Scored pistons

[Boomer 87]

Heres something ive been wondering. If a piston gets scored will it continue to get worse even if the intial cause was corrected?

 

[Boomer 87]

I guess what im saying, ive discovered a couple scored saws but only after i pulled the muffler to just have a look, if i hadent done that i would of never known anything was wrong

 

[alexcagle]

I would replace them.....CAD will cause you latent psychological problems. You will always be thinking about it......replace it.....replace it......

 

[Full Chisel]

A scored piston has been overheated and likely has microscopic stress fractures that could grow and cause failure down the road. Definitely replace them!

 

[Acornhill]

It depends on the saw, and $available. If sitting on shelf most of the time etc or just a beater, I say leave it until a good deal for one comes along

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[grack]

I replace scored pistons but my friend worked for a small engine repair business for over 20 years and left it up to the customer I've seen gnarly pistons wire wheeled and put back in and they were happy.

 

[Boomer 87]

Im sure and im not a hillbilly i want to do the right procedure, what im getting at is if rings arent stuck and a person never looks at the condition a saw may run for years that way.

 

[grack]

The loggers saws i work on are seldom checked they run good mix and tune them and if it stops running they just buy new and have me rebuild the old saws as backups or they sell them yes some of the pistons are scored to some degree and run a long time on scored pistons but i wouldn't do it to my saws it just leads to more damage.

 

[Boomer 87]

Thats basically what i mean, for instance someone straight gassed a saw and they scored it but not horrible bad how long would it go after the correct mix was put in or would the scoring continue to get worse

 

[HarleyT]

Scoring is evidence of metal transfer, which eventually pins the rings down. Once started, it will continue to be a problem
due to friction, and get worse.
But that being said, I've seen old Homelite xl12s run for years with scored, scarred pistons.

 

[Acornhill]

i am going to find out, i have the 3500 and plan to run it until it blows up, i also had a XL12 that was scored and ran for years until i sold it and the guy says it is still running

 

[Boomer 87]

Thats what i thought but like you seen some pretty gnarly looking stuff that ran

 

[Marshy]

Scoring is evidence of metal transfer, which eventually pins the rings down. Once started, it will continue to be a problem
due to friction, and get worse.
...

This... I was going to say the same thing.

 

[diezelsmoke]

As long as the ring is not stuck or the transfer is not enough to stick the piston they will run just fine.

 

[Marshy]

As long as the ring is not stuck or the transfer is not enough to stick the piston they will run just fine.

The point is, a score means some of the piston material was sneered on the cylinder wall and eventually it will continue to give up more material on the cylinder until it gets stuck in the bore or pins a ring in its land. Plus you lose performance from the ring riding over a piece of transfer on the cylinder wall losing its seal to the wall. If you cleaned the cylinder but reused the piston it's possible the piston is outside of manufactured tolerances and had a high or low spot on it. Eventually it's going to lead to some type of catastrophic failure. It's anyone's guess as to when. You wouldn't put only new brake pads and rotors on a car you knew had a frozen caliper would you? I wouldn't, I'd change the caliper too. Same idea, Id change a piston if it was scored, even if I cleaned the cylinder. That's my 2c.

 

[Boomer 87]

The ammount if time one will run that way also depends on the saw, a xl 12 is probly made to looser tolerances so it wouldnt affect it as much as like a brand new 661 or something more closely machined

 

[Boomer 87]

I have an 031 stihl that has one 1/8 wide carbon scrape down the front but runs perfect, i got two good used jugs and pistons, so im gonna run it till it blows then swap em

 

[ARsawMechanic]

While I do not suggest it, I once took an 028 super with a good amount of scoring, cleaned the transferred metal from the cylinder walls, re-opened the ring grooves carefully with a razor knife, then used fine emery cloth on the sides of the piston to smooth the scoring there. Slapped in a new set of rings obtained from the bay, & cut quite a fair amount of wood with it with no problems. It was an experiment done on a shoestring budget, and while I don't use it much any more, it's been 5 yrs since I did that.

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