Originally Posted by wsmurdoch
Tell me, what am I changing when I flatten the piston rings? Am I making the ring wider, that is increasing the width of the ring thus making the outside diameter greater and the inside diameter smaller? Or, am I making the piston ring longer so that the gap disappears thus making the piston ring bigger in diameter?
Do you have any pointers or technique? I think a re-rebuild is in my future.
You are changing the OD (outside diameter) of the Delrin rings so they fit tight against the inside of the brass cylinder.
The steps I use:
1. Gently tap one side (the flat surface) of both rings to expand them slightly.
And by slightly, I estimated a millimeter, but this measurment will vary with each head
. I used a medium weight ball peen hammer with smooth face and placed the ring on a smooth metal dock
cleat. I don't recommend using a framing hammer (too heavy) or a hammer with any sort of pattern on the face. Don't place the ring on wood (too soft) or concrete (too rough.)
2. Place both rings on the piston and insert the piston and rings into the cylinder.
I used a thin, sharp blade to coax the rings into the cylinder being careful to not cut the rings.
3. Check for fit.
Move the piston up and down the cylinder with your fingers. Does the piston slide easily? (Rings are still too small.) Can't move the piston up and down? (Rings are now too large.)
4. Repeat step two until the rings fit
really tight, but you can still (just barely) move the piston up and down in the cylinder.
5. Remove the piston and rings and lubricate the rings with marine grease.
6. Reinstall the rings and piston inside the cylinder.
The specs for a newly built head
call for .001" of clearance between the OD of the rings and the ID of the cylinder - a really, really tight fit - but most people don't carry a micrometer onboard. And the plastic rings are a challenge to measure accurately since they are flexible.
When we rebuild
the head again in 6-12 months, we'll take pictures and post a complete set of color work instructions on the forum.
Let me know if you have any more questions - happy to help. (We are headed into the Sea of Cortez
in three days and will be out of internet
range for quite some time.)