The two fought a full two double-hours without either gaining the day. It was, in truth, a bronze basin meeting an iron broom, a jade chime answering a golden bell.

兩個時辰 is two double-hours, about four hours of continuous fighting, and 不分勝敗, nothing to choose between them (分 fēn, to divide, hence to decide). Then two similes with the same shape: 銅盆逢鐵帚, a bronze basin meeting an iron broom, and 玉磬對金鐘, a jade chime answering a golden bell. Both pairs are hard, both are loud, and neither can dent the other.

Now the Great Sage, guarding the Tang Monk and standing close at his side, watched with staring eyes as the two contended upon the water,

保著 … 望著, guarding and watching (著 zhe in both, the marker of an action held). 眼巴巴的 is the phrase for staring with helpless longing — the look of someone shut out of something they badly want. He is not worried about the fight. He wants to be in it.

only he could not well lend a hand. Then he saw Bajie feint with his rake, make a show of losing, turn tail and head for the eastern bank.

虛幌一鈀, a feint with the rake (鈀 pá), and 佯輸詐敗 — four characters that say 'pretending to lose' twice over, once with 佯 and once with 詐, for emphasis. Bajie is executing the plan exactly as given.

The monster came chasing after, and had all but reached the bank,

將近到了岸邊, 'was all but at the bank' (將 jiāng, 'about to'). The bait is working. The demon is four strides from dry land and the monkey is waiting on it.

when the Pilgrim, unable to hold back, left the master, drew his iron rod, sprang to the riverside, and struck straight down at the monster's head.

忍耐不住: could not hold himself in. The same failing wrecked the first duel, and here it is again, at the exact moment the plan was about to work. He strikes before the demon is clear of the water, which is the one thing that could have spoiled it.

The fiend dared not stand and meet him, and with a whoosh dived once more into the river.

不敢相迎, 'dared not close with him' (相 xiāng). 颼的 is the sound of something going fast — a whoosh — and 又鑽入河內, 'bored into the river again.' The word to feel is 又: again. The chapter is now repeating itself on purpose.

Bajie bawled: 'You Ban-Horse-Plague, you're an out-and-out impatient monkey! If you'd only hold off a bit longer,

弼馬溫 is the joke that never dies. When Heaven first wanted to keep Wukong quiet it invented a grand-sounding office for him and gave him the celestial stables. The title has the shape of a real post, but it puns on a phrase meaning 'ward off horse-plague' — which is to say, stable-hand. He was furious when he worked out how junior it was, and it has been a reliable way to needle him ever since. 急猴子, 'hot-headed monkey' (子 the light zi), names the fault precisely.

'wait till I've lured him up to high ground, then bar the riverside so he can't turn back — wouldn't we have him then?'

Bajie's correction is the obvious one and it is right: 哄他到了高處, coax him up to high ground first, and only then 阻住河邊, block the bank behind him (教 jiào, the causative). Cut off the retreat before you swing. The monkey will eventually adopt this, one failure later.

'Now that he's gone back in, when will he ever be willing to come out again?'

幾時又肯出來, 'when will he ever agree to come out again?' The plainest statement of the trap the pilgrims have built for themselves: every premature blow drives the demon further into the one place they cannot reach him.

The Pilgrim said with a laugh: 'Idiot, stop your bawling, stop your bawling. Let's go back and see the master for now.'

獃子, 'Idiot' (子 the light zi), is what the monkey calls Bajie roughly always. 莫嚷, 'stop bawling,' doubled, brushes the whole complaint aside without answering it, and the two go back up the bank with nothing settled.