Expert advice needed please: 1986 500 distributor

[john rh]

Hi

Today I replaced the distributor cap and rotor arm on my 500SEL.

This is the view inside the distributor:

I'm inexperienced with MB's but it seems to me that a spring MIGHT be missing.


EDIT: looking at the central circular part of the distributor, in the middle of the photo:

There is a small spring at approx 5 o'clock in the photo, held in by two pegs.

There are identical pegs opposite (at approx 11 o'clock) but no spring between them.

There is no debris and no sign of a broken spring inside.

Can anybody tell me definitely whether I have something missing?

Thanks

John

 

[BlackC55]

Are you talking about the cap retaining screws?

 

[john rh]

No, the small spring in the centre of the distributor body - middle of the photo.

Thanks

John

 

[Druk]

You could well be correct. They are bob-weights which fly out under centrifugal force and provide mechanical advance/retard. If the ones without a spring move out under light pressure from a screwdriver then dont come back the spring is missing. It's also possible for just one spring to be sufficient for both weights although probably not.



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[219]

I'll have a look at mine in the morning .

 

[john rh]

I'll have a look at mine in the morning .

Thank-you. That would be great.

John

 

[john rh]

You could well be correct. They are bob-weights which fly out under centrifugal force and provide mechanical advance/retard. If the ones without a spring move out under light pressure from a screwdriver then dont come back the spring is missing. It's also possible for just one spring to be sufficient for both weights although probably not.

.

The single spring does pull back both weights. But the "empty" pegs look as though they are designed to have a spring attached.

IF I do have a spring missing, what would be happening as a result... too much advance as revs increase, or not enough?

John

 

[grober]

There should normally be 2 springs- they are usually of different "strengths" to extend the range of the ignition advance so you have probably lost one. This would probably result in too much initial ignition advance but this could be compensated by retarding the initial static setting by rotating the distributer result = poorly performing engine but with a big V8 you might not notice?

This is a good explanation from a Triumph "Dolly Sprint" article



HOW TO CORRECT POOR IGNITION TIMING.

Maybe you've just built up a brand new engine, or upgraded the cylinder head and changed the camshaft, perhaps you're simply trying to improve the running of your stock standard engine on ULP or PULP. In any of these scenarios, one area of tuning that is highly overlooked and greatly misunderstood is timing. All too often, people drop in their distributor, making a quick adjustment with their timing light, and set off thinking that all is well.

Timing is everything, and without a proper timing curve, every thing else goes out the window. Jetting changes, and other adjustments, are all useless, if first the timing is not set correctly.

There are numerous articles available, that go through the how and why information about ignition timing. What will be explained here, are some basic problems that can be encountered with mechanical distributors.

The basic mechanical distributor has 2 functions relating to ignition timing. The first function is the rate of ignition advance, (advance curve) and the second function is the amount of total ignition advance available.

The advance curve is controlled by the springs attached to the bob weights within the distributor. Most distributors have 2 springs, one light spring and another stronger spring. The relationship between these springs calibrated the speed that the bob weights move and therefore the advance curve. If the springs are too soft, the ignition advances to fast, which will cause pinging at relatively low rpm. If the springs are to hard the motor won’t perform to its optimum, due to lack of ignition advance for the given RPM.

The bob weights control the amount of maximum ignition advance that is available from any given distributor. Usually stamped on the weights will be numbers like 8,10,12, etc. This is the amount of advance that is available form this particular distributor. (Remember that 10 distributor degrees = 20 crankshaft degrees). If you have to much total ignition timing the motor will ping at high RPM, ie the distributor is a full advance, and if you do not have enough ignition advance, the motor will lack performance and usually return poor fuel economy.

The total ignition advance varies from engine to engine. You can identify what your motor is currently running at, by adding the static timing figure to the total advance taken from the bob weight. 10 static + (10 distributor x 2) = 30 total.
Most motors are at full advance by about 3000 RPM, so as stated earlier if the motor pings below full advance, more than likely the springs are soft.

The easiest fix for pinging is to retard the ignition timing. If the problem is right through the RPM range, (high RPM pinging under full load can be hard to detect), retard the distributor timing, but if it pings in the low/mid range RPM, retarding the distributor can have major effect on the performance of the motor at high RPM.

 

[grober]

A rather nicely illustrated article on the Pagoda SL Distributor. I came over all nostalgic reading it. Pagoda SL Group Technical Manual :: Electrical / Distributor

 

[219]

Well , I went out to check mine , thinking it would only take a couple of minutes .

Unfortunately , two of the three screws holding the cap on are pretty rusty looking and exerting a fair bit of force on one was starting to chew the cross head , so I decided discretion was the better part of valour and have given both a good 'scoosh' with penetrating oil . I will leave for a couple of days as I don't actually need to take the cap off and try again .

I do have a new spare cap which has three shiny new screws in it , but wasn't planning on fitting it while the old one is still serviceable .

If I manage to remove the old cap anytime soon , I will post a pic of the spring(s) .

 

[khimani_mohiki]

i thought on the 2nd generation engines the igntiion advance was controlled by the EZL, does your EZL have 4 pin sockets or 8 pin sockets?

 

[john rh]

What is an EZL?

John

 

[john rh]

Well , I went out to check mine , thinking it would only take a couple of minutes .

Unfortunately , two of the three screws holding the cap on are pretty rusty looking and exerting a fair bit of force on one was starting to chew the cross head , so I decided discretion was the better part of valour and have given both a good 'scoosh' with penetrating oil . I will leave for a couple of days as I don't actually need to take the cap off and try again .

I do have a new spare cap which has three shiny new screws in it , but wasn't planning on fitting it while the old one is still serviceable .

If I manage to remove the old cap anytime soon , I will post a pic of the spring(s) .

I had the same problem with mine, although only one was siezed. I ended up using a grinder to remove the cap and I needed heat to remove the stuck screw. You can see part of it snapped off in my photo! So I don't blame you for a tactical retreat: many thanks for trying.

Can anybody else help me with a photo of the internals of a 1986 500 distributor?

Thanks

John

 

[ray_hennig]

Ezl

The EZL is the Electronic Ignition Controller - it exists in Mercedes of 80s and early 90s vintage and it's often on the left-hand (from driving position) bulkhead in the engine compartment.

The EZL will have a vacuum tube going to it from the inlet manifold, as well as other inputs from other engine sensors. It measures engine conditions and, simply, it decides when to fire the spark in each cylinder. When it fires the spark, it does so via the ignition coil and then up to the centre pole of the distributor cap for "distribution" to the appropriate spark plug.

Modern (1980s+) EZLs are mapped to optimise performance under varying conditions. There are publications from Bosch that go into great detail.

Your '86 500SEL will have one somewhere.

RayH

 

[grober]

There is a definitive thread about this somewhere if I can find it? In the meantime this thread would indicate there may only be one spring. ignition advance question - Benzworld.org - Mercedes-Benz Discussion Forum

quote:- Ignition advance is handled by the EZL. The counterweights add a mechanical advance to prevent flashover and the wrong plug from firing, i.e synchronized.

 

[219]

Your '86 500SEL will have one somewhere.

RayH

It is on the nearside front wing , just forwards of and below the ABS unit .

 

[john rh]

There is a definitive thread about this somewhere if I can find it? In the meantime this thread would indicate there may only be one spring. ignition advance question - Benzworld.org - Mercedes-Benz Discussion Forum

quote:- Ignition advance is handled by the EZL. The counterweights add a mechanical advance to prevent flashover and the wrong plug from firing, i.e synchronized.

Thanks. The consensus on that thread is that one spring is correct. So I'll take it that I have nothing to worry about, unless someone tells me different! To me, the car seems to run fine, but it's the only one I have driven so I have no benchmark.

Cheers

John