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As E60525d has stated perhaps overall this particular engine design is somewhat flawed, we've seen from my records easily getting on for 100 of these engines with almost identical issues which tells you something the design of many of the components(be it the guide bolts the guides themselves and the chain tensioner have evolved over time which tells you all you need to know)
The other thing to take in to consideration is that most dealers will have the majority of the parts on the shelf or can order what's needed very quickly kind of tells you that the parts are fast moving items.
Re Keith's estimate of £700 for carrying out a timing chain job, for may sound about right but for me sounds a wee bit low and I'll tell you why.
A lot of garages will remove replace the chain and guides remove clean the vanos solenoids and simply re fit them along with replacing the rocker cover gasket after the works done. We've seen vanos solenoids compromised due to carbonisation issues cleaning them is a fix but sometimes issues can arise later on causing certain knock on effects to take place, the solution we always adopt is to replace these units (however they cost just over £84+VAT each and not clean them).
The other thing to ask yourselves is this when you see or get an issue re the chain/chain guide area its not unusual for the guides to fragment and drop in to the sump(seen loads of these engines with this fault) when this usually takes place its more than likely that you will see a 30C1 oil pressure static fault if this is the case the sump needs to come off to clean out the debris(and ideally thoroughly clean the sump out of sludge at the same time)at the side of the block there is a hydraulic valve(this can get either contaminated with sludge/chain guide debris or can when removed and inspected separate plus the oil pressure switch at the side of the block can again get contaminated and again should really be replaced)plus its not unheard of to see issues re the suction pipe(which takes oil to the oil pump being contaminated with debris as well 90%+ of the time out of precaution we replace this as well)
When we've seen these cars come to us with issues we've been told on several occasions that the guides and chain have been replaced yet issues have returned I think what I am trying to say is most places repair what they see in front of them(remove replace the chain perhaps the guides-even when the guides are damaged/fragments/separated they venture no further than simply replacing them)so the car goes out with debris still in the sump(draining oil won't get rid of the most of the debris as most of it sits in the sludge left in the sump in most cases)
If you look at say the parts side of things you are rought plus VAT looking at the following figures
chain £46.00+VAT main chain guide £35.00+VAT top slide chain guide £20.00+VAT bottom chain sprocket £12.00 main chain tensioner £41.00+VAT bearing bolt for the chain guide assembly £9.45+VAT torx bolt for guide assembly(2 required) £.77 each +VAT bolts for the vanos adjusters (2 again required) £2.70 each +VAT rocker cover gasket £27.00+VAt ideally 2 fuel pump gaskets £6.60 _VAT each ideally 4 spark plug ali tubes (should replace these when replacing a rocker cover £2.12 each +VAT the parts bill starts to add up if you were dropping the sump £27.00+VAT for the gasket 22 bolts for the sump ideally required(£1.05 each +VAT) if the hydraulic valve which I talked about earlier is compromised they are £85.00+VAT a go plus the oil pressure unit is some £32.00+VAT it all adds up and the suction pipe for the oil pump if needed is another £55.00+VAT a go.
Add 2 vanos solenoids in the mix £84.17 + VAT each suddenly £700 seems to me too little money wise to do a thorough one stop complete fix.
May sound to many to be OTT but with these engines along to a lesser degree the N46's and N45's it seems doing everything is the best way forward to ensure no come back is seen/felt observed. And yes they are/can be financially expensive to own where the idea of buying a4 cylinder BMW was to run it with lower overall costs than the 6 cylinder set ups.
Add to the mix possibilities of injector issues, which are not unheard of(never IMO replace 1 injector due to compatibility issues seems the only way forward is to go for 4) and on the subject of diagnostic worth an investment for sure but don't overall base your conclusions on the results seen, we've seen a few of these with good smooth running results only to pull the plugs see they are black wet smell of fuel and when injectors are scoped we see injector issues yet diagnostic doesn't show these symptoms so you move on. So beware
Its sad really that this is the case but it seems to be a story with these engines that as Google seems to back up will not go away
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