Dimple/Hole in Piston

[kstill361]

I was changing the clutch drum on my 910 today and I used the rope method.
As I brought the piston to the top I noticed thru the plug hole, what looked to be a little hole right in the center of the piston, I used my hook to see if it was a hole or a dimple, to my relief it doesnt go all the way through the piston. So my question is, are there dimples in new, certain brand pistons ? I have never seen this before.

 

[kstill361]

I looked at some pistons on ebay, i guess its supposed to be there.

 

[ShoerFast]

I was changing the clutch drum on my 910 today and I used the rope method.
As I brought the piston to the top I noticed thru the plug hole, what looked to be a little hole right in the center of the piston, I used my hook to see if it was a hole or a dimple, to my relief it doesnt go all the way through the piston. So my question is, are there dimples in new, certain brand pistons ? I have never seen this before.

From the hip

It would certianely provide a posative EGR flow, reducing NOx emmission, and provide a life limiting unit to the saw-life.

But no, there is not a real world (outside the EPA) reason for it, piston time.

Edit: I read it wrong, your looking at a machining mark, a point to chuck the piston up 'on-center' ,, I read that the hole went through.

 

[timberwolf]

I think it is just used to simplfy manufacturing, just an indexing hole to center the piston for machiene work. you see these on all sorts of round parts that are turned like axels and motor shafts.

 

[Jacob J.]

The 910 piston does have the dimple in it from the factory, as does the early 820 and 920 pistons also.

 

[Rookie1]

They call my aunt Dimples.