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1973 450SL, (Previous 2008 ML350,2002 E320 Wagon, 2000 SLK230)
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Discussion Starter #1
This has been driving me crazy in the past year - year and a half and here's what I or my indie have replaced so far - plugs, wires, cap rotor, plugs again, insufficient hose to the AAV (thank you group for identifying the URO vs OEM differences), and timing, I've recently ordered a new Bosch coil as it appears to be original and I have 98,000 miles on the car in case it has degraded with time and heat exposure over almost 50 years. My only other consideration was to try a Pertronix 91885. I was wondering if I had to do anything with the trigger points whether leave as is, disconnect, or what part they played if I did a Pertronix conversion. I appreciate any input.
 

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1999 SLK 230, 1973 450 SLC
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This has been driving me crazy in the past year - year and a half and here's what I or my indie have replaced so far - plugs, wires, cap rotor, plugs again, insufficient hose to the AAV (thank you group for identifying the URO vs OEM differences), and timing, I've recently ordered a new Bosch coil as it appears to be original and I have 98,000 miles on the car in case it has degraded with time and heat exposure over almost 50 years. My only other consideration was to try a Pertronix 91885. I was wondering if I had to do anything with the trigger points whether leave as is, disconnect, or what part they played if I did a Pertronix conversion. I appreciate any input.
Pertronix upgrade helped my '73 with all those issues. I believe the trigger points are still going to control the fuel injectors. Just follow instructions from this forum to install Pertronix and it will help and certainly won't hurt a thing.
Good luck.
 

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This has been driving me crazy in the past year - year and a half and here's what I or my indie have replaced so far - plugs, wires, cap rotor, plugs again, insufficient hose to the AAV (thank you group for identifying the URO vs OEM differences), and timing, I've recently ordered a new Bosch coil as it appears to be original and I have 98,000 miles on the car in case it has degraded with time and heat exposure over almost 50 years. My only other consideration was to try a Pertronix 91885. I was wondering if I had to do anything with the trigger points whether leave as is, disconnect, or what part they played if I did a Pertronix conversion. I appreciate any input.
I installed a Petronix kit on my 1973 450 SL a couple of weeks ago after going through most of what you have done and it made a world of difference. The kits are relatively inexpensive, so it's worth a shot. Good luck.
 

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1973 450SL, (Previous 2008 ML350,2002 E320 Wagon, 2000 SLK230)
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51 Posts
Discussion Starter #5
Thank you for the posts so far. I installed the coil last night and it was worse - sputtering, backfiring, and utterly undriveable. I cleaned and reinstalled the original coil and all was fine, just the intermittent issues. I ordered the Pertronix last night so I'll see how that goes once it arrives.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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10,459 Posts
Was the Bosch coil the correct replacement for the original? There are different types.

Pertronix 91885 is a Pertronix II and it does not seem to be the best choice for our cars. They say that our copper cored wires may interfere with that unit. The simple plain old 1885 is what is recommended in the instructions in the stickies and it is the one many of us have used with our OEM wires. One owner recently installed the 1887LS and it seems to work too. But 1885 is still safest bet.

If the ignition module (aka switchgear) is the problem, it can be bypassed using again the instructions in the stickies. Then you are better off with the Pertronix Flamethrower coil. There is a difference in the windings of a conventional coil like the Flamethrower and the original Bosch coil that needs the external ballast resistor.

When car is backfiring and hardly running, I would heed Djenkas comment. It sounds like a timing issue. Check the timing with a timing light. Set it to about TDC or even 5deg BTDC at idle. Then increase rpms and watch the advance. It should advance gradually and eventualy reach about 27 BTDC at 3000rpm. If it doesn't do this, the centrifugal advance is not functioning (more in stickies on this in distributor rebuild)

Ignition points/Petronix have nothing to do with Trigger Points. They are part of the fuel injection system.
 

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1973 450SL, (Previous 2008 ML350,2002 E320 Wagon, 2000 SLK230)
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51 Posts
Discussion Starter #7
Was the Bosch coil the correct replacement for the original? There are different types.

Pertronix 91885 is a Pertronix II and it does not seem to be the best choice for our cars. They say that our copper cored wires may interfere with that unit. The simple plain old 1885 is what is recommended in the instructions in the stickies and it is the one many of us have used with our OEM wires. One owner recently installed the 1887LS and it seems to work too. But 1885 is still safest bet.

If the ignition module (aka switchgear) is the problem, it can be bypassed using again the instructions in the stickies. Then you are better off with the Pertronix Flamethrower coil. There is a difference in the windings of a conventional coil like the Flamethrower and the original Bosch coil that needs the external ballast resistor.

When car is backfiring and hardly running, I would heed Djenkas comment. It sounds like a timing issue. Check the timing with a timing light. Set it to about TDC or even 5deg BTDC at idle. Then increase rpms and watch the advance. It should advance gradually and eventualy reach about 27 BTDC at 3000rpm. If it doesn't do this, the centrifugal advance is not functioning (more in stickies on this in distributor rebuild)

Ignition points/Petronix have nothing to do with Trigger Points. They are part of the fuel injection system.
Thank you for that response - I immediately contacted the source, and they had not shipped the 91885. They exchanged and the 1885 will be shipped today. Great timing! I will also look at the timing issue and appreciate the input on that.
 

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'72 450SL, 107.044-12-000422
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Pay attention to mbgrahams specs on the timing. His numbers are different than what the manual calls out and in my experience, runs much better. I believe the service manual settings were designed to help with NA emissions requirements.

Definitely check out the stickies on this in the eg107. Lots of good info there.


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1973 450SL, (Previous 2008 ML350,2002 E320 Wagon, 2000 SLK230)
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51 Posts
Discussion Starter #9
OK- here's the latest update. On Saturday I prepped myself for the motherload and dove head first. Plugs again (NGK 7333 - BP6ES), Bosch Coil - 00027, Pertronix 1885, and lastly a timing light. My first positive indication was fired up immediately ran much smoother than before, but when driving there was sputtering. I then thought maybe the timing was off with all the new items thrown into the soup. The baseline - where it was currently set was 5 ATDC. I ranged from 3, TDC, 5BTDC, 7ATDC, then 10 and at that point it was much more stable without sputtering. I then left it to go cold and tried the next day. Driving cold it was intermittent sputtering and backfiring. Once warmed up it minimized, and when I stopped at a store, came out, started and was fairly smooth with just a mile intermittent loping. I was going to play around with the timing again, but now I am questioning the potential of trigger points. I am lightly leery, but willing to try one of two options - removing the distributor, remove the trigger points to see if they need cleaning (98000 miles) or if they're covered or in desperate need of cleaning, or buying a rebuilt distributor with newer or rebuilt trigger points already in them. I'm leaning towards the removal and cleaning first, but want to make sure I have a good detailed procedure for removal of the distributor and reassembly. Look forward to responses.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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10,459 Posts
10deg B or A?

Set at 5deg BTDC at idle (700rpm) then rev engine to 1500 and 3000 rpm and note the timing at each. You should see timing advance to about 27 BTDC.

Did you check the angle that each set of trigger points stays closed? That will give an indication of how worn they are
 

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1973 450SL, (Previous 2008 ML350,2002 E320 Wagon, 2000 SLK230)
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51 Posts
Discussion Starter #11
10deg B or A?

Set at 5deg BTDC at idle (700rpm) then rev engine to 1500 and 3000 rpm and note the timing at each. You should see timing advance to about 27 BTDC.

Did you check the angle that each set of trigger points stays closed? That will give an indication of how worn they are
I just bought a tach/dwell meter. I'll try to use this in conjunction with timing and double check before I dive in further.
 

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'72 450SL, 107.044-12-000422
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I just bought a tach/dwell meter. I'll try to use this in conjunction with timing and double check before I dive in further.
Dwell meter is for ignition contact points, not trigger points (pulse generator). If you want to check trigger points, read MBGraham’s thread on distributor removal/cleaning in the Eg107. It doesn’t get much more detailed than that.

If you are 10ATDC at idle with vacuum plugged, that’s probably too for advanced.


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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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If you are 10ATDC at idle with vacuum plugged, that’s probably too for advanced.
ATDC is retarded, I believe ;)

Whatever, I can't imagine setting timing that far retarded! 10 BTDC maybe, but that is not right either.

TDC to 5BTDC with vacuum is a starting point (A/C should be turned off) Then disconnect vac line from distributor and plug it with golf tee or similar. Then see what timing is at idle. Might be 8-10BTDC? (I forget) Then rev to ~1600rpm and ~3000rpm. Just have someone sit in car watching the tach doing that. And you watch the timing light and note how much timing advances. Engine will make a lot of noise, so do this in short bursts! This just to be sure that the internal centrifugal advance weights are free to move and doing their job.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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1973 450SL, (Previous 2008 ML350,2002 E320 Wagon, 2000 SLK230)
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Discussion Starter #16
ATDC is retarded, I believe ;)

Whatever, I can't imagine setting timing that far retarded! 10 BTDC maybe, but that is not right either.

TDC to 5BTDC with vacuum is a starting point (A/C should be turned off) Then disconnect vac line from distributor and plug it with golf tee or similar. Then see what timing is at idle. Might be 8-10BTDC? (I forget) Then rev to ~1600rpm and ~3000rpm. Just have someone sit in car watching the tach doing that. And you watch the timing light and note how much timing advances. Engine will make a lot of noise, so do this in short bursts! This just to be sure that the internal centrifugal advance weights are free to move and doing their job.
Let me ask a BTB(back to basics) question on ATDC vs BTDC on this vehicle. When I'm staring at the front of the engine, and looking at the timing marks:

BTDC........10.....5.......0TDC.....5......10 ATDC

is this a correct assumption?? Want to make sure I'm stating and timing correctly. If this is correct, before all my timing adjustments it would have been sitting at 5ATDC when I last received it from the mechanic after the new cap, rotor, and waterpump. Timing light was indicating the 5 at the right side of TDC.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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Let me ask a BTB(back to basics) question on ATDC vs BTDC on this vehicle. When I'm staring at the front of the engine, and looking at the timing marks:

BTDC........10.....5.......0TDC.....5......10 ATDC

is this a correct assumption?? Want to make sure I'm stating and timing correctly. If this is correct, before all my timing adjustments it would have been sitting at 5ATDC when I last received it from the mechanic after the new cap, rotor, and waterpump. Timing light was indicating the 5 at the right side of TDC.
If you are standing in front of car looking at engine, BTDC will be to the right of the TDC mark (And ATDC to the left) (Note that the we usually refer to left and right as though we are sitting in car facing forward. But for now we stay with your reference which is facing the engine. So, I think you have it backwards. It does sound like you may have been at 5BTDC as I usually suggest. If so, just check if it advances from there to say 16 BTDC at 1500rpm and 27 BTDC at 3000 rpm.

Your timing light should be on the #1 cyl plug wire (the front one on left side when facing engine).

You should mark the balancer at TDC so it is clearly visible. Then also mark it at 5, 15 and 25 BTDC using white paint or whatever. (maybe at 5ATDC too using different color?) You will probably have to do this from under car, so remember that engine is turning CW, so BTDC markings will actually be on left side when looking up under car (again assuming we are talking about facing engine!)

PS: Masand68 and others - please check my post. I am doing this quickly, so hope it is correct :)
 

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1973 450SL, (Previous 2008 ML350,2002 E320 Wagon, 2000 SLK230)
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Discussion Starter #18
My next question if the timing is corrected and issues still persist - trigger points. Can I remove this without removing the distributor (turn distributor, unscrew, and pull out) or do I have to remove. And either way, the other end of the cable (the square 2x3 rubber covered end) how is the best way of separating that from the connector. I don't want to break that off (I was also wondering if there was corrosion on this as well contributing to the issues).
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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10,459 Posts
I don't have that plug on the trigger points cable. But it is just a 6 or 5 pin plug . One side pushes into the other. Pry apart.
Don't know about your late 73, but it is not possible to remove trigger points on my car without pulling the distributor. Distributor comes out easily enough, but you have to be careful putting it back so it goes back exactly where it was (without rotating engine in-between). Best to leave wires on cap attached or mark them carefully!

If you do rotate, you need to set balancer to TDC as well as timing marks on passenger side cam, Then reinstall distributor so rotor points at mark at about 1 o'clock. Distributor will rotate on gears as it drops in, so you have to watch that it gets back to where it should be. Then re-time.
 

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If you are standing in front of car looking at engine, BTDC will be to the right of the TDC mark (And ATDC to the left) (Note that the we usually refer to left and right as though we are sitting in car facing forward. But for now we stay with your reference which is facing the engine. So, I think you have it backwards. It does sound like you may have been at 5BTDC as I usually suggest. If so, just check if it advances from there to say 16 BTDC at 1500rpm and 27 BTDC at 3000 rpm.

Your timing light should be on the #1 cyl plug wire (the front one on left side when facing engine).

You should mark the balancer at TDC so it is clearly visible. Then also mark it at 5, 15 and 25 BTDC using white paint or whatever. (maybe at 5ATDC too using different color?) You will probably have to do this from under car, so remember that engine is turning CW, so BTDC markings will actually be on left side when looking up under car (again assuming we are talking about facing engine!)

PS: Masand68 and others - please check my post. I am doing this quickly, so hope it is correct :)
Before VS. After TDC: I think Graham has it right. It helps to visualize the damper turning CW (as you face the engine). So as the marks pass the pointer, it hits 20 BTDC first, then 10, then TDC, then 10 ATDC, and so on.

Removing the distributor is not a big deal. As Graham says, you can do it with the crank in any position as long as you don’t turn the engine over with it removed. Before removal, mark the position of the rotor on the edge of the distributor. The rotor has a little play in it, so I actually like to wiggle it from side to side and make two marks so I have a range. The teeth on the gears are coarse enough that you won’t have any problem getting it back in in the correct position.

As far as the plug, I don’t have it on mine either but have had difficulty with similar ones. As much as possible, try to work it back and forth by hand, rather than trying to pry or grab with tools-persistence pays off.


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