Yamaha XV1600A1999 Service Manual page 15

Oil-pressure-operated valve lifters
Since the oil-pressure-operated valve-lifting mechanism maintains a valve clearance of zero, periodic
valve clearance adjustments are unnecessary.
The advantages of this system as compared to conventional techniques include the following: me-
chanical noise is reduced, the camshaft action on the valves remains unaffected by engine speed or
temperature, and the valve timing is kept stable.
The oil-pressure-operated valve-lifting system functions as follows:
1. As the camshaft rotates, the valve lifter is pushed up by the passing cam lobe.
2. Since the check valve 4 prevents the engine oil contained inside the high-pressure chamber from
escaping, the plunger 1 moves up along with the valve lifter body 8 and pushes up the push rods,
causing the valve to be lifted.
3. As the camshaft continues to rotate, the valve lifter moves back down to its original position, where it
remains while the cam heel passes.
When a positive valve clearance is caused by either heat expansion of the cylinder head or engine oil
leaking from the valve lifter during stage 2, the plunger, which no longer receives pressure from the
push rod, is pushed up by the plunger spring 7 . As a result, the valve clearance is zeroed and engine
oil is allowed to return to the high-pressure chamber from the reservoir 2 through the check valve 4 .
When, on the contrary, a negative valve clearance occurs (this is the case when the cam heel is pass-
ing the valve lifter, but the rocker arm, pushed by the push rods, is lifting the valve), the plunger 1
continues to receive pressure from the valve push rod. As engine oil contained inside the high-pres-
sure chamber leaks from the gaps between the valve lifter body 8 and the plunger 1 as well as be-
tween the valve lifter body 8 and the check valve 4 , the plunger 1 moves down and the valve clear-
ance is zeroed.
FEATURES
1 Plunger
2 Oil reservoir
3 Check valve spring
4 Check valve
5 Spring retainer
6 High-pressure chamber
7 Plunger spring
8 Valve lifter body
9 Oil supply inlet
10 Push rod cup
Plunger retaining clip
11
12 Valve push rod
1-5
GEN
INFO