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JohnJL's Avatar
 
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Right side cam timing

I am following "the book"s directions for high-lift, high-duration cam timing starting on page 167. I have the left side timed and set at 2.3mm at .1mm overlapping tdc.

This is on an 83 sc with DR20 cams.

The book seems a bit vague on the crankshart-to-camshaft orientation, and where in the cycle to take measurements on the #4 cylinder's valve keepers...

1. The book says to set the dial gauge with 10mm of preload. THis doesn't seem possible with any combination of the short or long gauge extensions and the z-block.

2. The directions are unclear about whether to take the measurements on Cyl4 when Cyl1 is just opening, or when?

3. I see the references to having the "930" marking on the cam ends facing down to start with. However, I am not clear about the next section referring to the measurements.


Could someone pls point me in the direction or spell out a bit more clearly the procedure for the right-side cam timing?


thanks
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Old 11-11-2005, 07:21 PM
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PS. I did see this...anyone care to spoonfeed me the right-side directions as the left are spelled out in the book?

Cam Timing Confusion
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1978 911 3.0 Lichtbau toy "Gretchen"
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Old 11-11-2005, 11:57 PM
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I remember my own confusion the first time I did cam timing. The factory manual instructions for the right side were basically "rinse and repeat" which wasn't very helpful at the time.
Here are some data points that might help, some of them are probably obvious but I'll mention them in the interest of completeness:
A. With the distributor pointing at #1 and the pulley at the TDC mark; the writing on the end of both cams will be right-side-up. The intake valve on #1 will be closed and the intake valve on #4 will just be starting to open. The amount that it should be open is the number specified for the particular cam you are using (2.3mm say).

B. When you turn the crank one revolution from "A" the distrubtor will point at #4 and the writing on end of both cams will be upside down. The intake valve on the #1 will just be starting to open and the intake valve on #4 will be closed. The amount that it should be open is the number specified for the particular cam you are using.

C. When timing the left side cam you start at "A" and compress the dial indicator so when the valve opens the dial indicator can extend as the valve opens. If you are using a digital indicator and zero it at this point, the value will go negative as the valve opens.

D. When timing the right side cam you start at "B" and compress the dial indicator so when the valve opens the dial indicator can extend as the valve opens. If you are using a digital indicator and zero it at this point, the value will go negative as the valve opens.

-Chris
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Last edited by ChrisBennet; 11-12-2005 at 05:06 PM..
Old 11-12-2005, 07:42 AM
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Maybe something in here might help:

http://members.rennlist.org/911pcars/camtiming-1.htm

Sherwood
Old 11-12-2005, 02:08 PM
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Thanks guys. Chris, thanks for all the detail.

I think your "C" and "D" both refer to timing the right side...is "C" for left cam and "D" for right cam?


thanks
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1978 911 3.0 Lichtbau toy "Gretchen"
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Old 11-12-2005, 03:37 PM
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Quote:
Originally posted by JohnJL
Thanks guys. Chris, thanks for all the detail.

I think your "C" and "D" both refer to timing the right side...is "C" for left cam and "D" for right cam?


thanks
"C" uses state "A" and "D" uses state "B". I edited my post to make the part you missed bold.
-Chris
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Old 11-12-2005, 04:16 PM
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But the first part of both "C" and "D" say "When timing the right side..." One of those should start with "When timing the left side..." right?
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1985 911 Cab - Wife's toy
1982 911 3.2 Indiash Rot Track Supercharged track toy
1978 911 3.0 Lichtbau toy "Gretchen"
1971 911 Targa S backroad toy
Old 11-12-2005, 04:42 PM
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Quote:
Originally posted by JohnJL
But the first part of both "C" and "D" say "When timing the right side..." One of those should start with "When timing the left side..." right?
Ah, had a blond moment there.
-Chris
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Old 11-12-2005, 05:05 PM
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I got it now, thanks a lot. Completed the timing, did piston-to-valve clearance measurements throughout the cycles, all back apart now and off to PR for twin-plugging in the morning...
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1982 911 3.2 Indiash Rot Track Supercharged track toy
1978 911 3.0 Lichtbau toy "Gretchen"
1971 911 Targa S backroad toy
Old 11-12-2005, 09:35 PM
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