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Strato spit back / 576xp

Jimmy in NC

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Working on a 576xp. Saw is pretty high hours and acted like an air leak. Flywheel side up and it accelerates. Rotate back to normal and it almost always dies.


Passes pressure and vac check fine with OEM testing flanges.

Did a flywheel side seal anyways... bearing is fine in there. No change.

Popped the top end and evidence of being very hot on the flywheel side. Looks like lite scoring hours ago through some lines in the jug... piston looks fine.

Since I had a set it got new OEM rings. No change.

I do notice quite a bit of spit back through the strato ports. Piston also shows signs of rocking with wear below the intake and exhaust; machine marks elsewhere on the piston.

Could the piston just be worn out? Saws runs fine with good power other than it won't idle and tip over. Will run fine off idle.

Swapped carbs off another 576xp and still has an issue rolling side to side.. but now seems to die with a low rpm flywheel up. Two junk carbs? Original carb pressure tests fine.
 

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Jimmy in NC

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Look at the blow by line from the top of the piston from the rear handle. Strange to me that it has a distinct line on the "cool" side of the cylinder. I am at wits end.. and baffled.
 

Jimmy in NC

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s soon as he called me I figured air leak. I'll pull the PTO seal tomorrow or the next day as time allows... crank does not move at all in there though. The amount of strato spit back is also very strange to me. Normal intake spit back I understand... the strato should be 'dry' unless it's picking up spit back from sloppy piston.
 

Jimmy in NC

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Well I admit defeat...

I have installed a NEW OEM piston and cylinder, two different OEM carbs, non-modded muffler, new OEM seals, new fuel pickup filter, and a new plug just because.

For now I am going to say its a lousy intake setup that's pooling or something. Bearings are fine.


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dangerousatom

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Is there wobble in the piston at 180-TDC….all the way down? Could be it’s ever so loose and the skirt is hitting on the way up/down. There should be a ware mark on the jugs bottom edge along with a corresponding vertical line on the piston ( maybe very tiny ) if it’s got low stroke play.
 

Jimmy in NC

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Is there wobble in the piston at 180-TDC….all the way down? Could be it’s ever so loose and the skirt is hitting on the way up/down. There should be a ware mark on the jugs bottom edge along with a corresponding vertical line on the piston ( maybe very tiny ) if it’s got low stroke play.
Pictures above... the piston is certainly rocking just a bit.
 

Jimmy in NC

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So in a final act of frustration I swapped the intake. I even added clamps where the strato butterfly intake runners attach to the mount. No change. The issue has to be in the cases/crank/bearings. The rest of the saw's condition does not warrant splitting the cases. In reality the saws's condition does not warrant what I have done to it but in a quest to learn sometimes you have to go down those roads. Resized_20241228_104721.jpegResized_20241228_104901.jpeg
 

dangerousatom

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Does it seem to lose any power or rpm once warmed up? I wonder if your fighting in more then one front of issues. I understand it’s hard to gauge but if it’s a thermal issue causing warp to an already minor misalignment to get out so much that it’s causing case or crank irregularities. You’ll never get it sorted without splitting the case and being sure it’s true. Then putting it all back together to test it out again. 🙄

Next time you pull the jug try and keeping the flywheel from turning in a few different positions and pull up/down on the piston to see it there’s a lot of wiggly play.
 

Jimmy in NC

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Does it seem to lose any power or rpm once warmed up? I wonder if your fighting in more then one front of issues. I understand it’s hard to gauge but if it’s a thermal issue causing warp to an already minor misalignment to get out so much that it’s causing case or crank irregularities. You’ll never get it sorted without splitting the case and being sure it’s true. Then putting it all back together to test it out again. 🙄

Next time you pull the jug try and keeping the flywheel from turning in a few different positions and pull up/down on the piston to see it there’s a lot of wiggly play.
Next time it comes apart it will be harvesting parts from it. The more I think about it, I wager the crank is going out. This customer has a history of breaking cranks from repeatedly / regularly hitting the chain brake with the chain still moving. At this point I have abput 10hrs into a saw that's not worth it.
 
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