5.7 Vortec cold tap/knock HELP!

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Pinger

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Turning the distributor on a Vortec does NOT change the timing.

It changes the alignment of the cam sensor and the crank sensor, so the computer "knows" which cylinder is firing; and it changes the alignment between the rotor tip and the distributor cap terminal, so the spark doesn't jump to the wrong terminal.

Has NOTHING to do with ignition timing otherwise. Base (initial) timing is handled by the CRANK sensor, changing the distributor position doesn't change the crank sensor location.

Ideally, the cam sensor alignment should be within 2 degrees.

This has been on my mind re pending inlet manifold gasket change.

To be clear here, the cam sensor is on the cam - yes?
And the orientation of the distributor is only important for connecting the rotor tip to the appropriate terminal inside the cap - yes?

So, If i mark the body of the distributor to some reference point and re-fit in exactly the same position there shouldn't be a problem. But what's vexing me is that the skew gear will rotate the distributor shaft during removal and on refitting it will have to re-engage with the exact same tooth on the cam - how is this achieved? If the shaft rotates at all within the distributor when it is removed that orientation will be lost. Locking it to the distributor before distributor removal will then lose the distributor body position.
How do you guys deal with this?
NB, I don't have a scanner so have get this right manually.
 

Hipster

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This has been on my mind re pending inlet manifold gasket change.

To be clear here, the cam sensor is on the cam - yes?
And the orientation of the distributor is only important for connecting the rotor tip to the appropriate terminal inside the cap - yes?

So, If i mark the body of the distributor to some reference point and re-fit in exactly the same position there shouldn't be a problem. But what's vexing me is that the skew gear will rotate the distributor shaft during removal and on refitting it will have to re-engage with the exact same tooth on the cam - how is this achieved? If the shaft rotates at all within the distributor when it is removed that orientation will be lost. Locking it to the distributor before distributor removal will then lose the distributor body position.
How do you guys deal with this?
NB, I don't have a scanner so have get this right manually.

The cap indexes to the distributor housing so put the cap on and make a reference on the distributor housing for the number one tower. When you drop the distributor down the rotor needs to face the reference mark on the housing. Sometimes you need to turn the oil pump drive shaft a touch with a long screwdriver to get the distributor to drop all the way down and engage the pump driveshaft. it takes a bit of fiddling to get them to drop all the way down.

I normally put the engine on tdc #1 compression and mark the housing to the manifold and rotor to the housing before pulling one apart.
 
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Pinger

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The cap indexes to the distributor housing so put the cap on and make a reference on the distributor housing for the number one tower. When you drop the distributor down the rotor needs to face the reference mark on the housing. Sometimes you need to turn the oil pump drive shaft a touch with a long screwdriver to get the distributor to drop all the way down and engage the pump driveshaft. it takes a bit of fiddling to get them to drop all the way down.

Aha! The gear isn't on the distributor but the oil pump drive and the distributor merely slots in. That takes a load off my mind - cheers!

I normally put the engine on tdc #1 compression and mark the housing to the manifold and rotor to the housing before pulling one apart.

Intend doing that - it's like leaving a trail of pebbles.....
 

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Aha! The gear isn't on the distributor but the oil pump drive and the distributor merely slots in. That takes a load off my mind - cheers!

The gear should be pinned on the distributor shaft and it spins as it engages the cam on the way down as it is a helical cut gear. On the bottom of that gear/distributor shaft is a slot that engages the oil pump shaft.
 

Pinger

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The gear should be pinned on the distributor shaft and it spins as it engages the cam on the way down as it is a helical cut gear. On the bottom of that gear/distributor shaft is a slot that engages the oil pump shaft.

Ah - I was right with my first assumption!
Just let it spin within the distributor on the way out and in? And don't let it move while the distributor is on the bench?
 

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Ah - I was right with my first assumption!
Just let it spin within the distributor on the way out and in? And don't let it move while the distributor is on the bench?
It will be more clear once you get into it. When you pull the distributor up the rotor will rotate away from the witness mark for #1 tower as it comes off the cam gear, when you reinstall you have to start with the rotor behind the witness mark as it engages the cam gear on the way down the rotor will rotate towards the the witness mark. If you find you can't get it to drop that last quarter inch you might have to pull it and reach down in the the hole with a screwdriver and turn the pump driveshaft a touch. Not uncommon for it to take a few attempts, and sometimes you get lucky and they fall right back into place on the first shot.
 

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You need a Genuine GM service manual. Some years are/were available on this web site. I've heard that the links have quit working, but I've not confirmed that.

To be clear here, the cam sensor is on the cam - yes?
No. The cam sensor is in the distributor housing. All the wires coming out of the distributor are for the cam sensor.

And the orientation of the distributor is only important for connecting the rotor tip to the appropriate terminal inside the cap - yes?
Sort of. Getting the distributor positioned properly allows the computer to know that, for example, #1 is misfiring, not #8 or #2.

So, If i mark the body of the distributor...
The distributor is already marked in terms of rotor position. You might need to mark the housing position on the manifold. Or maybe not--some distributors seem to have a "captured" hold-down that doesn't allow the distributor to turn.

I could turn the distributor on my 7.4L, when I bought the truck it was 20+ degrees out of alignment. I reduced that to 1 or 2 degrees.

I don't have a scanner so have get this right manually.
Get a scan tool. I don't think you're gonna be accurate enough otherwise. The engine might "run", but the alignment with the crank sensor is not likely to be adequate. If you don't have a scan tool, how do you know that it's properly-aligned BEFORE you take it apart?

Be sure to verify that the distributor gear isn't excessively worn. Common problem.
 

east302

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Ah - I was right with my first assumption!
Just let it spin within the distributor on the way out and in? And don't let it move while the distributor is on the bench?

Before pulling the distributor, make a mark for where the rotor is. As it’s pulled, it’ll rotate to a second point. Mark that point and position the rotor there when you reinstall it. It should then rotate back to the first mark.

Also mark the distributor base relative to the intake.

Assuming that you don’t rotate the crank between removal and installation, that would get you back to where it was at the beginning.

A scanner (or Bluetooth app) is then used to set the CMP offset. Some aftermarket distributors (Summit, for instance) come with a fixed hold down clamp, preventing adjustment. Remove and reuse the existing clamp in that case.


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Pinger

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Get a scan tool. I don't think you're gonna be accurate enough otherwise. The engine might "run", but the alignment with the crank sensor is not likely to be adequate. If you don't have a scan tool, how do you know that it's properly-aligned BEFORE you take it apart?

I still don't understand.
If I retain the orientation of the rotor in the distributor and the distributor wrt to the manifold, don't allow the crank (or cam) to turn, and re-engage the gear on the same tooth - how can I lose the original timing (which may or may not be correct but I've no reason to doubt it right now)?

And if a scanner threw up that the timing was wrong - where can it be altered (if the cam sensor only reads for mis-fire info)?

I'm in the UK and a scanner really isn't an option right now .
 

Schurkey

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If I retain the orientation of the rotor in the distributor and the distributor wrt to the manifold, don't allow the crank (or cam) to turn, and re-engage the gear on the same tooth - how can I lose the original timing (which may or may not be correct but I've no reason to doubt it right now)?
1. It's really easy to be more than 2 degrees off, even when "aligning marks".
2. You don't know that the cam/crank alignment is correct now. Timing chain wear, cam gear wear, distributor gear wear, distributor housing wear can all affect the cam/crank synchronization.

And if a scanner threw up that the timing was wrong - where can it be altered (if the cam sensor only reads for mis-fire info)?
The scan tool doesn't tell you that the TIMING is wrong. It tells you that the cam sensor isn't synchronized to the crank sensor. That has NOTHING to do with the ignition timing, but it does affect alignment of the rotor tip to distributor terminal.

TIMING is set by the crank sensor and the reluctor on the crank snout. That signal gets modified by the computer, the computer controls the timing based on it's programming--but it all starts with the crank (not cam) sensor.

I'm in the UK and a scanner really isn't an option right now .
I'm not sure how your location in the UK affects not being able to get a scan tool.
 
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