Neat B&S piston

[izualangel]

Found the mower on the side of the road. Cheap bottom-of-the-barrel WalMart Murray mower. Got it running, but it smoked. And never stopped. Got curious, so I started to tear down the engine (why not, right?) Don't recall ever seeing a piston like this before with the 4 indentations in it. The rusty crud on the inside of the piston (and the general poor shape of the rest of the mower) tells me that maybe this had some water in it. Anyway, thought I'd share.

Edit: the engine is a 10A902 2180 B1.

 

[Bud_One]

Interesting indeed .

All three grooves have rings or just the top two ?

 

[izualangel]

Yeah, two compression and one oil rings. I pulled them off for a clearer picture.

 

[oldhp]

OK. Why the four notches??? More oil splash to lube piston???

 

[Kruse]

Originally Posted by oldhp
OK. Why the four notches??? More oil splash to lube piston???


Perhaps. But my WAG says there is less piston expansion when the piston is heating up to help avoid seizing in or scoring the cylinder wall.

 

[CR94]

Originally Posted by oldhp
... Why the four notches??? More oil splash to lube piston???
Maybe to clear some other part at BDC?

 

[SubieRubyRoo]

Originally Posted by oldhp
OK. Why the four notches??? More oil splash to lube piston???


I'd bet it's actually the opposite; with the rod splasher there is probably plenty of oil on the bore walls & piston, the grooves are to help return it to the crankcase faster than it splashes so that it doesn't drink oil and/or just force it's way right past the oil control rings.

 

[Lou_Boyle]

I think Subie may have the answer.

From the photos I can't see any holes in the piston to drain the oil from the oil scraper ring. It's been several decades since I saw a B&S piston, but I seem to remember slots behind the oil ring for drainage.

 

[Kamele0N]

I have one B&S 3.5hp classic engine for parts....
Piston has holes at oil ring...