Hole (sorta) in top of piston?

[bplust]

Hi all,

I recently picked up my third 920, which came with no spark plug. I took a gander inside of the cylinder through to hole, and saw a small hole in the center of the piston. While it was dead center, and looked very intentional, I wasn't pleased. I just got home from work, and looked at a blown up piston from another 920, and saw the same hole, which upon inspection, is actually just an indentation. So I guess it's some kinda design feature.

So what's the deal with this?

Thanks,

Bryan

 

[blsnelling]

Wrong kind of piston stop used.

 

[67L36Driver]

Center drill for lathe/grinder setup during manufactureing.

 

[blsnelling]

So is this hole simply a dimple in the crown, or is it an actual hole?

 

[bplust]

It's a dimple. Intuitively, a hole wouldn't help much with achieving ideal compression. If you look underneath the piston, you can see the material displaced AKA, a raised portion of material.

 

[splitpost]

If it has displaced material then i'm with Brad on this one

 

[pops21]

Yep brads right. Sounds like the piston stop was probably dug into the piston with the help of a impact wrench maybe?

 

[Opihi59]

They appear to be manufactured that way. I have this piston in my hand, hole doesn't go thru all the way, it's just a dimple.

Roper built Craftsman 3.7 piston shown above.

 

[shawn022]

I've had 1 or 6 of these saws apart and they all have that dimple.

 

[67L36Driver]

They appear to be manufactured that way. I have this piston in my hand, hole doesn't go thru all the way, it's just a dimple.

Roper built Craftsman 3.7 piston shown above.

That's a center drill hole for lathe tailstock etc..

Without a pic. from the O.P. everything is speculation.

 

[bplust]

I checked, and all three of my 920's have it. I'd go with the opinion that it's part of manufacturing. Thanks for all of the replies.