秤鉈壓斤 Small but of Substance
行者笑道：「你原來沒眼色，認不得人。俗語云：『尿泡雖大無斤兩，秤鉈雖小壓千斤。』他們相貌，空大無用：走路抗風，穿衣費布，種火心空，頂門腰軟，吃食無功。咱老孫小自小，斤節。」行者笑道：「你原来没眼色，认不得人。俗语云：『尿泡虽大无斤两，秤铊虽小压千斤。』他们相貌，空大无用：走路抗风，穿衣费布，种火心空，顶门腰软，吃食无功。咱老孙小自小，斤节。」
逐句解 Line by line
Pilgrim said with a laugh, “You have no eye for men, it seems, and cannot tell one person from another.
眼色 (yǎnsè), discernment, an eye for judging. 認不得 (rèn bu de), unable to recognize; 得 read de.
As the common saying goes: ‘A piss-bladder, though large, has no weight; a steelyard-weight, though small, presses a thousand catties.’
尿泡 (suī pāo), a bladder — large but empty; 尿 read suī, 泡 read pāo (the coarse Ming-vernacular reading; the standard modern reading is niào pào). 秤鉈 (chèng tuó), the sliding weight of a steelyard, small but heavy; 鉈 read tuó. 斤兩 (jīn liǎng), weight; a catty and a tael.
Those two are all show and no use: they breast the wind as they walk, they waste cloth on their clothes, they are hollow-hearted as a banked fire, soft at the crown and weak in the loins, and eat their food to no purpose.
相貌 (xiàngmào), outward appearance; 相 read xiàng. 抗風 (kàng fēng), to breast the wind (being so large). 種火心空 (zhǒng huǒ xīn kōng), hollow within as a banked ember. 吃食無功 (chī shí wú gōng), to eat to no good end.
But old Sun of ours, small though he is, is small and solid.”
咱 (zán), we, us — here familiarly of himself. 斤節 (jīn jié), compact and substantial, “all in one solid piece.”
Wukong’s rejoinder turns the princess’s mockery on its head with a pair of marketplace proverbs, the empty bladder set against the little steelyard-weight, wit answering scorn in the plain coin of folk wisdom. He then repays her in kind, cataloguing his brothers’ bulk as sheer useless show — breasting the wind, wasting cloth, hollow within — before claiming for himself the compact solidity the proverbs celebrate.
The passage is a fine instance of the novel’s delight in the demotic register: the highest hero speaks the idiom of pedlars and market-stalls, and his self-vindication rests not on any display of power but on a homely truth about weight and worth. The comedy of scale — the small containing the mighty — is the very principle of Wukong’s character, and here he states it himself, in the tongue of the common people.