My faith in humans is pretty low of lateSundayjumper wrote: Mon Sep 14, 2026 10:01 pmWell, it depends on who did the diagnosis. Was it a specialist ? We have had two examples recently of specialists not being able to correctly diagnose, quoting for the wrong thing and happily taking money to not fix it - my neighbour's 1-Series, and DJ's BiL's Passat. Maybe they had a scary quote and are cutting their losses. Has the owner self-diagnosed with "help" from the internet ? There could be all manner of wrongness based on the kind of guff I've seen posted over the years plus the internet paranoia of "OMG u can't drive it no more ur will die". Forums are weird.
These engines are prone to worn big end bearings so it's not a surprising fault. And unless it's spun one or more of them - which you would definitely know about - I don't think I've seen one needing work on the crank. It could have bent a rod if it's been modded. That turns into a big job. Or it could be something else. Without having a good look (and listen) in person none of us know anything. And you still won't totally know the answer until you start taking it apart.
FWIW the M6 GC was £24k more than an M5 when newso this for £10k plus a few grand of parts could be a bargain. I'm nearly £15k into my M5 so far and it's still only an M5.
It could indeed be slightly worn bearings and if it is just a case of fitting new ones and a slight polish then it's a huge saving. I wonder what these break for in parts, M specific interiors and bumpers etc ?
A rod knock is very very easy to diagnose with a long screwdriver and I'd be surprised if it ran at all with a spun bearing as that bearing will have seized on the crank with no oil supply.
The S6, RS6 running costs and parts availability with 150hp less. A shame they aren't catered for more as with an exhaust it's a lovely sounding thing and very practical.
Dave!

