A Warning and a question

[Chris in WI]

Some of you may know this, but for all the other first time piston/cyl. re-placers out there drain your gas tank before you start taking the saw apart. I didn't and ended up taking a gas shower when I pulled the gas line off the carb. Now to my ? - Would a missing heat shield behind the muffler cause cyl. scoring? I'm still getting pieces for my leak/pressure tester, but looking in the intake the cyl. looks good but its scored on the exhaust side.

 

[ericjeeper]

Nope

Not in my opinion. Dirt through the intake, or an air leak, either in a fuel line , impulse line or leaking cylinder base gasket. Or worse case scenario, bad crank seals.

 

[THALL10326]

Some of you may know this, but for all the other first time piston/cyl. re-placers out there drain your gas tank before you start taking the saw apart. I didn't and ended up taking a gas shower when I pulled the gas line off the carb. Now to my ? - Would a missing heat shield behind the muffler cause cyl. scoring? I'm still getting pieces for my leak/pressure tester, but looking in the intake the cyl. looks good but its scored on the exhaust side.

99 times out a 100 the scoring will always be on the exhaust side because the intake side gets cooled with that nice cool fuel coming in. Don't know what saw your referring to comment on the heat sheild but many shields are also used to make sure all the cooling air goes around the cylinder, not out the front of the saw.

As for the gas shower I learned that the hard way many years ago so don't feel bad....

 

[HiOctane]

The missing heat shield didnt make your saew to get a scored piston.Check for an air leak instead and also your hi speed adj could be responsible too if run too lean .

 

[Chris in WI]

The saw is an 046.

 

[THALL10326]

The saw is an 046.

The saw is a 046, hmmm. The sheild behind that muffler is curved to the flywheel side of the engine, hmmmmmmm, wonder why. It directs the air from the flywheel directly across the cylinder fins and blocks it from being blown out past the muffler. Can't say whether it had anything to do with your scoring but running that saw without it sure didn't help the cylinder stay cool as it could have been. Its on there for a reason other than to just sheild heat. Why was that sheild removed anyway???

 

[Lakeside53]

Yes.. you have another probem (air leak, bad carb/fuel delivery or bad tuning) , but you NEED the shield back in...

 

[Chris in WI]

The saw is a 046, hmmm. The sheild behind that muffler is curved to the flywheel side of the engine, hmmmmmmm, wonder why. It directs the air from the flywheel directly across the cylinder fins and blocks it from being blown out past the muffler. Can't say whether it had anything to do with your scoring but running that saw without it sure didn't help the cylinder stay cool as it could have been. Its on there for a reason other than to just sheild heat. Why was that sheild removed anyway???

I got the saw off E-bay and it was missing when I got it.

 

[Chris in WI]

Yes.. you have another probem (air leak, bad carb/fuel delivery or bad tuning) , but you NEED the shield back in...

I am going to do a vac/pressure test when I get a plate to go over the intake made- hopefully next week, and am going to get a carb kit as well. By fuel delivery do you mean the carb or fuel line or something else?

 

[Jacob J.]

You could have a cracked impulse line, although that would have manifested itself in a performance problem long before your piston was scored. Main causes for exhaust side scoring are bad gas, bad diaphragms in carburetor, carb too lean, leaking oil seals/compromised main bearings, and base gasket compromise/head bolt issue. So make sure all of those issues are 100% before returning the saw to service. A lot of used saws are missing the heat shield because people take them apart and almost always forget to put the heat shield back in. When they see the heat shield laying there on the bench they think "well it's no big deal anyways".