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

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Offline hessaacd

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MS250 - piston / cylinder need replacing ?
« on: May 03, 2014, 08:25:53 am »
My stihl MS250 doesn't have very good compression - 90 dry, 120 PSI wet.

The images attached to this post show the piston and cylinder. I was curious if I should replace them or not.

Any help is greatly appreciated!

Alan

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Offline 660magnum

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Re: MS250 - piston / cylinder need replacing ?
« Reply #1 on: May 03, 2014, 08:38:29 am »
Look on Ebay at the pistons and cylinders or complete power units offered?

It looks pretty ragged to me? I'd be trying to determine what happened?
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Offline KilliansRedLeo

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Re: MS250 - piston / cylinder need replacing ?
« Reply #2 on: May 03, 2014, 09:13:10 am »
+1, I agree pretty rough. You already obviously have it torn apart, replace the cylinder and piston. Also given the scoring on the piston you may have a leaking seal. They are cheap so you should also replace them. Have you checked the bearings?

You can get everything needed here:

http://www.hlsproparts.com/category-s/82.htm   Use 'chainsaw' in the coupon code field and get 10% off your order.
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Offline tinkerswithengines

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Re: MS250 - piston / cylinder need replacing ?
« Reply #3 on: May 03, 2014, 12:35:34 pm »
I agree with the others....you need to replace the piston and cylinder. While you have your saw torn down, check your impulse line and your intake manifold boot for any leaks or dry rot cracking. I also agree with the others...looks like you got a air leak!

On the re-build, unless you have or have access to the Stihl  hookless circlip installation tool, you will most certainly have fun installing the "hookless" type of circlips! Since I retired and I do not own the Stihl tool, I like to use the "G" type circlips as seen in the picture on this link. They are very "controllable" during installation with good needle nose pliers. Also the price is right....

http://www.ebay.com/itm/Cylinder-and-Piston-Kit-Fits-Stihl-MS230-MS250-023-025-Free-Shipping-Low-Price-/271143412712?pt=LH_DefaultDomain_0&hash=item3f216823e8

Replace your crank case seals too. On the clam shell re-builds, I use and Dirko HT sealing compound. 

Tip, when installing the crank shaft seal on the clutch side, put a layer of electricians tape around the crank shaft stub over the retaining ring groove. Put some light grease on the seal and ease it into place, The electricians tape will keep you from damaging the seal when it goes over the groove.

Dave

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

Offline KilliansRedLeo

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Re: MS250 - piston / cylinder need replacing ?
« Reply #4 on: May 03, 2014, 12:57:56 pm »
Neat trick with the tape Dave!
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

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Offline Fish

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Re: MS250 - piston / cylinder need replacing ?
« Reply #5 on: May 03, 2014, 04:24:14 pm »
He does some real kinky chit with Duct Tape!!!!!

Or in his case DUCK tape......

Offline wisecobandit

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Re: MS250 - piston / cylinder need replacing ?
« Reply #6 on: May 04, 2014, 05:42:55 am »
As everyone else says replace the piston and rings.
They aren't the highest compression saws tho and off the stihl line only pulled about 120-125 psi when new, obviously that went up a bit as they where "run in"

Offline hessaacd

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Re: MS250 - piston / cylinder need replacing ?
« Reply #7 on: May 04, 2014, 12:32:11 pm »
Many thanks for the ideas. Just ordered new piston and rings.

Offline KilliansRedLeo

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Re: MS250 - piston / cylinder need replacing ?
« Reply #8 on: May 04, 2014, 12:37:32 pm »
Make sure you figure out what caused the scoring on the piston and correct it! Otherwise you will be doing this again.
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

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Offline hessaacd

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Re: MS250 - piston / cylinder need replacing ?
« Reply #9 on: May 05, 2014, 08:39:31 pm »
After checking for dry rot on the hoses and intake boot and doing a soap bubble test on the crankcase seals it seems they are OK.  The rubber gasket between the carb and the crankcase is a little torn around the edges. Could air leaking in there cause the pistons to wear?

I don't understand how air leaking into the crankcase can cause the pistons to get damaged like that.

Alan

 

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