MS440 Piston

[taddat]

What would cause the wear on the bottom of the piston skirt on the intake side? Or is this normal? This piston (and cylinder) was just replaced and only has about 45 mins of use on it. The pic is not the best but the piston is shiny on the bottom of the skirt.

 

[computeruser]

Intake side wear is usually a dirt-and-debris issue from poor or absent air filtration.

 

[PB]

Why was that piston replaced? If it has only 45 minutes on it, I would guess it is from the break in process. I don't see any scratches from the skirt to the ring.

 

[blsnelling]

I see it on every saw I tear apart, new included. It was explained in another thead yesterday.

 

[WidowMaker]

thrust face

 

[Sawdustmaker]

I believe that is normal.

 

[taddat]

Why was that piston replaced? If it has only 45 minutes on it, I would guess it is from the break in process. I don't see any scratches from the skirt to the ring.

This is from a saw that I rebuilt last week (thanks to alot of help from reading AS). After I got it back together, I ran it for about 45 mins and it ran great. After reading some of the info on the "less then perfect" Stihl castings, I pulled the muffler just for kicks (and it is only the 2nd saw I have rebuilt). I could see a few scratches that just didn't look right. I pulled the jug and there was a chip out of the plating next to the intake port. I wish I would have snapped a photo of it but I didn't. The size of the chip was about the size of what a Q-tip would cover. I took it back to the dealer and he replaced the piston and cylinder without question(hopefully they arrive tomorrow). The dealer's opinion was that it was an obvious defect in the casting. The chip look just like the chip in the jug that Brad posted but this chip was slightly bigger and near the lower corner of the intake port.

Thanks again for the help!

 

[blsnelling]

I don't see the scratches. And that is the intake side of the piston you said the chip was on.

 

[taddat]

I don't see the scratches. And that is the intake side of the piston you said the chip was on.

On the first photo I posted, you can see one scratch by the bottom ring (intake side). The photos below are the exhaust side. The chip was missing from the lower edge of the intake port.

 

[Evan]

those bad stihl jugs posted in other threads will last a lifetime

if your getn scratches id put blame towards dirty assembly before i blamed stihls cylinder

forget you ever saw those crappy stihl cylinder threads.

you have to be very clean going back together. parts aswell as your hands that are handleing the parts. it doesnt take much to cause a scratch like those.

 

[WPanhandler]

My son just pulled apart a 34 year old truck engine that look about like that, only it has 150,000 miles. The skirt of the piston can be scratched with a fingernail if you try hard enough. I don't see a problem here.
Unless you are real careful you can do that much damage putting it back together again

 

[Evan]

I agree.

also forget about 70% of what youve read on this site in the last week and youl be much better off