Stihl 028 super rebuild went bad

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It does look like a lean issue though, it got too hot there. But there is alot of marks around the cylinder by the looks of it

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it just seems like a lean seize.

either lack of lubrication, excessive heat built up due to other means (but I'm doubting the saw was so caked in grime since you rebuilt it that it over-heated that way, unless the flywheel fins were also totally caked closed but again I'm assuming you cleaned the saw), or excessive air intrusion causing a very lean mixture at full song

oh, was the crank/rod checked when it first came apart? slight bent rod causing undue stress on the exhaust side?
 
It had plenty of power and idled down fine.
They normally do have lots of power when they run lean up top as long as they don't lean out such as from a seal or boot leak where the leak gets worse with speed/load. Idle is affected by the idle circuit...so you had a good idle tune and probably no leaks...but the high side was a bit lean

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Hmmmm. It was running perfectly, everything was perfectly perfect, carb settings were normal, all the bolts were tight, gaskets and seals good and everything was just perfect and then that happened. No.
Well the person assembling it (me) was/is imperfect...
 
They normally do have lots of power when they run lean up top as long as they don't lean out such as from a seal or boot leak where the leak gets worse with speed/load. Idle is affected by the idle circuit...so you had a good idle tune and probably no leaks...but the high side was a bit lean

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Watch "Stihl 028 t2" on YouTube

Heres the saw running after my first rebuild.
 
Watch "Stihl 028 t2" on YouTube

Heres the saw running after my first rebuild.


Not that you can tell a whole lot from a 20 second video- but for my ear, it sounded a bit boggy shifting from idle and ramping up to wide open throttle- which is not exactly a bad thing with a fresh rebuild tuned a bit rich low. But for what little we see at WOT, it might have been a bit lean- seemed to be high in the RPM stakes- but that is just guessing.
Did however sound like the chain was plenty tight- might be the case, or it might just be the way the recording device picked up the sound, but an over tight chain is a good way to flog out a PTO side oil seal and lead to a lean condition failure.
 
it just seems like a lean seize.

either lack of lubrication, excessive heat built up due to other means (but I'm doubting the saw was so caked in grime since you rebuilt it that it over-heated that way, unless the flywheel fins were also totally caked closed but again I'm assuming you cleaned the saw), or excessive air intrusion causing a very lean mixture at full song

oh, was the crank/rod checked when it first came apart? slight bent rod causing undue stress on the exhaust side?
I cleaned after each use. I visualy inspected the crank, looked ok as far as i could tell.
 
I cleaned after each use. I visualy inspected the crank, looked ok as far as i could tell.

I have not cleaned my truck for months- but it still drives good.
A visual inspection of the crank will not tell you much of nothing- except maybe it has not snapped.
Bolt the cylinder back on, block the inlet and outlet, put the pug back in and pump in some pressure- check crank oil seals with soapy water after removing the round bits of metal to give you access.
 
Yeah, na. Im not reading through 11 pages to see what you did or did not do, be easier for you to narrow it down to a list of parts replaced and if they were OEM or AM.
If it had a heap of hours on it before you dropped a new top on it only- without any other expendable items being replaced- then something designed to keep air out might have failed since your new top end was fitted.
Carb rebuild, new gas/impulse lines, fuel filter, gear for oil pump, chain guards, drive sprocket and needle bearing, piston and rings, everything was oem excepting rings and pistons.
 
Not that you can tell a whole lot from a 20 second video- but for my ear, it sounded a bit boggy shifting from idle and ramping up to wide open throttle- which is not exactly a bad thing with a fresh rebuild tuned a bit rich low. But for what little we see at WOT, it might have been a bit lean- seemed to be high in the RPM stakes- but that is just guessing.
Did however sound like the chain was plenty tight- might be the case, or it might just be the way the recording device picked up the sound, but an over tight chain is a good way to flog out a PTO side oil seal and lead to a lean condition failure.
I didnt know that about a too tight chain
 
Carb rebuild, new gas/impulse lines, fuel filter, gear for oil pump, chain guards, drive sprocket and needle bearing, piston and rings, everything was oem excepting rings and pistons.

Cool, so intake manifold and oil seals were NOT replaced at last build- both are areas where stray air can enter the system if there is a failure, both were probably of an age where they are due to fail and possibly the oil seals were helped a little on their way out.
 
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