As pressure builds up in the combustion chamber from the oxidation process, it is perpendicular to the the piston head.

Due to design, the piston is at an angle with its connecting rod. This angle forces the piston into the side of cylinder from the pressure build-up.

Pistons have a notch/symbol showing the assembler the forward direction as a reference. The piston wrist pin in not in the middle of the piston, it is off to the thrust side to aid in 'balancing' the force upon the piston in the bore.

Too much piston-to-cylinder wall clearance and/or a cold engine, and piston slap will be heard, until the engine warms up or it eventually destroys itself.

 

Wow good explaination.. i knew the answer but i couldnt of explained it better than that.

so ... yeah what he said!!

 

Thank you, Kyle.

 

As you look from the front of a clockwise rotating engine, the thrust side of the bore is the left side, closest to the exhaust ports on the passenger side and closest to the intake ports on the driver's side ( provided you aren't in Australia ).

 

Thanks all. I had thought the thrust side was the exhaust sides on both banks (no good reason though). Appreciate the insights!

 

Thanks all. I has thought the thrust side was the exhaust sides on both banks (no good reason though). Appreciate the insights!

The piston/rod pushes on the crank after it has passed TDC, and it can only push from the side opposite where the crank journal is.

 

And fwiw, you can gain a schosh more power by installing the stock offset pinned pistons backwards b/c you gain a little bit better angle push, BUT they will slap more when cold!

Hot, fine!!

I ran the pistons in my junk301 this way after my Machinist told me to b/c it's an old "roundy-round" engine trick.

pdq67

 

Nevermind, I misread.

Good Luck!