Ring gaps are often a confusing
and misunderstood part of a rering job. There re MINIMUM
and MAXIMUM ring gap specifications which must be observed
for the best performance of a new ring set.
Minimum gap tolerances must be
observed in order to prevent the ring ends from butting
together as the ring expands when the engine approaches
operating temperature. Hastings recommends a MINIMUM
of .0035 gap per inch of cylinder diameter. Example:
4" (bore) x .0035 = .0 14 minimum gap.
Maximum ring gap is an important
part of ring performance in that too much gap results
in lost compression, power loss and ultimately poor
oil control. The following chart indicates the specifications
for compression ring gap as outlined by the SAE (Society
of Automotive Engineers) as standards for the automotive
piston ring manufacturers.
RING GAP CLEARANCE
An important fact to remember
is that the manufacturers rigidly adhere to these tolerances
and that the ring gaps are inspected in gauges accurate
to .0001" at the cylinder diameter the ring is
manufactured for. Any increase in the diameter of the
cylinder is being used in, over the designated size,
results in an increase of approximately .003" in
ring gap for each .001" increase in cylinder diameter.
In order to check ring gap, the
rings should be placed at the lowest possible part of
the cylinder (below ring travel area) as this is the
portion of the cylinder which is unworn and which the
ring is sized for. Checking ring gap in the worn portion
of the cylinder will show a gap increase in direct relation
to the amount of cylinder wear present. The illustration
on the following page shows the effect of cylinder wear
on ring gap.
This graphically illustrates
the effect on ring gap that cylinder wear has. You will
notice that the tapered cylinder has .012 wear at the
top portion of ring travel which increases the ring
gap .036. Therefore, it is entirely possible for the
ring to have .061 end gap in that portion of the cylinder
and be within recommended manufacturing tolerance.
For this reason, Hastings recommends
a MAXIMUM of .003" wear per inch of cylinder diameter,
not to exceed .012" in any case for successful
reringing. If a cylinder is worn in excess of this it
should be rebored and the proper oversize ring installed.
Checking ring gaps can give an approximation of cylinder
wear as well as keep you from installing wrong sized
rings for the application being rerung.
DIAGRAM BELOW SHOWS EFFECT OF.012
CYLINDER TAPER ON RING GAP IN FOUR-INCH BORE.
EFFECT OF .012 CYLINDER TAPER
ON RING GAP IN FOUR INCH BORE
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