There is a campaign in Australia to replace timing chains because of the worldwide issues but, in contrast to the approach taken in the UK and the states where the cylinder head is removed to check if there is valve to piston crown contact, they just change the chain tensioner and the timing chains. It seems like a risky short cut.
The N20 engines have problems in the same area, many folks have had to get new engines by 60k miles. Inexcusable. If the chain begins to stretch, it becomes a positive feedback of stretching everytime you get on and off the gas (diesel), until at worst case the chain breaks. Pistons and valves live-bumping are only a part of the problem, as the broken shards of chain can travel through the engine, wreaking havoc on cams, lifters, and oil pumps.
I guess what I'm really trying to find out is whether an engine with extended timing chains results in sufficient change in timing to allow the inlet valves to contact the piston crowns. This could lead to bending moment in the valve stems, leading to valve failure and the resulting catastrophic engine damage. If there are timing issues, shouldn't an inspection of piston valve contact be the first thing to check as part of BMW's campaign?
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