026 Piston skirt wear

[Baddboyy21]

I am rebuilding an 026. I was thinking about reusing the original piston. Does the skirt look like it has too much wear to reuse? I have a new set of caber rings for the piston but now I am not sure I want to use it.

 

[backhoelover]

do you see the little line on the piston that is for holding oil. you can see that they are starting to ware away at the bottom of the skirt. you could reuse the piston. if it was mine i would install a new one. but its what you like and have the budget for

 

[backhoelover]

*little lines on piston

 

[drf255]

Still looks OK, but I'd probably change it for cheap insurance.

Look underneath and compare the skirt thickness. They tend to wear most on the intake skirt.

Then pop the rings off, stick it in the cleaned jug, and stick a feeler gauge between the jug wall and the piston.

I believe there should be .002 of clearance between the piston skirt and wall. So that would be .001 on each side. If it's over that, toss the slug.

Someone please correct me if I'm wrong on that measurement. I rarely will use any worn piston in my builds.

 

[Baddboyy21]

I'm going to replace it.

 

[Dave27483]

I'm going to replace it.

I would also

 

[Mad Professor]

Still looks OK, but I'd probably change it for cheap insurance.

Look underneath and compare the skirt thickness. They tend to wear most on the intake skirt.

Then pop the rings off, stick it in the cleaned jug, and stick a feeler gauge between the jug wall and the piston.

I believe there should be .002 of clearance between the piston skirt and wall. So that would be .001 on each side. If it's over that, toss the slug.

Someone please correct me if I'm wrong on that measurement. I rarely will use any worn piston in my builds.

0.002 is too tight. New OEM 038 P/C I checked were 0.0025", I'd sat 0.004-5 " is getting worn

 

[backhoelover]

stihl manual states 0.2-0.4

 

[backhoelover]

i would upload the manual but the file is to big for web site

 

[Mad Professor]

stihl manual states 0.2-0.4

What units are you using? Even if those are mm/milimeters that would be 0.007-0.015 inches!!!

That is WAY loose even for a chevy V-8 with forged pistons!!! Slap slap slap.........goes the skirt

 

[Dave27483]

At the end of the day despite measuring anything I would not use a piston with that much shine,
The shine on the side is wear, there is no more visable signs of the origanal machine lines which as backhoelover said is what carries the oil fuel mix

 

[backhoelover]

that is the limit for a new ring anything large should be replaced. that doesnt mean it needs to be replaced

 

[Mad Professor]

that is the limit for a new ring anything large should be replaced. that doesnt mean it needs to be replaced

All over the place...... Ring gap or piston skirt clearance? What units are you using?

IMHO 0.007-0.015" piston clearance is just waiting for the skirt to break off.

 

[backhoelover]

here is where i got the info

 

[backhoelover]

that is where i got the info from.

 

[motor head]

That's ring gap,

 

[spudulike]

Those port shapes look like the saw has been parked up for a while and the aluminium has a witness mark on it which is nothing serious. The piston skirt should have around 2-3 thou on it when pushed to one side and measured on the other. You can usually push the piston in to the bore and move it from front to back to gauge how loose it is in the bore, do enough and you know if it is shot.

You can also compare the dimensions of the piston from where there are still machining marks and where the polished bits are and that will show you how much wear is present.

Placing your thumb over the plug hole and pushing the piston up and down in the bore without rings also tells you how worn it is, if it feels squishy then it is sealing OK but if it slides in to TDC easily then it is worn.

026/MS260s are a bit prone to having a bit of slap on high hour units, I have seen skirts shatter due to piston slap!