Forgive the simplistic inquiry....being a child of the 80's and a gear-head of the late 90's and early 2000's, my knowledge of LS motors far exceeds that of my GEN 1 SBC.

Am I correct in that if I'm going to be replacing my distributor, I can set the motor to 11 degrees before TDC on the compression stroke, pull the original distributor out, drop the new one in with the rotor pointing at the #1 cylinder, and just ensure that the cap and rotor line up and this should at least get me in the ball park for initial timing and start up?

Thanks for the input....learning as I go here.

-Greg

 

Greg
that is pretty much right on. If you go too far past #1 you will have to just lift the distributor up a little and set it back down. You will notice the gear will mesh and move forward some. Keep lifting (known as walking) until you get back to #1 again. Hard to explain but once you try it a few times it becomes natural.

 

If you're simply pulling one distributor and replacing it with another, simply put a mark on the adjacent valve cover to where the rotor is currently pointing (doesn't need to be in any particular location), pull the old distributor and insert the new one with the rotor pointing at the mark you made from the previous distributor. Or, you can bump the starter until the rotor is pointing dead straight to the front of the engine, pull the old and insert the new with the rotor pointing in the same direction. Don't overthink this one.

 

As the others have said, make sure you mark the rotor before you remove the old distributor. The crank rotates twice for every one rotation of the distributor. You can match the marks on the harmonic damper and be 180 degrees out of time. If you have already removed the distributor without marking the rotor position, you will need to find TDC on the compression stroke of #1 piston to set the new distributor in. You already knew that, but thought I would remind you.

 

Just to clarify when you drop in the new distributor you will want to start with the rotor "a bit" counter clockwise to your index mark. The cam gear is helical and as you engage it the rotor will rotate clockwise as the unit seats. If you overshoot your index mark you can use a long straight blade screw driver to rotate the oil pump shaft back counter clockwise and try again. Had mine in and out 6-7 times after blueprinting it, it's an easy job.

 

Greg,
As you can see, there are many ways to skin that cat! Easy Peasy! Good luck.

 

Understood on the cam gear being helical and the rotor moving as you drop it in....I watched a couple videos.

Just want to make sure I understand a starting point before I pull the stock unit out....

-motor 11 degrees before TDC on the compression stroke
-mark position of old rotor
-remove old distributor
-install new distributor with rotor facing mark
-install cap
-point on cap that rotor is pointing at is you're #1 plug wire
-work your way clockwise for plug wires in the firing order 1-8-4-3-6-5-7-2

 

Prior to removing a distributor I ALWAYS recommend setting the crank to what you believe is the "correct" initial timing spec - degrees BTDC #1 compression stroke, NOT TDC as so often stated. If the wires are properly indexed on the cap and the distributor gear is properly oriented (dimple pointing the same direction as the rotor tip) the rotor should point to #1 tower as illustrated in service manuals, and the plane of the cap widow should be near normal to engine centerline.

As you pull the dist. up the rotor will rotate CCW and clear the cam gear when it is pointing approximately along engine centerline.

Upon installation, start with the cap window normal to centerline and the rotor tip normal to engine centerline. As the gears engage the rotor tip will rotate CW. If the dist, base does not contact the manifold remove and check the orientation of the intermediate oil pump drive shaft slot and tweak it as necessary with a paint mixing stick.

Once seated rotate the dist. base CW to the limit then back CCW until the points just begin to open. You can do this visually or connect an ohmmeter. At the opening point the window should be near normal to engine centerline. This should allow the engine to start easily, then set either initial or total WOT advance with a timing light.


Duke

 

sorry, should have mentioned, this is an HEI going in temporarily while I send the stocker out for a rebuild

 

Oh wow!!!! Now you tell us..... JKDon't think it matters as long as long as the engine is set BTDC, on compression stroke and the rotor still points to #1 you should be good.but I am sure more will give better tips.

 

I'm so geeked out that when I pull the old dizzy, I mark (using tape) the position that the rotor was at when it disengaged from the cam gear when it was being pulled out also. Then I use that mark to initially clock the new dizzy before dropping it in. It may or may not make a difference, but I'm not as good as the guys above. ^^^^

 

Thanks for the input guys, hoping to get this knocked out this weekend!

 

I wouldn't fuss over the 11 degrees. A points distributor and HEI distributor won't fire at exactly the same time based on where the rotor is pointing. The firing time on a points distributor is, more or less, when the points open. The rotor can move through quite a bit of rotation and still fire on a specific plug. Look at how big the terminals on the rotor and distributor cap are and you'll see what I mean. Once the rotor gets to a certain position before a terminal, a minimum spark gap is maintained until the rotor moves past the same terminal by about the same amount of rotation. Somewhere in there, the points open and the coil sparks. With HEI, whenever the rotor ring prongs move to a specific point with respect to the pick up coil, same thing.

The spark timing changes because the point opening or pick up coil triggering changes, not because the position of the rotor.changes.

Just put the motor on TDC #1 or TDC #6 before pulling the distributor, and then get the rotor close to the proper plug terminal on the cap when you put it back in. Marking the rotor position is ok, but there's no guarantee the rotor will end up indexed in the same place when you put in the HEI distributor. You might be a 1/2 tooth off.

 

Here’s an old “shade tree mechanic” technique , using modern tech for back up .

Take off the distributor cap.
Crank the engine so that the rotor tip is lined up with the vacuum advance can input tube
Mark the location and alignment of where those two things point to using tape or grease pencil.
Take a cell phone picture!
Remove the distributor part way up, paying attention to how much and which way the rotor turns away from that alignment mark
Note the direction and alignment of the rotor now that the distributor shaft is disengaged from the cam gear. Mark that alignment
Take a cell phone picture!
Remove the distributor.
DO NOT CRANK ENGINE, Maybe disconnect battery to be safe.
When reinstalling start with vac can pointing towards first mark and rotor towards the second one
As distributor seats down in the two should both point towards the first mark and the timing should be very close.
Reinstall cap, wires etc
Adjust dwell and timing as necessary

 

[QUOTE=tuxnharley;1602129389]Here’s an old “shade tree mechanic” technique , using modern tech for back up .

Take a cell phone picture!
Take a cell phone picture!
/QUOTE]

My fourth great-grandpa always took cell phone pics when doing repairs on his Conestoga Wagon while heading west on the Oregon Trail.

 

[QUOTE=Easy Rhino;1602129720]Who was he - Doc, from “Back to the Future”. ?

 

[QUOTE=tuxnharley;1602129764]Kind of looked like him.