Intresting failure: sheared distributor rotor cam adapter - Mercedes-Benz Forum
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post #1 of 39 (permalink) Old 01-20-2016, 02:37 PM Thread Starter
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Post Intresting failure: sheared distributor rotor cam adapter

Had an interesting failure in my '93 2.6 Sportline the other day. I'm driving home late at night, and I pull away from the last stop sign about 2 miles from home. I pull hard through first gear and am halfway through second gear when the engine stumbles hard. I immediately shifted into 3rd, but the engine was dying. I pull over and get the car to a safe spot to see if I can diagnose the issue.

No luck. I flat tow it home the next day with a buddy and then finally set to work testing out to see what was going on. I quickly determined that there was no spark at the spark plugs. The coil wire sparked pretty well when I tested there, so that told me there was an issue in the distributor.

Mercedes M103 distribute rotor failure by craig richmond, on Flickr

Sure enough, I pull it all apart and find this:

Mercedes M103 distribute rotor failure by craig richmond, on Flickr

That's the back side of the rotor - the adapter that it bolts to sheared off flush. Here is the view of what remains in the head, attached to the cam:

Mercedes M103 distribute rotor failure by craig richmond, on Flickr

I've removed the retaining screw, but the stub doesn't want to come out. I'm waiting on the replacement I just ordered, so I have a few days to try and work the stub out. I'll tap threads if needed... but I suspect I can get it to come out before going to that extent.


I read a bit on the forums about no spark conditions and things that could result in the engine dying suddenly, and none of the examples I was able to find quite lined up with mine as there was no leading indicators like hard starting (failing CPS) or the like.

Just thought I'd share this failure with the group. Anyone seen this before? Is it common?
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post #2 of 39 (permalink) Old 01-22-2016, 10:31 AM
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You may not find an extractor big enough to fit in the hole....better yet, go to autozone and borrow their pilot bushing puller. It took me less than 5 minutes to take it out.
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post #3 of 39 (permalink) Old 01-22-2016, 05:23 PM
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There has to be a cause. The distributor drive / worm gear may merit a closer look.
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post #4 of 39 (permalink) Old 01-23-2016, 05:36 PM Thread Starter
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Originally Posted by Teutone View Post
There has to be a cause. The distributor drive / worm gear may merit a closer look.
I agree that there should be a cause... Can you elaborate on what worm gear you're referring to? All the photos and illustrations I have of an M103 shows the "rotor arm drive sleeve" fitting directly into the end of the camshaft at the timing sprocket hub. This sleeve or adapter is what failed - no gears involved. I'd love an explanation on what worm gear you're referring to.

Thanks!
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post #5 of 39 (permalink) Old 01-23-2016, 05:50 PM Thread Starter
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Quote:
Originally Posted by javelin68 View Post
You may not find an extractor big enough to fit in the hole....better yet, go to autozone and borrow their pilot bushing puller. It took me less than 5 minutes to take it out.
Sure, you *could* do things the easy and rent a proper puller. But who likes that?

I scrounged around my shop and found that a 5/16-18tpi bottom tap was just about perfect for the job of cutting some threads into the broken stub stuck in the end of my camshaft. So I ran it in and found a proper bolt to thread in.

Failed w201 m103 ignition rotor adapter by craig richmond, on Flickr

Then, with a 13/16" socket and a few washers, I threaded that bolt into the broken stub and turned until it started to pull the stub out. I had to start and stop a few times to adjust bolt length with washers as needed.

Failed w201 m103 ignition rotor adapter by craig richmond, on Flickr

It was pretty snug, but it backed out quite nicely. Out:

Failed w201 m103 ignition rotor adapter by craig richmond, on Flickr


Here is the bore - you can see there is a little corrosion in there, as well as the swarf from cutting the threads. I cleaned those up with a quick swipe of a magnet.

Failed w201 m103 ignition rotor adapter by craig richmond, on Flickr

All the pieces on the bench:

Failed w201 m103 ignition rotor adapter by craig richmond, on Flickr

And finally, here is the fit of the two pieces, clearly showing the shear line.

Failed w201 m103 ignition rotor adapter by craig richmond, on Flickr

Regarding the failure, since the distributor seals everything up pretty well, any condensation that occurs naturally being the interface of a cool area and a warm area doesn't really have any place to go. I suspect that resulting corrosion played a big part in this component failure.

I had just replaced the cap and rotor about two months back - matching brands, so no strange interference. Looking at both parts, there is no strange wear markings.

I find it odd that this is such a common part - leads me to believe it is something of a wear item, or that the failure is typical. Pelican stocks FOUR varieties of the same part. I've got a genuine MB part on order.
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post #6 of 39 (permalink) Old 01-23-2016, 08:45 PM
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Wow, I've never seen a break like that before.

1969 280SL
1984 300CD
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post #7 of 39 (permalink) Old 01-24-2016, 03:28 AM
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Quote:
Originally Posted by Mezzanine View Post
I agree that there should be a cause... Can you elaborate on what worm gear you're referring to? All the photos and illustrations I have of an M103 shows the "rotor arm drive sleeve" fitting directly into the end of the camshaft at the timing sprocket hub. This sleeve or adapter is what failed - no gears involved. I'd love an explanation on what worm gear you're referring to.

Thanks!
My mistake. Does not apply to M103.
This happened on a M117 V8 that kept eating rotors.
The culprits turned out to be worn worm and snail gear (on the bottom of THAT distributor and the drive it inserts into.
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post #8 of 39 (permalink) Old 01-25-2016, 01:52 PM
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Originally Posted by Mezzanine View Post
Sure, you *could* do things the easy and rent a proper puller. But who likes that?

I scrounged around my shop and found that a 5/16-18tpi bottom tap was just about perfect for the job of cutting some threads into the broken stub stuck in the end of my camshaft. So I ran it in and found a proper bolt to thread in.

And finally, here is the fit of the two pieces, clearly showing the shear line.

Failed w201 m103 ignition rotor adapter by craig richmond, on Flickr

Regarding the failure, since the distributor seals everything up pretty well, any condensation that occurs naturally being the interface of a cool area and a warm area doesn't really have any place to go. I suspect that resulting corrosion played a big part in this component failure.
You can crazy glue those two piece together and use as spare... ; )
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post #9 of 39 (permalink) Old 01-28-2016, 02:47 PM Thread Starter
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Originally Posted by javelin68 View Post
You can crazy glue those two piece together and use as spare... ; )
Believe me, I was tempted to just tig weld it up and slap it back in.



Parts arrived today, and I got it swapped in. Strange thing is that it still won't start. I've got spark, and the plugs are a little wet, so I know it is getting some fuel at least. It's hard to see if starting fluid will get it to crank given I haven't found a place on the intake manifold that's convenient to spray it into. I've sprayed in down the metering plate, but it's too far away to have any impact with such a liquid spray like I have.

Time to start the troubleshooting plan. Can anyone tell me what pins to jump on the fuel pump relay to get the fuel pump to run? I want to ensure that is working.

Multiple simultaneous failure is always suspicious, and I'm really scratching my head on this one.
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post #10 of 39 (permalink) Old 01-29-2016, 02:49 PM
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This happened to me on a M103 when I had my 300TE.
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