Builder was crushed by faulty quad bike in friend's cowshed.
John Williams was cleaning the shed on Drwsycoed Uchaf Farm, in Rhydd Ddu, near Caernarfon, for his lifelong friend Hugh Evans Hughes.
The Caernarfon inquest, heard before a jury, was told the bike had a faulty warning light that indicated it was permanently in neutral, even when it was in other gears, as well as a highly responsive accelerator.
Also a railing surrounding the shed was positioned higher than it should have been, according to experts from the Health and Safety Executive.
Mr Williams's prone body was found crushed against the railing by Mr Hughes, who owned the farm.
Police vehicle examiner Kenneth Stone told the inquest that the bike must have shot forward into the railing before Mr Williams, from Beddgelert, had a chance to react.
The inquest heard the bike's accelerator was so powerful even someone experienced in using it could have underestimated the potential to shoot forward.
Mr Stone said, 'There are three possible scenarios - that he thought it was in reverse and went forward, that he thought it was in neutral and went forward or that he knew it was in first and went forward.'
Mr Hughes said though he could not remember a specific discussion with the 57-year-old builder about the neutral indicator light problem, he was sure the builder was aware of it.
He said, 'I could hear the bike going, but I had never known him to take so long to clean the cowshed. So I went to the cowshed and I could hear the engine still running, but I saw John in a prone position.
'I couldn't release him and I knew he was dead.'
The HSE said the prime factor in the death was the bar surrounding the cowshed, because if this had been lower down, the point of collision would have been with the quad bike rather than Mr Williams's chest.
Consultant pathologist Dr Anthony Caslin told the inquest Mr Williams died as a result of crushing injuries to the chest and abdomen.
Deputy coroner for North West Wales, Nicola Jones, said Mr Williams died in February 2004 but the case could not be heard before an inquest, until the HSE had completed its investigation into the tragedy.
The jury returned a verdict of accidental death.