Replacing Piston Rings

[RES]

I have a couple Stihl 020Av's that have seen alot of service. Compression is running about 120-130 psi. There are no scratches on the cylinder walls. Is it worth it to put in a new set of rings to freshen up the compression? How durable is the chrome plating on the cylinder walls or does it eventually wear out?

 

[Mr.]

It wears out, but if it looks good and the saw runs now you should be OK.

You can mic the jug to verify it's ok, but most wouldn't bother if the siuation is as you describe.

Fred

 

[Lawn Masters]

since you say everything looks alright, I'd just stick new rings in and go.

 

[Lakeside53]

Check the piston skirts for wear.. I find the pistons wear out about the same time the rings do. 4 thousandths an inch taper is a lot...

 

[RES]

If the piston skirts wear, is it advisable to replace the piston and rings without replacing the cylinder?

 

[Lakeside53]

If the piston skirts wear, is it advisable to replace the piston and rings without replacing the cylinder?

Yes. Cylinders that are chrome plated have a very long life if not scored.

 

[bugfart]

Watch out for aluminum stuck to the walls of the cylinder also. That can make your efforts fruitless.

 

[Gypo Logger]

The new rings should give you added performance. A little trick is to just put a new one in the top leaving the used one where it is.
I don't think I have ever witnessed a saw of my own get a worn skirt. This is usually indicative of ingested dirt such as on a cuttoff saw, but as Lakeside suggested you might want to check that out as well as the general condition of the cyl. but it sounds like it's in top drawer shape.
John

 

[RES]

Thanks guys for the advise. I like the little trick idea. It sounds like an economical way to squeeze out a little more life out of an engine. Do I need to hone the cylinder walls or can I get by with a scotchbrite treatment?

 

[Lakeside53]

Don't hone Chrome... It's plated after honing. Assuming you have no scoring and accumulation of any debris, just leave it alone. The rings will bed-in; might take another tank full, but...

Yes, Gypo is correct - skirts wear mainly from dirt, and carbon buildup in the exhaust port. Air-filters (and operators!) aren't perfect and particularly so on the 020. If you have taper, you can often hear the piston slap when you turn it over with the pull starter.