Someone please tell me I didn't burn a piston

[Robin Wood]

i dont want to speculate anythin more at this point, dont want to rub salt on the wound. anyway look at the bright side you get rid of this p&c which you dont know the history about and get a new p&c which will give you a peace of mind for few years and you dont have to worry about anything but putting it to work

 

[shawn022]

Look at the exhaust port in the pics. Op never ported the cylinder. He opened up the muffler. Calling him a shade tree hack is ridiculous. Taking the cylinder off before pressure and vacuum testing for leaks is also not good advice.

 

[Big Block]

Yup it's toast

 

[Robin Wood]

Look at the exhaust port in the pics. Op never ported the cylinder. He opened up the muffler. Calling him a shade tree hack is ridiculous. Taking the cylinder off before pressure and vacuum testing for leaks is also not good advice.

your're right, he needs to check for air leak so that he can rule that out
dont want this to happen to a new p&c do we now ?

 

[Big Block]

That gouged spot on the piston looks like debris

 

[Marshy]

I guess a little clearer info from the OP would help. No fault of his own, he probably doesn't know but when someone says "ported the exhaust port" to me that means the cylinder port. If in fact he was grinding the cylinder exhaust port with it on the saw I consider that shade tree work.

 

[Robin Wood]

That gouged spot on the piston looks like debris

thats what i thought but pic isnt very clear
i had this kinda damage on my brushcutter before, dont ask me how it happened lol

 

[Okie]

That's really all I want to hear

Short story: Opened up the exhaust port to about twice what the stock hole was. Then tried to retune the carb. Low adjustments went fine. But then while doing the high adjustments, the saw shut off with no explanation.

Longer story: Decided I waned to get set up for milling (Alaskan). Decided I needed a big saw to do the job. An 088 popped up on CL so I grabbed it. Not a crazy deal, but it seemed reasonable. The guy fixes saws for fun / extra cash. On this one, he had replaced a flywheel and piston. We fired it up when i bought it. Seemed great. Didn't run it very long. Took it home. I never got to actually cutting anything with it. But I did get around to grinding out the exhaust hole. It just seemed so easy on this saw, I couldn't help myself. Even though I have very little actual experience with saws, so I probably had no business doing that. But like I said... seemed like it was too easy NOT to do. After that I tried to retune the carb. Low adjustments went fine, though i couldn't quite get it to idle without the chain rolling a bit. But I moved on to the high adjustment. I know I started lean, but I tried to move quickly toward rich out of fear of causing piston damage. I thought I was getting into the right range, but then the engine quit. This took place after the saw was at full throttle for maybe 30 seconds. Wouldn't start back up until it cooled down for a while. Then the same thing happened again. Third time, it wouldn't start back up.

Any thoughts? I know it could be a lot - coils, spark plug come to mind. I'll probably get some help from the local dealer or the guy I bought it from, but just wanted to see if anything sounds obvious to you lovely people... I couldn't have cooked the piston that quickly (in a matter of seconds) running too lean, could I?

I couldn't have cooked the piston that quickly (in a matter of seconds) running too lean, could I?

YES.
You bought it. I would not even bother contacting the seller. Once you DICKED WITH the saw it's your baby. Don't whine to the seller and if you knew the guy had changed the piston and other that should have been a heads up to go elsewhere even if he gave you a warranty period YOU voided any warranty by dicking around with the saw immediately.

I recently started using both a tach and a infrared thermometer to make sure that a chainsaw cylinder is not overheating when tuning. A tach by itself will not indicate the actual temp of the cylinder due to saw being lean or getting hot.
After I starting using the infrared thermometer I seen saws cylinders start heating to and above 400 degrees within 15 seconds when in a cut loaded and the saw would have seized or damaged the piston/cylinder within 30 sec or less than 1 minute.
Saws (Stihl, Homelite, Poulans) I've checked maxed and stayed at around 360 in the cut and the cylinder temp did not rise fast eventually getting to the 360 area and stabilizing.
The infrared temp was easy to take safely by myself aiming it at the cylinder fins while the saw was buried in a big downed log, full bar cut, full throttle with a sharp chain. Would be more user friendly if had a helper doing the infrared temp aiming.

But you need to check the obvious things, like bad spark plug, no spark, shot of gas in the carb throat then no choke and crank with wide open throttle, does it give the jerk like before when pulling the rope indicating compression, etc.
(or have someone experienced with saws, not a shade tree Bubba doing the tests)

 

[The Abominable Snowman]

Look at the exhaust port in the pics. Op never ported the cylinder. He opened up the muffler. Calling him a shade tree hack is ridiculous. Taking the cylinder off before pressure and vacuum testing for leaks is also not good advice.

Thanks Shawn. Geeze - some guys get real negative real quick. I didn't port the cylinder. Just opened the exhaust hole a bit.

Problem is I also added a screen, because it was missing. Seemed like a good idea for safety. but it didn't hold up (not sure why - maybe I screwed it on too tight and ripped it or something). So it's possible part of the screen got sucked in (scavenged, as you say).

Anyhow, it's at the shop for a new piston/cylinder. They also convinced me to spring for a new carb, since they were skeptical that what I did caused the problem. Given the uncertainty, it seems very possible that I bought a saw with a bad carb in the first place. Could explain why the repair guy had it to begin with. He never ran it except to verify operation.

 

[smokey7]

Please get your old parts back from the dealer once they complete your saw.

 

[cus_deluxe]

and not sure how a bad carb will score your top end....i expect shane hit the nail on the head, that this saw has an air leak that was not addressed when the first piston was swapped. and dont mind the negative comments OP, hope you get your saw sorted out, and keep us posted.

 

[Definitive Dave]

I will buy your old carb piston and cylinder, shoot me a message here or an E-mail
Dave

 

[HarleyT]

and not sure how a bad carb will score your top end....i expect shane hit the nail on the head, that this saw has an air leak that was not addressed when the first piston was swapped. and dont mind the negative comments OP, hope you get your saw sorted out, and keep us posted.

Just incorrectly adjusting a carb can damage a piston easily.

 

[cus_deluxe]

Just incorrectly adjusting a carb can damage a piston easily.

Yes, but thats different than replacing a carb with no real reason to know that its "bad" and usually a saw with a "bad" carb wont run long enough to damage anything.

 

[HarleyT]

Yes, but thats different than replacing a carb with no real reason to know that its "bad" and usually a saw with a "bad" carb wont run long enough to damage anything.

I'm not following that....

 

[cus_deluxe]

I'm not following that....

OP said the dealer " convinced" him to spring for a new carb. How do they know that the carb caused that type of cylinder damage on a saw that no longer runs? Im saying that a poorly adjusted carb is easily remedied, which is completely different from a carburetor that is "bad". Whats not to follow?

 

[Okie]

OP said the dealer " convinced" him to spring for a new carb. How do they know that the carb caused that type of cylinder damage on a saw that no longer runs? Im saying that a poorly adjusted carb is easily remedied, which is completely different from a carburetor that is "bad". Whats not to follow?

Kinda indicates to me that the dealer is doing a little extra milking and maybe needs THE carb for another saw or a excuse for the dealer to void any warranty work if the customer declines the NEW carb and may not really get your SAME old removed parts back.
I would have most likely went somewhere for a second opinion or chalked this one up to experience and more careful on next purchase. (everyone screws up sometimes, if you are not screwing up every once in awhile you are not doing anything). (just don't let the wiffee know and you will eventually live it down and it will go away)

Say to yourself from bed experiences:
I'm not as good as I'm gonna get-but I'm better than I used to be.

 

[HarleyT]

OP said the dealer " convinced" him to spring for a new carb. How do they know that the carb caused that type of cylinder damage on a saw that no longer runs? Im saying that a poorly adjusted carb is easily remedied, which is completely different from a carburetor that is "bad". Whats not to follow?

I missed that post where he took it into the dealer.

 

[Rockjock]

Gents are the 070/090 carbs even available? I do not see them on my pars list.

 

[TBS]

New aftermarket 070-090 carbs are available.