How to set your ignition timing correctly

Dave-R · Post by **Dave-R** » Sun Jan 09, 05 9:38 pm

Following on from a post on carb tuning I thought it might help someone to post this here.

I am going to take you through this right from the start one step at a time. The first thing you have to do is....

IDENTIFY CYLINDER #1

You would be amazed how many people I have found that have this wrong!

Cylinder number one is the cylinder right at the front of the engine on the drivers side (next to the battery). On a small block this is right next to the timing marks on the crank damper. Where some people get confused is that on the big block the timing marks are on the other side of the engine. But number one is always the front drivers side no matter which engine you have.

Next step is...

FIND TOP DEAD CENTER ON CYLINDER #1

Now the problem is that on a 4-stroke engine every cylinder hits top dead center twice during the engine cycle. So just lining up the timing marks is no good because you could be at TDC on the exhaust stroke instead of the compression stroke.

Remove the valve cover on the drivers side. When you do this you can see the valve springs. The spring right at the front of the engine is the exhaust valve for cylinder 1. The spring next to it is the inlet valve for #1.

You need to rotate the engine by hand with a 1-1/4" socket on the crank bolt which is in the center of the crank pulley. Remove all the spark plugs (and put the trans in neutral!) to make this easier.

Rotate the engine clockwise until you see the intake valve open (that is the second spring in from the front) When it has opened watch for it closing. When it has closed look for the timing mark on the crank damper as you continue to rotate the engine. As the piston in #1 rises to the top of it's compression stroke the timing mark will come into view. When it lines up at the zero mark on the timing tag you are at top dead center (TDC).

As a check that you have got this right try twisting the pushrods on #1. They should both be easy to spin. If one or both pushrods are stiff to twist you may be at TDC on the exhaust stroke instead. Try again and make sure you are looking at the intake valve. When it closes the next time the timing mark lines up it will be at TDC.

If you suspect that the timing mark on the crank damper is not right (ot if the timing tag is missing) you can check it by using a piston stop. This is a long bolt that screws into the spark plug hole. You screw it in when the pistion is down in the cylinder. Then you rotate the engine BY HAND until the piston contacts the bolt. Mark this poistion on the damper and then turn the engine in the opposite direction until the piston hits the bolt again. mark the damper in the same way. Your TDC mark on the damper should be EXACTLY half way between these two new marks.

Now remove the distributor from the engine.

Inside the hole the distributor sits in you will see a gear with a slot in it. This is the distributor drive gear. It has a slot in the top that engages with the end of the distributor shaft. You need to pull it up and slot it in so it lines up as in the photos below.

On a small block (LA) engine you need to line up the slot like this;

Dave-R · Post by **Dave-R** » Sun Jan 09, 05 9:39 pm

On a big block engine (B, RB) you need to line it up like this;

Dave-R · Post by **Dave-R** » Sun Jan 09, 05 9:43 pm

Now...

INSTALL THE DISTRIBUTOR

Remove the cap from the distributor so you can see the rotor.

Small Block (LA) Engine
Install the distributor so that it engages into the drive gear with the vacuum can pointing straight across to the passenger side fender at 90 degrees to the crank centerline. The rotor can end up in one of two positions. You need to install the distributor so that the rotor is facing towards the #1 cylinder. If it is pointing to the rear of the engine then lift the distrubutor and turn the rotor 180 degrees.

Big Block (B, RB) Engines
Install the distributor so that the vacuum canister is pointing towards the drivers side fender at 90 degrees to the crank centerline. You need the rotor to point down at the 4:30 position (as if the rotor was the small (hour) hand on a clock).

Both Engine Types
With everything lined up make a mark with a felt pen on the casing of the distributor right under the tip of the rotor so that when you put the cap in place you can tell where the rotor is.

Now put the cap on and see which spark plug lead terminal tower is closest to the mark you made. You should be lined up almost exactly with one.

If it is not exactly lined up make a second mark on the distributor case right under the nearest tower and then line the rotor up with that. Make sure the vacuum can is not going to hit anything when you twist the distributor to adjust the timing later.

Bolt the distributor down.

This terminal is now going to be your #1 spark plug lead so draw a #1 on that terminal tower.

INSTALLING THE SPARK PLUG LEADS

Now you can re-fit your spark plugs and put the valve cover back on.

The cylinders on a V8 are numbered from front-to-back and side-to-side so on your drivers side you have odd #s 1 3 5 7 (front-to-back) and on the passenger side you have even #s 2 4 6 8 (front-to-back).

Connect a spark plug lead from your #1 terminal in the distributor to the spark plug in cylinder #1.

You now need to install the rest of the leads.
The firing order for our V8s is 1 8 4 3 6 5 7 2.
BUT on a small block the distributor rotates clockwise and on a big block it rotates counter-clockwise

You already have #1 in so the next lead to install is #8. So on a small block #8 is the distributor terminal next along in a clockwise direction. On a big block it is the next in an anti-clockwise direction.

Continue adding one lead at a time by first placing it on the distributor and then to the spark plug in the 18436572 order.

Now the engine should start from this position. If not try turning the distributor a small amount anti-clockwise (small blocks) or clockwise (big blocks) to advance the timing slightly.

When started you can time the engine with a timing light in the usual manner.

On small blocks it is simple to connect up to the #1 plug lead to time the engine and see the timing marks on the drivers side of the car.

However on BIG BLOCKS the timing marks are on the other side and some people have trouble making their timing light reach over to that side when connected to #1. If this is the case then here is a TIP.

Try using #6 to time the engine instead!

HOW?

Well when #1 is at TDC on the exhaust stroke your #6 is at TDC on its compression stroke so they use the same timing mark but just 360 degrees apart!
Think about it. The engine has to rotate twice to go a complete cycle.

In the first 360 degrees rotation only 1 8 4 and 3 fire. Then the timing mark is back lined up again and 6 5 7 and 2 fire during the next 360 degrees of rotation.

So you can use #1 or #6 to time your engine!

Dave-R · Post by **Dave-R** » Sun Jan 09, 05 9:44 pm

With the engine running the exact engine timing can be set. To do this right you either need to mark your damper with timing marks from 30-40 degrees (use a stick-on timing tape) OR use a dial-back type timing light that allows you to "dial in" the advance so you can use the TDC mark on the damper.

You will also need an accurate rpm (tach) gauge. DO NOT use the factory tach as it is VERY inaccurate!

Pull the carb vacuum line off the distributor and plug it to prevent a vacuum leak. With this removed you will now have no vacuum timing effecting this set-up procedure.

Get a friend to rev the engine to 3000rpm. Set the timing to 35 degrees at that rpm.

Now set the idle speed at the carb so it idles correctly (factory settings are 600rpm manuals and 800rpm automatics)

See what the initial timing at idle is now. It should be around 10-15 degrees. Any more than that and you should limit the amount of mechanical advance in your distributor and set the timing again.

Now re-connect the vacuum line from the carb. This line should be connected to the timing port on the carb. If the engine timing increases when you fit this line then either you are not on the timing port or the carb needs holes drilled in the primary throttle blades. See my "carb tuning" posts for details.

Now take your rpm back up to 3000-3500, With the vacuum line in place you should now have about 50-55 degrees timing. Chrysler distributors have adjustable vacuum canisters. To adjust place a 3/32 Allen key into the can through the line connection and turn clockwise to increase the vacuum advance. If you get any pinking with the vacuum connected you might want to decrease the amount of vacuum advance.

Anonymous · Post by **Anonymous** » Sun Jan 09, 05 11:23 pm

NICE ONE!

Holly · Post by **Holly** » Sun Jan 09, 05 11:40 pm

Hey Dave, would it be ok to pop this in Connected? (since less than half the members are on here ... and even less regularly so!)

Anonymous · Post by **Anonymous** » Sun Jan 09, 05 11:44 pm

I always wondered what that little cast bit on the front of the small block manifold was for.

Dave-R · Post by **Dave-R** » Mon Jan 10, 05 9:09 am

Yeah OK James but can someone proof read it for me to make sure I have not said anything stooopid?

Dave-R · Post by **Dave-R** » Mon Jan 10, 05 10:45 am

DISTRIBUTOR MODS

If you want the best possible performance and throttle response from your car then the ignition timing curve is an area where great improvements can be found for next to nothing as far as cost is concerned.

First of all you must make sure that your distributor is not worn. Obviously, for high performance, an electronic distributor is best.

Another thing you can do is to check that there is a ventilation hole in the top of the cap. If not, then drill a 3/8" hole directly in line between the coil wire terminal and the No.1 cylinder terminal, as close to the No.1 terminal as possible. If you shine a light into this hole you can line up the rotor to get the engine started if you have had the distributor removed. This hole will also vent the cap. Venting lets the ozone out which builds up wherever there is high voltage. Ozone is not as good a conductor as air. I might not do this on a slant six engine as the dizzy is in a good position to collect dirt and water.

CUSTOMISING THE ADVANCE CURVE

If you have a lot of money to burn you can buy an ignition timing computer which will electronically set one of a number of timing curves for your car or can be programmed and adjusted with a lap top computer. Neat and cool!

The rest of us poor folk have to fiddle with the centrifugal weights and vacuum advance. You will need an adjustable (dial back) timing light and or a timing tape on the crankshaft balancer and an accurate meter to measure the engine rpm.

Total advance in a distributor as described here means the initial advance plus the centrifugal advance. Vacuum advance is measured separately and does not apply at wide open throttle.

CENTRIFUGAL ADVANCE

First of all it is essential that the points dwell (not points gap) is set as accurately as possible if you`re using points as this will have an effect on your results. The vacuum advance must also be disconnected and plugged to stop air being sucked into the inlet manifold.

Next the initial advance at idle must be measured and noted. Then increase the engine rpm noting the amount of advance in 500 rpm increments up to 4,000 rpm or until the advance reaches a maximum.

Now slowly decrease the rpm noting the same 500 rpm increments. If there is more than 2 degrees difference between the timing as rpm increased and that as it decreased then the centrifugal weights are sticking and need attention. You will then need to do these measurements again.

Subtract the initial advance from each of your readings to obtain the amount of centrifugal advance at each rpm.

You can buy kits with different weights and springs to modify both the amount and the rate of advance. Usually one spring will be lighter than the other. You can sometimes get away with just removing one spring.

It is difficult to generalise about the correct curve for any engine but I will give you pointers to get you in the ball park.

First try to get the total amount of centrifugal advance down to 21-23 degrees max. in order for a higher initial advance to be set. This is more important on a modified car with a hot cam and big gears. If you don't have a tuning kit with different weights you can do this by welding the slots in the weights or filling them with epoxy resin in order to limit the amount they can swing out.

Make sure you are only on initial advance from idle up to 1200-1500 rpm.
You want about half your centrifugal advance in by 2200-2300 rpm and the rest in by 3000-3200 rpm.

Now set your total advance by revving to 3000-3500 rpm and moving the distributor until you read 35 degrees.

Make a note of the advance at idle now as this is your new initial setting. It should be around 12-14 degrees.

A real world test of your ignition curve is to set a slightly higher initial or total advance so that the engine is just starting to "ping". If you get a ping at all rpm then you have done a good job and you just need to set it back to where you had it. If though, for example, it only pings at high rpm then it needs more advance at low rpm.

VACUUM ADVANCE

You need to use a vacuum advance on the street in order to get good mileage and to keep the plugs clean. But because you are now running much more advance in the distributor you need less vacuum advance. In fact you only need about 15-20 degrees. How much depends on many factors and the only way to tell is to increase vacuum advance until you get knocking at light throttle/cruise and then back off until you are SURE it is gone.
Remember: The more advance you can get away with - the better your mileage and the cleaner your plugs.

Ivor · Post by **Ivor** » Mon Jan 10, 05 1:43 pm

Top stuff Dave, even I understand it.

Dave-R · Post by **Dave-R** » Mon Jan 10, 05 1:52 pm

Thank you Ivor.

I shall be checking the dizzy drive gear slot position on everyones engines at the next Nats. Anyone found to have a drive gear slot in the wrong position at TDC will be punished!

Anonymous · Post by **Anonymous** » Mon Jan 10, 05 2:33 pm

Crikey, better get some revision done then

Top tips Dave.

Anonymous · Post by **Anonymous** » Mon Jan 10, 05 3:54 pm

Dave i agree with Ivor,great post and very usefull.I will be out there this week checking my dizzy and carb.thanks and well done

Ivor · Post by **Ivor** » Mon Jan 10, 05 5:24 pm

Ahem.
I just drop the dizzy/pump drive down the hole and rearrange the HT leads when the vacuum resorvoir is facing the right way.

Anonymous · Post by **Anonymous** » Mon Jan 10, 05 5:52 pm

Me too Ivor, makes for interesting spaghetti!
Thanks to Dave for taking the time and making it so clear