Point gap changes! - PeachParts Mercedes-Benz Forum

Chaosmosis · #1 02-26-2003, 08:05 AM

Hi, I have a 1973 Mercedes 450SL engine117.982 chassis 107.044
When I set the points the car will run well for five minutes then die if I go back in and check the point gap it has closed or almost closed. The screw to set the gap is not stripped and is in good working order. My question is this because the distributor bushings are worn or is it something I am missing?? Thanks in advance for your response!!
Thanks,
Chaosmosis

autozen · #2 02-26-2003, 11:03 AM

Did you bypass the ignition module and go back to standard ignition setup without changing back to a black coil?

Peter

Chaosmosis · #3 02-26-2003, 07:07 PM

Thank You for your reply, you may be on to something I've owned this for about three months and it ran fine; then one day it wouldnt start, turned out the black coil was cracked and the ballast resistor started to smoke and get very hot, I ordered a new ballast resistor and replaced the coil with a blue one from A franchise Auto Parts Store.
I do believe the ignition module may be bypassed because when I trace it back it comes from the positive of the battery to the ignition switch through a relay then to the ballast resistor then to the positive of the coil from the negitive it goes to the condenser in the distributor.
If you have time could you explain how this would affect the point gap and how the wiring harness that plugs into the bottom of the distributor controls the distributor and how the black coil differs from the blue coil. Thank you you have been a great help! A little knowledge can save a lot of time and money....
Thanks Again,

Chaosmosis

Greg in Oz · #4 02-26-2003, 07:24 PM

You have described a conventional Kettering ignition in describing how yours is wired. Obviously the transistor ignition module has failed so someone has reverted to a conventional system where the points switch the coil primary current directly to chassis. In this instance a regular black coil is used.

With the transistor module in use the points switch a much smaller trigger current (to extend their life) from the ignition module. The module in turn switches the positive (rather than chassis) side of the coil primary. In this case a blue coil with a lower primary resistance (= higher current & higher output) is used. If the points are used to directly switch the primary of the blue coil they will have a very short life.

The best option would be to obtain another transistor module and have the system rewired as originally intended. The less costly option requiring greater maintenance (and offering less spark energy) is to replace the blue coil with a regular black one and continue having the points switch the coil directly.

Chaosmosis · #5 02-27-2003, 06:51 AM

I will price the Transistor Ignition Unit; but would you know the part number for the black coil? Or perhaps what years the black coil was used when I try to look it up they show a picture of a silver coil, is that the same thing?
Thanks In Advance...
Chaosmosis

ctaylor738 · #6 02-27-2003, 09:11 AM

Another option is to install a Pertronix or Crane breakerless system. This costs less than the ignition module and is a good solution if you don't care about originality.

www.durranceeng.com is a great web site for information. Pertronix and Crane also have web sites

autozen · #7 02-27-2003, 10:50 AM

That ignition module is going to cost you some serious change. If it were me, I'd go with either of the two suggestions in this post. Since you have a low compression that runs on regular unleaded the black coil standard ignition should work fine. The car would even be more reliable, because there is no module to fail or tempramental points. The downside of the MB transistor system is any slight foreign matter between the points and you lose spark.

Peter

Chaosmosis · #8 03-08-2003, 06:48 AM

Thank you to everyone that replied, I bought a black coil and points, and adjusted to .024 and now it works great. My next job is to check the compression and cahin stretch and then just drive it!

Thanks again
Chaosmosis

ctaylor738 · #9 03-08-2003, 09:56 AM

What did you do about the condensor? I think you need one if you don't use the ignition module.

autozen · #10 03-08-2003, 10:52 AM

The condensor should still be in the distributor, but the lead may have been cut as was the custom in those days which means a replacement is in order.

Peter

Chaosmosis · #11 03-10-2003, 06:48 AM

I put a condensor in it but the plugs are getting extreme carbon buildup, I checked the dwell but it is ony registering around 2400. I tried to adjust it by moving the distributor but the needle doesn't move. The car runs great with lots of power but I am confused about the dwell...
Is .024 correct for the gap? I also checked the compression and all cylinders are between 125-128. What is causing the plug fouling?

Thanks For your help!
Chaosmosis

ctaylor738 · #12 03-10-2003, 08:06 AM

It sounds like you are reading the RPM, not the dwell angle off your meter.

As for the point gap, I looked it up on the CD, and they don't give a gap, only a dwell angle of 47 degrees.

You adjust the dwell angle by changing the point gap - by turning the distributor you are changing the timing. I suggest that you get the dwell right, and then set the timing with a timing light. The CD says 10 degrees BTDC.

Carbon on the plugs means you have a rich fuel mixture. It could be from several causes. I would get the gap and timing sorted out, then take the car for a drive that allows it to get fully warmed up. Then pull a plug or two and see what the carbon situation is.

If you need the dwell and timing procedure, send me an email.

autozen · #13 03-10-2003, 11:37 AM

Chuck's advice is spot on except the 47 degree dwell part. All the transistor controlled ignitions in those years were set to either 30 or 34 dgrees depending on model without regard to # of cylinders. When you go back to a black coil ignition system you go back to dwell angles in relation to # of cyls. A 4 cyl is set at 48 degrees, a 6 cylinder is set at 37 degrees, and I believe an 8 cylinder is set at 24 degrees. You best check, because I can't remember the setting for the 8 cyls for sure. Also you really need to use a dwell meter to set points on these things; feeler gauges just don't cut it. Pull all the plugs, remove the cap and rotor, and have someone crank the engine while you tweak the points and watch the dwell meter. Tighten the points hold down screw and check dwell again. Sometimes it changes when you tighten the screw.

Good luck,
Peter

ctaylor738 · #14 03-10-2003, 01:41 PM

I hear you. I did a double-take on the 47 degrees myself, but there it was on the CD.

autozen · #15 03-10-2003, 11:32 PM

I think the CD is wrong. I have several dozen original MB shop manuals and have found many mistakes and misprints.

Peter