Ben Grabham continues to dominate the seven-day Australasian Safari, being conducted in the Western Australian outback.

Riding a factory-supported Honda CRF450X, Grabham has led the 4400km marathon from the start in Kalgoorlie last Sunday, and after the first four days is on track for his second consecutive Safari win.

The battle for second place has really hotted up. With the demise of last year's runner-up, Todd Smith, Grabham's brother, Damian, has moved into second position, but as the day neared an end he held a slender 19 second margin over Rod Faggotter.

It seems only bad luck can deny Ben Grabham victory, as he increased his lead to nearly half an hour over the longest and toughest leg of this year's event.

"It was a long day and I'm sure some of the guys will have done it tough out there," Grabham said. "The two long stages will have really knocked people around.

"Although today was the longest of the event, I treated it the same as the others, and probably rode a bit quicker, if anything. The bike ran well and I'm happy with my lead."

Damian Grabham started the day first on the road, but challenging navigation made his task difficult, although he wasn't on his own in getting lost.

"It was good starting first on the road, but I got lost in the second section for a while. Then Ben got lost in the next stage, and we did a bit of swapping of positions until eventually he got ahead of me," Damian Grabham said.

Third placed Faggotter crashed heavily and suffered facial injuries on the final stage of day three, but bounced back brilliantly with the second fastest time on two of today's stages.

"It was pretty rough out there," Faggotter said. Despite his injuries from yesterday, he has that steely determination to finish Australia's toughest motorsport challenge.

"I've come too far to give up now," he added, seemingly oblivious to his potential podium placing.

It has been a disastrous day for the factory Yamaha squad, with brothers Jacob and Todd Smith both retiring from the event. Todd was the first to strike trouble when a stick tore an oil line off and drained his engine of oil.

His brother, Jacob, also stopped with mechanical problems. Both Yamaha riders are hoping to rejoin the event for Leg 5, from Meekatharra to Mt Magnet.

Leg 4 was the Safari's longest and most demanding day, with nearly 600 kilometres of stages. It started at 6am with a monster 232 kilometre stage, which was quickly followed by another stage of over 220 kilometres in length.

The route, a loop from Meekatharra and back again, headed into the Little Sandy Desert. Once in the desert country, it ventured into spinifex encrusted sand plains, before skirting along the rough and rocky Carnarvon Ranges. It crossed very rough, tight, and twisty terrain, and followed a section of the Old Rabbit Proof Fence.

Light rain developed in Meekatharra during the day, but competitors had fine, yet windy, conditions on the stages, which were held to the north of the mining township. The temperature was in the mid- to high twenties.

The conditions were again competitors' biggest enemies. Shane Diener, who was second after Leg 1, hit a kangaroo in thick dust and fell off, breaking his leg, while West Australian, Garry Whittle, also crashed, breaking his collarbone.

ALF legend, Tony Lockett, had moved up the leaderboard during the day, and is 25th position.

Steve Riley continues to hold the lead in the Auto section after 13 of the 24 stages. Driving a Mitsubishi Pajero, he is nearly eight minutes clear of the Nissan Patrol of Des Harrington, with Bruce Garland now in third place in his Isuzu D-Max.

Tomorrow competitors head south west to Mt Magnet, where overcast conditions and some light rain is expected. Over 471 kilometres of stages await the remaining crews, including two stages of over 150 kilometres in length.