Web cam timing mystery: bad grind?

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Web cam timing mystery: bad grind?

Post by Crawdad » Mon Aug 28, 2017 5:42 pm

My numbers are way off from the cam card. This is a Web 86A.
Granted, this is my first time degreeing a cam. Am I missing something, or is this a bad cam?

The card reads:
IO 18 deg before TDC
IC 54 deg after BDC

EO 54 deg before BDC
EC 18 deg after TDC

I mounted a huge degree wheel on the crank, made a pointer, found TDC. In my first round of measurements I placed my dial indicator on a modified lifter, with the case halves assembled. The numbers didn't make sense. Maybe I didn't grind the end of my lifter tool perfectly square and it was rotating in its bore? In any case, I decided to eliminate that variable. I split the case and put my indicator directly on the cam lobes.

I will be using 1.4 ratio rockers. Therefore, I reasoned, the checking clearance of .050 lift at the valves corresponds to .050/1.4 = .036 lift at the cam.

After making sure I was getting solid, repeatable measurements, here is what I have. These numbers are at .036 lift at the cam.

IO 23 deg before TDC
IC 38 deg after BDC

EO 46 deg before BDC
EC 16 deg after TDC

If it was simply a matter of the cam gear being mis-indexed, the numbers would be consistently advanced or retarded. But they are all over the map. The intake closing event is 16 degrees off! The lobe center on the #1 intake lobe works out to 97.5 degrees; it is supposed to be 108 degrees.

Is this a bad cam?

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Re: Web cam timing mystery: bad grind?

Post by 66brm » Tue Aug 29, 2017 12:09 am

I don't think it's the cam, 0.050 checking lift is just that, you don't involve rockers at all

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