Stihl 028 AV Super died on me *Update* new pictures

[ctf58]

Ok I inherited a Stihl 028 Super AV. It ran great for about 3 tanks of gas cutting Red Oak logs for firewood. Then mid cut, running WOT it just stopped and smoke came out from under the covers. I could not tell where the smoke was coming from, it smelled like oil. It will not restart and has compression (no tester, but will hold it's own weight on the cord) spark and gas. I have a borescope and the cylinder and piston look terrible to me. I've never worked on a saw but willing to try. If I do rebuild it will a cheap Amozon head kit be okay or are they junk? I don't mind using a Dremel to clean it up some. Should I go with a Hyway kit? Heck is the Head my problem and would have caused it to die suddenly?

Thanks in advance,
ctf58

 

[singinwoodwackr]

Uh..no mix?

 

[ballisticdoughnut]

The top end is smoked. I’d recommend finding a good used piston and cylinder and buy new rings before going aftermarket. Or you can probably clean that cylinder up and run a meteor piston. You’ll also need to find out why the saw went lean. You’ve got a air leak in that saw that’s why it gave up the ghost.

 

[ctf58]

Thanks, mix was fine, fresh 1 gallon of gas and small bottle of Stihl oil. Air leak very possible. I don't have tools to hone and clean cylinder and I have heard good things about the Hyway stuff.
Any recommendations on locating the air leak if it is not the boot from the carb?

 

[Mad Professor]

Thanks, mix was fine, fresh 1 gallon of gas and small bottle of Stihl oil. Air leak very possible. I don't have tools to hone and clean cylinder and I have heard good things about the Hyway stuff.
Any recommendations on locating the air leak if it is not the boot from the carb?

You can clean the cylinder by hand with wet/dry sandpaper.

Also, hydrochloric/muriatic acid will dissolve aluminum transfer.

 

[HarleyT]

Lean seizure can be caused by lots of things. running leaner makes the engine go faster, and since oil is in the fuel, faster with less lubrication.
Lots of things are possible.

 

[irhunter]

I would not be buying anything until you try cleaning up the cylinder. I prefer the sandpaper method...only requires a variable-speed drill and a home-made mandrel.



Even before doing that...you need to decide how you will do a pressure/vac test. You can buy the tester, or pay someone to do it. For future reference, the time to test is before pulling the jug. Now, you will need to re-assemble, test, fix leak, test again.

Roy

 

[ballisticdoughnut]

Thanks, mix was fine, fresh 1 gallon of gas and small bottle of Stihl oil. Air leak very possible. I don't have tools to hone and clean cylinder and I have heard good things about the Hyway stuff.
Any recommendations on locating the air leak if it is not the boot from the carb?

You’ll have to inspect the crank seals, also check the pulse hose. If your gonna be repairing the saw you should replace those parts anyway.

 

[ctf58]

I would not be buying anything until you try cleaning up the cylinder. I prefer the sandpaper method...only requires a variable-speed drill and a home-made mandrel.



Even before doing that...you need to decide how you will do a pressure/vac test. You can buy the tester, or pay someone to do it. For future reference, the time to test is before pulling the jug. Now, you will need to re-assemble, test, fix leak, test again.

Roy

Thanks, I haven't pulled the jug yet. I'll look into a tester. From what I saw on the borescope I figured it was beyond repair.

 

[ctf58]

What is the tester called? I'm finding all kinds..

 

[ctf58]

Mini vac?

 

[Mad Professor]

What is the tester called? I'm finding all kinds..

MityVac MV8500, ~$65-80

 

[Okie]

As Harley says.

I've seen that happen to saws.
Most generally it happens when the saw is placed into big wood and a long heavy loaded up cut for 2 minutes or longer The saw will lean out, piston starts expanding and scuffing the cylinder and saw sounds like it's loading up and losing power, lift it out of the cut and rev few times and it cools down little bit and back into the cut. I've seen them also seize up, let it cool and might re-start but it has ruined itself inside.

Cutting small wood in and out of a cut a lean saw might run long time but put a lean running saw in big wood for a long loaded up cut that is going to take over couple minutes (a lean running in a loaded up cut will usually start the overheating process within one minute) and the engine running lean is going into a heat runaway. Lots o things can cause such.
If the saw was running and idling good before and no issues noted most generally the carb is running too lean and most likely due to incorrect adjustment.
And re-building the power head without correcting the original issue will get the same results again.

Just a hint:
When I first started seeing saws with scuffed pistons/cylinders I started testing for overheating by using a IR thermometer and I could purposely adjust (lean out) some saws carbs and get the overheat results fast on the IR thermometer when testing in big wood.
The saw would sound great idle good and have good power in the big wood but would be overheating fast and destroying itself due to overheating of the block.
One of the saws I was testing was a Stihl 028 old model with points and condenser and just a 1/2 to 5/8 turn in on the H jet would cause the saw engine to leave the rich 4 cycle and overheat FAST (within 1 1/2 minutes) in a long cut due to the carb being adjusted too lean. The saws engine actually sounded smoother running and cutting when adjusted lean but would have destroyed itself fast in big wood.

By adjusting a saws carb for the 4 stroke sound, running rich instead of lean would most generally keep the engine from overheating and confirm by monitoring with the IR thermometer if all else was correct.

You can finds lots of info on-line and at this site about how to properly adjust a chainsaw carb. Someone might put up a link for you to a video of how a saws sounds to the ear when it's 4 cycling

 

[ctf58]

As Harley says.

I've seen that happen to saws.
Most generally it happens when the saw is placed into big wood and a long heavy loaded up cut for 2 minutes or longer The saw will lean out, piston starts expanding and scuffing the cylinder and saw sounds like it's loading up and losing power, lift it out of the cut and rev few times and it cools down little bit and back into the cut. I've seen them also seize up, let it cool and might re-start but it has ruined itself inside.

Cutting small wood in and out of a cut a lean saw might run long time but put a lean running saw in big wood for a long loaded up cut that is going to take over couple minutes (a lean running in a loaded up cut will usually start the overheating process within one minute) and the engine running lean is going into a heat runaway. Lots o things can cause such.
If the saw was running and idling good before and no issues noted most generally the carb is running too lean and most likely due to incorrect adjustment.
And re-building the power head without correcting the original issue will get the same results again.

Just a hint:
When I first started seeing saws with scuffed pistons/cylinders I started testing for overheating by using a IR thermometer and I could purposely adjust (lean out) some saws carbs and get the overheat results fast on the IR thermometer when testing in big wood.
The saw would sound great idle good and have good power in the big wood but would be overheating fast and destroying itself due to overheating of the block.
One of the saws I was testing was a Stihl 028 old model with points and condenser and just a 1/2 to 5/8 turn in on the H jet would cause the saw engine to leave the rich 4 cycle and overheat FAST (within 1 1/2 minutes) in a long cut due to the carb being adjusted too lean. The saws engine actually sounded smoother running and cutting when adjusted lean but would have destroyed itself fast in big wood.

By adjusting a saws carb for the 4 stroke sound, running rich instead of lean would most generally keep the engine from overheating and confirm by monitoring with the IR thermometer if all else was correct.

You can finds lots of info on-line and at this site about how to properly adjust a chainsaw carb. Someone might put up a link for you to a video of how a saws sounds to the ear when it's 4 cycling

It was a huge piece of wood. 34"+ red oak. I was in the wood a long time. And no I didn't notice it 4 stroking. Thanks for the info.

 

[ctf58]

I bought the MityVac MV8000 in error. It only does Vac test even though the cover said Vac/Pressure tester. I will return it. But I did use it on the impulse line to pull a vacuum and it would not hold at all. I blocked off the intake and exhaust with heavy leather and used the muffler and carb to secure the leather. Does that help me in any way or should I order the Vac/Pressure tester??
Thanks!

MityVac MV8500, ~$65-80

 

[Okie]

You need a Vac/pressure tester or something that will do pressure.
If you can return that mityvac W/O problems I would do such and get the one you need.
You say they had it listed as both so should not be any issues with return, especially if it's amazon the return is free, just a trip to town to the UPS depot. They will even pack it for you no charge.

Some guys get a blood pressure bulb from ebay and a low pressure gauge.
I use my standalone blood pressure bulb mainly for small engine carb testing.
I apply pressure to the crankcase FIRST because leaking air is easier to find as compared to finding a vacuum leak. Check all your gasket area first that you used as block off's.


When you apply pressure to your chainsaw, do not go over 5 -7lbs and have a water/soap mix handy to check for air leak watching for bubbles.

 

[ctf58]

Thanks, i will order the correct item.

 

[ctf58]

Pressure tester/vacuum came today. I tore down the saw ( first time ever), made something to block exhaust and covered intake with inner tube. Pressure held at 5-7psi and never moved in 5 minutes. Vacuum was same. Pics below are at 5 minute mark. I was using the impulse line. I'll check the intake boot next.
Would you say it is time to open the jug and have a look.
I took plenty of pics as I took it apart so I'm hoping to be about to reassemble it at some point.
Thanks in advance for any useful suggestions,
Ctf58

 

[Okie]

You need to spin the flywheel/crankshaft by hand while it has some pressure and also with a vacuum just to make sure the seals are still holding while the crank moves.
If it passes that I would guess that probably your carb was causing it too run lean.
When you get it rebuilt you need to confirm immediately that the carb will go rich and 4 stroke. You say you know it was not straight gassed. I still use the old style Stihl oil mixed 50:1 for my 028's. I've never ran the higher priced synthetic type Stihl oil yet.
Keep in mind what I said about it's really easy on the 028's to adjust the carb H jet too lean because the saw will sound great, run and piss rev good and really sound and run strong in the wood and all smooth but overheats fast when in big wood, full bar type heavy load cut when the engine is being heavy loaded for 1 minute or more. (heat will start rapidly taking off within one minute, saw will sound like it bogging down or chain loading up with chips or being pinched, lift the saw out of the cut, rev few times and it picks up power and back into the cut.
What you are hearing is the excess lean condition is overheating the piston, the piston is expanding into the side of the cylinder and the saw is friction eating itself. (piston and cylinder is getting scored mainly from the piston skirt at first)

 

[ctf58]

Thanks that will be my next step. The saw might have been lean when I got it. Like I said, I inherited it from a family member.