Advice on whether to replace piston+rings in a good running MS462C

[MtnMike68]

Hello arborists!

I've really learned a lot from this great forum -- thanks so much for helping folks out with their questions. I'm hoping to get a bit of advice on the piston shown below. It's in a used MS462C that I recently purchased for a good price -- it has great throttle response and the compression seems fine, but as you can see it has some cratering on the top from fines that have got past the filter and I'm not sure what's happening below the right side of the piston ring.





So my question is this: would you run it as is, or is this a situation that should be repaired sooner rather than later before it leads to other damage (cylinder wall, etc.)?

Thanks so much for your guidance,
--Mike

 

[MtnMike68]

Two additional pictures:





Thanks!
--Mike

 

[Vintage Engine Repairs]

Hey Mike, it looks like it’s been run on a cheap oil and flaking carbon has resulted in what you see. I’d be keen to know if he ran stihl HP ultra, you should ask him! Ultra runs cleanly in their motomix but with normal pump petrol it tends to make quite a mess over time.

If it was my saw I’d take the top end off and remove the carbon on the crown with scotchbrite, gently try and remove the smearing on the skirt in the same way, check the cylinder and clean it then check ring end gap. If it’s good then re use it. I tend to be more cautious than others. Some may say forget it, damage is done, run a good oil and move on with your day. Depends on your experience and confidence. There are a lot of really good guys that will help you when you need.

Edit:

This looks a bit concerning. Can you confirm it’s not a chip?




Also, this isn’t caused by fines getting past the filter, it’s carbon damage. As above, reach out to him, ask him what oil he uses and recommends - it will tell you a lot about how this happened. Richard Flagg on YouTube has a number of videos showing the damage stihl ultra oil has done, this looks somewhat similar!

 

[MtnMike68]

Thanks very much for the insight. Unfortunately this originated from an estate sale so the oil mix history is unknown, but I bet you're right. I do see a lot of carbon build up in the exhaust port (which has been resistant to chemical cleaning), so that seems to confirm that the oil choice was not the best. I'll need to see if I can feel anything in that corner.

 

[MtnMike68]

I cleaned the piston a bit near the ring discoloration and investigated for surface differences as best I could with a plastic toothpick. The only surface difference I can feel is at the ring itself. On the opposite side of the exhaust port, there is a similar carbon pattern building up near the ring, so I'm thinking this is getting built up in the corners due to all the carbon gunk in the exhaust port. What do you think? New close-ups of the two corners below:





So I'm inclined to run it for a season and see if it cleans up at all with better oil (I currently use the reddish-purple VP Racing full synthetic.) I do have an OEM piston+ring kit to install at some point, but thinking I might wait.

Thanks again!
--Mike

 

[Vintage Engine Repairs]

Sure thing, see how you go. I don’t know why it’s like that, someone more knowledgeable on the subject may. Enjoy cutting with your new saw!

 

[Jza]

I'm with vintage , try a better oil and keep up maintenance. Warm it up , sharp chain and run it hard .