getting compression back

[discounthunter]

i checked my 143mx and it was at about 135psi(sat outside in 65-70 degree weather for an hour or so). little low. piston looks good with minor wear(exhaust side) didnt pull carb to look at intake.would putting it new ring be a viable solution on a milling saw or would a new p/c be a better route. i dont mill alot ,and only pull this one out for really big firewood.

 

[hamish]

Although i am not familiar with the Dolmar 143mx, compression numbers vary amungst different saws. At 135 you have a runner, especially if its a cold saw that hasn't been run in awhile. Compression numbers are a rough gauge as to what state the heart of the engine is in, but doesn't account for the lungs and the kidneys of the beast (crank seals and boots etc...).To be able to gauge most things you need to establish a baseline on that saw, so reading on a regular basis all recorded............gives you a quick heads up if things are going wrong. For a daily use saw (130-180/year) re-ring and vac/pressure test twice a year, and in between keep er clean, and serviced before you even think of taking off your boots.

 

[equad99]

hows the cylinder?

how do the cylinder walls look?a small high intensity penlight shined in the exhaust port,and looking in the plug hole can tell you a lot about how your saw is doing.wear and scuffing generally starts around the exhaust ports,(sometimes it takes a very small mirror that will go into the plug hole to see)if its an iron liner cylinder,(i dont know on that particular saw)look for mainly scoring,some tiny lines wont hurt here,and are expected,if its chrome or nikasil,any scoring other than dull spots can become an issue.with an iron liner,probe the score line or other visible irregularities with a piece of 1/16 rod with a round point on it.it will give you an idea of how bad they are.anything you can feel with the rod can be of concern.with both types of cylinders,look for uneven wear,particularly with plated cylinders.newer saws are a lot better about this,(made in china and taiwan saws are horrible about this) but on some older saws,the cylinder would expand unevenly as the saw warmed up,if youve encountered a saw that loses power radically when you push it hard,and has low compression when trying to start it hot,but its fine when it cools off, this is whats going on.if its worn unevenly,and it loses power i would replace the cylinder,piston and rings..if its chrome or nikasil,i would replace the piston,rings,and cylinder always as a set,no matter what the problem. if its iron liner,and the cylinder is in good shape,i would replace the piston,and rings.(piston you ask?the ring grooves also seal up the piston in the cylinder,and wear to match the rings,the bottom of the ring lands can wear tapered when the ring expands in the cylinder as it wears,a new ring wont seat on the ring land properly ) and very lightly hone the cylinder,just enough to get a crosshatch pattern.its not a good idea to try and hone out cylinder wall damage.if the cylinder looks okay,and the saw performs okay,i would put it to work,and check the compression regularly.if it goes down,its telling you that it needs some tlc.i would keep everything especially the airfilter meticulously clean,use good synthetic oil at the manufacturers recommended ratio (ive seen people buy high grade synthetic oils and lean out the mix with disastrous results,the oil also cools the engine)compression is subjective and can vary a lot,according to altitude,temperature,what type of oil youre using,what guage you are using,i live at 6000 feet altitude,and compression readings are 15 pounds lower just from that.another post said get a baseline.i couldnt agree more...art b