The assessment fee works like this.

You send the crank to NSR-World. It is then fully stripped, clean and inspected. If it deemed to be serviceable (many aren't) it is rebuilt. If it's found to be damaged in a way that can not be repaired (such as pitting to the big end pins, an integral part of the crank web) then you pay £25.00 and they send you your crank back.

If however the crank is in serviceable condition and can be rebuilt the assessment fee is included in the price of the rebuild.

The heat treatment of the cranks depends on the model and age of the cranks as different processes have been used though out the NSR engine life.
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If I have to take the carbs off once more...