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Thread: My timing issues...

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Posts: 21-30 of 61
2010-08-20 15:28:37
It's hard to tell what is moving because the angle of the camera changed, and what is moving because something actually moved. =/
2010-08-20 15:43:47
Look at the #1 intake lobe relative to the valve cover gasket surface.
2010-08-20 15:45:27
I see what you mean. It's just odd the #4 lobe doesn't appear to move at all. So odd.
2010-08-20 15:47:09
Yep, Exhaust cam jumped a tooth. If memory serves me well (and hopefully Dre chimes in), every tooth on the crank is 32 degrees of mechanical timing. Every TWO teeth on the cam gear is the equivelant of ONE tooth on the crank gear.

With this being said, one tooth of advance on the exhaust cam is 16 degrees of mechanical timing. This fully explains why your distributor is the way it is in order for you to acheive 15 degrees of ignition timing.

Hope that makes sense to you.
2010-08-20 15:52:00
I guess it's possible the intake cam moved one tooth and the exhaust cam moved two teeth and that would explain why they both look like they are moving, but the exhaust looks like it's moving more.

Or maybe the chain is slack in the image with the chain guide in place, and then the chain is tight in the after picture with the chain guide removed and the exhaust cam took up the slack by turning some.
2010-08-20 16:00:26
I'm sorry, my timing marks were off when I said 8/16 degree mechanical timing increments.

I just double checked, and it's 1 TOOTH = 10 DEGREES for the cam gears, and 1 TOOTH = 20 DEGREES for the crank gear.

This still applies like I mentioned (for two teeth on the cam, it's one tooth on the crank).

For reference in the future if anyone's curious:

There are 36 teeth on a cam gear.

There are 18 teeth on a crank gear.
2010-08-20 16:05:16
Or both cams moved equally and no cam teeth were skipped, but the crank sprocket skipped a tooth. This would cause ignition timing to be off by 20 degrees as Cliff said. The direction the crank rotated when the tooth skipped could be either way, so it could cause the distributor to need turning either way to "fix" the problem.
2010-08-20 16:12:18
It's very difficult to skip a tooth on the crank. VERY difficult.

Also, note that the cam profiles are different as well, which may be confusing you, Ben.
2010-08-20 16:33:51
The intake lobe on 4 looks like it did not move.

The exhaust on 1 and 4 clearly show that it moved.

Either way, I have a great diagram of what it should look like stock. I am aiming for this. I physically moved the dizzy back to where it would be at from the factory. I am leaving it there until I pop the valve cover.

Please, keep it coming, I need help to identify this from the pics!!

The angle does not help and it causes the 2nd and 3rd lobes to look different, along with the fact that the assembly lube is on there also.
2010-08-20 16:44:52
It's easy.

Your exhaust cam is advanced 1 tooth.

When you fix this, first set the exhaust cam with the cam gear off of the intake cam, and the tensioner removed.

Set the exhaust cam for the dowel at 12 o'clock, and with ZERO slack between the cam and the crank. You should not be able to move the chain AT ALL.

Then, install the intake cam gear for the dowel at 10 o'clock. 20 pins between the dots on the cam gears. Pull the chain tight (by turning the intake cam counter clockwise) so that there's minimal slack between the intake and exhaust cam.

Install tensioner, and lightly rotate the intake cam clockwise and counterclockwise to release the hook on the tensioner, and allow it to take up the slack between the crank and the intake cam.

Once you accomplish this, rotate the motor by hand a few times, make sure that intake and exhaust cam line up at 10 and 12 o'clock when the motor's at TDC. Install cover, set dizzy to dead center, start car, and check timing.
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