Why'd it die? Lean vs Straight gassed vs Overheated

[Rx7man]

I've come across a few saws now that have been scored to death, and I'd like to know more about the symptoms of each root cause

Anyone know a good way of figuring it out? Perhaps with some pictures of what each cause does and doesn't damage?

I got a 394 for cheap (have the saw if you fix the recoil on my MS170).. Piston scored to death, cylinder has tons of transfer on it, no detonation pitting on the top of the piston, bottom end good and tight, cooling fins a little dirty, but not bad. With a new top end the saw runs awesome.

Other saw (Husky L65) had a ton of detonation erosion, rings stuck, clean saw inside and out.. run lean?

 

[Yukon Stihl]

D Dave had a Stihl tech manual that showed a bunch of different pistons damaged in different ways and the cause.
My self any saw i get that shows signs of scoring gets a pressure,vac test.Any saws i think of fixing to sell get a pressure vac test.Peace of mind for a few minutes work.If they don't pass the test then it takes a little longer to find the cause.
Thomas

 

[Rx7man]

I just have to make the blockoff plates to do do the test... I'd like to make one to eliminate the cylinder entirely, but with the con-rod in the way it sounds like a bit of a job

 

[Chainsaw Jim]

The L65 could have had bar oil and water in the mix.

 

[Rx7man]

Water damage I didn't think about.. it would have had to be a lot of it to do that kind of damage.. the piston was nearly dished along it's outside edge from the pitting. It's been sitting for YEARS since it died though.. it doesn't even have traces of a fuel line left (it could have had a crack and ran lean).

 

[zogger]

I just have to make the blockoff plates to do do the test... I'd like to make one to eliminate the cylinder entirely, but with the con-rod in the way it sounds like a bit of a job

That's an interesting idea, something to do with old cylinders that won't clean up good, make them permanent bottom end crankseal testers.

 

[GlynnC]

For what it's worth to you, here's a picture of piston and cylinder of a little top handle Echo CS330 that had been straight gassed. When I acquired it, the engine was locked, and gas tank had over 1/2 tank straight gas!

 

[wde_1978]

http://www.smellofdeath.com/lloydy/piston_diag_guide.htm

Came across it here on AS and bookmarked it, maybe it will help in diagnosing the cause of failure.

 

[wde_1978]

For what it's worth to you, here's a picture of piston and cylinder of a little top handle Echo CS330 that had been straight gassed. When I acquired it, the engine was locked, and gas tank had over 1/2 tank straight gas!

That almost looks like that piston "ate" some debris.

Here are some of mine:
1) 30 years of carbon build up scoring , plus piston ring worn thin allowing lots of blow by


2) 9 years of carbon build up in the exhaust port caused scoring, piston and piston ring are damaged


3) con-rod needle cage failure, piston "ate" the debris at ~13k WOT, also visible blow by and piston wear (open port cylinder)

 

[lone wolf]

I've come across a few saws now that have been scored to death, and I'd like to know more about the symptoms of each root cause

Anyone know a good way of figuring it out? Perhaps with some pictures of what each cause does and doesn't damage?

I got a 394 for cheap (have the saw if you fix the recoil on my MS170).. Piston scored to death, cylinder has tons of transfer on it, no detonation pitting on the top of the piston, bottom end good and tight, cooling fins a little dirty, but not bad. With a new top end the saw runs awesome.

Other saw (Husky L65) had a ton of detonation erosion, rings stuck, clean saw inside and out.. run lean?

Pics of what you are trying to figure out?

 

[fordf150]

this should help out

 

[Rx7man]

@wde_1978 That's a good link, and good pictures.
It looks like a lot of the chainsaw problems I see are from carbon buildup scoring the piston. The 394 I bought had some bearing trash go through it, it was pretty obvious.. thankfully the cylinder was perfect. The parts saw I got had a seriously scored piston with a ton of transfer on the cylinder, both rings stuck too.

I wasn't looking for information on a particular problem, I was looking for general guidelines. One that has me stumped was a Homelite XL925, cracked skirts, black piston top, shiny-like-new cylinder dome.
Then there's all the Poulan 4218AVX's I have.. they're all like new and all are scored up and worthless.. I steal starter ropes and handles from them... I figure those are set too lean at the factory for EPA and it kills them

 

[Rx7man]

@fordf150 6.5mb is a bit a big download for my connection, I'll download it when I go to town.

 

[president]

this should help out

thanks , exellent ,I have the (stihl)piston failure manual ,and this is better

 

[Chainsaw Jim]

For what it's worth to you, here's a picture of piston and cylinder of a little top handle Echo CS330 that had been straight gassed. When I acquired it, the engine was locked, and gas tank had over 1/2 tank straight gas!

I suspect the straight gas was introduced when troubleshooting. This looks like a different kind of failure.

 

[fordf150]

@fordf150 6.5mb is a bit a big download for my connection, I'll download it when I go to town.

i compressed it some but it has such good pictures in it i didnt want to compress it too much and lose that.

 

[GlynnC]

I suspect the straight gas was introduced when troubleshooting. This looks like a different kind of failure.

.

Could be--I have no history--bought it off CL from a guy who had bought it from someone else! What would you guess--running lean? New short block, opened up adjustment screws, runs great now!!