dwell changing on its own 66 230 sl

[merrill]

so this is strange,  I sure hope Dr Dan does not reply with my distro is messed up.

I have a rebuilt 051 distro on my  66 230 sl.

When it was installed the dwell was perfect at 38, I checked it the other day and dwell was 35 - 36

Saturday I re set the dwell to 38 exactly, today the dwell was 35 - 36. 
I drove a total of 44 miles since Saturday

To get the dwell back to 38 I have to DECREASE the gap at the points.

Is this a Distro issue or something else

The dwell is stable over different Rpm's

thoughts?

[Benz Dr.]

I had to read that about 10 times before I figured out what you were asking.

 As long as you have proper dwell angle that makes the engine run OK and you have timimg that makes the engine pull hard without pining then the numbers are only there as a guide and are not absolute. We try and set as close to the recomended numbers as possible but it's not a disaster if they're off somewhat. It's HOW the car runs that's important.

As the points wear the dwell angle will change - that's normal. I set most of my rebuilds at about 40 degrees but I will change that depending on how the unit is working.  Even if everyone here understood complely it wouldn't matter because you HAVE to use a distributor machine to do all the set up. You can use a dwell/tach meter to set the points but that won't tell you start of advance, point of fire or several other key inputs to set everything up. Plus there's a number of small shims to set the end play on the main shaft and the cam lobes.

Some are fairly easy to do - some aren't. It's at least 2 - 3 hours of set up if you have expirience and sometimes all day if it won't dial in. I guess what I'm trying to say is a distributor looks like a pretty simple part. Not much in there and it all kind of makes sense - should be easy, right? Well, it is..... sort of. All I can tell you is that the most simple job can turn into more than you ever counted on when it won't work. In truth, there are NO simple jobs.

Ever strip a spark plug hole? That was supposed to be a simple job until you ended up pulling the head to fix it.

[merrill]

Dan
Hi, Thanks for the reply, I woke up a 4 Am last night an realized my post was incorrect

I have to make the gap smaller to get the dwell back to where it belongs.  So the gap on the points is actually getting Larger...?

I had a reply from a friend who asked me to check to see if the screw holding the points is a
Pan head screw & if there is a lock washer on the screw.

I think the answer is no to both. 
I will have to take a look later today.

The screw tightens ok so I do not think it is stripped

[waqas]

I recently changed my points, and there was no lock washer under the pan head screw holding the points in there, to my recollection. Is there supposed to be a lock washer? My parts book does not show the details inside the distributor. I remember noting that the plate underneath is burred a bit, in order to serve as a 'lock' for the points plate.

[Benz Dr.]

You know, I don't go to my dentist for legal advice. Everyone is bound to give you some based upon what they believe or some sort of expirience they've had but they're not lawyers. That kind of advice you have to pay for and hopefully it's worth it. They other kind is free and plentyfull and not always so usefull.

There's no washer under the screw holding the points. Wide gap - small dewll angle. Small gap - large dewll angle. It has to do with how long the points stay closed as the main shaft turns.
 If you are loosing dwell angle the points are wearing a little bit. That's mostly normal but if they close up ( and quit working ) in thousand miles I'd say that's not normal. Check your battery voltage with the car running. It should be around 13.4 - 13.8  If it's a lot higher your voltage regulator is frying things.

[merrill]

ok, I did some investigation on the distro today and I can already sense a lesson from Dr Dan on its way

The attached photos show what I found, I guess the hardware holding the points in place is ok.
There is a washer under the screw holding the points at the contact end.

This is an interesting set up, there are 3 places that hold these points in place.
1. screw at the contact end
2. some sort of very small adjusting screw at the pivot end of the points
3 some sort of lock mechansim at the pivot end of the points

I'm not sure of the procedure to set the points on the 051, I tried loosening the 2 large screws and using the small adjusting screw.  This did not work too well

I ended up just loosening the screw at the contact points end and then adjusting the points using a screw driver and the notch in the points plate and post on the distro.

once done I made sure the 2 large screws were tightened.

Right now the dwell is 37.9 - 38

If there are any tips on setting the 051 points I'd appreciate them.....

[Benz Dr.]

Some early units have this small screw which is on an eccentric. If you have a set of points that has a long tail on them it's supposed to fit into the eccentric so that you can make fine adjustments.
Don't bother with that and make your adjustments right at the points. There may be a washer under the screw for the points but I've never seen one on any that I've worked on and I wouldn't have put it there. I doubt it has any effect one way or the other.

A lot of people have hand held digital dwell meters today. I don't have one and use my machine for all of those adjustments. Maybe I'll compare it some day and see how close it is but I'm more intersted in overall function rather than one particular piece of the puzzle, even if some are more critical than others.

[merrill]

Thanks for the info Dan!