Cam timing tolerances: how close is close enough?

RD is on to something. If you read my article again I tell you how to find lobe centerline. It is not a nebulous point. Lobe centerline is an old method that works 100% of the time perfectly on symetrical cam lobes. The opening method also works 100% of the time too. I'm thankful that more diy'ers are using either method of timing lobe centerline or opening methods. My writing leaves little to be desired. Sometimes reading what others have written helps the understanding. Here are a couple articles on chevys but they apply to ferraris just the same.

http://www.webcamshafts.com/pages/degreeing.html

http://www.carcraft.com/howto/116_0701_how_to_degree_a_camshaft/index.html

http://www.lunatipower.com/Tech/Cams/HowToDegreeACam.aspx

 

Whilst not doubting the necessity of doing this, I do have 2 questions:

1)
Thousands of these cams were made. How is it possible that there is a spread within a machiened part making the procedure needed, as opposed a zero-mark that is accurate?
2)
Instead of using a difficult, wanting set-up with a gauge, why not simply use the points where the shim can no longer be rotated under the lobe? Just a degree-wheel should suffice?

 

Assuming the marks are accurate, it would still be difficult to line them up accurately enough to meet the spec. 1 degree of timing at the crank, is 1/2 degree of rotation at the cam. That is roughly .005" inches of movement of the mark on cams surface. I know I could not eyeball that. You could probably get within 5 degrees pretty consistantly, but probably not within spec.

About rotating the shims. I tried that, and it did line up pretty well. I found that you can rotate the shim when it is still slightly depressed by the cam, so feel would play into it a bit. When I did it, the point I picked by feel vs by indicator was different by about 2 to 4 degrees depending.

 

Where can I get that special mirror? I have not seen it on the Snap-On truck or McMaster Carr......;-)

Refreshing to see someone actually degreeing their cams.....

 

I liked it a lot, too!

Desperate times call for desperate measures!

 

I was having enough trouble getting repeatability with the dial indicator the last time I did this, so ended up going by feel. I got very repeatable results.

It helped to degrease the cam lobe & top of the shim I was using to get the 0.5mm clearance and just smear a couple of drops of a very light machine oil on them. With the thin oil, the beginning/absence of drag was much more detectable.

 

That is why it is the factory method. It is easy, repeatable and requires no special equipment.

 

I suspect that this works more precise with the clearance widened to 0,5mm, but can it be done accurately with the standard working clearance?

 

It has to be set at .5mm. That is one reason I use a dial indicator out of the car. I don't have to keep readjusting valves.

 

Setting up the dial probably takes just as long as swapping a shim, but I see your point.