dolmar rebuild? help

[dumbhunter]

first, my compression tester wont screw all the way in, its to long, but it started failing on the drop test. still runs good, but when i pulled muffler i noticed some minor scarring on piston. the cylinder looked good from the muffler side and spark plug hole.

the saw is a dolmar 120si

now i am in the middle of trying to harvest my wood for this winter and need to keep my saw going. i have seen pistons with rings on fleabay reasonably cheap. are they just that= cheap. i hate to have to drop a fortune in this saw, not knowing how deep i will have to go on rebuilding it. now if the cylinder is fine can i get by with a new piston and rings or will i need to hone the cylinder to remove the glaze to allow for better break in? right now thats is what i am hoping for.

 

[drmiller100]

what is the problem with the saw?????

lots of 2 strokes everywhere have scraches in pistons all over, and run just fine.

compression is a funny thing. until you do a few saws, and "calibrate" it, compression readings are pretty worthless, other then whether they have over 100, or under 100.

the longer the hose, the lower the reading. the bigger diameter, the lower the reading, the more leaks, hte worse the reading. lots and lots of testers work just fine on 350 chevy's that give really weird readings on good small displacement 2 strokes.

so, back to the original question. what is the problem you observed on the saw?????? poor start? low power?

 

[dumbhunter]

seems for the displacement of the saw, she seems as if it is cranking over easier, like it doesnt have the compression it should, after sitting for a few weeks it fires on the 5-6 pull though. just seems to pull over to easy and does seem to bog down easier than it should. still cuts three times faster than my wild thingy.

 

[cuttinscott]

The 120si had a large recoil rotor for a 68cc saw it does pull over easier than todays saws. if it not scored and just has light scratches keep running it. Check the fuel and air filters make sure their clean and not worn thin(air cleaner) Parts are readily available from Dolmar dealers. Air filters run about $15 and A new OEM piston is less than $75.

Scott

 

[dumbhunter]

it has a new filter in it. and new piston only 75 buckaroos. might have to just do it as soon as i finish my wood for the year. thanks cutting scott

 

[pioneerguy600]

first, my compression tester wont screw all the way in, its to long, but it started failing on the drop test. still runs good, but when i pulled muffler i noticed some minor scarring on piston. the cylinder looked good from the muffler side and spark plug hole.

the saw is a dolmar 120si

now i am in the middle of trying to harvest my wood for this winter and need to keep my saw going. i have seen pistons with rings on fleabay reasonably cheap. are they just that= cheap. i hate to have to drop a fortune in this saw, not knowing how deep i will have to go on rebuilding it. now if the cylinder is fine can i get by with a new piston and rings or will i need to hone the cylinder to remove the glaze to allow for better break in? right now thats is what i am hoping for.

The older Dolmars like our 120`s and 116`s like a extra bit of oil in the mix, I use 40 to 1 in mine and even if they have light scratches in the piston on the exhaust side they will run a long time before they need piston replacement. The rings will wear and it will cause a loss of compression so you may get away with a set of rings. The ball type of hone works best if you need to hone the cylinder just to polish it up a bit but it can be done with a little care with emery cloth just work it around and remove only the stains and high spots of buildup. The aftermarket pistons work fine in the Dolmars as I have run them for many years now with no problems in firewood saws. Hope yours works long enough to complete this years wood duty,then take it apart and clean it up well,with either new rings or piston and rings it should run for another 10 years or more. I have them in continueous service since 1985 and still running fine. Pioneerguy600

 

[harrygrey382]

first, my compression tester wont screw all the way in, its to long, but it started failing on the drop test. still runs good, but when i pulled muffler i noticed some minor scarring on piston. the cylinder looked good from the muffler side and spark plug hole.

the saw is a dolmar 120si

now i am in the middle of trying to harvest my wood for this winter and need to keep my saw going. i have seen pistons with rings on fleabay reasonably cheap. are they just that= cheap. i hate to have to drop a fortune in this saw, not knowing how deep i will have to go on rebuilding it. now if the cylinder is fine can i get by with a new piston and rings or will i need to hone the cylinder to remove the glaze to allow for better break in? right now thats is what i am hoping for.

if you're worried about air leaking round the gauge threads put plumbing tape on the thread, but careful none goes in afterwards!

I reckon if it's doing its job now leave it. Then pull it down after the season ends. Put new rings in, and decide then whether you need a new piston. At only $75 I'd probably go the new piston... After a hone or light sanding (rough it up)