Cylinder wall honing surface finish & ring gap
- Thread starter jpowel29
- Start date
Expansion from heat. The skirts are furthur away from the heat source (combustion) than the tops and would expand slower (or am I off base).
Ovaling the piston skirt keeps the clearances tight in the rocking direction yet lets things be a little looser across the pin where the tight tolerances are not needed. The skirt is what primarily keeps the piston aligned in the bore.
The top is always undersize of the skirt and is round to match the bore. This is the part of the piston that expands with the heat of the chamber the most.
There is more to the geometry of the piston, but that is the basics of it.
The top is always undersize of the skirt and is round to match the bore. This is the part of the piston that expands with the heat of the chamber the most.
There is more to the geometry of the piston, but that is the basics of it.
No gas ports.
Especially on the cast pistons with the keystone rings, I don't think they are needed.
But they are not recommended on a diesels or long run engines anyway. They clog up too easily.
Especially on the cast pistons with the keystone rings, I don't think they are needed.
But they are not recommended on a diesels or long run engines anyway. They clog up too easily.
sorry to bump this up but just built my engine with .020 over mahle pistons 16:1 comp and i followed the mahle instructions and went .004 per inch of bore and added a little so i ended up with .018 gap on the top and bottom rings im aiming for around 700-800hp at the wheels will these ring gaps be ok or should i pull the rods and pistons and re-gap as its only a short block at the moment (complete with sump etc just no heads fitted) if so what ring gap should i aim for 
Last edited:
Are you referring to second ring as bottom or the oil ring that us at the bottom? 18 on the top for a street engine would be OK if not ran hard. I probably would run it a little looser. Second ring should be 4 to 5 thousandths looser than top ring.anyone
Do you just post in threads to regurgitate what you've read in a book? What does that have to do with the guys question?
I was just adding to whom had mentioned the cam-ground shapes and mentioning they thought it was new technology.
Rings and cylinder wall hone finish should be done per-the-ring package PA, just because you may grab a ring or two, you must know what type of ring you are using before you decide on the finish, which has obviously been mentioned. If you would like to go deeper, you must look at the cylinder wall materials too.
Your Rockwell hardness of the cylinder wall will also have a hand in your rings and hone finish.
Rings and cylinder wall hone finish should be done per-the-ring package PA, just because you may grab a ring or two, you must know what type of ring you are using before you decide on the finish, which has obviously been mentioned. If you would like to go deeper, you must look at the cylinder wall materials too.
Your Rockwell hardness of the cylinder wall will also have a hand in your rings and hone finish.