Help? Weird ignition (points) problems - '68 220 - PeachParts Mercedes-Benz Forum

aircap · #1 02-10-2007, 10:59 PM

Howdy again...

If you've been reading my other posts, you know I've been doing an ignition tune-up bit by bit on my car, and that my old set of points were completely shredded. I put new ones on, but mistakenly gapped them a little too tightly at first (I looked at the wrong spec in the manual), and today set out to widen the gap.

I discovered that the points are not seating up evenly for some reason...I mean, the round faces of the points should contact one another pretty much full-on square, but they don't. They are a little crooked from one another, and as a bonus, it looks like metal is migrating from one point to the other; one side is already slightly hollowed, and the other has a little bump! What the hell!?

Added to this misery is the fact that the wee ground strap running from inside the distributor wall to the breaker plate has come loose from the plate and I can't get it reattached. I soldered it, but it wouldn't stay. How is the car running at all when that gets loose...is it just arcing to ground? That would explain the weak engine performance, I suppose. Anybody have any tips for how to reattach the ground strap to the advance plate?

Help me if you can, I'm feelin' down (and I do appreciate your bein' round).

Tomguy · #2 02-10-2007, 11:13 PM

If the points are shorting out that quickly, I'd suspect bad ballast resistors and/or a bad condenser. Lastly, your coil could have too much resistance as well - but that is the last place I'd check. The inside plate does still contact ground, even without that strap. The strap just helps lower resistance between the plate and the distributor itself. With the strap not being there, periodic non-grounding of the plate could occur, resulting in an intermittent misfire.

aircap · #3 02-10-2007, 11:18 PM

Hmmm...I was going to replace the condensor today, too, but I wasn't sure the one I picked up at the parts store was right, so I chickened out. Plus my distributor has the condensor mounted outside, with a plastic plug that sticks through the distributor body...how do you replace that? It looks like it would break if I tried to just snap it in there.

Mr Basil · #4 02-11-2007, 02:01 AM

I had the same problem with that darn pigtail wire. For me it was more than intermittent misfiring. When the wire wasn't touching, the plate was not grounded(my electrical tester confirmed this). It would die at inopportune times (like in busy intersections). Worse, it looked like it was connected! I finally discovered it and made up a new one with the two ends the same. One I attached to the plate like normal. The other end I managed to attach to the bolt that holds one of the housing clips on. It's threaded hole was open on the inside of the distributor housing. I got a longer bolt and was able to put the wire to it on the inside with a nut. I used the shortest bolt I could get to work and I still had to bend some tabs of unknown function gently and temporarily out of the way. Tight work, but looks like it belongs, and she ran like a dream.

New points are easily damaged because the contact area is minimal. The contacts should match up. I'd get some new ones and tweak them if you need to.

You might also consider getting a dwell meter for $20. You get an assistant to crank the engine, with the coil wire to the cap grounded so it doesn't start a fire, then you adjust the gap until it's on spec (with the engine turning over). Stop cranking then tighten it, and check it again to make sure you didn't change it and you're set to go. Takes two minutes. Ten or less your first time. When your dwell is dialed in, then you can properly set your timing and she will really run sweetly! Plus your points life will be greatly extended with periodic checks.

Good Luck and let us know how you fare!

-Basil

250 Coupe · #5 02-11-2007, 07:49 AM

While hunting down info on points I found this. It maybe intended for MGs but dang, there is a lot of good stuff. Including the pencil test for coil polarity.

Michael

cth350 · #6 02-11-2007, 08:32 AM

About that condensor... Yours has a plastic plug attached to a green wire, and that gree wire goes off to the rest of ignition circuit, right?

That's not what one finds in a 220/8. As I hinted at in your other thread, I suspect a motor swap has happened. That or the car is a 250 with an identity crisis.

-cth

aircap · #7 02-11-2007, 09:07 AM

Mr. Basil: You say you attached the wire to the plate "like normal." How the hell did you manage to do that? I can't get mine to stay attached with solder...getting ready to try a conductive metal-filling glue.

250 Coupe: Very illuminating reading...I'll be bookmarking that one.

cth350: Yeah, my condensor does have a second wire trailing off to the coil. But the new one I ordered, which is ostensibly for a 1968 220, has the same configuration. It just spooked me because the snap-in plug didn't look like it would fit in the hole in the old distributor, and I didn't want to screw up the old one trying to get it out, just in case.

So far all the parts I've ordered sight-unseen for a 1968 220 have matched up with the car...or at least have all fit. Maybe my distributor has been updated? I dunno...another member here suggested my car should not have come with two carburetors. But it does indeed have two carburetors.

Where would I find an engine ID number on this thing? That ought to sort things out, no?

Thanks again for all the input, folks. I really appreciate it. I've been scratching my head a lot.

cth350 · #8 02-11-2007, 11:07 AM

My first car was a 1969 230/8. It ate a set of points every other month until that wire got fixed. If you seem to fix yours but it breaks again, it might be too short. Then again, it might just be the quality of the soldering job and higher quality solder, cleaner environment and seriously more heat may be required.

A rebuilt distributor should cost under 200$. But I wouldn't do that just yet. However, you might want to talk with a rebuilder to see what they do to fix it.
One of these days soon, I'll be visiting this guy, since he's close to me.

http://www.glenn-ring.com/

-CTH

Mark DiSilvestro · #9 02-11-2007, 11:36 AM

The earliest W115 220 4-cylinder DID have dual downdraft Solex carbs. The Stromberg came later.

The factory ground-wire inside the distributor was originally welded to the breaker-plate. It may be almost impossible to solder it back in place. If the original is too short, you may need to make a new ground wire long enough to add a ring-terminal, and attach it at the points mounting screw. Note that you may need a sligtly longer point screw if you attach the ground there.

A good condenser is more important than slight misalignment for decent point life. Unfortunately, I've seen problems with defective replacement aftermarket condensers, so unless your replacement is an original Bosch part, you may be playing the chicken & egg game here.

If your point misalignment is severe -
Are your points in two sparate parts, with the moveable part sliding onto a shaft permanently attached to the breaker-plate? Some Bosch distributors of this design used to have a little spring clip atop the shaft to keep the moveable part in place. Is yours missing? If the shaft itself is slightly bent that may be tricky to put right.

If the points are the one-piece design, and they weren't correctly seated onto the little pin stamped into the breaker-plate, that could cause misalignment.
Also, don't forget a tiny bit of high-temp grease at the plastic point rubbing-block to prevent excessive wear and rapid gap closure. And a couple drops of oil to the felt inside the distributor shaft under the rotor.

Happy Motoring, Mark

Arthur Dalton · #10 02-11-2007, 11:38 AM

Drop a Pertronix pick-up in there and be done with it.
No Points , No Condensor, No Dwell to fool with...and short $$$$..

aircap · #11 02-11-2007, 11:59 AM

Interesting information, folks...thanks for the ideas about reattaching the ground.

For all those curious about whether I have the original engine, etc., I just went outside and took a bunch of photos. Check them out here. Included are captioned shots of the engine number and chassis plate info. Please holler back if you can help elucidate what the numbers mean.

Seriously, everybody...thanks, thanks, thanks. I appreciate your patience and kindness. Just so you know, I do search the old threads first before posting...I just couldn't find any solid answers on this set of problems, and wanted to get some fresh opinions. Thanks.

Tomguy · #12 02-11-2007, 12:01 PM

That isn't the engine number - it's actually the part number for the head. Your engine number is stamped on the bellhousing.

aircap · #13 02-11-2007, 12:09 PM

D'OH! OK, I found the number and fixed it in the image. Engine No. 115 920 10 000678.

Oh, and can somebody tell me which Pertronix or other electronical doodad will fit the distributor in the pictures? Just for future reference.

Arthur Dalton · #14 02-11-2007, 12:50 PM

That is the correct engine for that chassis..........

Get the Bosch # of the side of the dist for the Pertronix module part# ...

OldPokey · #15 02-11-2007, 12:52 PM

If your points look like they are burning out quickly, it is very likely that your capacitor (archaic name is condenser) is not doing its thing. The capacitor actually performs two functions in a points system:

1. It allows the spark coil to oscillate after the points open - making a better spark.
2. It protects the points by absorbing the high voltage that builds up as the magnetic flux in the coil while the points were closed collapses.

If the capacitor isn't there to absorb that voltage, it jumps across the points - and you get all the symptoms you are describing.