on the model.

Also, since the lube is in the fuel, the leaner the mix, the less lube there is for the engine, which makes it overheat
exponentially.  So if one is using his saw, and it starts acting squirrelly and dying, he needs to shut it off and fix the problem.

Offline KilliansRedLeo

  • Nitro Hotsaw
  • *******
  • Posts: 2361
  • Karma: 80
  • Location: Rochester, NY
    • RoCHusqvarna
Re: MS250 - piston / cylinder need replacing ?
« Reply #12 on: May 06, 2014, 12:13:40 pm »
+1 Fish, good advice as usual!
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

Thomas Jefferson
1743-1826

Offline tinkerswithengines

  • 4 cube
  • **
  • Posts: 26
  • Karma: 5
  • Location: Pennsylvania
Re: MS250 - piston / cylinder need replacing ?
« Reply #13 on: May 06, 2014, 07:41:40 pm »
WOW! Fish said it all and then some! ;D

Those that want to set up their saws by "sound"....usually end up with scoring of the piston and cylinder. Buy a good reliable tachometer, then tune! I have seen many a good saw go to ruin by those that relied on "set to sound" method of tuning. In fact, the shop where I retired from, all new Stihl saws came with a nice little orange handled screw driver...we actually had several hundred of them all bunched up like a bouquet of flowers in a big vase....in the shop area! All for the simple reason we didn't want the "new owners" tuning their new saws! When we sold a new saw, we serviced it before the new owner got it into his hands. Hardly ever a time we had to actually "tune" a NEW Stihl product! I can't say that about the others we sold or serviced! ;)
We also had a saying in our shop with "some" warranty claims that came in....warranty doesn't cover stupid!

Dave
NOTHING BUT STIHL! 028WB, 029, 029 Super, 024, 026(2), 026PRO, MS250, MS290(2), MS310

Offline 660magnum

  • Global Moderator
  • Nitro Hotsaw
  • *******
  • Posts: 6437
  • Karma: 249
  • For The Love Of Chainsaws
  • Location: NCO
Re: MS250 - piston / cylinder need replacing ?
« Reply #14 on: May 06, 2014, 08:06:15 pm »
The newer designed chainsaws do not have such a definite two cycle - four cycle break point as the chainsaws from 20 or more years ago.
We should share what we know... someone may learn...
That knowledge can live after us... and that "Pays It Forward".
Be all that you can be . . .

Offline hessaacd

  • 3 cube
  • *
  • Posts: 9
  • Karma: 0
Re: MS250 - piston / cylinder need replacing ?
« Reply #15 on: May 11, 2014, 07:17:09 pm »
Well, I put in the new piston and rings, it started normally, I ran for about 15 seconds, felt like it had good compression, then I turned it off for the night, planning to put on a bar and chain today. 

Now it's back down to 90 PSI.

Does this indicate I might need a whole new cylinder/piston assembly?

Offline H 2 H

  • 5 cube
  • ***
  • Posts: 100
  • Karma: 11
  • Location: Were the Pacific Northwest Soft Woods Grow
Re: MS250 - piston / cylinder need replacing ?
« Reply #16 on: May 11, 2014, 11:06:08 pm »
Try a different gauge JMO
"People ask me where all my money went, I tell them half of it I spent on gambling, fast women and liquor, the other half I wasted!" W.C.

"..... nothing more funnier than watching some ole coot make a fool out of himself, especially sideways”

"You can't argue with someone that doesn't have any real life experience on the subject."

Offline sharkey

  • Piped Saw
  • *****
  • Posts: 367
  • Karma: 37
Re: MS250 - piston / cylinder need replacing ?
« Reply #17 on: May 12, 2014, 12:40:25 am »
Compression psi only tells you that an engine will run, not how well.  It also takes a little longer than 15-20 minutes of run time for your new rings to seat onto the cylinder wall.  Run it through a couple more heat cycles and then test it again.  Keep the carb rich for the first few tanks of fuel and try a different gauge.  If the cylinder has alot of time on it, it may also need to be replaced.  To give you an idea how long it may take for those rings to seat, some engines take 6-10 tanks of fuel before everything seats.     

 

Related Topics

  Subject / Started by Replies Last post
28 Replies
1765 Views
Last post February 16, 2012, 06:58:36 am
by brokenbudget
12 Replies
641 Views
Last post January 26, 2012, 09:09:40 am
by ECpirates96
19 Replies
2423 Views
Last post October 19, 2013, 06:25:02 pm
by Cut4fun .
63 Replies
2391 Views
Last post October 26, 2013, 05:32:17 pm
by davbell22602
38 Replies
1202 Views
Last post June 05, 2013, 09:15:45 pm
by Al Smith
8 Replies
498 Views
Last post July 30, 2013, 09:20:17 am
by farmboy
19 Replies
464 Views
Last post September 09, 2013, 09:51:10 pm
by doreadeal
54 Replies
1041 Views
Last post February 09, 2014, 05:37:39 pm
by wbhburn
1 Replies
224 Views
Last post March 09, 2014, 03:41:36 pm
by stihls066
21 Replies
576 Views
Last post November 29, 2014, 08:29:17 am
by weimedog