Author Topic: Tell me what these score marks came from  (Read 697 times)

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Offline LeeB

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Tell me what these score marks came from
« on: April 21, 2014, 05:19:25 pm »
Any idea what caused this? the scoring is only on the exhaust side. The intake side is clean.

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Offline 3000 FPS

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Re: Tell me what these score marks came from
« Reply #1 on: April 21, 2014, 07:29:02 pm »
If only on the exhaust side then I would say the saw was ran lean.   

Now there are all kinds of things that can cause it to go lean.

Wrong fuel mix or bad mix.
The crank seals could be going bad and allowing air into the crankcase.
Something in the carburetor has changed and the mixture went lean at WOP.
If the saw has an impulse line it could be going bad allowing an air leak.
Loose hardware on the carburetor.

What happens when lean at WOT the cylinder get very hot the piston expands and then starts rubbing on the cylinder wall galling the aluminum from the piston.  The more you run it the worse it gets and the galling gets deeper.
PP 505, 475, 445.

Offline Cut4fun

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Offline LeeB

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Re: Tell me what these score marks came from
« Reply #3 on: April 21, 2014, 07:34:30 pm »
When a saw is just about to run out of fuel it will overspeed. Is it possible that this could have caused this?

Offline KilliansRedLeo

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Re: Tell me what these score marks came from
« Reply #4 on: April 21, 2014, 07:35:48 pm »
3000FPS is most likely to be correct. Do not even attempt to run the saw. It probably won't start anyway because the rings look to be stuck in the grooves.
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

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Offline KilliansRedLeo

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Re: Tell me what these score marks came from
« Reply #5 on: April 21, 2014, 07:39:54 pm »
When a saw is just about to run out of fuel it will overspeed. Is it possible that this could have caused this?

When you speak of 'over speed' that is LEAN because the saw is sucking air from the tank along with fuel leaning out the saw. Usually does not make a big difference unless the saw was tuned too lean in the first place.
"When the people fear the government...you have tyranny....When the government fears the people....you have liberty"

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Offline LeeB

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Re: Tell me what these score marks came from
« Reply #6 on: April 21, 2014, 07:43:14 pm »
No worry about running the saw. When the hired help trashed it, it died in the middle of a cut, or so he says. I wasn't home. (Wife has been severely chastised for letting anyone use my saws.) When I got home (work overseas) and tried to start it, I could tell right off the bat it had no compression just from the sound. Most assuredly won't run now, as it is in pieces.  ;) Trying to decide which AM p&c to go with to rebuild it.

Offline LeeB

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Re: Tell me what these score marks came from
« Reply #7 on: April 21, 2014, 07:45:18 pm »
Quote

When you speak of 'over speed' that is LEAN because the saw is sucking air from the tank along with fuel leaning out the saw. Usually does not make a big difference unless the saw was tuned too lean in the first place.

Does increasing the idle speed "lean it out"?

Offline 3000 FPS

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Re: Tell me what these score marks came from
« Reply #8 on: April 21, 2014, 08:11:43 pm »
Quote

When you speak of 'over speed' that is LEAN because the saw is sucking air from the tank along with fuel leaning out the saw. Usually does not make a big difference unless the saw was tuned too lean in the first place.

Does increasing the idle speed "lean it out"?

No that will not cause what you have or running the saw out of gas.   When it runs out of gas it does not run long to do that kind of damage.

Well now that we know it was loaned out I would check the oil to fuel mix that was put in it.
PP 505, 475, 445.

Offline 3000 FPS

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Re: Tell me what these score marks came from
« Reply #9 on: April 21, 2014, 08:18:20 pm »
When a saw is just about to run out of fuel it will overspeed. Is it possible that this could have caused this?

When you speak of 'over speed' that is LEAN because the saw is sucking air from the tank along with fuel leaning out the saw. Usually does not make a big difference unless the saw was tuned too lean in the first place.

Remember the oil is in the fuel and if the ratio of fuel mixed with oil to air is not correct then the saw does not get the lubrication it needs and then it overheats causing what you have.   Lean means less fuel but also means less oil.
PP 505, 475, 445.

 

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