96ZRDR

On a 95-97 style optispark unit, is there any special instructions to installing it?

For example: Many say that as long as the opti notch (with the timing mark) is aligned with the cam dowel pin, it should be OK.

But, I have another example that explains that both the crank sprocket and cam gear need to be at the 12:00 o'clock position. The cam dowel pin would then be at the 9:00 o’clock position. This way the engine would be at piston #1 TDC. Once this is done, only then would the optispark unit be in sync with the proper cam timing.

Should I be concerned? Is it possible to install the optispark 180 Degrees out of phase even if you align the opti notch (with the timing mark) with the cam dowel pin properly?

Thanks for listening….

shoebox

If you don't have the timing cover off, how can you see the dots on the gears? You also must have the cover on to install the opti. As long as you line up the dowel pin with the special slot on the opti drive you are good to go. Absolutely nothing more.

The gear dots are for indexing the cam to the crank. Nothing to do with the opti.

96ZRDR

1. You could align the timing marks as explained with the timing cover off and then re-install the timing cover without moving the crank or you could just watch for both intake and exhaust valves being fully closed on # 1 piston.

Please let me understand……

Proper cam timing or aligning of cam and crank timing marks only allows for accurate valve timing (Opening/Closing of a valve in relation to piston position).

Proper spark timing calls for indexing of the opti to the crank/piston position. In any SBC, the distributor asks for piston #1, which is no different in an LT1. So to properly align the opti would it not be proper to place piston 1 at TDC. Even if you have proper cam timing set up, it does not mean the cam dowel pin would be at piston 1 every time it points at 9:00 o’clock position. Cam gear travels at ˝ speed of the crank gear. Am I going about this the wrong way? Is it not possible to install it 180 degrees off if you are just going by the just align the opti timing notch to the cam dowel pin method?

orbitalshock2k

How do you know if you need a new opti? Other than car not starting

96ZRDR

I do not need a new opti, this is for another build-up, I am just talking about installation of one.

shoebox

True.
Sort of. If the cam and crank are set up right to begin with, the opti is indexed to the cam.

Yes, it does. Every time the cam pin is at 9: o'clock, you are at #1 TDC.

Think of it this way, the crank gear turns two times for every 1 time of the cam gear. One revolution of the cam gear is a complete 4 stroke cycle of all 8 cylinders. So TDC for every cylinder comes around at one particular clock position only once per cam revolution.

I promise you, that it does not matter where the dowel pin is, as long as you put the special slot of the opti over it. You cannot get it 180° out of time.

visual

The reason people get regular SBCs 180° out of time, is because they routinely mistake #6 TDC for #1 TDC and drop the distributor in. This is because they are watching the timing mark on the balancer (since it comes around twice in the full firing order) and not verifying with the valvetrain or cylinder compression which cylinder is actually at TDC.

Mtrhds94Z

LT1's, unlike other SBC motors,[in which the distributor gear can align with any cam gear tooth] the opti only aligns one way, so as long as you align the 'missing cog on the shaft'[early] or the 'dowel pin'[late] it can only index the cam one way[in one spot] It doesn't matter where the cam is [what 'o'clock' ]so long as you align it correctly, it's timed right..

96ZRDR

Got it now!! Thanks......