Here’s my translation

Alan

Hey mikið lá á vellinum um daginn er hirða skyldi en naut Helga af Hjöllum gengu í. 
Much hay lay in the-field during the-day which (one) should get in but (the) cattle of Helgi from Hjallar went into (the field).

Gunnar spurði því að eigi skyldi reka nautin úr vellinum.
Gunnar asked for that (reason) that (ie why) (one) should not drive the-cattle out-of the-field.

"Ekki þykir oss það tjóa," segir Eyjólfur, "því að jafnskjótt eru aftur rekin nautin sem vér rekum í brott."
“(That) seems to us not to avail (ie of no use),” says Eyjólfr, “because the-cattle are driven back (ie into the field) as soon as (jafnskjótt…sem) we drive (them) away.”

Gunnar segir: "Það þykir mér yður skömm mikil, venslamönnum Þóris, að sitja ójöfnuð bændum hér í Þorskafirði."
Gunnar says: “That seems to me a great dishonour to you kinsmen (dative plural) of Þórir, to submit to (sitja e-t e-m, Z6) (the) tyranny at the hands of landowners here in Þorskafjörðr.”

"Þann veg ræðir þú um," segir Eyjólfur, "sem þér sé ókunnigt skaplyndi Helga eða Þórarins ákafa sonar hans."
“You would-speak (subjunctive, roeða) about (it) in that way,” says Eyjólfr, “when (the) temper of Helgi or the vehemence of Þórarinn his son is (sé, subjunctive) unknown to you (þér, dative).”

Gunnar segir: "Ekki ætla eg að ganga vagur fyrir skaplyndi þeirra."
Gunnar says: “I intend not to step watchful (ie tread carefully, vakr?) as-a-result-of their temper.”

Hann hljóp til nautanna, barði og elti út með sjónum sem gatan lá og ofan fyrir einstigi það er var við ána. 
He ran to the-cattle, beat (berja) and drove (them) out along the-sea (?) where the-path lay and down that narrow-path which was by the-river.

Grímur var úti staddur, son Eyjólfs, og telgir kylfu. 
Grímr, son of Eyjólfr, was situated outside, and carves (present tense) a club.

Hann segir föður sínum um nautin og spurði hvort engi maður skyldi fylgja þessum manni. 
He says to his father about the-cattle and asked whether no person (man) should follow this man.

Eyjólfur kveðst letja hvern sinna manna að fylgja honum. 
Eyjólfr declares-of-himself to dissuade each-one of his people (men) to follow (ie from following) him.

Grímur kvað engum tjóa mundu að letja sig og hljóp þegar eftir Gunnari með kylfuna.
Grímr declared (it) would avail for nothing (ie be of no use) to dissuade him and ran at-once after Gunnar with the-club.

En er Gunnar kom í einstigið var þar fyrir Þórarinn ákafi með fimmtán menn og vilja þegar aftur reka nautin. 
But (And) when Gunnar came to the-narrow-path, Þórarinn (the) vehement was there before (already) with fifteen people (men) and (they) want (present tense) at-once to drive back the-cattle (to the field).

Gunnar sækir þá að í ákafa en þeir ráða fast í mót. 
Gunnarr attacks (soekja at) them impetuously (everyone´s full of ákafi today) but they attack him (in return?, cf ráða í móti e-m, Z16) hard.

Helgi sat á hesti fyrir utan ána og eggjar þaðan liðið. 
Helgi sat on (his) horse beyond (on the-other side of?) the-river and urges the-troops from-there.

Þar vó Gunnar Þórarin og tvo aðra en Grímur drap einn. 
There Gunnarr killed Þórarinn and two others but (and) Grímr slayed one.

Gunnar kastaði steini fyrir brjóst Helga svo að hann féll af baki og lömdust bringspelirnir. 
Gunnarr cast a stone against the breast of Helgo so that he fell of (horse) back and the-lower-part-of-the-chest (‘breast-rails’) was severely-injured (lemjast, Z3)

Fór hann við það heim og lá í rekkju lengi.
With that he journeyed home and lay in bed a long-time

En meðan þetta bar að tók Eyjólfur söðul af hesti Gunnars og söðlar tvo hesta. 
But (And) while this happened (bera at), Eyjólfr took (the) saddle off Gunnarr’s horse and saddled two horses (a good trick if he did it with the one saddle?).

Hann bað þá Grím og Gunnar fara til Þóris "og segið honum þessi tíðindi" og biðja hann ásjá.
He bade then Grímr and Gunnarr to go to Þórir “and say to him these tidings” and to ask him for help.

Eftir það fóru þeir á Þórisstaði og sögðu honum til og leita ráðs við hann.
After that they journeyed to Þórisstaðir (Þórir’s-Steads) and said (the tidings) to him and seek advice from him.

Þórir tók ekki mjög á þessum tíðindum og bað þó Grím fara til sín "en ekki vil eg taka við Gunnari," segir hann, "því að þær einar spurnir hefi eg frá honum að hann hafi meiri verið í hreysti en hamingju.
Þórir took not much (ie was greatly underwhelmed) at these tidings and bade nevertheless Grímr to go to his (home) “but (and) I want not to receive Gunnarr,” says he, “because I have (ie get, receive, hafa, Z8) those very (einn, Z3) tidings about him that he has been greater in valour than (in) good fortune.