1.Of many thousand spare parts does not come up to the standard but one.
在成千上万个备件中,只发现一个不合格.
把句子的语序变一下：But (only) one of many thousand spare parts does not come up to the standard.
这样就好理解了.
2.That which is good cannot be done too soon.
好事做得越快越好.
这是英语中的understatement修辞手法,即否定其反面来达到肯定的目的.这句可以理解为：好事做得多早都不过份.类似的还有：I cannot thank you enough.谢你谢多少都不够（非常感谢你）