NISSAN VALVETRAIN GEOMETRY
The Nissan S.O.H.C. engines have
a complicated valve geometry. If standard valve train geometry is not
maintained when modifying the engine, performance can be less than satisfactory
and in severe cases, damage to the valve train may occur. The dimensions in the
valve train likely to cause serious changes in geometry are: valve stem length
(top of stem to spring seat area), base circle diameter of the camshaft and
changes in the lift measured at the valve. Any of these dimensional changes can
be corrected by changing the thickness of the valve rocker guide located in the
top of the valve spring retainer.
When a valve job is performed, we
recommend the valve stem be shortened sufficiently to restore standard valve
stem dimensions. It is then a simple matter to correct the geometry by
installing the recommended thickness valve rocker guide.
The proper thickness valve rocker guide for the above
listed cam is:
| |
|
Set of 8
|
Set of 12
|
268N
|
.117 (Stock)
|
E911523
|
E911522
|
280N
|
.140
|
E911513
|
E911524
|
288N
|
.171
|
E911533
|
E911532
|
298N
|
.171
|
E911533
|
E911532
|
310N
|
.207
|
E911543
|
E911542
|
The formula used to arrive at these figures is:
To the standard valve
rocker guide thickness (.117) add ½ decrease in camshaft base circle diameter
and ½ the increase in lift at the valve (to compute valve lift, multiply cam
lift by 1.493) the sum is the thickness of the valve rocker guide that should
be used.
If non-standard valve
stem length is used, any added length should be subtracted from the valve
rocker guide thickness and any loss of length should be added.
The tolerance should not exceed +/-.010
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