Ignition

[Harry]

1966 230SL.  I recently acquired this car and began to "refresh" fluids and the other things that you often do upon buying a used vehicle.  For me this included points, condensor, plugs, coil, rotor and spark plug wires.  The car had been missing when I bought it and I wanted to clear that up immediately.  I recently installed the parts and now I'm having trouble getting the car to start at all.  It will occasionally, but even then it stumbles.  I have re-verified TDC and the position of the rotor so I feel confident about timing.  (I had removed the distributor so I wanted to be sure I had reinstalled it correctly.)  I did change plug types from the Bosch Super Plus to the Bosch Platinum (intended as an upgrade).  Is it possible the resistance of the platinum plug is higher and resulting in a weaker spark?  Any other thoughts/suggestions?

[mdsalemi]

Harry,

Welcome to the group here.

The Bosch Platinum plugs are generally not recommended, and you'll find conventional plugs better suited here; I use NGK BP6ES.  However the plugs should not prevent starting.

Time to go through each plug wire, ensure you are getting a spark.  There are simple testers for that, you can place them in line.  There are other ways to test the high voltage at the end of each wire such as with another plug.  If you get no High Voltage at any plug wire, back track to the distributor and ensure you have all properly connected in there.  I think the wiring diagrams are available for full members here...

[Benz Dr.]

You really want to use a non resistor type spark plug. I believe that Bosch has discontinued any of their non resistor plugs and only makes resistor plugs. Platinum is one of many the produce.

 I use NGK BP5ES which are equivalent to the old Bosch W9DC. I found that the W7DC, which is what is called for, is a bit too cold for modern fuels. Only engines with perfect compression seem to run OK with these cooler plugs. Since most engines run at less than optimum compression, I use the same BP5ES plugs in everything. 

You can always upgrade to the hotter '' red '' coil which almost doubble your high tension voltage. Make sure your spark plugs are set to at least .032''  Some manuals state .024 which is not enough gap. I run a 38 - 40 degree dwell angle.
You should also check your coil wire. I find that some sets use a carbon core in this wire which cuts voltage down to almost nothing. Replacing the coil wire with a steel core type will make the engine start instantly if that's what you find.

[Harry]

Thanks very much for the help.  I will change plugs and run down potential wiring issues.  And I'll report back!

[mdsalemi]

Summarizing what Dr. Benz and I have said--

NO resistor plugs.
NO resistor wire.
The ONLY resistance you have in the setup is in the plug ends.

But, you are trying to just get the car started; try to go back to what you had when you got it, and then add in the new bits one by one...

[Harry]

I returned home from a week or so away and I am anxious to get back to the 230SL.  While away, it also occurred to me that I made another adjustment  to the car once home.  It had been idling around 1200 RPM even when warm.  I adjusted the spring loaded idle adjustment screw located on the intake manifold near the engine and was successful in bringing the RPM down to more normal levels.  I don't think that I have been able to get the car to re-start well since then.  I will "unadjust" the idle correction to see whether that is a contributor. At this time, the original components are back on the car except the points (new) and the coil (red).  And - the plugs are the recommeded NGK's.  I have been able to get the car to start intermittently but certainly not up to par.
I also checked compression while the plugs were out and found that generally the compression is low all around - 105 to 120 range.  I squirted some oil into a couple of cylinders and found no improvement so I expect that sometime soon I may need to look into removing the head and having it reworked.  I'd like to research that some and see if there are any good recommendations.  It seems it would be desirable to upgrade to accomodate unleaded fuel but perhaps not.  (BTW - the car shows about 88K miles on the working odometer.)
Thanks,
Harry

[Benz Dr.]

Those are very low compression numbers. If extra oil didn't bring the numbers up you're more likely looking at cylinder wear along with valve wear. Part of why the engine won't start is simply because you have next to no compression. A good 230SL engine should be in the 150 PSI + range.
Check your engine oil by pulling out the dip stick. If it smells like gas this will also cause hard starting as the much diluted engine oil won't seal the piston rings. Low compression causes less than optimal combustion which in turn leads to fuel dilution of the engine oil.
Your engine will run at those low numbers but it won't run very well.

Once you have the head removed you will be able to have a better loook at the cyinders. Your KM or miles could be 100,000 plus what's on your odometer since it only goes that high before it starts counting from zero again.

[Harry]

She runs!  Since my last post, I removed the distributor and set the points gap on the bench to 0.014".  I also replaced the new Condensor with the original.  I had just installed a new (green wire) Bosch Condensor so I find it hard to believe that this component was faulty but perhaps so.  I lean more towards the points gap.  I had set them at 0.018" before.  My books on the car actually recommended 0.012 - 0.016.  Either way, the car runs much better than when I picked it up.  It still isn't Mercedes smooth but as I reported earlier, the compression is low across the board.  More to play with later!  Where is the best place to source parts for these cars?
I will now check on oil capacity/weight/grade and recommended filter, transmission oil/filter, and brake fluid.  Also - is there a recommended hoist for lifting the top to the garage ceiling?  I was considering a stand but I prefer not to handle it that much and to save on garage space.
Thanks for the helpful advice,
Harry