Hei Help

[MrHotRod5263]

Here is what i am working with;

I have a 71 c-20, with the stock 350/Th350. With a Quadra Jet

P.O. swapped to Hei. it has a #368 Centerplate and #41 weights

I checked the timing yesterday and it was at 8 deg After TDC (idling at 800rpm), so i started to adjust it , and was able to get a max of 4 deg Before TDC before the vacuum advance hit the intake.

Here is what im looking for advice on.


1. I need to figure out how to adjust it so I can get it to advance further

1a. I've read that i need to pull the distributor and turn the oil pump
shaft but noone ever specifies which way to turn it, or how much.
I am guessing that i would need to turn it Counter Clockwise in
order to get more advancement, but then there is the question of,
How much do i turn it??

2. What are your thoughts on Initial / Base timing setting

3. How much advance is that weight combination going to give me

4. Is the vacuum advance better to be hooked up to Ported vacuum off
the carb. (like it is now), or is Manifold vacuum better.

[truckster]

Let's see if I can help with your questions.

1. Turn it enough to be able to clear the intake with the timing set correctly. It sounds like probably two teeth would do it. You need to be able to turn the distributor cap farther counterclockwise (advance the timing) so you need to turn the distributor body (and oil pump shaft) clockwise to get the clearance.

2. Since you're close to sea level, I'd start out with 8 degrees BTDC.

3. Don't know.

4. This is a long-standing argument. As I understand it, ported vacuum simply introduces some advance at idle to reduce NOx emissions. You can run either, but I believe the 71 ran manifold vacuum (not sure on that).

Good luck.

[dznucks]

If the distributor was installed correctly, you should not have to remove it and adjust it a tooth or two. In order to gain more clearance you can reclock the spark plug wires counterclockwise on the cap and then re-time the motor. what i mean by re-clock the plug wires is to remove the #1 wire and #2 wire and plug the #1 wire on the #2 post. unhook #7 and connect #2 to that post. unhook #5 and connect #7 to that post. continue doing this around the distributor to all eight wires. this should allow you to turn the distributor clockwise to time it correctly and have clearance.

I said IF the distributor is installed correctly.....you said the timing was at 8 deg after TDC. You may want to verify the distributor is installed correctly. If it is installed incorrectly this would also cause your interference issues.

You do not need to worry about clocking the oil pump shaft. If you have to move the distributor a tooth or two you can lift it just enough to rotate the shaft (you can feel the teeth if your are careful). Make sure you have verified TDC. Once you are sure you have engaged the distributor correctly you can turn the motor over until the distributor shaft and the oil pump align, the distributor will drop into place on its own. Reverify the distributor is pointed to the #1 wire when the timing mark aligns with the timing tab.

Use manifold vacuum source.

You will need a dial back timing light or timing tape on the balancer to determine how much mechanical advance your weight combination is giving you. You will rev the motor until the timing stops advancing. Subtract that number from your initial. you should have roughly 20-22 degrees mechanical. so if you are at 8 initial, you should see 28-30 degrees total.

Start at 8 degrees initial, drive it and get a good feel for its power in all rpm's. move the initial to 10 deg and go for another test drive. if it improves and you dont hear knocking, go to 12 degress and see what happens. typically 36 degrees max mechanical is what 350's like.

this is a very in depth topic and its hard to give basic answers to your questions. There are numerous good articles on this on our site and online.

[GMCJOE]

http://rmcavoy.freeshell.org/HEI.html

That site will provide you with about everything you need to know on the timing. There is a little left out.

As it state's. Your advance should be unhooked from vacuum and then set your timing to 8-10 degrees BTDC. Your vacuum should be hooked up after it is set and be hooked up to the Ported Vacuum. Ported increases vacuum as your engine rises in rpms, which will advance your timing correctly. Manifold vacuum will give you a full vacuum like is provided to your power booster. It would defeat the purpose of vacuum advance to have it hooked up to a full vacuum source.

When your vacuum is hooked up, it should be now running between 16-18 BTDC at idle. 750-800 rpms is what I usually run for idle, some like to run lower from 650-750. At about 2500 rpms you should be at about 32 BTDC.

[airdale94]

You need to pull that distributor and re-stab it. What you do is bring the engine up to Top Dead Center on the compression stroke (#1 piston). The easiest way to do this is with a remote starter switch but you can do it with a breaker bar and socket on the harmonic balancer bolt . Pull #1 plug and hold your finger over the hole. Rotate the engine clockwise, when your on the compression stroke the pressure will blow your finger off the hole. Now stick a slim screwdriver into the hole and feel for the piston. Rotate the engine until the piston is at it's upper most point. You're now at TDC on the compression stroke. Find #1 on your distributor cap (leave conected to distributor) and mark it on the the side of distributor. Put your distributor in the position you would like it to sit ( just rotate it ) don't pull it out yet. Pull your cap and see how far off your rotor is from #1. Then you'll have to play around with getting it into position (pull distributor up, postion , line up rotor with #1 mark on dist., push back down into engine). Don't worry if it won't go all the way down yet. You are just trying to get it where you want it to sit. Once you find it pull distributor all the way out and look at the slot on the bottom of distributor shaft (drive for the oil pump) note position. Get a flash light and look down into dist. hole. Note oil pump drive slot position and turn oil pump drive to match match dist. You just have to play around with it till your satisfied. This is a good time also to make sure your wires are correct on cap. Actually you want to do that first!



It's not your oil pump drive that's out of alignment, it's your distributor/rotor position. You'll see what I mean once you start playing with it. The reason for lining up the slots will be obvious. 1) the distributor won't go down all the way 2) If the distributor isn't down all the way you won't have oil pressure when it's running (bad!)

[MrHotRod5263]

you guys are awesome, i have the distibutor pulled now .

I found that the vacuum advance is leaking and doesnt pull in at all , so i need to replace it.

- Any recommendations on which factory advance unit i should be using? I have no idea what this distributor came out of.

But i also found that i can push and pull the shaft up and down in the housing, there is not side play at all , but if i put a tape measure on the top of the gear while pulled down, and then push it up i get 1/16" movement. is this normal?

[MrHotRod5263]

I grabbed a set of feeler gauges and measured the actual end play, it is 0.066 inch.

I have read that it needs to be no more than 0.010 inch.

I have found the Mr. Gasket shim kit and it has a 0.050 in. shim, which will bring the play down to 0.016 in.

My question is should i put one of the 0.010 in shims with it and bring the play down to 0.006 in , or would that be too tight of a tolerance ?

[davepl]

You're going to have to (as mentioned above) remove the distributor and move it one tooth in order to get proper room to advance the distributor body. You'll likely have to either rotate the oil pump driveshaft by hand, or with the coil off and some downward pressue on the distributor, crank the engine until it drops into place.

There should no little (and ideally no) vacuum present for the vacuum advance at idle, in my opinion. The vacuum advance line (ported) represents the airflow through the venturies, NOT manifold vacuum. But not everyone agrees.

Ideally for your advance curve you should figure out what it wants for max timing at max torque, what it wants for the best idle, and have a mechanical advance curve that supplies the delta between them. Hard to do without a dyno (and someone with a distributor machine). But it can be done by trial and error and different weights and limits and springs if you pick your initial timing and then assume some typical number (like 34) for max.

[VetteVet]

Here's a good site for the HEI distributor.
..........http://www.rustpuppy.org/ignition2/Ignition%202b.htm