Rebuilding my m103 Brabus 3.6

[Brabus3.6]

I recently posted about hesitation around 2000rpm on my Brabus. When cylinder leakage was measured it ranged between 52%-64%, heard from the bottom end! So I've now stripped the engine down completely.
The block has 2-3 thou of wear and so is shot. I'm getting a standard 300e block and having it bored to spec (92mm). Brabus want £800 for piston rings and £580 for a headgasket, ridiculous.
So, I think I may go with Gapless Top Rings, which seem like a more advanced piston ring than would have been offered at the time my engine was built.
As for a headgasket, it seems the basic gasket layout (position of bore, water & oil galleries and sizes) is the same as an M120. Cosmetic's left hand bank Zonda gasket(!) seems to do the trick but is 1mm small in bore size. I've sent a gasket over to the US for inspection and I'm praying the gasket is the same bar this as Cosmetic will do a custom bore size. Anyone ever used an MLS gasket on a benz, I'm guessing it's a better solution than copper?
Incidently the Brabus gasket blows around every 10,000 miles anyway and is just a standard Victor Reinz, nothing special!
Any tips on re-assembly (i.e. assembly oil?) and running in etc?

 

[Dieselman]

Any tips on re-assembly (i.e. assembly oil?) and running in etc?

Obviously go mad with oil during the rebuilding process and run the engine in on a basic mineral oil.

For running in don't spare the horses otherwise it will suffer blow-by and oil consumption.
Get it warm quickly then give it full beans on and off for a few miles. 2nd gear foot down then lift off again, then repeat, etc.

Preferably find a few steep hills to drag up to get the combustion pressure nice and high, this will seat the rings properly.

Then change the oil and filter as this is when most bits will be released and loose ones will be caught.

If this sounds shocking read THIS.

 

[Brabus3.6]

That oil would be assembly oil or just normal engine oil? SO I should change the oil and filter after its first run, then again after 1000 miles; switching from mineral back to better oil? Being a new bottom end can I use fully synthetic 15W-50 mobil one again or back to semi-synthetic stuff?

 

[Brabus3.6]

Oops

 

[Dieselman]

That oil would be assembly oil or just normal engine oil? SO I should change the oil and filter after its first run, then again after 1000 miles; switching from mineral back to better oil? Being a new bottom end can I use fully synthetic 15W-50 mobil one again or back to semi-synthetic stuff?

Yes, change the oil and filter after the initial blast but continue with the mineral oil for the 1000 miles then switch to the best synth you can get.

Oil viscosity depends on the clearances of the bottom end, if larger than average use a 50 grade oil, if a normal clearance than use 40 grade.
A higher viscosity oil will provide more protection against bearing contact assuming there is the clearance to get it in there.

The reason performance engines have wider clearances is so more oil can be squeezed into the clearance so creating less drag as it can then slide over itself more readily.
The engine will need a higher flow oil pump though if the clearances are greater than standard.