MS362 scored piston

[Travis-Mc]

This is kind of a continuation of this thread: https://www.arboristsite.com/community/threads/325806/

But I started a new one because I want to ask specifically about the piston and cylinder and there is a lot of unrelated stuff in that thread.

Long story short, a few months ago I might have straight gassed (or ran bad gas) through my Stihl MS362 C-M and scored the piston. I caught it pretty quickly, so I don't think I did too much damage.

I finally got around to tearing the saw down. Pressure and Vacuum tested good. I wiped the cylinder out with a rag and wiped the piston off. No further clean up yet.

Do you guys think this cylinder is okay? I can post more after I try to remove the little bit of aluminum from the walls. I'm hoping I can clean up the cylinder and just get a new piston. The saw had 145psi compression before and after the cylinder was scored.

 

[Travis-Mc]

I decided the cylinder should be fine and ordered a piston. I'll know for sure once I clean it up. I'm going to run Amsoil Saber at 40:1 and give it a go.

 

[Jed1124]

Clean the aluminum transfer off completely or you will be tearing up the rings on your new piston. Do a search on cleaning up a cylinder and plenty should come up.

 

[cuinrearview]

This is all you need.

 

[Travis-Mc]

What grit of emery cloth and what's the gray stuff below it?

 

[cuinrearview]

The red one is 240, the grey is 500

 

[Travis-Mc]

Thanks.

 

[SteveSr]

This is all you need.
View attachment 716569

What is that black rubber looking mandrel "thingy" below the drill chuck... and where can I get one ?

 

[cuinrearview]

What is that black rubber looking mandrel "thingy" below the drill chuck... and where can I get one ?

A friend had that for a very specific application. When the shop he works in changed materials for some of the work they do it became obsolete. It works great for stuffing a scotchbrite pad into jugs to finish them. If the cylinder is too small or open port I'll just cut a strip and use it like I do sandpaper.

 

[drf255]

A little muriatic acid applied with a qtip and then hand sanded inbetween applications won’t hurt and may make it easier to get the transfer off. Just wear hand and eye protection and watch port edges. Then finish with the sanding.

 

[Travis-Mc]

I got the cylinder all cleaned up. It cleaned up nicely. I did hit the top of the chamber with the end of my mandrel, but I don't think it'll affect anything. You can see it in one of the pictures and in a reflection off the cylinder wall.

The squish with the new piston is about .010 without a gasket, .025 with the oem gasket, and .015 with a pop can gasket. I was hoping for .018", so I'm thinking of either making another gasket from some .008 aluminum, or cutting .008" from the piston to make a pop-up piston. Is it worth trying a pop-up for only .008" removed? I have a lathe and it would only take a few minutes.

Should I just use the OEM gasket? From my calculations, using an .008 gasket instead of the oem one will decrease the combustion chamber size by about 4-5%. Maybe I'm doing the math wrong, but I would expect about a 4-5% increase in compression, so 6-7 psi. Is it even worth it for that? Does a 4-5% increase in compression mean 4-5% more power?

Now if I do a pop-up piston I should get quite a bit more gain in compression, but I have no idea how much and don't want to do any more math.

 

[James Sawyer]

curious what you end up doing with you 362 and what you end up with in a squish measurement and compression?

 

[Lightning Performance]

curious what you end up doing with you 362 and what you end up with in a squish measurement and compression?

Four year old thread.
The OP hasn't been around in three years.