Head scratcher for me anyway

[bobbyb13]

Have you guys heard of getting a scorched piston "knurlized" That is probably spelled wrong, but, a fellow here in a machine shop, cleans up damaged rare or hard to get pistons in 2 strokes, and other engines and does this to them. I had not ever heard of it. I saw a couple of pistons he had cleaned up, and it looked like a heavy cross hatch on the skirt. Just curious if it is a snakeoil deal or what.

 

[Dan Forsh]

I think the term (over here at least) is just knurled.

Whereby a pattern as you describe, like cross hatching is pressed into the surface with rollers. I've no personal experience of it, but I've heard of it being done as a last chance kind of solution on old cast iron pistons.

 

[bigjake]

Yes this was a older machine shop service you would then file the piston to
fit its a very basic fix .All your doing is making the skirt a bit bigger the
cylinder still suffers from all the same wear and tear .And the piston will
still have issues. Oh wait i have one

 

[Geno44]

Knurling/Knurlizing

Either term is correct. The skirt of the piston is rolled on a knurling tool and it stands up little bumps or ridges on the outside, effectively increasing the piston's outside diameter. The problem is that the side thrust on the piston is now carried on a much smaller contact area which will wear down faster than full skirt contact. It certainly will work. The question is how long it will last. If you have no other options, it is inexpensive and will last "a while". This was commonly done on cast iron pistons in automobiles 60 years ago. With labor as high as it is today, it's seldom used as a repair procedure.

 

[bobbyb13]

Thank you, Gentlemen

As a last ditch effort for a old play toy engine, this is a good "old" idea. I learned something new to me.

 

[alpinecrick]

Either term is correct. The skirt of the piston is rolled on a knurling tool and it stands up little bumps or ridges on the outside, effectively increasing the piston's outside diameter. The problem is that the side thrust on the piston is now carried on a much smaller contact area which will wear down faster than full skirt contact. It certainly will work. The question is how long it will last. If you have no other options, it is inexpensive and will last "a while". This was commonly done on cast iron pistons in automobiles 60 years ago. With labor as high as it is today, it's seldom used as a repair procedure.

That's interesting--didn't know that....


Casey

 

[biggen0_8]

These other guys have told you right. We used to do that years ago in the automotive world. But now days the only time we would even think of doing it is on a VERY rare engine that is impossible to get a new piston for. And then I would only do it on an engine that operates at lower rpm's and isn't going to be ran very much. I can't believe that it will hold up on an aluminum piston that is going to operate at 9000 plus rpm's for very long. Just my thoughts.

 

[stihlboy]

These other guys have told you right. We used to do that years ago in the automotive world. But now days the only time we would even think of doing it is on a VERY rare engine that is impossible to get a new piston for. And then I would only do it on an engine that operates at lower rpm's and isn't going to be ran very much. I can't believe that it will hold up on an aluminum piston that is going to operate at 9000 plus rpm's for very long. Just my thoughts.

it will hold up.....just not for a long time anyways. your better off replacing a piston because when the knurled piston fails you replace the piston. so instead of taking it apart twice do it right the first time

 

[Modifiedmark]

I think the term (over here at least) is just knurled.

Whereby a pattern as you describe, like cross hatching is pressed into the surface with rollers. I've no personal experience of it, but I've heard of it being done as a last chance kind of solution on old cast iron pistons.

I hope you really didn't mean cast iron pistons?

 

[Lakeside53]

There is a recent discussion (this month) on this... AS Search is your friend...

Irrespective of the efficacy of the approach, I doubt you'd be able to effectively knurl open sided 2 stroke pistons - way too much pressure required (and other mechanical/setup issues), and, the piston wear is asymmetrical.

 

[Lakeside53]

I hope you really didn't mean cast iron pistons?

Yep.. common in the 20's and 30's... They sure did slap...

 

[rocky226]

I hope you really didn't mean cast iron pistons?

they would be kind of hard to balance eh??? LOL

 

[Lakeside53]

Young guys....:greenchainsaw:

They are still made....

http://www.stationaryengineparts.com/cast-iron-piston-5-1-6-1-10-2-12-2-353-0.html

 

[rocky226]

I think I been corrected.:monkey:
No arguing the website.