Timing marks on 4.3 vortec ??

[gtfireftr]

So I wanted to check the timing on my port engine to verify that it is indeed set correctly....
I look at the front cover, and see that there is one "tab" with a notch in it. I assume that this is the mark that is used to determine the timing.
I look at the harmonic balancer and see only on large line. I assume this is for TDC..... My question is how to determine the degree of setting on the balancer.
The starboard engine has the degrees marked on the balancer. Is there a way to determine the degrees on the other balancer? I have no idea why there would not be any degree marks on the port balancer....
Thanks in advance

 

[BillK2632]

Couple of ways.

1. Is there not a white mark on the harmonic balancer?
2. You can probably get some sort of sticker with the deg. marked.
3. Use a timing light with an advance feature - in that case you set the timing light to the correct setting (10deg btdc I think)
but actually time it to 0 tdc, the light handles the advance. That probably why there is only a tdc mark on it.

Also, depending on the ignition system there are different timing procedures that involve putting the system in
base timing mode.

 

[gtfireftr]

Couple of ways.

1. Is there not a white mark on the harmonic balancer?
2. You can probably get some sort of sticker with the deg. marked.
3. Use a timing light with an advance feature - in that case you set the timing light to the correct setting (10deg btdc I think)
but actually time it to 0 tdc, the light handles the advance. That probably why there is only a tdc mark on it.

Also, depending on the ignition system there are different timing procedures that involve putting the system in
base timing mode.

There is definitely a white line on the balancer.... I was not aware of a timing light that would give me the degrees of BTDC that I need.
I think you are correct in saying that there is a procedure to put the ignition system into timing mode.... i need to find that out as well..
Thanks for the reply

 

[BillK2632]

Is your engine EFI or carburetor? Most V6/V8 engines with Thunderbolt Ignition call for 8deg BTC, it should be on the sticker on the engine. If it is carburetor, the timing procedure is easy. I have a carbureted 4.3 with Thunderbolt IV and this is exactly how I do it. I use an old timing light that does not have the advance feature, so I put it in base timing mode, make sure the rpms are correct, and point/shoot it to the white mark on the balancer. The EFI procedure is different, I've never done it.

Like I said, if you are buying a timing light, get one with advance and idle built in - in that case you literally set the timing advance on the light to whatever the timing should be (ie 8deg BTDC) and time it so it looks like it is at 0 TDC, the light figures out the timing offset. Google it - but it makes setting timing easy, no trying to figure out where the marks are - just need to know where 0 TDC is.

I just made up a little jumper with alligator clips, to ground out the purple/white. You know when it is in base timing mode because there is no advancing, if you check timing whithout putting in base timing mode, the marks will be jumping around all over, that's the spark knock sensor constantly adjusting the timing advance and if you rev the engine you will see the timing advance. Once you lock into base timing mode, the timing stays steady and does not advance when you rev the engine.

Connect timing light to number 1 spark plug. Connect
timing light power supply leads (if applicable)
to 12 volt source.
2. Connect a shop tachometer to engine.
3. Using a jumper wire, connect the ignition system
timing lead “13” (PUR/WHT wire) to a good engine
ground (–). This locks the ignition module
into the “Base Timing Mode”.
4. Start engine and run at normal idle speed. Allow
engine to reach normal operating temperature.
5. Aim timing light at timing tab, located on the timing
gear cover and crankshaft torsional dampner.
6. Adjust timing using the conventional method.
IMPORTANT: Be sure to disconnect the jumper
wire from the ignition system test terminal before
attempting to resume normal operations. If the
jumper wire is left in place, the ignition module
will operate in the “Base Timing Mode”. This
means that the additional timing advance features
would not function.
7. Make sure that the distributor has been tightened.
Remove the jumper wire from the timing terminal.
8. Stop engine and remove timing light.