Cam timing again.

[David]

I just set the cam timing on an SC engine for the first time using the method from Wayne's book. This involves setting the valve lift at .040" at the Z1 notch on the crank pulley. After years of using a degree wheel this seems less than ideal. If it wasn't for a stubburn engine mustache bar stud, I would throw on a degree wheel and check the lobe centers. I guess my question is: "Is this really an accurate way to set cam timing?"

[Type961]

Hi,
I also don't like this way to time cams and never use it.
I use lobe centers using a micrometer to time the cams using REAL TDC (also checked with micrometer). Real measured TDC and cam center often have a 2 to 6 degrees offset.
I think the lobe center for the SC is something like 102° ATDC, but you have to check it since my memory probably faults

Regards,
Luc.

[snowman]

If you check TDC first and verify the Z1 notch is where it is supposed to be, the method Porsche use is very accurate. If you set it on nominal it is well within one degree, at the max tolerance it is about 1.5 degrees or so off. Depends on the cam and timing spec a bit.

Lobe centers is almost always a better way to go, but there you need a degree wheel and have to do things right as well, but its generally worth the trouble. In general you are probably more likely to mess up though and should double check with the Porsche method, to make sure your didn't mess up radically. Thats unless you have enough experience you wouldn't be asking this question to begin with.

[David]

I removed the stud so I could put on the degree wheel (I don't see how anyone can get one out without an acetylene torch). I set the cam timing with the Porsche method, with 0.040" (1mm)valve lift at TDC. I also checked the lobe center with the degree wheel and found it to be 114 degrees. Porsche spec for the 78 SC is 116. Since I'm using a 7" degree wheel, I figure that's pretty accurate. Now I'm convinced that the Porsche method works and it's much faster.

I also found that there are several degrees of movement between the pinned cam and sprocket before the nut is tightened. If I didn't tighten the nut the exact same way with each adjustment, I didn't get repeatable readings.

Thanks to Bob aka RW7810 for his help.