Stihl 028AV siezed up, then later spins ok?

[pioneerguy600]

Running lean is not actually low on lubricant it is low on the cooling effects of the incoming fuel charge that evaporates when it contacts the piston that prevents the overheating in the first place. The oil in the mix does lubricate everything but the cooling effect of the richer fuel setting allows for more cooling than the lean condition.

 

[Okie]

pioneerguy:
Thanks for the info! I was thinking a combination of both oil and gas for and too much air!

Was not thinking of evaporation cooling of gas hitting the piston!
I order a echo pet-304 2 cycle tach after few recommendations from others. I see that it has access to replace the battery, whereas several of the other chainsaw or 2 cycle tachs are sealed.

The Echo pet-304 has several good reviews.

 

[Wood Doctor]

OP said. "Heck Ronnie Milsap could hear and detect that the saw was not overreving in the cut when it started overheating the engine was bogging and carrying a heavy load."
-----------------
Ronnie Milsap was one of my all-time favorites, even back when I worked for Conoco in Ponca City and Phillips in Bartlesville. I predict that your 028AV will now be around for awhile. Many of our readers will lean the carb mixture out to make the engine run hot and fast for awhile at a GTG, just to show off. Then they later enrichen it back up again when it's time to cut firewood. No law against it, so they do it anyway.

 

[SteveSr]

One thing that appears to have been missed is that if that saw is really 35 years old you really need to disassemble it and check and/or replace most of the rubber components which can easily cause an air leak. The culprits are the crank seals, cylinder boot, and especially the impulse hose. Rubber rots over time and due exposure to oil contamination and atmospheric ozone.

A stock Stihl saw should run properly at specified stock carburetor settings. Stihl calibrates their carburetors for a specific saw model to achieve this. The only normal deviation is to lean the mixture out for operation in high elevations. If you are near sea level the saw should run properly at the stock carb settings. If it doesn't you likely have an air leak caused by the failure of one or more of the above mentioned rubber components.

Another indication of an air leak is an erratic idle or failure to idle down. However, if the leak is caused by stretching the intake boot and impulse hose when pulling up on the handle while in the cut it may not show up at idle.

The symptoms that you describe are what we used to call "partial seizures" when working on 2-stroke motor bikes. It occurs when, due to excessive temperatures, the piston expands in the cylinder more than the cylinder itself and removes any spacing between piston and cylinder. Since the top of the piston and cylinder are the hottest this is where any damage should be visible. If this condition is caught in time little or no damage may occur. The only way to know for sure is to pull the jug and do an inspection.

 

[kr5258]

If you've never changed out the fuel filter, pull your carb and check the internal filter screen. The older fuel filters are known to deteriorate internally and send the goo to the carb where it clogs the screen resulting in a lean condition. I cant find a pic of an 028 screen but here's one off an 020AV, same issue.

 

[blsnelling]

You need to pull the cylinder. I don't think it's possible to seize the piston in the cylinder without causing damage. That cylinder can be pulled in about 5 minutes.

 

[Okie]

Finally got around to rpm tach testing the 028AV that was seizing due to lean carb.
Saw has been running great since I adjusted the H jet richer by 1/2 turn which is where the saw slightly 4 cycles when reved.
I used a new Echo PET-304 pulse tach: Idle average 2250, High rpm unloaded 10,200, under full load in the cut with 16 inch bar and aggressive cut chain, 18 inch green pine log, average 6000-7200rpms. Very fast responding tach and very user friendly. The unit allows access to the internal batteries for replacement.
I confirmed that the saw was overheating due to lean H jet instead of overspeeding.
I'll be using the 3M infrared thermometer in the future to check jug temps under load on MY SAWS after doing carb work.

After experiencing this one I strongly suspect that several good chainsaws are ruined (scored piston and rings) due to lean operation instead of improper oil/gas mix after seeing how fast this saw's engine was overheating due to slightly lean H jet adjustment, possibly due to the engine leaning out own it own due to age, etc. Checking the jug temp under load will allow for monitoring or confirming that the saw is operating at normal temps or checking for high operating temps due to other causes also, such as maybe timing, air leaks, high friction under load, etc.

 

[tomdcoker]

One thing that appears to have been missed is that if that saw is really 35 years old you really need to disassemble it and check and/or replace most of the rubber components which can easily cause an air leak. The culprits are the crank seals, cylinder boot, and especially the impulse hose. Rubber rots over time and due exposure to oil contamination and atmospheric ozone.

A stock Stihl saw should run properly at specified stock carburetor settings. Stihl calibrates their carburetors for a specific saw model to achieve this. The only normal deviation is to lean the mixture out for operation in high elevations. If you are near sea level the saw should run properly at the stock carb settings. If it doesn't you likely have an air leak caused by the failure of one or more of the above mentioned rubber components.

Another indication of an air leak is an erratic idle or failure to idle down. However, if the leak is caused by stretching the intake boot and impulse hose when pulling up on the handle while in the cut it may not show up at idle.

The symptoms that you describe are what we used to call "partial seizures" when working on 2-stroke motor bikes. It occurs when, due to excessive temperatures, the piston expands in the cylinder more than the cylinder itself and removes any spacing between piston and cylinder. Since the top of the piston and cylinder are the hottest this is where any damage should be visible. If this condition is caught in time little or no damage may occur. The only way to know for sure is to pull the jug and do an inspection.

As I read through this thread I was thinking just what SteveSr wrote. Number one if the plug is orange the saw is running lean. Number two if you can back the high speed screw out 1 3/4 turns and the saw will still run something is wrong. That is way to rich. I have never seen an 028 that had to be more than one turn out My best guess is that you have an air leak, probably in the carb. boot that will open up when you put pressure on the bar. I still think you have have a problem . In my opinion you if he plastic and crank case are good and you have the knowledge and an 028 is worth a rebuild for use as ageneral purpose and home fire wood saw. Now that information and fifty cents will buy you fifty cents worth of what ever you want. Tom

 

[Okie]

You wrote: . I still think you have have a problem.
Yep: I could rip her apart (in few minutes) and most likely spend about as much or more on parts (that are going to crumble) than a new saw would cost and still have a old saw but,
Been my experience if very old vintage eq is doing ok and doing it's job I let it do it's job and don't go looking for trouble and something to fix, especially if the eq is 30 plus years old, anything that old if touched or bothered is going to cave in and can very easily be whipping on a old dying dead horse and throwing good money after bad. The saw has cut approx. 4 ricks of firewood since it had it's spell and it's doing ok. If it flys apart it will be used as a parts saw.
My main point is using the infrared thermometer proved very fast that the saw did have a problem overheating when loaded due to lean running condition and was not overspeeding under load (which was suggested as the most LIKELY cause) and the condition was immediately corrected and proved that the running engine temp is ok now.

The specs from the original Stihl manual on this old 028AV indicates for initial carb adjustments starting at 1 1/4 turn out (CCW) MINIMUM on both jets, L and H and warns against not reducing the setting (CW) any on the H jet due to possibility of leaning and states that lean condition can allow the max rpms of 12,000 to be exceeded and ruining the engine and when adjusting the carb to use a tach and check the no load rpm as not being exceeded or if rpm's cannot be checked and proper carb adjustments made, take the saw to a Authorized Stihl dealer and have the saw checked and adjusted.

 

[Philip Wheelock]

...Yesterday before I started using this saw and one other saw I had mixed new 1 gallon batch of Super Tech, 2 cycle oil at closer to 40:1 instead of 50:1 and ran a tank of gas thru the other saw first and about 3/4 tank thru the 028 before it seized...

Googled "Super Tech 2-stroke engine oil" & read a number of posts about seizes with this product. Seems to me that running this oil is asking for trouble.

 

[Okie]

Good info about Super tech. Thanks.
I'll check that out. I have over a gallon of the Super Tech (blue jugs) that I run in outboard motors and also use it in chainsaws every once in awhile. I seen some of it awhile back that happened to be in a clear plastic jug and the oil had separated from the gas and was settled in the bottom of the container. Been setting at rest for about 3 months mixed with non-ethanol gas.. If it had been dumped into a 2 cycle engine without doing a shake up mix the straight gas on top would have ruined the engine.
I now use Stihl in my good saws and do a careful mixing. The disposable type saws, Poulan, Craftsman, etc, will get the Super Tech until it's used up and no great loss if they evaporate or disintegrate.

 

[kevin j]

Outboard motor oil is typically rated for water cooled engines and not for high-temperature air cooled engines.