So do I need a piston, jug, or just rings?

[6530]

I recently picked up a Stihl 009 16" on Craigslist for $60. It's in reasonably good shape but stumbles when cutting.

I brought it to the local Stihl dealer, who replaced the plug & air filter and tried to adjust the carb but said he couldn't make it run any better. They did a compression test and it's at 120 psi against a spec of 150 psi. I've never worked on a 2-cycle, so thought this would be a good opportunity to learn - but before I buy any parts I thought I'd try to diagnose the problem.

I've pulled it apart and have attached photos of the cylinder & piston. Other than some carbon buildup on the piston I don't see any major issues, but since I'm no expert I thought I'd run it by the experts here. Could the carbon buildup on the top of the piston cause the stumbling? I guess it would change the compression ratio, and I'd guess the saw was run too rich.

The funny little thing in the lower left corner of the next to last photo is the LED light I used to light up the cylinder.

So does anyone have any ideas? I'd appreciate any thoughts.

Thanks.

 

[drmiller100]

can you feel anything with your fingernail or finger higher then the top of the exhaust port inside the cylinder???
it looks like there are some grooves, but if you can't feel them, they don't count.

she has some hours on it, evidenced by the wearing of the machine marks on the piston.

the rings are a little tired, and you can see burned oil between the rings on the side of the piston to show that.

if you can't feel the grooves, i would consider a piston and rings, get it honed, and run it.

carbon on top says the guy you bought it from ran junk oil, but decent gas, and has no detonation at all ever (which is a really good thing.)

 

[COLD_IRON]

That carbon build up - It looks like it was run on water cooled 2 cycle engine oil instead of air cooled.

 

[Cliff R]

Looks really good compared to most of the stuff I get in here. The majority of the engines we end up with looks like someone tossed a hand full of gravel into them!

I'd get some rings, gently sand the jug, and put her back in service.

Also check the air filter assembly, make sure it's sealed up well. The bore looks like it may have been getting some debris into it, from the light scratches/pitting?......Cliff

 

[blsnelling]

Hone it and throw a set of rings in it. Get a carb rebuild kit while your at it.

 

[Lakeside53]

That saw looks great inside... the piston wear is pretty minor for an 009...Light hone, re-ring, carb kit, fuel and vent hoses..

 

[Taxmantoo]

That saw looks great inside... the piston wear is pretty minor for an 009...Light hone, re-ring, carb kit, fuel and vent hoses..

+1. You can see the horizontal ridges all the way around the piston, it should measure within spec for a new one. If compression is off, replace the rings.

 

[6530]

Thanks for the advice! I got the parts ordered today (rings, carb kit, vent hose, fuel hose, cylinder gasket, & exhaust gasket).

I don't have a hone, so I'll see if the local dealer will lend me one for a few days. If that doesn't work, where's the best place to get one? I'll only need it for this job so I don't want to spend too much $.

 

[blsnelling]

Make sure you oil the hone and only run it for a very few seconds. Otherwise you'll go through the lining on the edges of the ports and ruin the cylinder. Easy does it.

 

[Lakeside53]

Yes... that an "open port" design and easy to damage. Don't use one of the three-fingered "brake cylinder" type hones...

I've used flex-hones (ball type) woith great sucess on this type of cylinder.


In your case, if you can't get a 320 grit ball hone of the correct size, just use scotchbite or just leave it alone - doesn't look all that bad from the pics.

 

[6530]

OK, so I finished up replacing parts. I replaced the piston rings & gently honed the cylinder with 320 grit emery paper by hand, and replaced the exhaust & cylinder gaskets. I also replaced the plug & air filter and scraped the accumulated carbon off the piston crown.

After reassembly it fired right up but idles way too fast - the chain is moving dangerously fast. So I turned in (clockwise) the high speed & low speed adjustment screws all the way down to their stops, then backed off 1 turn on each. I also turned the idle speed screw all the way in.

Since doing that I've fiddled around with all 3 screws but can't seem to get the idle speed correct (either the chain moves or the engine stumbles) or the full throttle engine speed right (seems not fast enough).

The exhaust has a lot more blue smoke than I remember, so it seems that engine is running too rich - but I can't seem to lean it out.

Any recommendations on how to get things right?

 

[Rookie1]

Smoke may be from oil used to assemble engine. Ill bet after you set carb and run in some wood it will clear up.

 

[blsnelling]

-Like you did before, lightly bottom both needles out and then turn out one full turn.
-Warm up the saw a little.
-Through out this process, keep the idle speed set just so that it doesn't die and the chain isn't spinning. Don't try to fine tune it yet.
-Set the low speed needle where the saw idles the fastest and then back it out 1/8-1/4 turn.
-Then adjust the high speed needle while running the saw at WOT. Make sure it's running too rich and then turn it in until it quits 4-stroking and peaks out. Richen back up a little from there until it's tries to 4-stroke just a little.
-Go back and play with the low speed needle and fine tune it to where you get the best throttle response from idle.
-Once satisfied with that recheck the high speed setting again.
-Finally set the idle where it doesn't want to die but where the chain isn't spinning either.
-Go cut wood!

 

[Lakeside53]

You might have an air leak...

 

[Scooterbum]

You could also have weak clutch springs.I had an 015 drove me buggy for awhile because I could'nt get it to idle slow enough to stop the chain,new springs and it's great.