Why does piston scoring matter?

[chilipeppermaniac]

Well, I am happy to report that the 353 & 346 are still doing just fine, I used them for most of the cutting all summer.
I normally do not use a 20'' bar on a 50cc saw but I did on this 346 to make it work hard, it bucked up a lot of 18-20'' red oak then ripped the 22'' long pieces twice.
I was surprised at how strong this saw was, 12 or 15 tanks thru it now, compression is 158.
The 353 with a 16'' bar was used for the smaller top of the trees 15'' on down, probably the same amount of fuel thru it as the 346, not nearly the power of the 346, I could have turned it up some more but it was such a jewel to run, always one pull start when warm always idled well, always ready to work, it made me smile.

Both of these pistons had been scored at the ex. port about an inch wide, I cleaned up the ring grooves, put in new rings, smoothed the scoreing, cleaned alum. out of the cyl.. Looks like it worked out.

old guy, do you have any before ( scratched piston and cylinder) and AFTER you smoothed the scratches and installed the new rings?

I have an 051, and an 075 that had scoring in both OEM top ends. I purchased new OEM P and C's for each, but wanted to try to see what kind of compression, running performance I could get out of cleaned up original top ends before I install the new OEM ones. Interested in how the 2 used top ends will compare to the 2 once I put the new top ends on each saw.

THEN, just for kicks, I have a 3rd saw, my 2nd 075. I will pressure test, compression test and evaluate that saw in comparison to the other 2.

 

[chilipeppermaniac]

O75 Pistons too.

 

[chilipeppermaniac]

I'll get pics of the OLD OEM cylinders and piston in the AFTER polishing up condition is attained at a point where it can be ready to install.

 

[old guy]

I have no pics, all I did was make sure the ring & groove worked freely, then lightly flat filed the scoreing so piston slid free in the bore, and of coarse cleaned the cyl. wall.
This was just an experiment which seems to have worked out well.

 

[old guy]

I have no pics, all I did was make sure the ring & groove worked freely, then lightly flat filed the scoreing so piston slid free in the bore, and of coarse cleaned the cyl. wall.
This was just an experiment which seems to have worked out well.

I did not try to smooth the scoreing, just took enough off that the piston slid freely in the bore, in fact if I were looking to buy this saw & pulled the muff. & saw that piston I would pass, but a closer look shows the ring is free in the groove.

 

[chilipeppermaniac]

I have no pics, all I did was make sure the ring & groove worked freely, then lightly flat filed the scoreing so piston slid free in the bore, and of coarse cleaned the cyl. wall.
This was just an experiment which seems to have worked out well.

Old guy, I hope it continues to show you good results. My first experience with a scored piston was in my old 1989 Honda CR 125 dirtbike. I found out about Nikasil back then. My friend and auto mechanic who also races bikes got it sleeved for me. I wonder if anyone ever mentions sleeving a chainsaw cylinder.

On a side note, I have seen demonstrations of exactly what you did in cleaning up the top end and installing new rings and getting a well running saw in the end.

 

[flatsfisher]

this means nothing as this piston was scored and previously sanded on. didn't even measure it. came out pretty ugly, just chucked it up, got it concentric. turned the chuck with one hand while holding pressure on the cross slide with the other. took a fair amount of pressure. would also want a wider knurling tool as I had to make 3 separate passes because both hands were occupied so I couldn't do a continuous run as I normally do when knurling. def not a great chuck for doing this. and if I was trying to accomplish something I would have used soft jaws. def raised the skirt surface up.