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Wednesday, May 25, 2011
Testing hydraulic valve lifters
Hydraulic valve-lifters are tested for their leak down rate. A good lifter will leak down slowly but, if it’s plunger is sticking, the leak down rate will be too slow. Its plunger is worn, or the check valve is leaking, then the leak-down rate will be too fast. The tester (figure 3.25) consists of a base with vertical standard carrying a ram. It has a cup with test fluid. The ram is operated by the weight on the end of an arm. A scale and pointer indicate movement of the plunger. A watch is used for timing.
1.Place the lifter in the tester cup and cover with fluid. Either a special light oil or distillate is
2.Place the steel ball in the push-rod cup under the end of arm.
3.Work the plunger up and down with the weight until the air is bled from the lifter and it is full
4.Adjust the length of arm so that point there is in line with the top mark of the scale when the
ram is just touching the ball in the push-rod cup.
5.Raise the lever and let the weight and ram force the plunger down.
6.Measured the time that the pointer takes to move across the scale. This is the leak-down
As an example, a used lifter must take at least 5 seconds, but not more than 60 seconds to leak-down and a new lifter should take at least 10 seconds but not more than 60 seconds. A Doubtful lifter should be tested three or four times. If a lifter does not test within specifications it should be discarded and replaced with a new one.
Hydraulic lash adjusters
Some hydraulic lash adjusters for OHC engines can be tested in a similar manner to that described for hydraulic valve lifters. Generally, hydraulic lash adjusters can not be dismantled, but they can be bled to remove air. This also provides limited cleaning.
A faulty lash adjuster will produce noise with the engine idling at normal operating temperature. Some noise is not unusual when the engine is cold and has been standing, because the plunger of that adjuster could have leaked down.
Hydraulic lash adjusters can be bled of air by working them in a container of distillate. Clean distillate must be used. To prevent contamination, the outside of the adjuster should be cleaned before it is a immersed for bleeding.
·If a lash adjuster is still noisy after bleeding, it will have to be renewed.
Valve refacers and refacing
Fig 3.26 (a)
Valve refacers consists basically of two grinding wheels and a work ahead which holds and rotates the valve (figure 3.26). Valve refacers are used to restore valves by producing a final ground valve face. This must be at the correct angle and concentric the valve-stem.
The main grinding wheel is mounted on a spindle and driven at high speed by an electric motor. The wheel must be well balanced to prevent vibration that would cause chatter marks when grinding the valve face.
The face of the grinding wheel is dressed occasionally to keep it flat. A dressing tool that contains small industrial diamond is used. The wheel is given only a light dressing as this will produce a fine surface on the face of grinding wheel. Dressed correctly, grinding wheel will produce a smoothly ground valve face.
Fig 3.26 (b)
The workhead is shown in figure 3.26 (b). This holds the valve by gripping it in a collet. The valve must be correctly centered in the workhead. Any error will be producing a valve with the face eccentric to the stem.
The workhead has a degree scale on its base so that the valve-face can be set and the correct angle to the grinding wheel. When the machine is being used, the valve rotates slowly against the face of the grinding wheel.
There are two hand operating controls:
1.A hand wheel that operates a feed screw to move the grinding wheel forwards and backwards.
2.A hand lever that moves the face of the valve across the face of the grinding wheel.
The valve is ground by using the hand wheel to bring the grinding wheel up against the valve-face and then using the lever to move the valve slowly across the face of the grinding wheel.
To produce a fine finish, a light feed is used And the valve is moved backwards and forwards across the face of the wheel. For best results, valve is kept against the face of the wheel during grinding and not to run off its of the wheel.
A small pump supplies coolant from a tank in the base of the machine coolant is directed to the face of the wheel where it keeps the valve cool and helps to produce a fine finish.
·The valve is ground just enough to produce a smooth face. If the margin becomes too thin, the valve should be scrapped.
Fig 3.26 (c)
Valve tip grinder
A cupped grinding wheel is fitted at the tail end of the machine. This is used with an attachment as shown in figure 3.26 (c) to grind to grind the tip of the stem flat. The valve is clamped in a v-support and micrometer fitting is used to adjust tip of the valve against the grinding wheel. The attachment with valve is swung backwards and forwards across the grinding wheel. The micrometer fitting enables the amount of metal being removed to be measured.
Rocker arm grinder
An attachment can be used to grind the worn ends of rocker arms as shown in figure 3.26 (d). The rocker arm is mounted on an attachment that moves its end across the cupped grinding wheel. An adjustment enables the rocker arm to be set so that it will be ground to the right shape. This is referred to as radius grinding of the rocker arm.