1.5 liters isn't much fuel through a fresh engine; all these 9 port OS engines seem to require a perfect break in that includes good fuel with plenty of castor as well as the proper temperature. I am still in the process of breaking in a 2105 but as we know the Beautiful polished cooling head gives false readings, I have replaced it with a 2102 head to help monitor more accurate readings..So far I have 2200ml through it with 11% oil package. 7% Putoline Castor R (My break in Castor, run in castor is Blendzall Green) and 4% Motul Rc1 after I did an oil bath on it. The engine has been in a buggy with a 16T bell to help keep rpms down but knock on wood no scratches yet. Once I get to 4000ml I will put a 13T bell on it to finalize the break in process by turning some rpm while being in the temp ranges of 220-240F. This is my first OS 9 port, so I am being overly conservative with. I can't help to believe if you run the best fuel (castor heavy), monitor the ACTUAL temps, keep the rpms in check and have a tune that is conducive to a well lubricated engine while retaining temps and altering/varying rpms you will end up with an engine that will accept a "race tune" without damaging the piston via cold weld spots .... I think and hope lol