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Break-in procedures are usually motor specific and vary based on motor design. Consult Mini for their recommendations. Here is the factory procedure for a recent vintage GM 5.3L:

Break-In Procedures
After installing the engine, ensure the crankcase has been filled with the correct (refer to instruction sheets that come
with the crate engine) motor oil (non-synthetic) to the recommended oil fill level on the dipstick. Also check and fill as
required any other necessary fluids such as coolant, power steering fluid, etc.
The engine should be primed with oil prior to starting. Do this by using an engine oil priming tool. If you do not have one,
one can be obtained through GM, part number 12368084. Follow the instructions enclosed with the tool. This is the sure
way to get oil to the bearings before you start the engine for the first time. Also, prime the engine if it sits for extended
periods of time.
Safety first. If the vehicle is on the ground, be sure the emergency brake is set, the wheels are chocked and the car
cannot fall into gear.
Start the engine and adjust the initial timing. Set the ignition timing to timing specified in the instruction sheet and the
engine idle to the speed as specified in the instruction sheet. Rotate the distributor counterclockwise to advance the
timing. Rotate the distributor clockwise to retard the timing. Leave the vacuum advance disconnected.
When possible, you should always allow the engine to warm up prior to driving. It is a good practice to allow the oil sump
and water temperature to reach 180° F before towing heavy loads or performing hard acceleration runs.
Once the engine is warm, set the total advance timing as specified in the instruction sheet.
The engine should be driven at varying loads and conditions for the first 30 miles or one hour without wide open throttle
(WOT) or sustained high RPM accelerations.
Run five or six medium throttle (50%) accelerations to about 4000 rpm and 55 mph (if application is a vehicle), and back
to idle (0% throttle) in gear.
Run two or three hard throttle (WOT 100%) accelerations to about 5000 rpm and 55 mph (if application is a vehicle), and
back to idle (0% throttle) in gear.
Change the oil and filter. Replace with 20W50 racing motor oil (not synthetic) and an ACDelco oil filter. Inspect the oil and
the oil filter for any foreign particles to ensure that the engine is functioning properly.
Drive the next 500 miles (or 12 to 15 engine hours) under normal conditions. Do not run the engine at its maximum rated
engine speed. Also, do not expose the engine to extended periods of high load.
Change the oil and filter. Again, inspect the oil and oil filter for any foreign particles to ensure that the engine is
functioning properly.
Do not use synthetic oil for break-in. It would only be suitable to use synthetic motor oil after the second recommended
oil change and mileage accumulation.