Correct me if I'm wrong but doesn't it come with a total of 0.25mm in shims (0.15+0.1, so exactly what Rody and Ielasi have said to be correct for 25%) installed out of the box?

I believe you are correct.

I was back at the track on 3/28, I like the TR02/MR03 combination as it wakes up the 2104 nicely. That said the testing was cut short and didn't get to run it under race conditions. It appears the motor may be having a connecting rod issue . Hopefully the crank pin is ok and I can salvage it for a practice motor.

R2014

To be honest with the Italian manufacturers on low profile due Covid lockdowns more brands and racers did switch to OS. With such a huge demand I am afraid that the quality is under pressure.

I completely agree. As you've pointed out regarding the chrome flashing in the exhaust port previously. The motor had an EBIS breaking in and had seen limited use at race tune, clearly a failed part unfortunately. Lets hope it improves.

That motor looks very dry. It seems it was ran verrryyy lean...

It looks very dry but it was not, 239' max temp with an ambient temp of 82 F at the time - I was running VP 25R. The grey look is a paste generated due to the bushing rubbing against the back plate when the rod started to come apart (the same gray coating was prevalent though out the case and backplate when I opened the motor). The rod bushing fell into pieces as the motor was disassembled.

R2104 bushing failure

many of my friends who were recently running in their 2104, they said the piston is more tight than previous 2103,...the piston was hardly cranked up even it was pre heat with a heat gun, some were ending up with a scratch piston at the exhaust side or dead stuck.
i am being skeptical to buy 2104 lately.

I did not notice it being overly tight when new out of the box. I'm using the Protek "Blue Flame" engine heater with a 3S pack and it get the motor to over 200F (the system has a 10min timer wired into it). Without getting enough heat into the engine when new you will struggle to turn it over when new.

*That said, the build-up set I recently installed in a 2104 took more fuel to break in than the original piston and sleeve, not sure why?

from my previous experience of running in 2103 or the earlier version, it took normally 2.x bottles of fuel to almost complete run in.
many friends said it took much more than that and the piston is still even tight, some were even scratched as a result.

The last 2 2104's I broke in took approximately 4-5 bottles with the build-up kit taking 5+ bottles before I could put a race tune in the motor.

Use heat and be patient with the process, the motors may vary in what is required to achieve the needed piston lap in the sleeve.

I just got myself a couple new fresh 2104s will be running them in on the hudy break in bench, hopefully with some better results than last time.

Believe my issue previously was running it in too cold and babying it too much.

Engines torn down, all looking good ready for break in

1500ml through one of my 2104s today, first time I've done this set up so learning a lot trying to keep in the 80-85°c range.

Seems to be okay, I added +3% castor so total of 13% but internal looks brand new nothing like a Hasi or Ealasi.

3D you have a PM

Here are some pics from my 2104 #2 this has done 1560ml on the Hudy Break in bench, kept at 80`c.
running +3% oil in this fuel also.

Having seen some internals of "pre run in" engines using energy fuel with large castor build up this wasn't what I was expecting.