only rings or new piston+rings (pics)

[goatchin]

Background info: My 372xp was lackin power so i had it checked for compression, resulted in 120 psi. I pulled muffler off and looked at piston and cylinder walls from exaust port...piston and cylinder walls looked shiny and no visible scratches. I decided i would order just rings and scotchbrite the cylinder walls as i have no access to a hone (see question at end of post) to help seat new rings. My rings arrived from Bailey's, I tore down saw, but...now...that i pulled off the cylinder and looked at everything I'm concerned, or maybe just thinking too negitively.

Piston: As far as i can see this is the biggest of my problems. I'm assuming the dimple/hole in the top of the piston is from a "too" hot of a spark plug (bout the saw used) and burned through the chrome layer. The second concern of the piston is that on the intake side of piston the outer edge is shined up and the exaust side has black carbon like most of piston top...is this to be expected since the exaust side is where the "dirty" exaust is leaving from (lack of better terminalogy).

This second pic shows some "heat damage" on the bottom of the exaust port side of the piston skirt...sign of new piston in need??

Cylinder: I see only a few concerns with the cylinder other than differnt colorations at differnt levels. It seems that there are either oxidiztion or "heat damage" imprints of the piston skirts on both sides at BDC on the cylinder walls. Second concern is that above one of the "wall ports" there is a light brown streak, i feel no scratches w/ my fingernail. 3rd concern is that at the top of the cylinder there are white chuncks of carbon, one area is large and spotted (bout a bit less than half of the cylinder head) and the other is small but a thick chunk (bout half the size of a std. nail head). I'm thinkin these may have been from when the saw was running way lean-discovered that when i had the saw's compression checked by a friend at small engine shop. Are these "concerns" of mine actual eventual problems or are they just usualy cylinder features after a long time of use.

Now for the scotchbrite honing. I know that I'm only lightly roughing up the "glaze" that the old rings had created so that the new rings will be able to create their own "glaze" and be able to seat themselves after 6 or so tanks of fuel...am i on the right track. Any other things i should do before/after i use the scotchbrite pad. Clean the cylinder w/ mix after scotchbrite??


Thanks for any help or suggestion yall may be able to offer to me, it will be greatly appreciated.

p.s. sorry the large pics...tried resizing w/ photobucket but didnt work and also for some of the pic quality, it was hard gettin the camera at right angle for the cylinder pics

 

[Four Paws]

That dimple is there from the factory...not from nearly burning through.

Everythign you have shown in the pictures is typical of a saw that has been used.

Put the rings in it - take some time to clean the ring grooves out - carbon can build up in there. Also, clean the carbon off the top of the piston and out of the exhaust port. Put it back together, and go cut. I doubt your piston is worn enough to warrant replacement.

 

[goatchin]

Thanks thats what I was hoping to hear. I guess i was expecting it to look a little bit "cleaner". guess i have my standards to high lol.

 

[pops21]

That looks like a day in the park compared to my dolmar 5100s that I just rebuilt. The owner before me ran straight gas threw it. You wanna talk about a mess.I had to take some muratic acid and clean he aluminum off the cylinder before I could ever think about putting a new piston in. What you have is just normal wear. A ring set and some scotch bright will do the trick. Just remember before you put it back together to wash the cylinder and piston and rings with some dish detergent and hot water to clean it GOOD. lube the piston baring,piston and cylinder before installation. Also make sure that the piston rings ends are in the locating pin when installing the piston or you will break the rings.

 

[goatchin]

thanks for the help guys, its been very much so appreciated.

one other question...Is it likely i'll have to retune the carb after i reassemble?

 

[Dan Forsh]

Only if you have fiddled with it while you had problems. Most saws basic settings are one full turn out on the H and L.

 

[goatchin]

nope i havent touched the carb other than wiping the sawdust off the bottom of it. I just didnt know if removing the carbon from the exaust port (pretty thick) and the top of piston would create any differences as far as the carb tune would go.

thanks for the help

 

[Scandy14]

Use Stihl Ultra mix oil and it will help keep the engine internals clean.

 

[goatchin]

right now im using the husky oil 50:1. I know i'll get the snot beat out of me for asking an oil question...but...being the p+c have been ran hard, would i want to start running 40:1 and premium gas (what octane?...around here each station has it's own "premium")? :deadhorse:

 

[woodfarmer]

heres what a leaned cylinder and piston look like, cleaned the cylinder added a new piston and ring, good as new

 

[goatchin]

ouch...thats a bit rough

just put my rings in...wow easier than i thought it was gonna be. everything went smooth. Got it all washed up and infront of fan drying, then gonna add a coat of 2-stroke oil to everything, and reassemble. On my piston bearing, would it be okay if I gave that a few drops of the oil just for some added lubrication, and also the crank bearing?

thanks for everybodies help, its been much appreciated.

 

[stevethekiwi]

scotch brite???

 

[Urbicide]

On my piston bearing, would it be okay if I gave that a few drops of the oil just for some added lubrication, and also the crank bearing?

Yes.

 

[goatchin]

I might have the wrong name for them...they're the lightly abrasive cleaning pads for washing dishes w/ dryed on food.

I used one thats been through a couple dishes already b/c they seem plenty rough brand new. I prolly could have used the new ones b/c it didnt seem to create much of crosshatch to the walls but slightly more than before to help create a better seat for the rings I hope.

 

[goatchin]

Anybody know how much I should torque the four cylinder bolts down to? I have access to the tools so no problem on that part. Right now they are tight to hand and the allen wrench but I'd rather get them tightened down to spec ratings.

 

[epicklein22]

Use 320 grit sand paper instead of the scotch brite pad, will work a lot better. Try to do a swirling pattern so you can get a cross hatch. Lube everything you can with 2 stroke oil.. Torque the bolts nice and tight, but not to the point of it possible breaking off. One of my local stihl dealers said he doesn't use the stihl torque specs because he has seen a few come loose.

 

[huskydave]

Clean er up rering her and run her! What do you have to loose? nothing and I will bet you will have decent compression and a good reliable saw afterwards. It is a good time to check out fuel/impulse lines change fuel filter do a carb rebuild etc..

 

[goatchin]

Epic-yea thats what pretty much how i have the bolts tightened down, turned till tight w/ good amount of pressure.

Husky-carb and fuel lines are all okay...carb is in good condition, fuel and impulse lines are are good and pliable in all areas including areas of coming though the casings.

 

[goatchin]

I got my rings installed without a problem, everything went back together smooth and easy.

I have one more question on this project, Is there any special way I should run the saw for the first couple of tanks? Should I let it idle for a little while when i first start it? or, no WOT for couple of tanks, or only WOT in the wood, only run it for a few minutes at a time the first tank, no cutting in large wood, or should i just giver 'er the berries and balls to the wall?

right now im using the husky oil 50:1. I know i'll get the snot beat out of me for asking an oil question...but...being the p+c have been ran hard, would i want to start running 40:1 and premium gas (what octane?...around here each station has it's own "premium")?QUOTE]

would the extra oil help me in any way or should i "dont fix it if it aint broke"

 

[AUSSIE1]

Scotch-brite (scourer), would do more cleaning than cross hatching.

Al.