I have re-bored my S3 3MB 2.25 Petrol Block to + 0.020 thou and am fitting a new set (4) of NOS +0.020 AE Hepolite over size pistons with new rings as supplied.


What is correct orientation for Top, 2nd and Oil control ring if front of engine is zero angle and camshaft is at 090 degrees (camshaft side is thrust face). Piston orientation appears to be undefined.

Q1. LR Green manual states: Position piston rings so that their gaps are staggered around the piston thrust face (camshaft side).
If 60 deg apart this would imply 1st, 2nd, Oil Rings at angles of 060, 120, 180 resp ie 1st and 2nd rings on thrust face, is this correct?

This seens to contradict what I've read elsewhere where ring gaps are arranged opposite to major thrust face 60 deg apart.

Q2. The rings are all marked +020 but only 2nd ring and oil control ring have TOP and +020 written on them with top ring marked +020 only.
Top ring and 2nd ring otherwise appear to be the same width & fit in either groove?

I can read the manual however the information sometines seems counter intuitive and needs expanding hence the question, can you advise?:fencing:.

Mingdiesel

space them so two compression rings sit on opposite sides to one side of gudgeon pin with oil control the other side of gudgeon pin ,20,180 ,340

Hi

Before someone asks,yes the oil hole on conrod is facing camshaft side but piston has no front orientation marking, only markings are: P25 PM15 020 ID 67.

Mingdiesel:attention:

pistons dont have offset pins or combustion chambers so it doesnt matter which way the fit, as long as you gap rings to their respective bore first

Thanks for quick reply.

jamesmartin said:

space them so two compression rings sit on opposite sides to one side of gudgeon pin with oil control the other side of gudgeon pin ,20,180 ,340

Click to expand...

If I understand you correctly you suggest the top ring at 020 (camshaft side), 2nd ring 180 (flywheel end), and oil control ring at other side of gudgeon pin from top ring ie other side to camshaft 340 deg.

I know some people suggest 120 degree spacing, why are gaps on thrust side? Later engines all seem to avoid ring gaps on thrust side, which would appear to make sense!


Mingdiesel

I have always gapped piston rings at 120 degrees it is to prevent any loss of compression by leaving an easy path for the compressed air to escape, I've never had any problems