Cam timing change when tightening camshaft bolt and other question

[Sam1905]

Trying to set my timing and am not having issues with the left side (has a cam with the 12mm bolt).

When I set my timing at 0.040 at TDC on the right, and then tighten the large 46mm nut I cannot keep the value constant.

I am essentially trying to keep both the torque wrench and extension on the P202 tool balanced to react to any dial changes. No matter how I try I always seem to end up at around 0.025 - 0.030...

Any hints?
One other question - when setting timing I follow Wayne's book. I rotate to hit my 0.040, pull out the pin advance the crank a few degrees to TDC and repin. What do i do when the 0.040 is a few degrees PAST TDC? Rotate CCW a few degrees, rotate a little less than 360 or a little less than 720? (Last seems right to me)

Thanks
Sam

[ertech]

I used a pic tool that I put through the hole where the pin goes and try to pry it in the direction I need.
Hope his is clear

[Sam1905]

I may have just got it.

I (for the tenth time or so) corrected for the change I usually see when Torquing (about 0.010) and set the lift at TDC at 0.030. Hey presto it actually ended up at 0.040 when done.....

[Flat6pac]

no need to comment them..but I was thinking
Bruce

[Sam1905]

Bruce - what were you thinking?

[Flat6pac]

I slightly advance the cam (CCW) to get the pin in where I want it but realize you have to load tension on the pin by turning the cam clockwise to get the final number.
Bruce

[DWit]

Folks,

Because I had nothing better to do a while ago, I measured the impact in cam timing due to "slop" in the timing pin. I have always used a degree wheel to measure cam lobe centers, so I don't know about how this correlates to the Porsche way of measuring lift at overlap. But the side-to-side clearance of the pin only changed the lobe centers less than 1 degree. Admittedly I didn't put this to an actual dyno test, but I know that circle track guys will alter their cam timing as much as 8 degrees to change the power peak by less than 1000 RPM. My guess is that 1 degree of cam timing would be challenging to measure on the dyno, have no impact on your lap times, and be absolutely impossible to feel on the street.

Dave

[Flat6pac]

Yes, there is some variable but if you're trying to match the spec for the build and you're there, do the spec as close as you can and take the slop you know exists and remove it.
Bruce

[DWit]

The point I was trying to make is that (it seems to me based on the threads I have read here) a lot of people unnecessarily worry about their cam timing. It's hard to get it really wrong.

On the other hand most people don't pay enough attention to piston-to-head clearance in order to get the optimum squish/quench clearance to mitigate detonation. This is extremely important in a race motor, but not unimportant in a street motor.

Dave

[Sam1905]

Thanks all.

I wondered about the impact and the data above helps with understanding sensitivity..

My greatest concern at the end of the day is that the 'in spec' value is 0.9 mm -1.1 mm and at 0.010 out of spec I was at either (both throughout the day) 0.762 mm or 1.27 mm. Just did not seem right to leave one side 'out of spec' even though it related to minimal crank misalignment from TDC

Thanks
Sam

[cgarr]

Something we were playing with was variable cam timing on the fly using a upper and lower tensioner which would shorten and lengthen the pull of the chain to advance and retard the cams. Similar to the 1.8 turbo vw motor.

[cmcfaul]

As the chain gets longer over time does the cam timing advance or retard?

Chris

73 911 E

[Flat6pac]

It would retard, thats why I try to set to high spec.
Bruce