AKA: How to get familiar with dial indicators and your 8V valvetrain so you can someday "degree" your cam properly.
Lets say you want to measure your cam geometry.
One of the things required is a way to set valve lash (gap between roller follower wheel and cam lobe) to zero.
If the lash is less than it should be, the valve will be "artificially" forced open when it should not be.
If the lash is larger than it should be, the valve wont open as far as it should.
"It should be" is generally zero for measuring a cam. If you actually were replacing the hydraulic lifters with solid ones, you would not set them to zero, but something more like 0.005" to 0.020".
The reason we set them to zero when measuring the cam, is because otherwise any random lash could be picked out and everyone would get different measurements of the cam. Zero is the logical choice because zero is what the ideal operating lash is and what the hydraulic lifters try to maintain in operation.
So, you could just buy an adjustable lifter and be done with it. They are little deals that let you adjust them while installed and measure the valve lash until its what you want, as described above.
But lets say you dont wan't to buy one. And, more importantly, lets say you want to mess around with your 8V valvetrain on a head you have laying around to get familiar with dial indicators and all the junk under the valve cover. This is a good exercise.
The goal here is to create a "solid lifter" using our hydraulic lifter (non destructively). If you notice, the hydraulic lifter plunger can be pushed into its body quite easily once its been drained of oil (i.e. engine off for a long time). You may need to push down on it for a while to completely drain it.
So, how do we make it into a solid one? And on top of that, how do we set it to the right length so that our valve lash is zero?
The short story: We'll add shims underneath it until when its fully compressed by the cam, its exactly the right length it needs to be to set valve lash to zero.
Things you'll need:
Flat table
Dial indicator
Extended very thin tip for dial indicator (you can make one somehow. Make sure its straight and secure)
Dial indicator magnetic holder with something heavy to stabilize it.
Two cam bearing caps with bolts
Cam
Head with all followers removed except one (the one you will measure)
Pulley attached to cam (makes things a little easier)
STEP 1: Measure the lifter.
Take it out and measure (using 0.001" accurate calipers):
-Uncompressed lifter length. (end to end without compressing it)
-Fully compressed lifter length. (put it in a vise and gently tighten it until it stops. Then measure vice jaw opening)
STEP 2: Measure lifter change in length when there is zero lash.
Install lifter, follower, and cam into head. Do not install bearing caps.
Place dial indicator tip so its touching top of lifter plunger through little hole in follower. Center it so it doesn't touch the sides.
Rotate the cam so the base circle is touching the follower.
Push down hard on the cam to compress the whole assembly and then zero the indicator.
VERY CAREFULLY let go of the cam, then lift the cam gently so its not touching the follower at all.
The dial indicator reading is how much the lifter is depressed at zero lash. We'll call this "zero lash change".
(That is zero lash because the lifter spring is making the follower just touch the cam lobe without pushing the valve open because its too weak)
STEP 3: Determine required shim/spacer thickness.
The required shim/spacer thickness is the uncompressed lifter length minus the zero lash change, minus the fully compressed length.
So in my case:
Uncompressed lifter length: 2.047"
Zero lash change: 0.094"
Fully compressed length: 1.854"
Required spacer = 2.047 - 0.094 - 1.854 = 0.099"
STEP 4: Install shim/spacer
Remove the lifter and follower.
Find a washer(s) or combination of metal things and measure them until you get 0.099" or within 2 or 3 thou. I got something close with two washers.
Drop the washers into the lifter hole in the head.
Then fully seat the lifter into the hole.
STEP 5: Verify
Reinstall the follower, lifter, and cam, but not the bearing caps.
Place the dial indicator again to measure the lifter top.
With the cam not touching the follower, zero the indicator.
Install the cam and rotate so the base circle is again touching the follower.
Fully install the bearing caps.
The dial indicator reading should show your spacer thickness + the 0 lash change.
So for me,
The dial indicator showed 0.195"
My spacer was 0.101"
My zero lash change was 0.094"
So the expected reading would be 0.195".
However, this means that I overshot the target lash by 0.002"
I think thats irrelevant. First of all, this whole process does not need to be more accurate than a few thou. If it did, lunati and crane, etc.. would not be okay with just eyeballing the dial indicator angle in their instructions for degreeing a cam. Second of all, the error at the lifter gets divided by the follower even further. So a 0.002" error at the lifter would probably end up being around 0.001" at the valve. Third, there is a gap between the cam journal and its head bearing surface which is not there during operation, but cams are degreed with that gap present.
One more to verify the lash is zero or very near zero is to try and compress the lifter while the cam is on the base circle. The lifter should not compress at all. That test wont tell you if the lifter is extended too far but it will tell you if its not extended far enough.
Sources of error:
Dial indicator plunger not collinear with lifter axis. (eye ball it as good as you can)
Dial indicator mount moving around. (mag base mounts and arms are floppy as heck. dont bump them)
Shim thickness not zero lash amount.
Other stuff maybe I forgot.
The following pictures are not meant as instructions, just to show the setup. You must read these instructions fully and understand whats going on in order to do this. And thats the point of this little exercise, besides providing a free solid lifter for degreeing/measuring a cam!
If this procedure doesnt make sense let me know and I'll correct or delete it. Dont want to spread lies from the filthy government!!!
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Originally Posted by johnl
