How to evaluate scoring? Pro Mac 10-10

[strad]

This is a saw that runs great and cuts great, feels like it has good compression. Looking through the intake port, I can see some light scoring on the piston. Basically it doesn't look like a new piston, but it's not scored to the point where I could look at it and say it's trash or soon to be trash. So maybe somebody could educate me lol, like post a pic of an example of acceptable piston wear vs unacceptable piston wear.

The saw has been in our family since new, been used solely for homeowner-type jobs (occasional use). Cosmetically it's in extremely good shape. The only thing I've done so far to it is rebuild the carburator -- was much easier to cold start after that lol.

 

[fearofpavement]

If it runs and cuts great keep running it and cut wood. A bit of scuffing on a piston is not unusual and nothing to get alarmed about, especially if there are no troubling symptoms. Just use a good mix and go to it.

 

[67L36Driver]

First rule of intelligent tinkering:

If it ain't broke, don't 'fix' it.

 

[Whiskers]

If you notice the saw running funny, or you have to richen it up to get it to run right you might have a small air leak somewhere. Could be worth a preesure/vac test on the crankcase and maybe some new fuel lines if you suspect a problem. An air leak will lean out the fuel getting to the piston resulting in heat and lack of lubrication.

 

[strad]

Well interesting you mention that. As far as I know (been running this saw off and on for 15 years) it's always run the same (I've never used another saw actually -- but this one has no trouble cutting if the chain is sharp). One thing I do notice is that it has an oil leak from the oiling system. When the saw is stored on the shelf it leaks oil, and not from the gasket between the oil tank lid and the oil tank. It's coming from somewhere else. Pretty sure it's down by where the oil comes out to lube the chain. I don't know if automatic oiling works, but manual oiling works just fine.

My understanding is that system is run by vacuum -- could it be that my leak is caused by a vacuum problem? If so I guess that could cause lean running. Kinda hard to dig into it without a manual.

 

[67L36Driver]

Well interesting you mention that. As far as I know (been running this saw off and on for 15 years) it's always run the same (I've never used another saw actually -- but this one has no trouble cutting if the chain is sharp). One thing I do notice is that it has an oil leak from the oiling system. When the saw is stored on the shelf it leaks oil, and not from the gasket between the oil tank lid and the oil tank. It's coming from somewhere else. Pretty sure it's down by where the oil comes out to lube the chain. I don't know if automatic oiling works, but manual oiling works just fine.

My understanding is that system is run by vacuum -- could it be that my leak is caused by a vacuum problem? If so I guess that could cause lean running. Kinda hard to dig into it without a manual.

Nope. Not vacume but crankcase pressure.

Loosen the oil cap after using the saw. Let it 'burp' any pressure build up.

 

[blsnelling]

If it's actually scoring, then I strongly disagree with the idea of leaving it be. If it's just wear marks, then do so if you so choose. If it's actually scored, then it should be disassembled and repaired before ever being started again.

 

[strad]

If it's actually scoring, then I strongly disagree with the idea of leaving it be. If it's just wear marks, then do so if you so choose. If it's actually scored, then it should be disassembled and repaired before ever being started again.

Well, that's the thing. I don't have enough experience to know the difference between "wear marks" and "scoring." Where could I get a good visual of the difference?

 

[homelitejim]

Now is a good time to learn how to post pics .

 

[gmax]

Well, that's the thing. I don't have enough experience to know the difference between "wear marks" and "scoring." Where could I get a good visual of the difference?

This piston is scored and should not be used again.....although I did because I could not find another one.

 

[strad]

Haha very funny. I was just trying to avoid taking the carb off again b/c I wasn't smart enough to take pics when I had it off the first time! I'll go get it done.

You can see the thin lines I'm talking about at the edge of the intake port. Basically the whole surface looks like that, although you can't see the rest of it b/c the flash washed it out. And yes, I know the sawdust shouldn't be in there. I've got to blow that out and possibly aquire a new air filter. My theory is that the old one's rubber may have hardened too much to seal.

 

[Duke Thieroff]

Haha very funny. I was just trying to avoid taking the carb off again b/c I wasn't smart enough to take pics when I had it off the first time! I'll go get it done.

You can see the thin lines I'm talking about at the edge of the intake port. Basically the whole surface looks like that, although you can't see the rest of it b/c the flash washed it out. And yes, I know the sawdust shouldn't be in there. I've got to blow that out and possibly aquire a new air filter. My theory is that the old one's rubber may have hardened too much to seal.

That there looks like some scrtaching from dirt ingestion.

Usually when a saw is scored from heat/lean condition it will scrape on the exhaust side.

Pull the muffler and have a looksee if you're concerned.


Chris

 

[67L36Driver]

Haha very funny. I was just trying to avoid taking the carb off again b/c I wasn't smart enough to take pics when I had it off the first time! I'll go get it done.

You can see the thin lines I'm talking about at the edge of the intake port. Basically the whole surface looks like that, although you can't see the rest of it b/c the flash washed it out. And yes, I know the sawdust shouldn't be in there. I've got to blow that out and possibly aquire a new air filter. My theory is that the old one's rubber may have hardened too much to seal.

Dirt/wood chip ingestion caused light scratching.

I've had several that looked scored when viewed thru the exhaust port but the scratches could not be felt when I pulled the cylinder off.

 

[67L36Driver]

This piston is scored and should not be used again.....although I did because I could not find another one.

Only reason to re-use a piston like that. Lost a lot of bearing and heat transfer surface. Often the case.

 

[GASoline71]

That is normal wear on the intake side of that piston. You need to look at the exhaust side. That's where 99.9% of the scoring will happen.

Gary

 

[promac850]

Here's a badly scored piston...

General rule... if your finger nail, a toothpick, etc. catches into the scratch/scoring marks, then it's time to take her apart and replace/refurb the piston and cylinder.

I still haven't gotten around to fixing this old Craftsman/Roper 3.7... here's what the piston looks like.

 

[Adirondackstihl]

Bad...

Good