Reading piston wear/scoring help

[Johnsobri]

Hi all, I have a question on some wear on a piston that I was hoping someone could help me out with what is going on and what caused it

Disclaimer: This is not a chainsaw piston. It's from a fs100rx string trimmer. And sorry for the crappy picture all I had was my iPad.

<a href="http://www.flickr.com/photos/50518372@N06/9943288856/" ><img src="http://farm3.staticflickr.com/2827/9943288856_3d5bccae1a_c.jpg" width="600" height="800" alt="image"></a>

If the picture is a little hard to see I will try to explain. There are vertical rows of wear marks on each side of the piston under the rings only. You can still see the machining marks in-between the rows of wear marks.

I just want to know what has caused this, the trimmer is running fine otherwise.

Thanks in advance.

 

[motoman.5150]

looks beautiful to me, don't see a problem, some of my best running saws look way worse than that

 

[o8f150]

looks good to me

 

[Johnsobri]

looks beautiful to me, don't see a problem, some of my best running saws look way worse than that

I too have seen and run way worse...but I am more concerned that I have never seen this kind of wear on a piston. This trimmer is not that old. Less than a year.

 

[discounthunter]

horizontal=machining marks. is the piston skirt tapered ? better pictures would help,but i agree with the above posts that it looks fine.

 

[Plan-b]

Pistons are actually funny shaped- the top is usually a bit smaller then the skirt, but in some cases it's not, they are not cylindrical and they are never perfectly round. This is all to account for expansion, thrust sides, and the underneath webbing, pin location, and a lot more...

I can not tell anything major form that picture, after all it's just a small engine... fuel it and flog it.

 

[Johnsobri]

horizontal=machining marks. is the piston skirt tapered ? better pictures would help,but i agree with the above posts that it looks fine.

Yes, there are still horizontal machining marks present. But there are vertical wear rows also on the piston where it has worn the machining marks completely away. The gray vertical areas on the piston are the worn areas I am speaking of.

 

[Plan-b]

Yes, there are still horizontal machining marks present. But there are vertical wear rows also on the piston where it has worn the machining marks completely away. The gray vertical areas on the piston are the worn areas I am speaking of.

Waves form the machining process, the cylinder just polished up the high spots for you .

EDIT> I am taking about the horizontal lines on the skirt.

from the picture it look like the crank is in focus not the piston.

 

[Johnsobri]

Waves form the machining process, the cylinder just polished up the high spots for you .

That all makes complete sense. Thanks for your help. I was making it out to be a lot worse that what it really is.

That wear is uniformed on both sides. I will have to check and see if the high and low spots line up with the oposite sides of the piston.

Thanks again.

 

[turtle561]

plan-b has it, the wear areas are uniformly spaced. if anything they reduce the contact area/friction , a good thing. check the other side and count the wear waves,see if they match.

 

[w8ye]

You guys have the cart pulling the horse?

The waves are in the cylinder and they are rubbing the piston.

It is because of the port shapes

 

[a. palmer jr.]

Why did you take it apart, didn't you say it was running good?

 

[Evan]

Has the thing ever been fired up?

 

[Plan-b]

You guys have the cart pulling the horse?

The waves are in the cylinder and they are rubbing the piston.

It is because of the port shapes

Port shapes? sure....

Problem is that is one of those trimmers with valves and a cam. No ports in the cylinder, just in the head.

 

[lone wolf]

Op could you get a better pic for us?

 

[Johnsobri]

Op could you get a better pic for us?

It was taken apart because it is making a knocking noise. Cylinder was pulled to check bearings and valves. I will take my camera tomorrow and snap a better picture of it.