Timing curiosity/observation

[euro911sc]

Just timed my cams last week on a stock '83 3.0. I read that I should watch the dial when I final torque the cam sprocket bolt and do my best not to let it move. So I did that and I could not keep it from moving, but did the best I could. Then I thought about it at lunch the next day... Why does it matter? The little pin is in and the woodruf key is there so as long as the chain stays tight nothing should move out of time even if the whole thing spins. Did I miss something here?

Also, I found it relatively easy to follow Wayne's instructions. The only tough part was getting the pulley to Z1 on the right side whilst not moving the cam. I ended up putting the pulley on Z1 and used a small screw driver to gently rotate the cam back to the correct number. Worked like a champ and checked after several rotations of the crank. *shrug* maybe I totally screwed up, but as best I can tell I'm right on the money:

Left:



and right...



Best regards,

Michael

[Eagledriver]

Do you have the big ports or small ports on that engine. (39mm or 34mm). The reason I ask is that the timing you set works best with the large port engines. If you have the smaller ports I would advance the timing to 1.5mm or so.

-Andy

[dtw]

The pin is not a precise fit, and can allow for a timing change to some extent. This is even more problematic on aggressive/high-lift cams where nailing the spec is important and small movements of the cam have a greater impact on lift. A little more wiggle room on CIS cams. It is possible to change the cam timing while tightening the nut by moving the cam independent of the sprocket, again, due to the slop in the pin. Once the nut (or bolt) is torqued, or close to it, the sprocket and cam will move together and you don't have to worry about the dial indicator anymore. Of course you always want to rotate the crank through 720 a couple times and check the measurement.

[euro911sc]

Originally Posted by Eagledriver

Do you have the big ports or small ports on that engine. (39mm or 34mm). The reason I ask is that the timing you set works best with the large port engines. If you have the smaller ports I would advance the timing to 1.5mm or so.

-Andy

It is an '82 930/10 motor. I am at work and without my spec book so I could not tell ya the port size. Didn't I read in wayne's book that advancing the timing here was not proven to add hp for a stock CIS engine? Would that held reduce my chance of detonation with my 9.8:1 compression engine?

Originally Posted by dtw

The pin is not a precise fit, and can allow for a timing change to some extent. This is even more problematic on aggressive/high-lift cams where nailing the spec is important and small movements of the cam have a greater impact on lift. A little more wiggle room on CIS cams. It is possible to change the cam timing while tightening the nut by moving the cam independent of the sprocket, again, due to the slop in the pin. Once the nut (or bolt) is torqued, or close to it, the sprocket and cam will move together and you don't have to worry about the dial indicator anymore. Of course you always want to rotate the crank through 720 a couple times and check the measurement.

My pins were pretty tight and would only fit in one set of holes period. Still, I understand what you are saying as I went from .99 to 1.02 while I was tightening things up.

Best regards,

Michael

[Eagledriver]

Advancing the timing will not increase HP, it will increase torque and not hurt the HP significantly. I suggest it because if you have a USA spec 80-83 SC motor then you have small intake ports. They run out of breath above about 6200 RPM or so. Since there is no power up there to gain with the retarded setting you have selected I suggest you go for the improved torque of cam setting for the stock 80-83 USA motor (1.4-1.7mm).

-Andy

[euro911sc]

Its a euro spec and the valve port sizes are 34 in & 35 ex. Of course, these are the same size as the US Spec for 81-83 and not the 'big port' heads that had 39 in & 35 ex. All according to BA's book on p. 110. The US specs had lower compression and a different fuel distributor. So does this still mean I'll need to open it up again and re-time it to 1.4-1.7?

Best regards,

Michael

[Eagledriver]

I know the BA book shows small ports for the Euro 80-83 but other sources suggest they had the bigger ports. My experience with these cams is with a 3.2 motor and with big port SC motors with carbs. Even the big port motors I run at 1.25mm. The concensus seems to be that advancing the cams provides a more satisfying engine. I was disappointed when I set my 3.2 carrera to 1mm in hopes of more top end power.

-Andy