MikeFleming
05-08-2013, 07:30 PM
A short description on what is involved in degreeing a cam. This is the same process for any valve-piston engine, only the specific tools involved in the measuring change.
First one needs a pointer of some material - I bend up a coat hangar wire and use one of the water pump bolt holes on the front of the block to secure it. I also used a 1" hex stock extension to mount the degree wheel away from the crank, with one end threaded into the crank snout (same thread as the front pulley bolt) and the other end with a bolt hole to mount the center of the degree wheel. The hex part makes it easy to rotate the crank using a spanner (open-end wrench in American).
4148
Next are light weight valve springs. Not required to check the cam positioning (degreeing) but required for assembling a new engine to check valve to piston clearance.
4153
Paper pad & pen to take notes.
You will need at least one rocker arm of the same type that will be used with this cam and a solid, adjustable stud to use in place of a lash adjuster. Adjust the lash to zero before starting the measurements.
I mark the flywheel with TDC and 30 BTDC for both cylinders 1/4 and 2/3. There will be times when the degree wheel is NOT in place and you will need to know where exact TDC is (for each cylinder).
4149
4150
Mark the paper with degrees values from 0 - 720 in 10 degree steps (close enough for what we're doing here). if you're mapping a cam lobe profile, do it every five degrees.
For degreeing a cam, we only need to measure one cylinder (assuming we trust the cam grinder to position each lobe set exactly 90 degrees apart!) . Install the head onto the engine using an already compressed head gasket of the kind you will assemble the engine with. Then install the assorted cam belt sprockets, tensioners, guides, etc. Since it's already compressed, we don't need to torque the head down or use all the bolts. four will suffice.
Bring the crank around to TDC compression (both valves closed) for the cylinder we're measuring (number one for now). Set the dial indicator onto the retainer so the indicator is perfectly (as close as possible) parallel with the centerline of valve movement - and away from where it can be hit by the rocker or cam lobe. Zero the indicator.
4151
4152
Rotate the crank in ten degree increments and note the dial indicator value. Write it down. Another ten degrees, notate. Lather, rinse, repeat. Keep going until the value read zero for 3 measurements in a row (30 degrees). Repeat whole process for the other valve, same cylinder.
4154
Optional when building a new engine: When the piston is near TDC on the overlap area, say 30 degrees before, push the light spring-equipped retainer down to see how much clearance there is before the valve touches the piston (with no valve stem seal installed) . Repeat this every five degrees until 30 degrees ATDC. You want a MINIMUM clearance between the valve and piston of 0.080". Note any values less than this - something will need to be changed or machined.
When you have all the measurements, enter the values into Excel or plot it out on graph paper. You will end up with something like this (your lift values may vary considerably!):
4155
Note the yellow vertical line. That is where TDC lined up on the first run. The blue vertical line indicates what is referred to as the "split overlap" point, where both vales are open the same amount. In the example the distance in crank degrees, between TDC and the split overlap point came to 11 [crank] degrees. So I advanced the cam sprocket 5 degrees to bring the split overlap up to TDC. Remember that cam degrees are HALF of crank degrees.
First one needs a pointer of some material - I bend up a coat hangar wire and use one of the water pump bolt holes on the front of the block to secure it. I also used a 1" hex stock extension to mount the degree wheel away from the crank, with one end threaded into the crank snout (same thread as the front pulley bolt) and the other end with a bolt hole to mount the center of the degree wheel. The hex part makes it easy to rotate the crank using a spanner (open-end wrench in American).
4148
Next are light weight valve springs. Not required to check the cam positioning (degreeing) but required for assembling a new engine to check valve to piston clearance.
4153
Paper pad & pen to take notes.
You will need at least one rocker arm of the same type that will be used with this cam and a solid, adjustable stud to use in place of a lash adjuster. Adjust the lash to zero before starting the measurements.
I mark the flywheel with TDC and 30 BTDC for both cylinders 1/4 and 2/3. There will be times when the degree wheel is NOT in place and you will need to know where exact TDC is (for each cylinder).
4149
4150
Mark the paper with degrees values from 0 - 720 in 10 degree steps (close enough for what we're doing here). if you're mapping a cam lobe profile, do it every five degrees.
For degreeing a cam, we only need to measure one cylinder (assuming we trust the cam grinder to position each lobe set exactly 90 degrees apart!) . Install the head onto the engine using an already compressed head gasket of the kind you will assemble the engine with. Then install the assorted cam belt sprockets, tensioners, guides, etc. Since it's already compressed, we don't need to torque the head down or use all the bolts. four will suffice.
Bring the crank around to TDC compression (both valves closed) for the cylinder we're measuring (number one for now). Set the dial indicator onto the retainer so the indicator is perfectly (as close as possible) parallel with the centerline of valve movement - and away from where it can be hit by the rocker or cam lobe. Zero the indicator.
4151
4152
Rotate the crank in ten degree increments and note the dial indicator value. Write it down. Another ten degrees, notate. Lather, rinse, repeat. Keep going until the value read zero for 3 measurements in a row (30 degrees). Repeat whole process for the other valve, same cylinder.
4154
Optional when building a new engine: When the piston is near TDC on the overlap area, say 30 degrees before, push the light spring-equipped retainer down to see how much clearance there is before the valve touches the piston (with no valve stem seal installed) . Repeat this every five degrees until 30 degrees ATDC. You want a MINIMUM clearance between the valve and piston of 0.080". Note any values less than this - something will need to be changed or machined.
When you have all the measurements, enter the values into Excel or plot it out on graph paper. You will end up with something like this (your lift values may vary considerably!):
4155
Note the yellow vertical line. That is where TDC lined up on the first run. The blue vertical line indicates what is referred to as the "split overlap" point, where both vales are open the same amount. In the example the distance in crank degrees, between TDC and the split overlap point came to 11 [crank] degrees. So I advanced the cam sprocket 5 degrees to bring the split overlap up to TDC. Remember that cam degrees are HALF of crank degrees.