HOW TO DIAL IN A CAMSHAFT USING 0.050" TIMING FIGURES.
The 0.050" timing figures are the most accurate way to dial in a camshaft. The quietening ramps which begin the acceleration process slowly on opening and lower the valve on to the seat gently make it difficult to take consistent and reliable readings at low lift. The 0.050" figure was chosen as the industry standard because it is higher than the quietening ramps of all cam profiles.
1. Attach degree wheel to the crankshaft and fix a pointer to a suitable position on the block.
Set the degree wheel to accurately indicate when the piston is at top dead centre.
2. Position a dial indicator on the valve lifter or the pushrod. Make sure the spindle of the indicator is aligned with the lifter not skewed at an angle.
3. Position the indicator so it is just touching the lifter and set the dial to zero on the back of the cam lobe. Note the position of the small needle.
4. Rotate the engine until the lifter has risen 0.050"
5. Read the position from the degree wheel noting that most cams with 0.050" duration less than 220 degrees will have a negative figure for inlet opening and exhaust closing.
6. Rotate the engine so that the lifter travels past full lift and begins to fall. Continue to turn until the indicator returns to the zero position with the small needle at the correct position.
7. Take note of the closing reading.
8. Move the indicator to the exhaust lobe and repeat the process.
9. Add the opening and closing figures together, add 180 and the result should be close to the duration. This will verify the readings as correct.
POINTS TO WATCH
* Check the dial indicator is imperial measurement not metric.
* Always take readings with engine turning in the direction of rotation. It is OK to turn the engine backwards but go past the measuring point and turn in the direction of rotation to the position required.
* Negative figures are important. If the inlet opens 5 degrees after TDC rather than before the reading should be minus 5. The reason for this is to obtain the correct duration figures as follows. Duration = open + close + 180.
* Record the lift at TDC on the inlet lobe as using this figure to set up cam in future rebuilds will save a lot of time.
When first setting up a cam in “V” engines check lobe lift on opposite bank to check indexing of camshaft.
Checking Cam Position using lift at TDC method.
1. Find top dead centre on the number 1 cylinder using a dial indicator. Mark this position with a pointer mounted on the flywheel or degree wheel bolted onto crankshaft.
2. After setting the dial indicator to zero on the back of the cam inlet lobe, rotate the crank until the pointer indicates the piston has reached top dead centre.
3. Compare dial indicator reading to the figure shown for inlet lobe lift at T.D.C. on the cam data card supplied with the new cam. The figure shown on the cam data is a minimum and may be up to .005" more.
TO FIND AMOUNT CAM IS OUT
1. Fit degree wheel of harmonic balancer with timing marks. ( Check TDC position)
2. Rotate engine until “Inlet lobe lift at T.D.C. figure” is indicator on dial gauge
3. Read cam advance or retard off degree wheel or balancer.
4. Correct by the amount indicated.