View Single Post
  #2   IP:
Old 04-28-2017, 12:51 PM
lat 64's Avatar
lat 64 lat 64 is offline
Afourian MVP
Join Date: Oct 2008
Location: Fairbanks, Alaska
Posts: 1,964
Thanks: 38
Thanked 240 Times in 157 Posts
Hey, great document.
It should be a good example to others.

I ran through it fairly quickly and noticed you were not sure about piston measurements.
Pistons are not round at all, but often have complicated shapes to allow for different rates thermal expansion in hotter areas during running.

The only real critical measurement for determining piston wear is the widest dimension of the piston skirt. That is at the bottom of the skirt, 90-degrees from the wrist pin axis. This is where typical(normal) wear occurs most and clearance* is smallest. This area is the bearing surface when the piston is pushed down the cylinder. This skirt-size measurement, plus clearance, is what a machinist will use to determine the size of the cylinder when fitting new pistons in a newly-bored cylinder or determining acceptable wear in an "overhaul".
Sometimes measuring at the top of the same area will get you different measurements even on a new piston.

*piston-to-cylinder wall clearance, Measured by subtracting piston diameter from cylinder diameter.

Cheers and salutations,

Whiskeyjack a '68 Columbia 36 rebuilt A-4 with 2:1

"Since when is napping doing nothing?"
Reply With Quote
The Following 2 Users Say Thank You to lat 64 For This Useful Post:
Dave Neptune (04-30-2017), jcwright (04-30-2017)