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ring gap clocking

I clock the ring gaps on pistons using the SBC [small block chevy] clocking chart, rather than the Volvo chart. I do it that way because it has worked very well for me; and because the logic behind the gap locations makes sense.

Do the ring gaps stay where you clock them at?

Well...I hope not. Or, more precisely: they should not. The rings are supposed to rotate, to keep the ring grooves in the piston clean. Which is one of the functions of the crosshatch on the cylinder wall: to encourage a sufficient amount of ring rotation: as in 'some' rotation.

If the rings do not rotate at all, or nearly not at all, then the likelihood of a ring getting frozen in place increases. The rings need to be able to move in and out in its groove, as well as ever so slightly up and down in its groove. If it cannot move, it cannot seal properly. By being able to rotate, and being encouraged to rotate via the cross hatch, the ring can allow compression/combustion gases to flow around it in the groove, thereby keeping the build up of carbon at a minimum.

And remember: part of what makes the ring seal against the cylinder wall IS the pressure of the combustion gases that does get behind the ring and pushes it out against the wall. A slight amount to be sure. But, a very necessary and needed slight amount.

Do the rings rotate the same amount? as in: do the gaps maintain the clocked positions as they rotate? No. Most likely, they will not. The rotation will vary, and the gaps will move. That is the way it goes.

BUT, it is good to start out with the ring gaps clocked the same on all the pistons.

...that said; on to the description:

Here is a shiny new B21F piston....Mahle 1st OS.

This view is from the major-thrust side...AKA the oil filter side of the motor. The blue arrow is pointing in the direction of the front of the motor.

The top ring end gap is clocked on this side of the piston: the major-thrust side.

The second ring is clocked 180 degrees away...IE, the second ring gap is on the minor-thrust side of the piston.

The oil ring that is shown here is the Mahle one piece oil ring...IE, the spacer and the two scrapers are one piece instead of the common American three piece oil ring in which the spacer is separate from the two scraper rings.

If using the Mahle one piece oil ring, the end gap is clocked on this side of the piston.

If using the three piece oil ring, the end gap of the spacer is clocked on this side of the piston.

The two pink arrows are pointing to the two places to clock the end gaps of the scraper rings...IE, the three piece oil ring is clocked so that the gaps are 120 degrees apart; with the spacer end gap on the major-thrust side of the piston.

SIDENOTE: regarding ring gap clearances

I gap the rings wider than what Volvo recommends; especially for boosted use.

And I have reached the point that I gap the second ring as wide as, and even wider than I gap the top ring.

The general rule of thumb for ring gap is 0.004in of gap per inch of piston diameter. I go for at least 6 thou of gap per inch of piston diameter.

And contrary to the myth that wide ring gaps lead to excessive oil burning/oil consumption:

wide piston ring gaps have only a negligible effect on oil consumption, if even that.

Let me state it this way, using an extreme example to make my point:

I WOULD MUCH RATHER HAVE RING END GAPS THAT ARE 20 THOU TOO WIDE THAN RING END GAPS THAT ARE 1 THOU TOO NARROW!


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