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An Article About Fitting Pertronix Electronic Ignition To The Mercedes 300 SEL 6.3
Written by Steve Barratt in December 2007
Some people reading this may well have already heard of Pertronix as they are a market leader in electronic ignition and some Members may well have fitted their systems. This article is primarily for those who have not.
As most classic car owners are aware points are often a weak link in the ignition system and can suddenly let you down. In the early 1980s I fitted coil boosters to improve the spark, but of course you still had the points! There are a number of electronic ignition systems on the market and some well known ones use a small light as the sensing method. These in general are ok, but if any dirt gets on the light it can let you down. I know this is unlikely and dirt can be cleaned off, but it is another thing to possibly let you down.
I spoke to Keith Brown at J Haynes and asked if he had heard of a decent, tried and tested electronic ignition system. He told me that a German contact of his had been fitting the Pertronix systems for a while with no problems. After a little research I decided to purchase this system for my Mercedes-Benz 300 SEL 6.3. The beauty of this system is that it is so simple, one of those cases in life where less is more. It is almost comical when you open the small Pertronix ignitor box – there is hardly anything there. Fitting this ignitor is a simple operation. The instructions provided are clear and simple with easy to follow diagrams, and there is excellent, friendly service from Mark Hannaford of Pertronix should you have any queries. Another beauty of this system is that, once it is fitted, there is no longer any dwell angle to adjust. The Pertronix ignitor uses a hall sensor which is switched by another circular magnet which fits under the rotor arm. Once fitted there are no ongoing adjustments to make inside the distributor.
Pertronix is an American company and the ignitor units are made there. Mark Hannaford, the English sales manager, explained to me that Pertronix has been in business for approximately 40 years. The English branch is actually Pertronix Europe and has been here for about 20 years. They are at present selling 600 to 800 units per month in Europe, with quite a few going to Germany. They also sell distributors, HT leads etc, if you visit the Pertronix website you can download their catalogue. To contact them speak to Mark Hannaford (UK Section) telephone 01276 65554. Mark’s service can be described as most excellent, he is not just a salesman he has good technical knowledge and is very efficient and friendly in sending your purchases out on time. The ignitor units are guaranteed for 30 months and for the 6.3 cost £115, with the coil £35 – both plus VAT and post and packing. Pertronix electronic ignition make ignitor units for many different vehicles.
A great selling point of these systems is that there is no drilling or permanent modifications to the distributor required, or electronic boxes to be fitted in the engine bay. In the case of the Mercedes 6.3 you do away with both sets of points, intermediate distributor base plate and condenser. As I also purchased the high-energy (Flame Thrower) coil I could do away with the ballast resistor as well. You can put all these items, along with their screws and clips, safely away so that if you ever want to return the car to its original set up it can be easily done. When storing all mine away I also purchased a new condenser and two sets of points, just in case in the future the points or condenser go out of production (you never know).
Once I fitted the system I noticed the engine was slightly more responsive and I will no longer have to replace the points or condenser or run the risk of them letting me down. In my opinion, if you fit the Flame Thrower coil,the Pertronix system also makes the engine a little more economical due to the increased spark size and hence better combustion. Pertronix also make this point in their advertising.
If you do not have a good timing light, ie one that gives a good white light, then for about £25 you can purchase the Draper TL3. This is available from motor factors or on-line stores. This timing light was recommended by Mark at Pertronix. I purchased it and am very pleased with it – you can easily see the bright white light on the crankshaft pulley during daylight. The quality of the light is comparable with those found in far more expensive units. I already had a good tachometer to set the engine idle speed at tickover and to make sure the timing is correct, but if you have not got one I believe these are fairly inexpensive to purchase.
Top view of Pertronix Ignitor and trigger magnet
The fitting instructions starting below are for the 300SEL 6.3, but they apply to many ignitor units for different models. They are easy to fit but it is essential to check for wear in the distributor cap, rotor arm, HT leads and caps, and spark plugs and it is a good idea to replace these items at the same time if they are old.
1. First remove the top radiator hose – this makes it much easier to get to the little screws holding the condenser on the side of the distributor. After removing the condenser I put the two little screws back into the distributor to keep the threads clean and keep out dirt. One of these screws also holds the distributor earth so make sure the connection point is very clean when re-fitting it. You might prefer to keep the condenser in place to keep the original look.
2. Unclip the distributor cap and then remove the intermediate base plate inside the distributor, along with the points and the black wire going from the negative side of the coil to the points. None of these items need to be re-fitted. Thoroughly wipe clean the inside of the distributor once it has been stripped. The earth wire inside the distributor’s moving plate is important and should be checked to ensure it is not frayed at any point.
3. When fitting the Pertronix ignitor do not put Loctite on the screw they supply to hold its base plate down. A star washer is fine if you wish to use one, as I did. This screw does not just hold the ignitor base plate down, it also serves as an earth connection and Loctite can act as an insulator. I used a 4mm x 0.75mm pitch tap to make sure the thread in the base plate was really clean, I also used a cotton bud dipped in a little methylated spirits to clean it out after tapping it out. If you decide to run a tap into the thread of the base plate make 100 per cent certain that you have the correct tap and just tap to the depth of the base plate.
4. Some distributors have a little felt pad which is intended to provide lubrication to the points. If you have one fitted you will have to bend it out of the way in order to fit the push-on trigger magnet under the rotor arm. I bent mine a slight angle upwards so that it did not foul the vacuum unit arm which connects to the distributor base plate. When I fitted a new rotor arm I noticed that it was a slightly taller design than the old one and, when put in place on top of the trigger magnet, it pushed the central graphite contact in the distributor cap too far up – leaving no free movement for its spring. Therefore I removed about 2mm from the bottom of the rotor arm by rubbing it on a sheet of medium grade emery cloth on a flat surface.
5. If you are fitting a Flame Thrower coil remove the ballast resistor. You will notice that the wire going from the positive side of the coil to the ballast resistor is thinner and of lower rating than that from the main loom which goes to the other side of the ballast resistor. This thicker wire will probably not reach to the positive side of the coil (to by-pass the ballast resistor). Do not join the lower rating wire to the thicker one to make up the short fall – apparently this can cause voltage problems and the system may not work well. To make up the shortfall use a piece of wire of the same gauge (2.5mm2 I believe in the case of the 6.3) or slightly thicker. I soldered two ring connectors onto a new piece of this wire and fixed it with a small bolt, star washer and nut to the wire from the loom at one end and to the positive side of the coil at the other. I then neatly taped the bolted join. I bolted it rather than soldered it so that it could be returned to the original set up. The bolted joint also makes excellent connection, it is advisable to neatly tape this joint.
6. When putting the ring connectors onto the Pertronix ignitor wires I cut off the plastic insulation crimped on to them and then soldered onto the wires, followed by small neat tape around the soldering, you could of course use shrink wrap. The red wire is connected to the positive side of the coil and the black to the negative side. Any other wires connected to the coil, eg tachometer, radio suppressor etc should be fitted back to the correct terminals.
7. Do not forget to make sure the new Pertronix wires are well away from the nearby engine belts.
8. The Pertronix ignitor has the effect of advancing the timing, so you have to re-time the engine even if it was spot on before you started. You might have to turn the air screw down a little, as I did, as you might notice an increase in engine speed at idle, due to the better quality spark at the plugs.
9. If the Flame Thrower coil is fitted you can open up the spark plug gaps to 0.7mm to 0.8mm to take advantage of the extra power from the coil, which is what I have done. If the HT leads, caps and distributor cap and rotor arm are all in good condition you should have no problems with the insulation coping with the extra voltage. Mark at Pertronix says increasing the plug gaps is a good idea however some models are prone to frequent distributor cap failure which might be hastened by any increase in voltage.
10. You may encounter a small amount of tachometer ‘bounce’, this is a result of the extra sharp signal from the ignitor and is nothing to worry about. If you wish to remove it apparently a 50,000 to 100,000 ohm resistor should be wired into the connection on the negative side of the coil. I found this information on an American on-line forum. On some vehicles it may be possible to adjust the tachometer internally to stop the bounce. I am not worried about a little bit of bounce and so have not made this modification. It might be that other models would need a lower value resistor.
Side view of Pertronix Ignitor and trigger magnet