Author Topic: - - distributor trouble - -  (Read 2984 times)

lurtch

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- - distributor trouble - -
« on: February 11, 2006, 21:45:24 »

Hello to all,

 I just resolved a troublesome issue with the distributor on my car.The following is the failure chain of events.

I had been experiencing a bothersome  misfire  on cylinder #5 on the last few trips to work and back. The engine was also running erratically in addition to the miss. Adjustments to the timing seemed ineffective.

Today I had the time to do an in depth analysis and found out the following:

Inspection revealed that the "T" shaped end on the rotor had completely broken off. The rotor had somehow climbed up the shaft and began striking one of the contact towers. Amazingly, the Pertronix upgrade kit I had previously installed continued to fire a spark across the 1/4 in gap between the tower pin and what was left of the rotor tip!  <<PIC>>

Also,  I was uneasy about not being able to locate the missing piece of metal tip. Questions arose - - Would further use cause some damage?  Should I try going around the block anyway now that I have the new rotor and cap  installed?  Answer:  YES

It started up nicely running on all six, so I pulled away from the curb confident in the certainty of my fix,  - - only to have it stall and quit three doors down.

It would not re-start and did some very strange backfiring. More questions - - Did the little piece somehow mess up my ignition firing sensor ? or had it dropped down and fouled the shaft somehow?

I pulled off the  cap and found I was able to quite freely spin the distributor shaft all the way around!  - - OH CRAP!  Had the shaft sheared? Had the engine thrown the timing chain? Had I just chewed up my sprockets by trying to start it?

Simple answer to this perplexing dilemma:  After years of over-tightening, the distributor hold down clamp had lost its ability tightly grip the shank of the housing.  <<PIC>>  The failure occurred  when the upward force of the rotating helical gear drive overcame the ability of the clamp to resist movement, and the distributor  climbed 3mm up out of the hole and disengaged the drive keyway!  I assume this 3mm was just enough to raise the rotor's swing path high enough to contact the cap and break the end off. (still uncertain about this  last part)

One more note for those of us who think we are Hot-Shot mechanics:  While troubleshooting this ignition problem   I had intentionally backed off the clamp bolt a little so I could more easily tinker with the timing after each lap around the block. SO - - those Kraut-Gremlins then identified this as a perfect opportunity to teach me a thing-or-two.

More Later, -  IF - my MB dealer can get me a new distributor clamp from The Classic Center in Los Angeles.

 - -  Regards, Larry Hemstreet



 










Download Attachment: dist-clamp.jpg
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Download Attachment: rotor-damage.jpg
12.16 KB
Larry Hemstreet  in  N. Cal.

1966  230SL  (restored) Met. Anthracite w/ Maroon leather
1981  300TD-T (Concours condition, 86K, GETRAG 5sp.)
1982  300TD-T (parted out)
1986  560SEC (totaled)
1991  300TE (gifted)
1998  E320 (sold)
2004  E320 wagon (gifted)
2008  CLK550 Cabriolet

ja17

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Re: - - distributor trouble - -
« Reply #1 on: February 12, 2006, 00:43:52 »
Hello Larry,

Yes these clamps cannot be left loose. In actuality there should be a small spring (#72 see diagram) under the distributor, between the distributor cog and the drive gear. This keeps the lash on the drive gear in check, but it also pushes the distributor upward if the clamp is loose!

Be careful to note that the cog (#63) on the distributor bottom is slightly off-set as is the slot in the drive gear. The cog can be forced into its slot 180 degrees off but will cause problems in the future.

Your rotor problem is probably not related to the loose clamp. The shaft inside the distributor is held down by the breaker plate and the pin through the cog and distributor shaft at the bottom of the distributor. Be certain you have the correct rotor. There are several wrong ones which almost fit but are a bit loose and will come loose and damage the cap. More often the rotor damage is accidentally caused by mis-fitting the cap or rotor.

Download Attachment: 230SL dist.jpg
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Joe Alexander
Blacklick, Ohio

« Last Edit: February 12, 2006, 01:21:48 by ja17 »
Joe Alexander
Blacklick, Ohio
1969 Dark Olive 280SL
2002 ML55 AMG (tow vehicle)
2002 SLK32 AMG (350 hp)
1982 300TD Wagon turbo 4spd.
1963 404 Mercedes Unimog (Swedish Army)
1989 flu419 Mercedes Unimog (US Army)
1998 E430
1974 450SLC Rally
1965 220SE Finback

George Davis

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Re: - - distributor trouble - -
« Reply #2 on: February 13, 2006, 14:59:15 »
Larry,

if you haven't already, take the distributor apart and find that broken piece, or convince yourself it's really not in there.  I hate to even admit this, but I once failed to check for a screw that came loose in a distributor a few years back.  It lodged in the advance mechanism and caused the drive dogs to get sheared off.  Muck like dropping a screw in a blender, not good.

George Davis
'69 280 SL Euro manual