Cam Timing Guru: Advanced vs Retarded?

[erikv11]

OK so all marks are on, but it looks like the cams themselves are off. Is that just the angle, or are they slightly off, slightly counterclockwise?

Because by looking at the pic, it appears you can rotate the cams only one direction right now, and that is clockwise. In other words, the only available cam timing adjustment right puts the car more *in* time, so you have nothing to worry about and are free to experiment. Setting it back to neutral will not require the tensioner to come off.

[cn90]

Were the cams locked when you did this?

No.

No fancy tool to lock the rear cam slots.
I did all this stuff the "ghetto" way.
Actually when the bolts are loose, the sprocket rotates back and forth because of the oval slots on the sprocket.
The camshaft itself did not move at all.

I mark the adjustment with scribed markings, tightened the bolts finger-tight while holding the sprocket itself.
Final torquing was done after the TB is installed.
Then I verified that nothing had moved during the process of TB installation/final torquing.

Car runs very smooth now.

[erikv11]

No one questions whether or not the car runs smoothly, I am sure it does! The discussion is about tweaking cam timing; with the cams slightly off of factory timing (slightly counterclock or what you called slightly retarded), is the power band lower or higher right now, and is that where you want it?

The good news is, you can tweak it all you want from the current setup, without removing the tensioner. Again assuming the cams are where they appear and how you describe, any adjustments move toward factory timing, not out of it. I think most people play with the intake/exhaust overlap when they do this, i.e. do not adjust the cams in synchrony. But you can check that out if you have the time and energy.

The other good news is that this is an LPT, so it is going to be peppy in the low end anyway.

[cn90]

Re: how to adjust camshaft.

I was thinking "in the box" because I did not read IPD instructions carefully (I was thinking moving cam sprocket!).

Now I think again, it is very simple:

- Loosen the 3 bolts on the cam sprocket. Loosen just enough so the camshaft can rotate w.r.t the sprocket.

- Leave the sprocket alone (its relationship with the TB and the crank sprocket is fixed) and move the camshaft(s) via the 3 bolts (a screwdriver may be needed to move the cam back and forth as you desire).

- Once happy with the adjustment, tighten the bolts to spec.

Simple!

[erikv11]

Yes,that's the point! Well, one of them.

[jimmy57]

OK. My point is the movement to center of slot can be retarded or advanced. Depends on whether you moved CCW or CW respectively to get in center from the original factory position. From factory some will have one cam bolts for one at CW end of slot for one and CCW end for the other.

[rspi]

I don't think it's safe or possible to move timing 7.5% either direction. There is a point that you may cause valve to piston contact. Does anyone know when that will be? I have read that people do get the timing off sometimes when they change the belt, maybe intake or exhaust off by one full tooth.

Anyway, How did you guys figure you can move the timing by a 15% sway? That seems pretty far. Did you give an account for the thickness of the bolt? If you measured 15% for the slot, the bolt is about 1/3 as thick as the slot, therefore the timing may only be able to be changed by 10% when you take in account of the center point of the bolts and how far they actually move with the adjustment.

[erikv11]

It's not 15% (percent), it is 15˚(degrees). So 15 out of 360 total, as in about 4% of a circle. Also, 15 degrees works out to be the same as 1.75 teeth, or just under one tooth in either direction. If the 15 degrees is correct (and I think it is), then just by moving the sprocket by the slots, it is possible to change timing by as much as 1.75 teeth. But in practice usually less, like 7/8 of a tooth. So anyway, 15 degrees of sway is not enough for the valves to hit the pistons.

Why we say there is 15 degrees of sway: It's what all the stuff you read says, like from IPD etc. Intuitively, it seems about right, so no reason to question it.

[rspi]

Thanks for clearing that up for me.

[cn90]

erik is correct.

The 15-degree adjustment span (7.5 degrees in either direction) was already thought out by Porsche engineers (who designed the 5-cylinder for Volvo).
So whether you set the cam(s) at extreme such as +7.5 degrees or -7.5 degrees, there is no collision between piston + valves.

This weekend I may set it back to:
Exhaust: some sort of Advanced.
Intake: Neutral or some sort of Retarded.

Stay tuned!