I searched for this issue in the forum here and came across this entry.

This issue with the worn-in engine halves caused by the Magdynamo is giving me a bit of a headache in my restoration.
We also had the idea of placing a thin metal plate between the two components after leveling the surface again with the milling machine like a few of you guys also had.

I have a few more detailed questions and hope you know more about them.

- The most important thing: How did you clamp the two engine halves in the mill?
Did you build an adapter plate and what did it look like? I'm still not entirely sure how to best mount this.

- I was thinking about removing about 0.5 to 1 mm from the housing halves to level it out again. I wanted to do the same thing with the Magdynamo, although I'm not so sure whether its housing walls are too thin for something like that. Afterwards I would have attached a 2 mm metal plate to the housings to compensate for the "loss".
A good friend said it was enough to remove something from the motor halves and just carefully level the Magdynamo on a glass plate with sandpaper (of course without the 4 retaining pins). What's your opinion?
I also wanted to mention - the cover of the Magdynamo (on the side of the gear) should not be sanded down when leveling... it is definitely too thin with its walls. But I measured the engine halves and saw that the cover doesn't rest at this point either way and is therefore "hanging in the air" so no compensation needs to be created here.

- Which brings me to the next point: How would you fix the metal plate? I would have anchored it in the housing with 4 small countersunk screws, if that's possible and I have enough "flesh" on the support surface... but I'm not sure - especially since such small threads in a cast aluminum are probably not productive (except with Helicoil threads but then it will be a doctoral thesis... :sweat_smile: ). Maybe you can overlap the metal plate on one side and attach it there.

Attached you will find a few pictures for visualization. The picture of the engine halves on the workbench is not mine, but a demo picture from the internet (I know these are not matching engine halves, etc.), I was only concerned with the worn contact surface.
The photo with the halves already welded is mine. The depressions have already been welded on here and I would now like to level them as mentioned.

The pictures of the Magdynamo are also mine - please look at the bottom of it - how worn it is.

I look forward to your suggestions and ideas! Thank you very much!

email (option): beachbraker@gmx.de

If I see more of them I will make a Jig plate Florian, but for now I have a large angle plate I mount to the timing side.
Only take just enough material to clean the faces, I would hope it would be well under 1mm
For the magneto remove the mounting pins and make some new ones that are a good fit in the crankcases.
The spacer under the magneto can be located using the four pins.
Small adjustments can be made using these.

https://pesltd.uk/?product=66-2347

Think long and hard before taking a cut.
Paranoia is your best friend.

Mark

email (option): pes.sales@btconnect.com

Thank you so much Mark for your incredibly valuable tips in this case.
I take your words very seriously and appreciate them very much.
Thanks also for the tip about the holder in the mill.

I'm also more of a fan of this - removing as little of the original material as possible and preserving everything in its original condition as best as possible.
Therefore, in this case I will try to apply a little more material to the worn areas on the engine halves and then ideally just remove the protrusions in the mill.
As a result, I would have to estimate 0 - 0.2 mm of removal on the surface of the engine halves.
With the dynamo I would also do it as you recommend - unfortunately I can't weld anything on here... but I think here too I'll only remove a minimal amount of material to create a flat surface - nothing more.
I take out the pins and replace them with better ones - crescent-shaped ones, which distribute the forces better across the adjacent material.

As I make progress I will share it with you all.

email (option): beachbraker@gmx.de

The magdyno platform wearing is very common as no one ever checks if the strap is tight. They put the magdyno on the bike and tighten the bolt and never ever check it again.

Before every time you ride your M20, put a spanner on the bolt and make sure it is tight!

I once saw an M20 with the magdyno literally dancing around on its platform to the point I was surprised the gears were meshing. The unconcerned pilot kicked it into gear & chuffed off.