Howell v4 engine drawing question

[scooby]

I was wondering if someone could help me with the piston drawing. I just want to verify I'm understanding this correctly.
It shows .872" dia (top land only) on the print. It shows .873" dia at the bottom of piston.
Does this mean after the first o-ring groove the diameter is .873"?

 

[peterl95124]

Yes, above the ring the piston-cylinder clearance is larger to allow gas to get down and behind the ring to help seal the ring against the cylinder wall. (FYI, the "rings" are cast-iron, not "O-rings" which would be rubber). this is a great looking engine (that I too have bought the plans for), let us know how your progress goes !!!

 

[scooby]

thanks, what got me wondering about it was where the drawing says the 3 ring grooves are .041" wide x .043 deep.
Figured all the ring grooves would be all starting at the same diameter b/c of their equal depth