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Distributor

This component is part of Ignition System.

Definition

The Ignition System consists of the Battery, Ignition Switch, ballast resistor, Ignition Coil, Distributor, Spark plugs, and low and high tension leads. Later Pagoda models (late 280 SLs) also have a transistorised module to reduce load on the contact Points and increase their service life.

Major components of the Distributor are:

  • Distributor Cap which sits atop the distributor
  • Rotor, which rotates with the distributor shaft so that each Spark plug can fire in the correct order
  • Points which trigger the flow of electricity
  • Condensor which ensures that electricity does not arc across the points gap when open, thereby preventing the Points from burning up.

Function

The ignition distributor performs several functions. The contact points provide the switching of current in the primary windings of the Ignition Coil to induce high voltage in the secondary windings. This high voltage is then distributed by the rotor and distributor cap to the right Spark plug at the right time with the aid of the high tension leads. It also has a centrifugal advance system to advance the timing of the spark at higher than idling engine speeds and a vacuum system to advance or retard spark timing at different engine load and throttle conditions.

The Pagodas used a variety of Bosch Distributors, depending on type and model year. Please see the table.

Bosch Distributor


A typical SL distributor



Exploded View of a typical distributor


The distributor is mounted on the front left of the engine and driven by a pair of helical gears one of which is fixed ahead of the sprocket that also provides drive for the oil pump, injection pump and the tachometer. The six lobed cam which opens and closes the points is indirectly connected to the main distributor drive shaft with the aid of two weights and springs. As the speed of the drive shaft increases, the weights fly outwards (centrifugal force) and rotate the lobed cam clockwise to advance the opening of the points. The degree of advance depends on the size of the weights, the strength of the springs and the speed of the drive shaft. As the engine speed drops, the weights are pulled back in to the center and retard the timing.


Distributor helical drive gear


Vacuum Advance or retard

A finite amount of time is needed between when the air fuel mixture is set alight (spark) and full power is developed. Hence, the distributor is timed to energise the spark plug just before TDC (Top Dead Center) so that maximum power is delivered on top of the piston just after TDC.

Here is a video of proceedings in the combustion chamber. Notice that the spark plug fires just before the piston reaches TDC on the compression stroke.

http://www.gizmodo.com.au/2007/10/micro_camera_shows_the_working

More advance is required as the engine speed increases to allow full power to develop. This advancing of the spark timing is achieved through the centrifugal advance mechanism. Vacuum advance fulfills a different function. At part throttle open (as indeed at idling) the air/fuel charge in the combustion chamber is a lot less than say at full throttle (less air and less fuel) and therefore needs a longer burn time to produce power. This advance is achieved by the vacuum cell advancing the spark timing by pulling on and rotating counter-clockwise the plate on which the contact points are mounted.


046 Vacuum Advance Distributor

When vacuum is applied to the vacuum cell, the rod from the cell rotates the contact plate counterclockwise, advancing the timing.

Strict pollution regulations brought about changes to what was coming out of the exhaust pipes and vacuum retard is used to achieve acceptable levels of NOx fume emissions. On the vacuum retard distributors, the vacuum cell is mounted such that the contact points plate is rotated clockwise. Timing retard is mostly used at idling and low engine speeds.


051 Vacuum Retard Distributor

When vacuum is applied to the vacuum cell, the rod from the cell rotates the contact plate clockwise, retarding the timing.

With ignition retard there is vacuum at the distributor only at idle and it is pretty much gone by 1,200 RPM. The reason they used vacuum retard is because you have maximum vacuum at idle even though you really only need about 5 - 6 inches to pull the advance plate to the zero position. As long as you have a vacuum signal it will pull it back to zero every time - it is a better system. Removing the vacuum line at 3,000 RPM will have no affect on timing with a 051 type distributor because there is no vacuum in the line at this speed. However,if the vacuum retard portion of the distributor is not even working then there will only be mechanical advance and about 20 degrees total. It will have an effect on a vacuum advance unit if you pull the line off because the vacuum builds up as you increase RPM's until maximum vacuum is reached. Again, the vacuum unit starts to move and is fully advanced long before the mechanical portion advances to full.

On the later cars vacuum is present at all times and a switch shuts it on or off depending on RPM and engine temperature. On these units the vacuum controls the advance more than the early units. On a #051 distributor there is about 20 degrees mechanical and 10 degrees vacuum control. On the later 061 and 062 units it is more like 20 degrees vacuum and 10 degrees mechanical. On these units vacuum control plays a larger part in terms of pollution control systems and it has to work for the engine to run at its full potential. These units actually swing over into the ATDC by 3 or 4 degrees.

Note: Throttle bodies for vacuum advance and vacuum retard are not interchangeable! The vacuum pickup points on the throttle body are either before or after the throttle valve. On vacuum advance engines, the vacuum take off pipe is at the top of the throttle body and when correctly adjusted, there is zero vacuum at idling. On vacuum retard engines, the vacuum take off is under the throttle body and there is maximum vacuum at idling. This retards the timing between 8 and 14 degrees compared to no vacuum at the distributor vacuum cell.


Centrifugal Advance Weights on the Distributor Drive Shaft

Note: One of the weights has an extra piece attached to it. On lower right showing the under-side of the lobed cam. The pins engage in the notches on the weights. Note: One of the pins is longer and controls the maximum advance.


Vacuum Advance Components

The plate on the left is fixed to the distributor body while the one on the right 'floats' on it and can be moved counter-clockwise by the vacuum cell. The steel ball and cupped spring controls any vertical movement.

SL Distributors

Early 230SL's used a Vacuum Advance distributor, whilst later 230SL used a Vacuum Retard distributor. If the incorrect distributor is used with the wrong throttle body (i.e. vacuum advance and retard are mixed) then you lose power, gas responsiveness, and the car does not sound right.

With a wrong match (vacuum retard distributor with vacuum advance throttle body) the distributor was adjusted too advanced, and during vacuum retard phase (initial run of gas pedal) this is corrected, but at the end of vacuum retard phase (with more gas pedal) the engine shows knock problems. Also it is important to adjust your distributor at the correct degrees (each distributor has different adjustments).

230 SL Distributors

TypeBosch Part #Dates UsedRemarksMercedes-Benz #Engine
Vacuum Advance
VJUR6 BR 49TMK0 231 116 04007/63 to 04/64Superceded by 0 231 185 005000 158 8401 
JFUR 6 (R)0 231 116 04605/64 to 10/65changed: 0 231 116 050000 158 9501 
 0 231 116 046 changed: 0 231 185 007002 158 3501Eng:10/20 <010786 and 12/22 <002990
Vacuum Retard
JF UR 60 231 116 047Information Requiredchanged: 0 231 116 051  
JF UR 6 (R)0 231 116 05111/65 to 01/67 001 158 0201 
 0 231 116 051 changed: 0 231 185 009002 158 3801Eng: 10/20 >010787 and 12/22 >002991

250 SL Distributors

TypeBosch #Dates UsedRemarksMercedes-Benz #Engine
250 SL     
JF UR 6 (R)0 231 116 051ALLchanged: 0 231 185 009002 185 3801 

280 SL Distributors

TypeBosch #Dates UsedRemarksMercedes-Benz #Engine
280 SL     
JF UR 6 (R)0231 116 051>06/69changed: 0 231 185 009002 185 3801 
 0 231 116 06207/69 - 09/70changed: 0 231 185 010  
 0 231 116 06710/70>changed: 0 231 185 010002 158 3901 

The early distributors(VJUR, JFUR,040,046,047,051) are cast iron units. Later distributors (062,067,007,009,010) are aluminum bodied.

Distributor Cap

Rotor

Maintenance

Regular maintenance besides checking points and timing should also include a dab of high temperature grease at the back of the points rubbing pad, lubrication of the felt pad under the rotor arm (a couple of drops of oil) and a couple of squirts with an oil can into the oiler at the side of the distributor body. This lubricates the two bushes for the main shaft in the distributor. Condition of the rotor arm, distributor cap and the carbon brush in the cap should aslo be checked at this time.


Grease behind contact point pad (but not too much!!)



Bosch supply a special grease for this purpose



Some oil for the main shaft bushes



The felt under the rotor arm should be just damp but not wet


Distributor Service Parts

TypePointsCondenserCapRotor
VJUR6 BR491 237 013 0071 237 330 067 1 234 332 088
JFUR6 (R)    
0 231 116 0461 237 013 0071 237 330 0671 235 522 1091 234 332 088
0 231 116 0511 237 013 0271 237 330 0671 235 522 0601 234 332 088
0 231 185 0071 237 013 0831 237 330 3181 235 522 1941 234 322 215
0 231 185 0091 237 013 1121 237 330 3181 235 522 1941 234 332 215
0 231 116 0621 237 013 0591 237 330 1811 235 522 0601 234 332 109
0 231 116 0671 237 013 0821 237 330 1981 235 522 0601 234 332 109
0 231 185 0101 237 013 1121 237 330 3181 235 522 1941 234 332 215

All the above part numbers are for Bosch items and the latest supersessions (09/2007)

Installing a distributor

If the distributor is to be removed from the engine for refurbishment or simply changing parts such as points etc. its best to set the engine at TDC for the #1 cylinder to fire. Turn the engine to align the TDC mark on the crank pulley with the pointer on the block and check the position of the #1 lobes on the camshaft. They should be at 10 to 2 position (i.e. pointing upwards). If they are not facing up, turn the engine through another turn (360 degrees) and check again. Now, remove the distributor cap and rotor arm and the notch on the distributor shaft should be pointing to the static mark on the distributor rim.


Static mark

Now slacken the 5mm allen bolt to remove the distibutor.

If the distributor has been previously removed without setting the engine at TDC, it can still be reinstalled by setting the engine at TDC as described above ant then distributor installed with the notch in the shaft alligned to the mark on the rim. This rough setting will allow the engine to be started, then exact timing can be set as per specs with a timing light.

Distributor settings

See also Points settings. For all Cast Iron Bodied Distributors:

 Point Gap 0.3 to 0.4 mm
 Dwell 38°, +3°, -1°.

The dwell value for US spec 280SL's with the transistorized ignition should be 30° - 36°. The minimum point gap should be 0.4mm.

DistributorTiming@Starter SpdIdle1500RPM3000RPM4500RPMRemarks
VJUR6BR49T4 BTDC4-715-1930+14+/-3W 
0231116046 02311160508 BTDC8 BTDC10-1230+14+/-3 W 
02311160475 BTDC3 +/-2 W13-2030  
02311160518 BTDC2 +/-2 W12-1930 Retard@Idle 8-14
023111606210 BTDC8 ATDC W0-5 W25-30 W Retard@Idle 17-23
0231116067      
 W = With Vacuum 
 W/O = Without Vacuum

Distributor Centrifugal and Vacuum Curves


Curves for a 230SL with a VJUR 6 BR 49 T distributor



Curves for a 230SL with a JFUR 6(R) 0231 116 046 and 050 distributor



Curves for a 230SL with a JFUR 6(R) 0231 116 047 distributor
Curves for a 230SL or 250SL with a JFUR 6(R) 0231 116 051 distributor



Curves for a 280SL with a JFUR 6(R) 0231 116 062 distributor


Ignition Timing


Timing Marks

The timing marks and pointer are viewed and aligned from the top driver's side. Use a good light to find the pointer: it is buried but visible. This sheetmetal pointer is mounted to the front of the block, just above and to the right of the large crankshaft vibration dampener. Spend some time cleaning the timing scale on the cast iron part of the dampener. Marking some critical points on the scale with white paint is very helpful (See Picture above). Do not be alarmed if you find two complete sets of timing scales in different areas of the same dampener! Sometime in the mid sixties the factory decided to change the length of the pointer so it would be easier to view from above. The factory now added a second timing scale to match the new style pointer. So most mid -sixties and early seventies six cylinder Mercedes engines have two sets of timing scales on the dampener. You need to find out which is the correct one to use for your engine. If you have a shop manual you can view and identify the two style pointers which are visibly different. If you cannot determine which scale to use, remove number one spark plug and turn the engine until number one piston is at top dead center. Your engines pointer will be at Zero on the correct scale. As far as turning the engine, you can sneak a 27mm socket between the radiator and the front engine pulley and onto the front crankshaft bolt. A 1/2" drive rachet handle and a short extesion will allow you to turn the engine by hand. If you remove all the spark plugs this will allow the engine to turn easily. Always turn in the correct rotation direction. (clockwise as you stand in front of the car looking rearward!!) Do not forget to remove the socket and ratchet handle when finished! A preliminary static timing can be set with a 12v test light or a meter while turning the engine by hand. Final adjustments should be made with a timing light with engine running at specified rpms. Specifications will vary depending on year, engine version etc (See Table above). Optimum settings may not be possible with todays fuel octane ratings, however specs should fall in the permissable range. Be sure a new set of ignition points are installed and set with a dwell meter before you go to all this trouble. Newly installed points seat themselves after initial use so you may want to run the car first, reset the points and then perform timing adjustment. Don't forget to lightly grease the cam of the distributor which moves the ignition points, also oil the felt pad under the rotor arm and refill the small resevoir on the outside of the distributor body. Distributor rotation can be carried out by loosening the 10mm slide adjustment or loosening the 5mm allen bolt at the distributor mounting base. Caution the distributor is spring-loaded and a downward pressure should be kept on the loose distributor before retightening to prevent disengagement. Set the correct advance at idling speed and tighten the distributor down before increasing the revs to check the correct advance at 3000 RPM.

Vacuum Cell Positioning

The auxiliary shaft drives the distributor, oil pump, and injection pump. There are only 9 teeth on the distributor drive gear (40 degrees per tooth), so for any given position of the auxiliary shaft sprocket relative to the timing chain, there are only 9 possible rotary positions of the distributor. This is not an issue for later cars – one of the 9 positions will certainly work. But clearances are tighter on the 230SL, with its rearward-facing vacuum advance unit on the vacuum advance distributor, particularly if the car has power steering, so the position of the auxiliary shaft sprocket becomes more important.


Rearward-facing vacuum advance unit

If one is just reinstalling a new timing chain only, the issue does not arise. But when reassembling an engine from scratch, some attention must be paid to the position of the auxiliary shaft sprocket. It is possible to install the sprocket to achieve any desired distributor position to an accuracy of a single degree (see below).

If the engine is already together, and the distributor position is unsatisfactory – for example, the vacuum advance unit prevents removal of the power steering reservoir lid, as it did in one case – it is easy to rotate the distributor by 40, 80, 120, 160, etc. degrees. Just pull it out, rotate the drive gear by 1, 2, 3, 4, etc. teeth and reinstall. But if there isn’t clearance to allow for a 40 degree rotation, here are two ways to achieve the intermediate rotations of 20, 60, 100, 140, etc. degrees without removing the timing chain from the crankshaft or the auxiliary sprocket:

  1. To rotate the distributor counterclockwise by 20 degrees, first put the engine at TDC. Then remove the camshaft sprocket and the rocker arms, and dismount the injection pump far enough to disengage it from the shaft. Then rotate the crankshaft 360 degrees and reinstall everything else just as it was. Then take out the distributor, rotate the drive gear 5 teeth (200 degrees) counterclockwise and reinstall, rotating the distributor body 20 degrees counterclockwise in the process to line it up with the rotor. Then of course reset the ignition timing, to get it exact.
    The reason for removing the rocker arms is of course to close all valves so the pistons won't hit them as the crank is rotated. (Alternatively, one could remove the head). The 360 degree rotation leaves the crankshaft in the same position as originally, and as the cam and injector pump were disconnected, they also stay in the same position. The only change is that the auxiliary shaft and the distributor rotor have rotated by 180 degrees. Then turning the drive gear and the distributor 200 degrees in the other direction leaves them 20 degrees from where they started.
    If you want a 20 degree clockwise rotation, just rotate the drive gear counterclockwise 4 teeth (160 degrees) instead of 5.
  2. This next procedure should be regarded as only a temporary solution until you have the time to apply the one above. To achieve a 20 degree counterclockwise distributor rotation, take the distributor and drive gear out, rotate the drive gear one tooth (40 degrees) clockwise, rotate the distributor body 20 degrees counterclockwise, and reinstall everthing. Then remove the plug wires from the distributor cap and reinstall them one socket in a clockwise direction from where they started. As above, reset the ignition timing.
    The initial 40 degree rotation of just the rotor leaves it misaligned with the distributor body -– there are 60 degrees between lobes on the cam and between poles for the plug wires. Rotating the distributor 20 degrees in the other direction realigns it with the rotor. But now the plug wires must be reinstalled because they are offset 60 degrees from where they should be. That is, whereas at TDC the rotor was originally aligned with the slash on the distributor rim, it is now 60 degrees clockwise from that, so the plug wires must be moved so the spark goes to the correct plug. This of course still leaves the slash mark unaligned, so the next time the distributor is installed it would be easy to get it wrong – which is why the procedure is only a stopgap one. But the car will run fine and the distributor interference problem has been solved.

I mentioned above that the auxiliary shaft sprocket can be positioned relative to the timing chain (that is, to the crankshaft and camshaft) to achieve any desired distributor position to an accuracy of a single degree. There are 40 teeth on the sprocket (9 degrees per tooth), and as mentioned above, 9 teeth on the distributor drive gear (40 degrees per tooth). To rotate the distributor clockwise by one degree, rotate the sprocket clockwise by 9 teeth (81 degrees) relative to the chain, and rotate the drive gear counterclockwise by 2 teeth (80 degrees). 81 minus 80 is one degree.

To get other rotations, just multiply the number of teeth above by the number of degrees desired. For example, to get a 10 degree rotation, rotate the sprocket by 10 x 9 = 90 teeth. The sprocket has only 40 teeth, so this is the same as 10 teeth (that is, 90 mod 40 = 10), or 90 degrees. Rotate the drive gear by 10 x 2 = 20 teeth (the same as 2 teeth), or 80 degrees. 90 minus 80 is ten degrees.

Thus any desired distributor position can be achieved.

Distributor Clamping

Two types of clamping are used. Earlier clamping was acheived by using a steel collar held round the neck of the distributor by an allen screw and the clamp then bolted to the distributor mounting housing. This system allowed minor adjustments to the timing when, for example, only fuel of a lower octane was available and the timing had to be retarded by a couple of degrees.


Early steel clamping system with minor adjustment possible



This was superceded by a much simpler steel clamp



Split distributor mounting

Very late cars have a split distributor mounting housing with a bolt through the split. Overtightening this bolt can crack the housing.

Verifying distributor installation

How to verify that your distributor installation is correct. You'll need a voltmeter to do these tests:

  1. Remove the distributor cap.
  2. Check the points and make sure that they are not sticking and have the proper gap.
  3. Crank the engine and make sure that the points open and close properly.
  4. Connect a voltmeter between the coil positive terminal and ground.
  5. "Bump" the starter until the points are closed.
  6. The voltage at the coil positive terminal should be about 8-11 volts.
  7. Bump the starter until the points open.
  8. The voltmeter should read about 7-9 volts.
  9. Leave the ignition ON with the points open and watch the voltmeter. The voltage should remain constant, no fluctuations. Watch it for a good 3-4 minutes just to make sure that it's OK. If the voltage fluctuates widely or drops completely, the switching unit is the likely cause (however, they rarely fail).
  10. If these tests are good, replace the distributor cap.
  11. Pull out the coil wire from the midle of the distribuitor cap and hold it about 1/2 inch above the port.
  12. Take a small piece of wire and connect it to the positive terminal of the battery.
  13. Briefly, touch the other end of the wire to the positive terminal of the coil. You should see a spark from the coil wire to the distributor port.
  14. Touch the wire several times; you should see a spark each time.
  15. If all of these tests are OK, then the points, coil, ballast resistors and switching unit (the black box under the battery tray) should be good.
  16. Similarly, if these tests are good, there is likely another problem, which could be vacuum advance in the distributor, vacuum problem in general, the fuel injector pump, timing, etc. Basically, the steps above will allow you to eliminate the components in the ignition system itself.

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JA: As far as specifications I strongly recomend the Factory "Technical Data" booklet available for less than thirty dollars at the Mercedes Dealers, (a real bargain about four hundred pages of in depth specs on Mercedes cars, every engine variation with specs will be listed.) These booklets do not describe repair procedures as do manuals, but only list data and specifications. Mercedes published one of these booklets for every model year. They cover engine, chassis, transmission, rear end, etc etc. You should be prepared to supply the dealer with the part number for the booklet. A listing of part numbers for available years was provided in the May/June "The Star" magazine page 80, thanks to Dave Todd. Here are some of the years and part numbers still available; (1963 passenger cars #S-2357-000), (1966 passenger cars #S-2358-000), (1969 passenger cars #S-2359-000), (1971 passenger cars #S-2360-000). If you have a factory shop manual you can fish the same data out of it. However these "Data" booklets are more concise and easier to use, a must if you’re a do-it -your-selfer.

Does anyone know the basic distributor point setting, Dwell angle, and idle speed for a 230 SL engine (127.981)? What is the reference you are using?

The point setting is not published anywhere, that I know of. However, you can start with about 0.018 inch and give it a try from there. Dwell angle is the preferred method of setting the points. I use a digital meter that also serves as a digital voltmeter, ohmmeter, etc. The dwell angle as I remember is 38 to 42 degrees.

Will Samples says: I have a Glenn's service book dated 1966. It gives the following:

 point gap: .012-.016"
 timing: 30 degrees @ 3000
 compression: 142-156 psi
 idle speed in neutral: 700-800

No dwell figures are given for the 230 SL. But, for every other 6 cylinder with identical point gap the dwell is listed as 38 degrees. There are 7 other 6 cyl MB that all say this. Hope this helps. Also, don't forget to disconnect the vacuum line to the distributor before setting timing.

I have three manuals, a MB-factory, a Haynes and a Chilton, they all list the timing at 8 ATDC, which puzzled me, but I figured all three couldn't be wrong ... but they must be. Based on your feedback I will reset to 8 BTDC where it was when I bought the car. I did a check at about 2500 RPM (I don't feel right free revving an engine beyond that) and it was near the 30 BTDC mark. I did notice that the timing marked 'jumped' every once in a while, what might that mean?

Will: I have my ideas on why the timing marks jump: weak advance springs inside the distributor, worn distributor shaft bushings, engine miss due to plug or injector or valve train. Anyone with better ideas or know for sure? I also do not like to rev an engine too high without a load. I suggest you have the timing light in use while you do the reving. That way you can see when the timing marks stop advancing, regardless of the engine rpm. The important thing here is to have the advance counterweights inside the distributor fully extended. Once that is done, the timing marks on the crankshaft stop advancing and you can now set the distributor.

The biggest culprit is the point system. Even with solid distributor bushing/shaft. Also, it is common for the advance plate to wear where the ball bearing sits (makes an uneven groove). The answer: Point conversion. Preferably optical.

Frank: earlier cars are generally timed WITHOUT vacuum to the distributor, but the 70/71 USA 280 SL is supposed to be timed at 8 deg. ATDC at 800 rpm WITH vacuum. The distributor vacuum on these cars gets switched from retard to advance (little known fact that most earlier 113s have vacuum retard); so if you set it at 8 deg. BTDC with the vacuum connected, you are likely to have too much advance when it switches to advance, which can result in severe engine damage. My advice: when installing a distributor on the 70/71 280 SL, set timing to 10 deg BTDC without vacuum; this should result in a setting of 8 deg ATDC at 800 RPM with vacuum. Rev engine to 3000 rpm (with vacuum) and adjust to 30 deg. BTDC. These values come from the 1972 Technical Data Booklet, with exception that it gives a range of 25-30 deg. for the 3000 rpm value. Exhaust gas value for 70/71 USA 280SL is 1.5 - 3.5 % CO at idle speed with engine warmed up.

While setting my timing, I noticed I'm only getting about 20 degrees of advance at 3000 RPM. The spec is for something like 30 degrees. I'm trying to determine if this is a mechanical advance problem or a vacuum retard problem. Should I have full vacuum retard at 3000RPM as well as at idle?

I think you're right. This is a replacement distributor and it only has 20 degrees of advance between idle and 3000 RPM. So I have set the advance according to the book at 30 BTDC @ 3000RPM, and it is idling at 10 degrees BTDC instead of the specified 0-4 degrees ATDC. I'm still puzzled because the vac retard is full on at idle AND 3000 RPM. Shouldn't vac retard disappear when the engine is revved?

Total ignition timing should be like 45 degrees @ 4500 rpm look in any manual in the tune up spec section, that includes static timing as well. Fixing that problem will make a very noticeable improvement in performance.

My distributor is 0.231.185.009, it is a replacement from FastLane. You can determine the amount of mechanical advance you have by disconnecting the vacuum and measuring with a strobe at idle and then at 3000 RPM. Should be a difference of 20 degrees +/- 2 degrees. Similarly, you can determine how much vac retard your distributor has by measuring at idle with and then without vac retard. The timing should retard by 10 degrees when vacuum is applied. Under running conditions, you lose the vacuum momentarily when you step on the gas. This provides an instant 10 degrees of advance, because the 10 degrees of vac retard disappears. I don't know if vacuum should have any effect at 3000 RPM. It does on my car (10 degrees retard), but that may be because the 3 way air valve (emmission control) has been taken out of the loop. The three way air valve was intended to shut off the vacuum at higher RPMs. I am trying to find out the optimum setting for this car at 3000 RPM and at idle. I suspect it is around 2 degrees BTDC at idle, and 30 BTDC at 3000 RPM. The published specs are a compromise due to emissions. Do you know what your advance is at 3000 RPM? Does removing the vacuum change the advance at 3000 RPM?

I contacted Bosch for some info a while ago, and according to them, your distributor JFUR6 0231 185 009 is the one that replaced 0231 116 051. My understanding is that the 051 unit is for a car newer than yours, so you may not have the correct replacement distributor. Some 113 distributors have "vacuum advance", and others have "vacuum retard", and so the vacuum ports are in different positions on the throttle body. Your replacement distributor has to be a match for your car's vacuum port. The 046 was replaced by the 0231-185-050; the 048 was replaced by the 0231-187-001.

Bernt Damm: the ignition retard distributor will do everything you need. High vacuum at idle assures that it will always return to the 0 position and no vacuum at speed allows the advance plate to move forward by spring pressure. Basically a good system.

I'm sorry to have to ask this question, but I searched the archives and am still looking for the correct points gap for a 1970 280Sl transistorized ignition. Is it 0.3 as stated in the Haynes manual or 0.4mm as I got from the German Sl Club Pagoda. Is this points gap adjustment accurate enough as it sounds like the standard MB procedure in the BBB is quite difficult and requires special equipment.

I have a 1970, US version and adjust it to between 0.3 and 0.4mm. I don't recall offhand what the exact measurement is for the feeler gauge that I used. The car runs well with the setting where it is now. I found that if the point gap is insufficient (below 0.3mm), then the car will sputter when I apply power and won't accelerate properly. I have been toying with the idea of going to a breakerless ignition, but I am a stickler for originality and I do not want a separate box.

Pete Lesler: my TDM states a range of .03 to .04. A better measurement is to use the dwell angle of 38 degrees +3 or -1 degree.

Vacuum problems

The spark plugs on my car are carbon fouled and the vacuum at the distributor hose is only 5. I can tell you the following: all warm up devices working, dry compression check - all cylinders above 137 lb., timing at 6 degrees BTDC, vacuum holds on distributor hose, new hoses and new brake vacuum booster, no leaks at valve pan cover into intake manifold, vacuum comes up to 15 when revving the engine, new gasket on intake manifold. Looking for ideas to vacuum problem.

Will: 137 psi is low compression. If the compression is low, then vacuum will be low. Not much you can do about it except install new pistons or piston rings. You can squirt a few shots of 30wt oil in thru the spark plug hole and redo the compression test. If the compression goes up, the fault is piston rings. If it does not, the fault is valves. Make sure the valves are properly adjusted before the test and hold the throttle fully open while cranking the engine.

I understand you're taking vacuum at the "distributor vacuum line" this is not manifold vacuum, but throttle plate vacuum. It varies with RPM because it's taken at the edge of the throttle plate, so that it can control the distributor advance. There is a small slotted, screw-type plug, at the base of the throttle, and just below the top mounting bolt, that will give you manifold vacuum. This takes a special fitting or a rubber tapered fitting must be held here to get manifold vacuum. My '67 230 SL does not have a plug in the intake manifold itself, for vacuum readings. I added cruise control to my car and in order not to modify any existing parts, I removed the banjo bolt at the rear of the manifold and drilled and tapped this plug, which can easily be replaced. This is the line that goes to the transmission modulator.

Dan Caron says: you have the wrong distributor in your car. 230 SL's were never designed for these aluminum distributors. Most 230's have vacuum advance - the aluminum ones are usually vacuum retard. The dwell angle on the cast iron distributor is about 38 degrees but on the aluminum one it's 30 degrees. This distributor is designed to be used on the CD ignition cars from '70 and ' 71. I usually take all that out if it quits working as it is expensive to replace. Works fine when it works - not so fine when it doesn't. There were 3 or 4 different distributors used in the 230 SL, the last one being a vacuum retard system. The 250 and early 280's all use the same one and the late 280 SL's use the aluminum ones. The early vacuum advance distributors used on the 230 SL have a very sharp advance curve, more than any other car they made. This engine actually produces more HP per cc than a 280 SL. These engines need to have the correct timing advance and fuel ratios to work right. Rebuild kits are available for the more adventureous. They have springs, bushings, all the washers and insulating plates. Really everything you need. About $40. Not hard to do, not easy to do. Experience makes it easier but not more fun. These old units are almost bullet proof.

I had a distributor problem on my 280. I bought a new distributor (rebuilt) through Kragen of all places on the Web. That solved my problem. Later when I had more time I looked at the old distributor and found my problem. The distributor shaft is two piece. The upper piece is held to the lower piece by a small circular clip that is locted under a round felt pad under the rotor. This clip had somehow popped off and the distributor shaft could lenghten. This caused the small pins attached to a plate on the upper shaft to ride up and out of the slots in the centrifigal weights. This made the car run very poorly until you got the rpm's up around 3000. I think the rebuilt dist was about $100, plus $50 core charge.

Tom Sargeant: the vacuum line should connect to the two way valve in a properly functioning emissions control system. That distributor has an advance curve that requires the retarded ignition during initial idle and partial acceleration for optimal performance. Without the vacuum hose hooked up and the related emissions relays functional, you will likely be in a state of perpetual advanced timing. This means you either have a fast idle (15 or better degrees of advance at idle to achieve 30+ degrees advance at speed), or if the distributor timing is adjusted to have a "normal idle", your advance range is likely no more than 15 degrees. This means that at mid and high range speeds, you are only 15-20 degrees advanced, vs the optimal advance of 30-35 degrees at higher rpms. This means poor combustion, a rich running condition, poor mileage and generally less than optimal performance-both on acceleration and at speed. Joe, since you have been active on this posted topic, pls check me where I may have technically mis quoted. I have now exhausted my knowledge in this area, but if you elect to bypass the emissions system, I think you can revert to an earlier distributor that is based on vacuum advance and not retard and improve your performance.

I just realized that the third vacuum hose that I was talking about was broken in two and it leads to the rear, trunk mounted expansion tank. I guess there is no performance issue here, mostly emotions, but I will reconnect it now that I know where it goes. Is there an easy way to check that my vacuum switch and all those speed switches work on my 1970 US Model? I'm going to check timing today after I put in new points today. The BBB is a little confusing regarding the ignition timing. They refer to a "starting speed" (idle= 800rpm?) and also, which of the two vacuum lines do I disconnect to check the values on page 00-0/3 with and without vacuum control?

The BBB describes how to check the relays but what I did was put a timing light on the crankshaft pulley and see when the vacuum retard cuts out. If you are at 800 rpm idle and your advance is set at about TDC (4 degrees after I think is spec), you should see advance progress to about 15-20 degrees BTDC through 2300 rpm. At 2400 RPM, you should see a sudden advance of 10-15 degrees. This is because the RPM relay is shutting off the vacuum at the 2 way valve, which eliminates the retard (which means allowing for more advance). Don't recall the vacuum hose connections. IF this happens, your RPM relay and 2 way valve is working correctly.

How do I set the ignition timing on this engine? I'm used to doing this on other cars by a strobe light that flashes on a timing mark on the crankshaft pulley, and adjusting the distributor. With the 230 I can't even see down to the bottom of the engine, let alone discover a timing mark!

I haven't done it on this car yet either but, from what I can tell by looking at the pic in the shop manual, you will need to time it from the bottom, looking up! The timing marks are on the vibration dampener aft of the belt pulley(s). The fixed mark (pointer) is on the left side of the block (your passenger side). It looks like you will have to time it by aiming the light horizontally at the marks, as opposed to coming up from the bottom (parallel with the wheel axle). I would suggest marking the correct mark with white chalk/nail polish/white-out to make it easier to see. An alternative method would be to static time it, but that is not as accurate.

The first thing you'll need to do is remove the hood, as you need to do for almost any maintenance on the engine, except Oil changes. Mark the pointer and damper on the proper marked with chalk or white paint, as suggested. (30deg BTC). You'll be able to see the marks by sighting the timing light beside the distributor. (I held the timing light on one side of the distributor and sighted down the other side that I could see the best.) It's a little scarry checking the timing with the engine reved up over 3000 rpm, but that's the most acurate. (Ie: 30deg BTC @ 3000-4500 rpm with the vaccuum line disconnected). The Idle settings shown in the manual, can be used initially, but the over 3000 should be your final check. If these are way off, you may have distributor advance or bushing problems.

It turned out my distributor static setting was just about exactly 20 degrees off, so I figured out a different way to solve the problem. I set the crankshaft at TDC just past compression on cylinder one, removed the head, rotated the crankshaft 360 degrees, and put the head back on. Hence the engine was still at TDC, just past the compression stroke on cylinder one. That caused the distributor drive sprocket to rotate 180 degrees, so I could then remove and reinstall the distributor drive gear 4 teeth (160 degrees) away from where it was. The 180 - 160 gave me the 20 degrees I needed. Of course, I then also had to remove the fuel injector pump, rotate it 180 degrees, and reinstall it. (I first thought I might not have to remove the head, but quickly realized one can't rotate the crankshaft independently of the camshaft with the head on, because the valves hit the pistons). Sorry to be carrying on a conversation with myself on the list in this way, but perhaps my experience may help someone else avoid the same problem.

Same poster: in an earlier note I mentioned that, in trying to install the distributor, I couldn't get the rotor to line up with the mark on the rim of the casing. After more thought, I realize that I must have incorrectly installed the drive sprocket relative to the crankshaft. So now my question is, what is the correct position for that sprocket (the one which drives the distributor and the injection pump)? The distributor drive gear has only 9 teeth, so moving it one tooth changes the rotor position by 40 degrees. The drive sprocket has 40 teeth, or 9 degrees per tooth. This makes it possible to reset the TDC distributor rotor position a degree at a time, if desired. For example, to move the distributor rotor 1 degree clockwise, move the sprocket 9 teeth clockwise relative to the timing chain, then move the distributor drive gear 2 teeth counterclockwise relative to the sprocket (that is, 9 x 9 - 2 x 40 = 1). (I realize the distributor body can itself be rotated a few degrees, but I would like to get the initial rotor position set exactly, with the distributor at the center of its adjustment range). If I'm correct in my figuring, there are 20 possible different positions for this sprocket relative to the crankshaft. Is there a mark on the sprocket that I didn't see, or is there some other way to correctly install it (without checking the distributor rotor each time)? I hope this explanation is clear.

There are so many people who said theirs is canted that it's hard to believe that it's a true problem. Perhaps yours was worse than others? Didn't someone take dash-to-wheel measurements? I'll take my measurements tonight and post and compare against others.


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