On my last post (rather a large post), I explained the critical settings of the spark plug and the benefits of quality ignition leads. That’s all well and good, but if you don’t have the correct pulses or power going down those leads at the right time then you will have problems. While I was checking and replacing spark plugs, I decided to strip down and rebuild the top end of the distributor.
Firstly what is a distributor?
A distributor consists of a rotating arm or rotor arm inside the distributor cap, which sits on top of the distributor shaft. This shaft has an insulated body to the vehicle’s ground or earth. The distributor shaft is driven by a gear on the camshaft on most overhead valve engines, and attached directly to the camshaft on most overhead cam engines. The distributor shaft usually also drives the oil pump. The metal part of the rotor contacts the high voltage cable from the ignition coil via a spring loaded carbon brush on the underside of the distributor cap. The metal part of the rotor arm passes close to (but does not touch) the output contacts of the distributor cap which connect via high tension (ignition) leads to the spark plug of each cylinder. As the rotor spins within the distributor, electric current is able to jump the small gaps created between the rotor arm and the contacts due to the high voltage created by the ignition coil. The voltage then travels down the HT leads to the spark plug where it again jumps a predetermined gap to ignite the air fuel mixture in the cylinders providing drive to the crank and thus power to the wheels via a transmission. (In a nut shell description.)
The principles are the same for a 4 cylinder, i6, v6, v8, v10, v12 etc. The rotors may travel in a different direction (clockwise or counter-clockwise), the number of leads on the distributor cap may be more, the firing orders will be different etc.
To show those principles of the spark, here is a simple 4 cylinder diagram with points. A v8 just more of plugs, more cap points, more cam lobes to open and shut the points etc. but you can see the idea on a less cluttered diagram.
Modern cars tend not to have points, but have electronic sensors to replace them. Latest technology has a sensor on the cam shaft which fires the spark plugs without the need for a distributor or even a coil, as the power for the spark is handled by ‘coil’ packs which are mounted on top of the spark plug lead fittings.
This post is a going to be a very cut down version of the whole process I have documented. The full rebuild with all the photos, explanation step by step can be found here. I will only be covering the Pertronix ignition process on this post, but I do cover the points process or refitting and setting as well on the full walkthrough.
* Disclaimer (just in case): If you are in any doubt on your ability to try this – DON’T. Get it wrong you and could damage the insides of the distributor, the car wont start or run properly. This is a guide on how I done it, I can’t held be responsible for your actions.
Dismantling:
First thing is to make a note of where the HT (spark) leads go and to what cylinder. Take a few photo’s if you’re not sure, label the leads up with a marker or sticky label of some sort. If you look closely the top of the Mustang distributor caps it has the number ‘1’ on the top, this is where you plug the lead for cylinder one. The diagram below right is for the firing order of 260/289/302 with a standard cam. Check your manual if you’re unsure.
Take the leads off and unclip the front and rear retaining clips to release the cap. The rotor arm can now be removed and the small usually oil soaked felt pad under it can be removed. Both my rotor and felt pad needed to be replaced.
Depending on your set up there will either be a set of points and condenser picture below left, the points gap is covered on the full process here.
An upgraded set of electronic points as mine (below right) will be set to the manufacturers recommended gap, more on that later once the rebuild is completed.
I removed the electronic set up, but once the condenser and points are removed (above left), the principle is exactly the same for dismantling and re-assembly up to the fitting of the Pertronix or points and condenser.
My Pertronix is held in place by a single screw at the bottom of the shoe which also pivots at the top where the original points screw would have held the top part of the points. Then remove the black sensor collar.
Disconnect the vacuum pipe to the front of the vacuum canister which goes to the carb. Check for any leaks or cracks on the pipe if you find some replace the pipe.
Next there is a metal lever that goes into the distributor (which will now be known as “dizzy” from now on). There is a tiny clip that holds the bar onto the pin. Remove the clip very carefully and make sure you don’t loose it. Remove the vacuum can from the dizzy.
Check for signs of perishing on the diaphragm on the inside. To check the function of the vacuum you can suck the can from the front and you should see the arm move towards the inside of the can, repeat a few times. If all is good you can clean it up and keep it safe, if not replace. Next remove the screw that holds the earth strap to the lower dizzy plate.
Next to the cam lobes there is another e-clip at the top of a pin. This holds a washer and under that a fairly strong sprung washer. Slip a small flat ended screw driver and gently tease it away. If you’re not careful it will ping up and be lost in the depth of the engine bay. Remove the washer, sprung washer and keep safe with the e-clip.
With the washer and spring washer out the way, you should now be able to lift the plate up and lift it up over the lobes of the cam.
The lower plate is now only held in place with a single screw the opposite side to where the cables come into the dizzy. Undo the screw and remove the lower plate.
Removing the lower plate there should be three raised points which separates the upper plate and should be smooth. I noticed one of mine was loose so I removed it then re-stuck it back on later.
With the lower plate removed you can now see the advancing weights and springs.
NOTE: The springs are different tensions. The one has less tension and and allows the weights to swing out under rotation to advancing the timing. The other spring is stiffer and at certain centrifugal force this spring takes over slowing down the advance. The larger and stronger spring is a loose fit to the anchor points and is normal.
On top of each weight there is again a an e-clip. Remove with a small flat ended screw driver and make sure it does not ping off. Make a note of which weight goes where and repeat for the other side.
Keep them separate or mark up a piece of paper and lay them on the paper so you know which pair go together and if they are the 13deg weight side or the 18deg weight side. Without taking the whole dizzy out this is about as far as you need to go.
You could possibly remove the springs, the two springs making careful notes on what one goes where. I decided against that just in case I stretched a spring putting it back on. This would have a detrimental effect on the timing and advance. My springs weren’t to bad so I decided not to chance it.
Now you need to clean the inside and remove any old dried grease and debris. Don’t go mad in here with the fluids, use just enough to clean. I found carb cleaner is good, and also sprayed onto a cotton bud to clean the springs and surrounding area.
You can move the move the weight plate with your fingers to clean parts that are partially covered. Don’t go mad with forcing open of the springs, you don’t want to stretch them. Make sure there is no bits of debris in the bowl or trapped anywhere.
The bowl should now be clean of all debris and old grease.
Assembly:
I started with the weights. take each weight and either clean with a degreaser or similar, or take some ‘000’ grade super fine wire wool to take the roughness of the weights.
Make sure that NO wire strands are left on the weights or fall into the dizzy bowl.
I used a small punch to wrap a little wire wool around and then clean the inside of the holes. You are lightly cleaning – not reboring the hole. Also clean the clip, any rough edges or rust could impede the movement of the weights.
With the weights and clips cleaned it was time to fit them back to the dizzy. You will need some proper lubrication. I researched a fair bit and the general recommendation is an engine assembly grease. Light smears not huge blobs!
If you examine the weights it easy to see where the wear marks are, apply a little grease to the weight. wear points and into the holes. Note that the whole weight doesn’t need greasing, just the hole, outside edges, the top where the clip holds it in place and the underside where it rests on the pin base.
Place the weight over the pin and lower it into position. There may be some excess grease, but that can be removed later. Make sure the weight is free to move and rests within the cradle. Apply a film of grease to the clip and place onto the weight.
You need to press the clip onto the post into the recess. I found again a small flat headed screw driver would do the trick. It can take a few goes to get right. Just make sure it doesn’t ping away. With both weights and clips in place it should look something like this.
Lower plate needed some love in respect that the plastic/nylon stop had worked a bit loose. Both the front and the back of the lower plate was cleaned with fine wire wool. You can see the slide pads are just hot pressed into the holes of the plate from the factory. With the plate now repaired I cleaned the yellowish and two red pads of the old grease and debris. I took some 5000grit and then 8000grit to remove any rough parts. Not sand it down, but more of a polish. Check the vacuum post has no wear and burrs.
Again make sure NO wire wool or cleaning material is on the plate before refitting. Place the plate back into the bowl area to cover the plate with the post side facing upwards. Align the hole and screw into place.
Take your assembly grease on a cotton bud and apply a film over the plastic pad areas and the post.
The upper plate may need a clean with wire wool or degreaser depending on the state of it. Pay attention to the brass bush which sits on the post of the lower plate. Brass is a soft metal and you don’t want to create a problem so be careful not to damage it with the small punch, degreaser with fine wool. Remove any burrs on the top side of the bush to allow the sprung washer to move without snagging.
On the underside of the upper plate you can see where the plate has moved across the slide pads over the years. Apply a film of the grease on these areas and into the brass bush and the vacuum post.
Place the upper plate onto the lower plate, locating it via the brass bushing. make sure it’s free to move all the way. Clean the components that hold the top plate to the bottom plate. Top washer, sprung washer and the e-clip all need to be clean and smooth in order to not snag the movement.
To refit a further film of grease over both sides of the of the sprung washer on top of the top plate brass bush with the curled edges facing up. Top washer with grease applied on the top and bottom, place the washer on top of the sprung washer.
Next refit the cleaned up earth strap for the top and bottom plates.
On the Pertronix setup, wipe over the plastic collar and slip it over the cam lobes with the recess facing upwards.
With the vacuum advance module clean the arm at the back and apply a film of grease on both sides near the hole and in the locating hole. The vacuum module can only fit on in one way following the curve on the outside of the dizzy.
With the arm located take the e-clip clip with some grease and again fit into place so that the arm is held down. Secure back in place with the two screws.
Setting up the Pertronix or points, don’t use grease here as you want the srews to hold in place. Place the Pertronix on the plate, and the other end of the earth strap that is attached to the bottom plate on top of the Pertronix while aligning the top pin to the other locating hole.
With the sensor and the collar in place you need to set the correct gap. A ‘tool’ is supplied with Pertronix which is a plastic strip to set the gap which is 0.80mm. Left pic shows the gap is to small. The right pic shows the correct way to gap the sensor. Keep the plastic gap tool flat to the sensor face and slide the the unit until there is a slight drag between the collar and the sensor. Tighten the screw fully.
In the centre of the dizzy where the rotor arm sits is a recess. This has a felt pad to oil which is to keep the cam lubricated lower down. I would recommend this is replaced with a new one and filled with fresh oil, or reuse the old one with the old oil it’s up to you. Most people use a drip of the engine’s dipstick at oil change. But my research leads to me to say that this should be a very light engine oil to allow the oil to run through the felt. It’s debated if this is still required. However, Ford wouldn’t have milled out the centre shaft and put a felt pad in there for no reason!
Place the rotor arm on top of the dizzy shaft and locate into place. These can only fit in orientation as there is a keyway on the inside of the rotor to match with the shaft cut out.
Now take your marked up HT leads or follow the chart and fit back onto the dizzy cap. Job done.
If you made it this far thank you. Another long post but still cut down a bit from the original page here.
I’m looking forward to using up some holiday and time off over the Christmas break, hopefully I will be posting some more, hopefully less technical or intense.
