Technical SBC. crank key way

SBC harmonic balancer comes with timing mark in 4 different locations using different timing tabs. Did the keyway in the crank move also or not? I cant figure how the marks can move when #1 tdc is in the same spot of crank.rotation. thanks, Bob

 

Timing tabs in different locations mainly due to accessories, crank keyway never changed.

 

Key way never moved,marker tab* that was mounted near H-balancer was move around on def. models too clear this or that,made def. timing marks*/on balancer=to match tab used.

 

So how can this be? #1 TDC is still in the same place on rotation of the crank, if marks just moved timming light would no flash with marks.

 

SBC engines have three (3) different timing pointer locations:-

1. Pre '69 engines, TDC mark is 2° to the left of the keyway centre line;
2. '69 and later, TDC mark is 10° to the left of the keyway centre line; and
3. 1984-'95 engines, TDC is at 12 o'clock position on the damper.

 

You can add a pointer and mark at 6:00 position and your light would be correct. You can do that at any of the 360 degrees or in between for any of 720 spots and it would be 100% correct

 

The groove in the damper, AND the pointer moved.

If you have a mismatch between the groove and the pointer, yes the light will flash with no reference point.

Luckily, you can buy tabs that align with each of all three possibility, and all of the known diameters.

 

It's also possible that the rubber part of the balancer twisted, so that *none* of your marks align with TDC.

That happened to me. To tune the engine, I just hooked up a vacuum gage and set the timing then idle mixture to max vacuum, then repeated a couple of times.