372XP advice

[jspell]

The area in question that is outlined in your picture - run your finger nail over it, if its scoring you will feel it and if it's just staining you should not feel anything,- personally if the dealer is willing to give it to you at cost I would go for it as long as it's not a long wait to get it.

I can definitely feel the scoring when I run my finger nail over it.

I was looking at Madsen's "How to Read a Damaged Piston" page and it says that the damage from running unmixed fuel and damage from a lean seizure can look very similar, but with unmixed fuel you can get scoring in the wrist pin area. I looked at that area on my piston and there is some marking, but I don't know if it's normal--I attached a picture. I really don't think I straight gassed it but I guess it's not impossible, and I'm just trying to educate myself before I take the piston and cylinder in to the dealer tomorrow and remind him that his mechanic leaned it.

Also--the fuel that was in it when it died definitely had oil in it, and I was partway through a tank. The dealer never claimed the fuel that was in it when I brought it to him was straight gas, and the piston definitely looked wet when I took it apart. I guess he is saying that at some point in the past it was straight gassed--wouldn't it have seized whenever that was, not later on when it was running "good" fuel? I'm obviously ignorant, so tell me if that's wrong. I figured a 2 stroke would be toast pretty darn quick running straight gas?

 

[John Stryker]

I agree that a straight gassed, and lean seized saw look pretty similar. Sometimes a cylinder and piston can be scored and continue to run for a while. Usually when the ring finally sticks is when the compression drops too much to be able to start back up, in my experience.

 

[huskihl]

Straight gas scores all the way around. There’s no lube on the walls so the intake side gets it as well. If it’s scored on the exhaust side only, it was either from tuning too lean, bad fuel that burned hot (which could also be somewhat rectified by a richer setting on the H screw to cool the saw down), or an air leak

 

[ken morgan]

Straight gas scores all the way around. There’s no lube on the walls so the intake side gets it as well. If it’s scored on the exhaust side only, it was either from tuning too lean, bad fuel that burned hot (which could also be somewhat rectified by a richer setting on the H screw to cool the saw down), or an air leak

+ one on a possible air leak, make sure you do a pressure test. The dealer could have tuned it OK but with a air leak it would have slowly destroyed the P&C. thats why you always leak test if you need to do a major adjust ment. you could have it tuned properly and with one air leak that progressively gets worse you could fry your replacement P&C.

 

[jspell]

Took awhile but finally got a new piston and cylinder from the dealer at cost. Gasket he gave me was in two pieces, so had to wait on another one, but ready to put this thing back together now. Sounds like from all the helpful comments I need to account for two possible causes of the damage--too lean carb setting, or an air leak. The local Advance Auto Parts loaned me a vacuum/pressure tester. Any advice on how to set the carb, and how/when to pressure and vacuum test is much appreciated.

 

[Woodslasher]

Took awhile but finally got a new piston and cylinder from the dealer at cost. Gasket he gave me was in two pieces, so had to wait on another one, but ready to put this thing back together now. Sounds like from all the helpful comments I need to account for two possible causes of the damage--too lean carb setting, or an air leak. The local Advance Auto Parts loaned me a vacuum/pressure tester. Any advice on how to set the carb, and how/when to pressure and vacuum test is much appreciated.

To set the carb, go to the Madsen’s website and they have a pretty good tutorial on how to tune a saw by ear.

 

[ken morgan]

to pressure test you need to make some block off plates for the carb and the muffler. different ways to do it, most use rubber plugs and a hose clamp for the intake and a plate w/gasket and sealer to block off the exhaust. pump it up to spec and wait. if pressure drops, pump up again and use a spray bottle of soapy water to search for leaks.

 

[jspell]

Well, this project got away from me for an embarrassing amount of time, but now it's planting time and there's a big red oak blown down into a field I need to plant soon, little too big for my smaller saw, so I finally put the new piston and cylinder in, pressure tested it, and can't get it to fire.
-Spark is clearly visible
-spark plug is wet when I pull it out
-compression release valve pops out on the first or second pull--is this a sign that it has enough compression to run, or meaningless?
-it was sitting totally dry for the past year, and I put TruFuel 50:1 in it before trying to start it.
-I set the L screw out one and a quarter turn and the H screw out one turn, based on what I read in another thread, but tell me if that's wrong.

Thanks for any advice.

 

[Gord404]

did you check your flywheel key to make sure it is not sheared, they wil spark but not at the right time .

 

[mbrick]

did you check your flywheel key to make sure it is not sheared, they wil spark but not at the right time .

I had a serious head scratcher that was the result of a sheared key. I'd definitely support checking this.

And torque the flywheel nut to the proper value...

 

[jspell]

No, I hadn't thought of that--will check it today, thanks!

 

[FrugalFirewoodDad]

If you got some muratic acid , soak a q-tip and dab it on the score marks. It will loosed the aluminum. Take your time and it should clean up.

Neutralize the acid in water ...

Just for clarification sake, water wont neutralize the acid, it will dilute it. Baking soda can neutralize it, if needed.

 

[a. palmer jr.]

Yep, that's pretty bad. What I'm reading here is the main reason I buy all my saws used; it takes the dealer completely out of the picture..