Here’s my translation

I must say I enjoyed this magical little tale, albeit I only joined in part-way through.  Good luck to all continuing on with Eyrbyggja Saga. Perhaps, at some stage, I will find time to join in on it too.

Alan

Jökull mælti: "Það er fáheyrt að eg, tólf vetra gamall, þurfi að taka fang
Jökull spoke: “That is virtually-unheard-of (lit: little-heard) that I, (only) twelve winters old, should-need to wrestle (lit: take hold)

við þig þar sem þú deyddir blámann Haralds konungs í fangbrögðum þínum, en
with you where-as you killed King Haraldr’s black-man in your wrestling, but

þó muntu ráða vilja.
still you-will want to-have-your-way.

Þeir Búi gengu þá austur undir fjallið til laugar. Þar voru vellir fagrir.
They, Búi (and Jökull) walked then east beneath the-mountain to (the) hot-springs. There were fine fields (and most suitable for wrestling).

Síðan klæddust þeir til fangs og tókust allsterklega og gekk svo lengi að
After-that they dressed-themselves for wrestling and took (to it) (ie wrestled, fangbrögðum implicit, see takast fangbrögðum, Z13) in very-strong-looking fashion and (but) (it) went thus a long-time that

hvorgi féll. Búi varð móður mjög.
neither fell. Búi became very weary.

Jökull mælti: "Þreytum þetta ekki meir og tak við frændsemi minni."
Jökull spoke: “Let’s prosecute this no more (How about we put an end to this madness) and (you) accept my kinship.”

"Nei," kvað Búi, "falla skal annar hvor okkar."
“No,” declared Búi, “one or the other of us shall fall.”

Jökull mælti: "Eigi mun þá betur."
Jökull spoke: “(I) will then better not (I will rather it not be me).”

Eftir það réðust þeir á í annað sinn. Voru þá allmiklar sviptingar.
After-that they came to grips for a second time. (The) tussles were then very-great.

Var þá við sjálft búið að Jökull mundi falla. Og í því var sem kippt væri báðum
(It) was (had) then reached the point that Jökull would fall. And (it) was at that (moment) when (it) were pulled with both

fótum senn undan Búa og féll hann áfram og þar varð við brestur hár og mikill.
legs at-the-same-time from under Búi and he fell forward (on his face) and a loud and might crash happened therewith (I´m not quite clear on the intricacies of this wrestling move ie whose legs did what but whatever, it left Búi lying flat on his face).

Búi mælti: "Fellt mun nú til hlítar og mátti móðir þín eigi hlutlaust láta vera."
Búi spoke: “Now (it) will be felled to sufficiency (Methinks this is the decisive fall) and your mother could not allow to remain having-taken-no-part-in-(it) (ie she couldn´t keep out of it and had to interfere).”

Þá hlupu að aðrir menn og sáu þar vegsummerki að bringspelirnir voru í
Then other persons (men) ran up and saw there (the) marks-of-glory (the tell-tale-signs of victory?) that (the) breast-rails (the lower part of the chest) were

sundur í Búa og hafði orðið undir steinn.
asunder in Búi and had become (positioned) under a rock.

Búi mælti þá til Jökuls: "Ekki hefir nú orðið erindi þitt hingað hagfellt
Búi spoke then to Jökull: “Your business hither has not now happened-to-be suitable (Your business here has not turned out well)

því að þú hefðir verið mannsefni enda mun nú skömm saga frá mér ganga."
because you had been a promising-young-man (you had the makings of a man) and-moreover now will a short (fem nom sg of skammr) story go (be told) about me (ie to match his shortened life).”

Eftir það var Búi borinn heim á rauðum skildi og lifði þrjár nætur og
After that Búi was carried home on a red shield and lived three nights and

andaðist síðan.
died (breathed-his-last) after-that.

Jökli þótti verk sitt svo illt að hann reið þegar í brott og til skips er
His deed seemed to Jökull so bad that he rode at-once away and to a ship which

búið var suður á Eyrarbakka og fór þar utan um sumarið en síðan höfum vér
was ready south in Eyrarbakki (Sand-Bank) and journeyed then abroad during the-summer and after-that we have

önga sögu heyrt frá honum.
heard no story about him.

Helga Þorgrímsdóttir bjó að Esjubergi með börnum þeirra Búa.
Helga Þorgrímr’s-daughter lived at Esjuberg with their children, Búi’s (and her own).

Þá stóð enn kirkja sú að Esjubergi er Örlygur hafði látið gera. Gaf þá engi maður gaum
Then (at that time), that church still stood at Esjuberg which Örlygr had caused to construct. No men then gave (paid) attention

að henni. En með því að Búi var skírður maður en blótaði aldrei þá lét Helga húsfreyja
to (it, the church which is a feminine noun). But with that that (ie because) Búi was a baptised man and never made-heathen-sacrifice, then wife Helga caused

grafa hann undir kirkjuveggnum hinum syðra og leggja ekki fémætt
to bury him under the more-southern church-walls and to place no valuables

hjá honum nema vopn hans.
beside him except-for his weapons.

Sú hin sama járnklukka hékk þá fyrir kirkjunni á Esjubergi er Árni biskup
That very iron-bell hanged then (at that time) at-the-front-of the-church which bishop Árni Þorlákr’s-son

réð fyrir stað, Þorláksson, og Nikulás Pétursson bjó að Hofi, og var þá
decreed for (the) place (church), and Nikulás Péturr’s-son lived at Hof, and (the bell) was then

slitin af ryði. Árni biskup lét og þann sama plenarium fara suður í Skálholt
broken from rust. Bishop Árni caused also that very plenary-session to journey south to Skálholt

og lét búa og líma öll blöðin í kjölinn og er írskt letur á.
and caused to prepare and to glue all the-blades (neut pl of blað, pieces of the bell?) into the-keel and Irish writing is on (it).

Frá Búa Andríðssyni er komin mikli ætt.
From Búi Andríðr’s-son is come (descended) a great family.

Og lúkum vér þar Kjalnesinga sögu.
And we close there Kjalnesinga saga (the story of the people of Kjalnes).