I recently replaced the points and condenser in my 250SE. Lubrication for the felt in the distributor shaft looked good. Lubed the points cam. Added oil (had some oil still in it) to the fitting on the side of the distributor. Set the dwell, all is good.
On this engine, the distributor is driven off of the cam chain. It goes into an aluminum front cover. The distributor looks like machined steel (although I read somewhere it is actually supposed to be cast iron; no matter it's a ferrous material, of some sort).

The ignition timing is off spec. I went to adjust the timing, loosened the socket head bolt pinch clamp, and the degreed adjuster on the side. The clamp is loose but the distributor refuses to turn.

I've tried plain oil, PB Blaster, CRC Freeze Off, heating the aluminum cover, cooling the distributor body (and the reverse), tapping with a brass mallet, torqueing with a band wrench; all in different combinations and together.

Nothing seems to help so I'm turning to my fellow Peach Shop Forum visitors for any suggestions you might have.

Thanks in advance! (No pun intended! )

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Vehicles 1968 250SE;4 speed manual on the floor, no marker lights

A few pics of the engine, and the distributor may be helpful.

You may need to remove the distributor in order to free it up to move. Index the distributor before removal and using your brass mallet tap it up from the bottom of the distributor housing. Snap on actually makes a slide hammer puller with a U shaped collar used to remove stuck distributors. Once the distributor is removed thoroughly clean the outside diameter of the distributor and the inside of the cover, then lubricate both.

Did you loosen the pinch bolt or the actual distributor hold down clamp?

The pinch bolt is a collar around the distributor housing and the hold down is a separate clamp located at the junction of the distributor and the engine block/front housing.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

Thanks for your suggestions!

The pinch bolt and clamp are loose. This engine also has a small scale adjuster with a cam bolt, which I read is for a quick manual adjustment to compensate for poor fuel. The retaining bolt is also loose. This device is free. They both move independently of the distributor housing.

I've tried several things up to and including using a slide hammer with a gear puller attachment. No luck.

I may try cooling the steel distributor housing next...

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Vehicles 1968 250SE;4 speed manual on the floor, no marker lights

Given it is cast iron, it is going to be brittle, there is a real chance you will crack it if hammered on.

The key point in getting this to move will be reversal of motion. At first it will move a slight bit then bind, the trick is reverse direction never applying too much pressure. Don't worry about trying to pull it out at first, concentrate in making it turn.

Does the area around the housing look corroded from road salt or is it greasy like an old engine?

If corroded from the outside, apply penetrating oil over a long period of time may get it to move.

In all likely hood, the housing is stuck from varnish build up from engine oil. Is there a way to access the crankcase side of the distributor? Applying carb cleaner from the oil side and letting it soak would slowly dissolve this. Application from the outside won't help as it won't get past the distributor o ring.

To do this right is easy. It just takes a lot of time.

You can remove the entire distributor housing from the engine. There is a gear, sort of a worm gear, that is driven from inside the engine and it is what is splined into the distributor gear to make the distributor turn.

And these can get into a bind. When they do nothing will turn and you have to remove the bolts that hold the alloy housing to the front of the engine, the housing that the distributor is mounted in. It would be good to have access to a factory manual before doing this.

The distributor is cast iron if it is an early one. They went to alloy bodies later in the run. The cast bodies have a big 'ol 'BOSCH' metal tag on the side of them.

There are some bushings on the ends of the worm gear. These wear and cause the worm gear to bind. When you fiddle with the distributor it upsets the bushings since they are already right on the edge of going.

This sounds like a lot of work but it's not. And if you need a new worm gear and housing there are usually some of them on Ebay. I don't remember what they cost new but it is eyeball popping.

Here is what you are looking at on the outside if you find you must remove the housing.

It's not hard to do. It just takes some time.

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And another view. As you can see the worm gear is driven off of a gear and the worm gear is what the bottom of the distributor tang fits into.

If this worm gear is binding removing it and replacing it and/or the bushing is necessary.

Or you can just replace the entire assembly with a used one.

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Thanks for the pics Idle.
I appreciate the information. I really didn't want to have to disturb the cover if possible. I thought it would likely be difficult for me to get the helical gear, the tabs for the distributor and the rotor repositioned for correct timing.

I was finally able to get the distributor to rotate (2 hours of work) by heating the aluminum housing with a heat gun. Took a few tries. My thermometer indicated about 200F. I was cooling the distributor with ice packed into a 'cone' around the distributor housing at the same time. Continuous soaking with oil may have helped at that point. Pic attached shows the rusty parts and tools used.

Ultimately, I had to use the slide hammer to get the distributor out of the Al. housing. It appeared that corrosion between the aluminum housing and the distributor was the culprit.

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Vehicles 1968 250SE;4 speed manual on the floor, no marker lights

It did give me the chance to restore the distributor to a better state than if I hadn't removed it. This pic shows the restored parts ready for reassembly.

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Vehicles 1968 250SE;4 speed manual on the floor, no marker lights

Now that you have the distributor out you may want to consider fabricating a U shaped collar that can be used with your slide hammer as opposed to the two jaws. Make it out of 1/4 inch steel with a hole threaded to fit your slide hammer shaft. For future use or to loan out.

Two suggestions.
#1 a liberal coating of an anti-seize compound on the housing
#2 Clean all your grounding points from the chassis to the engine block. Besides simple aging processes the number one cause of corrosion between metal surfaces is electrolysis.

__________________
“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now

This would also be a good time to install an new grounding strap. These are cheap and not exclusive to Mercedes and if you are removing it to clean the ends you might as well replace it. They will break down inside and while they will look great will not pass current like they should.

Thanks everyone!

I agree. The ground strap was replaced. I use the type that are simply braided wire, without insulation. I also use a copper grease/paste at all ground connections to prevent corrosion. I try to use the grease wherever practical for positive connections, also. I learned this trick from a boating buddy.
I'm near the ocean-everything corrodes quickly without it.

The slide hammer with the 3-point gear puller worked fine for gripping the housing. No issues with the tool. I would recommend it's use to anyone as it really helped. It did not damage the housing in any way.

The housing was coated with Anti-Seize prior to reinstallation. I don't think I'll need the slide hammer again. At least not on this car!

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Vehicles 1968 250SE;4 speed manual on the floor, no marker lights