Chainsaw Repair

Husqvarna - Stihl - Poulan - Jonsered - Dolmar chainsaws and more => Echo => Topic started by: Giles on April 21, 2016, 05:56:56 pm

Title: Piston Position?
Post by: Giles on April 21, 2016, 05:56:56 pm

I have a unique problem--
 I have built hundreds of chainsaw engines and know that pistons are marked, most to exhaust, for their position in cylinder.
 However, I was given an Echo CS590 and the unknown previous owner had cleaned up piston for reinstall.
 They put a mirror finish on the top of piston erasing the arrow mark.
 Piston ring pins line up perfectly in both the possible positions.
 I am thinking either way would be OK?

Title: Re: Piston Position?
Post by: 660magnum on April 21, 2016, 05:59:29 pm

Take a look at the skirt of the piston.    The intake side is sometimes different from the exhaust side.

Often the machine marks are worn from the intake side

Title: Re: Piston Position?
Post by: sharkey on April 22, 2016, 03:54:11 am

Pin in the rear.  The piston will have a pin in the ring land to keep the ring from turning in the bore.  Single ring piston has the pin smack dab in the center of the intake.  Actually the piston doesnt come down far enough to expose the ring one installed in the cylinder, but if it did it would sit right in the middle of the intake.  Pay attention to which way the ring rides in the land, which side of the ring is up, because the pin is at the top of the land.