460 bogging in willow.

Arborist Forum

Help Support Arborist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
agreed

Maybe try some of the Stihl decarbonizer......you pulling 15k without seizure was a sign of lowered compression..... and with lower compression comes less torque and that may also explain the black goo on the lower side of the exhaust.....blow by.....I can see it under the rings on the piston skirt as well.

Thats what I am thinking also from him describing the rings being stuck......:monkey:
 
Yah know....there is one other possibility....if the decarbonizer doesn't cure it by freeing up the rings you most likely have a cracked piston....I have seen this several times recently here and I think Dean had one recently as welline but the crack opens up when the saw heats up and it loses power and they blow exhaust down into the case and you get that weird black goo film
 
Last edited:
Should have pulled out my brass rods, I'll know for next time.

Are you guys saying that the rings should be loose to some degree?
 
They should have a little give to them when you push on them with a fingernail through the exhaust port it. You should be able to just barely feel the ring sticking up from the piston when you run your nail up and down over them and they should move in when you push them into the ring groove
 
Should have pulled out my brass rods, I'll know for next time.

Are you guys saying that the rings should be loose to some degree?

I just dont like to stick anything that could slip and gouge the piston but Im just weird that way. My buddy is a silver tech and he uses a screwdriver...

Yes they have to float to give you your maximum compression,,,,
 
How much use was on this saw before you got it/added the dual port? Is it possible that the rings are just worn out? This could cause them to stick after the fact and lowering back pressure would make it worse (adding the dual port muffler)

That glaze is from the flame blowing past the rings and cooking the sludge in the port
 
I bought it new in 2005. Tanks of fuel, hours, so far, couldn't tell ya. Loops of chain, between the 20", and 24" bar less than 12 loops, all with the original muffler on it. The DP from Stihl is only on there about two tanks worth.

Went out to look more closely at the rings, they have horizontal(longitudinal?) ridges on them, and the rest of the cylinder wall surface is nice and shiny/smooth, polished.
 
Ive seen a saw one time that would not start,,, 036 pro had 100 psi comp. guy said it had been sitting for over a year,,,, the top ring was stuck.... on a customers saw, we pulled the cylinder, removed the piston from the rod and that ring was stuck with brown gooey gunk. ... intake side of cyl was glazed, not scored just streaked kinda like yours,,,,, we put he piston and cyl in the power carb washer for about 4 hrs while we worked on other stuff and went to lunch,,,, when we pulled it out the ring was un stuck, removed the rings and first inspection didn't appear pitted, cleaned the grooves,,, re-inspected the rings really good could not see a blemish light hone on cyl... reinstalled everything and when we checked compression it was 155 psi that was over a year ago... We put a new starter rope rotor and pawls on it last week..... it screams Im sure Lakeside will have somthing to add
 
Last edited:
Try the decarbon liquid from Stihl and you should be good to go.....I would also do a direct comparison with stock muffler and dual port to verify if the reduced back pressure may be detrimental on this saw until the ports get cleaned up and matched.....I've seen it before not EVERY saw runs better with less back pressure.......it depends upon lots of variables
 
Lateral is around the same way the ring lays,,,

I bought it new in 2005. Tanks of fuel, hours, so far, couldn't tell ya. Loops of chain, between the 20", and 24" bar less than 12 loops, all with the original muffler on it. The DP from Stihl is only on there about two tanks worth.

Went out to look more closely at the rings, they have horizontal(longitudinal?) ridges on them, and the rest of the cylinder wall surface is nice and shiny/smooth, polished.

Cmon Lake I seen ya lurkin
 
Alos you could try seafoam

The Stihl decarbonizer is water based and needs to be poured in and let stand over night then completly drained out...you could try running a cap full or two capfulls of seafoam mixed in a full tank of fuel and see if you can free the rings by running it....I would put back the stock muffler for now though....it should run hotter and help clean up the messy stuff. THEN after you get it straightened out try the dual port again
 
Will look into the decarbonizer, does Stihl make the only thing that works, or the most effective product, or is there a basic formula/ingrediants product that is more commonly available that will be effective?

I'll try to find an instock comp-tester w/schrader valve, in the morning. Will figure out how to do the test solo, and post the results.

Will be putting the stock back to stock form, set the screws accordingly, and see what tach readings I get, and difference in cookie cut in the willow.

Okay, lateral grooves it is, thanks.

Seafoam? where can I get that? I was thinking Naptha based stuff, like for cooking a carb.

Thank you all for your patience and help, we'll pick this up again tomorrow.
 
The fine grooves on the rings will wear off in 20-50 hours of use - and are here to help bed the rings... The bore should be very smooth and almost polished - the diamond honing on stihls pro saws leave the finish almost "shiny".


The pic you show look quite normal. In fact, look just like my 066 and most of the saws I see every day.

I'm not sure you have anything wrong in the piston cylinder dept.... and I wouldn't do anything until you perform a compression test and reset your carb. If your saw likely survived the abuse of running at 15k - I see these from time to time - it will be fine.

The dual port muffler is not an issue - it is a standard factory item from stihl, and was shipped on new saws for many years. It will cause your rpm to go somewhat at standard settings, but that's normal - just a slight open up on the H is all that's requried.

As for the decarboniser - don't leave it in over-night. It might say that on the bottle, but Stihl now recommends not doing so. It has a habit of making a sludge in the bottom of your saw, and it gets in behind the bearings... A few hours is all you need - but put it in the engine just after it has been run. Best to leave the saw inverted with the muffer/carb plugged. Personally, I don't use it unless the piston etc is out of the saw.
 
Last edited:
Stuck rings would explain it...

Certainly more probable than a tough willow tree :laugh:

To answer the owner's question, rings on most engines should be free to expand and contract and spin around in their piston groves. The cylinder is tapered, tighter at the top and wider at the bottom. The rings expand and contract to keep a tight seal in the combustion chamber during the cycles of the engine (2 or 4 stroke). A stuck or stickey rings will not expand on the bottom of the piston stroke and thus you will get blow-by and loss of pressure (and power) in the cylinder. Thus the request by some earlier in this thread for a compression test (low compression can indicate blow-by from a ring problem).

I dunno about using degunk/decarb stuff on 2-stroke engines. If it is that gunked up with frozen or stiff rings, I would tear the engine down and clean up the rings and look at the piston. And as someone else here said, back pressure is really important in ballancing the flow of a 2-stroke. That was always a problem on my several 2-stroke Suzuki and Yamaha dirt bikes when I modified the exhaust. The exhaust pipes had to be modified to create back pressure through pressure waves which basically 'pushed' the pass-through gas/air/oil mix back into the burn chamber from the exhaust port. Not enough back pressure and you will have a lot of raw gas/air mix passing through the cylinder head from the crankcase and out the exhaust port. Then the gas and air will dissipate with the exhaust, but the unburned oil would form a goo.

So if I may surmise here, the saw was gunked up and had sticky rings before the muffler mods and the muffler mods cooked the goo... or there is a crack in the piston as someone else speculated (though less likely, but may have happened as the saw ran too lean and zipped at high revs)... or the muffler mods created a flow problem and there is a lot of buildup of oil and goo becasue of inadequate back pressure/too much flow-through (but the last post says that the muffler mods would not casue this problem???).


:blob2: :blob2: :blob2:
 
Last edited:
rings on most engines should be free to expand and contract and spin around in their piston grooves.

On my 346, there was a tab in the ring groove to stop it from spinning in order to prevent the ring ends from ending up in either the intake or exhaust ports. This is how it was explained to me at least.

Ian
 
Last edited:
On my 346, there was a tab in the ring groove to stop it from spinning in order to prevent the ring ends from ending up in either the intake or exhaust ports. This is how it was explained to me at least.

Ian

You are right, the piston rings should FLOAT but NOT SPIN, if they could spin it would only be matter of time untill it spun so that it would push itself into port and seize the engine...

If the ring(s) are stuck you can always take them of and scrup of the carbon from rings and "hone" the ring grooves with smooth sandpaper...
 
Something bugged my sleep all night

In those pics it looks like the exhaust port is tapered on top AND on the bottom.....I have never seen this on a muffler 2-stroke but I can guess why they may do it (emissions reduction perhaps) If the piston crown never completely clears the bottom of the port, I would say you NEED the stock exhaust. Something doesn't look/feel right.

Hey Lakeside and other Stihlheads.....was there ever an EPA 460?
 
The oval shaping is normal on lots of exhaust porting but I have never seen quite that much piston crown showing.....Is the third pic with the piston at absolute BDC?
 

Latest posts

Back
Top