- Measure ridge height
- Measuring Main Bearing Pins
- Measuring camshaft curvature
- Measuring axial bearing clearance
- Measuring Camshaft Sprocket Stroke
Measuring ridge height:
The camshaft cams can wear out due to age or lack of lubrication. The ridge height decreases as a result. Complaints that may occur with worn cams are:
- The fuel trims give a negative percentage: due to a shortage of air, the injection quantity is corrected (reduced);
- Reduced power: due to a shortage of air, the maximum torque can no longer be achieved. In the event that all cams are equally worn, the engine can run smoothly at idle;
- Irregular engine running: This is especially if only one or a few cams show wear and the others are still OK.
With the caliper we can determine the ridge height. A micrometer can also be used instead of a vernier caliper for higher accuracy. At one ridge we take two measurements to determine the ridge height, see the picture.
- A = diameter ground circle;
- B = total ridge height;
- C = actual ridge height / lift height.
The cam height (C) of the camshaft is the difference between size A and B.
The cam heights of the intake and exhaust camshafts are different. Cam heights on one camshaft must not differ from each other. We do have to deal with tolerances. The camshaft is only rejected when the measurement falls outside the tolerances.
The camshafts of a gasoline engine are measured. According to the factory data, the minimum ridge heights should be:
- Intake camshaft: 45,82 – 45,85 mm;
- Exhaust camshaft: 45,50 – 45,53 mm.
We take eight measurements and fill in the table below. In the table we see that the measured values are almost all higher than the minimum values. Only at cam 4 of the inlet camshaft we see a deviation: this cam is 1,03 mm lower than the minimum value. For this reason, the camshaft is rejected and must be replaced.
Measuring Main Bearing Pins:
Using a caliper or micrometer, we can measure the outer diameter of the main bearing journals. As with the ridge height, the minimum values can be found in the factory data and compared with the measured values.
Wear of the main bearing pins can occur after the bearing caps have been exchanged during previous disassembly and assembly. When two bearing caps are exchanged, or rotated 180 degrees, both the bearing caps and the camshaft wear where the space between the two parts is smallest.
If we measure a value that is too small for this measurement that deviates from the minimum value, there is a chance that oil loss will occur at this location: the oil flow can (too) easily pass this bearing, so that the flow along this bearing is greater than at the bearings at the end of the camshaft. As a result, the last cams lack lubrication and there is a good chance that the cams will wear out.
To measure camshaft curvature:
The camshaft curvature should be measured with a dial gauge on the center bearing section. When measuring with the dial indicator, we mount the dial indicator in a tripod and place the camshaft in holders in which we can rotate it. The pin of the dial indicator touches the back of the dial indicator; here we set a preload of at least 2 mm. When the camshaft moves, you can determine whether the camshaft is bent by the deflection of the pointer (from setting the preload to the maximum value at the cam height).
The curvature must be less than 0,02 mm on certain engines. The maximum allowable is 0,1 mm. When exceeding 0,1 mm, the camshaft must be replaced. Always refer to the factory specifications.
Measuring axial bearing clearance:
With a dial indicator we can measure the axial bearing play. For this, of course, the camshaft bearing caps must be tightened to the required torque.
The axial play of the camshaft in this example may be between 0,090 and 0,150 mm. So if we measure a clearance of 0,120 mm, this is OK.
Measuring camshaft sprocket stroke:
A motor with timing chain has a sprocket. When a blow occurs in the sprocket due to a defect, damage or assembly error, the timing chain will follow this movement with every rotation, resulting in increased wear or even breakage.
With again a dial indicator and tripod, the stroke of the sprocket can be measured. The pin of the dial gauge presses against the sprocket with a pretension, so that the pin follows every movement.
The chain wheel in this example should not exceed the stroke of 0,25 mm.