[rnp57]

I 'm wondering what the potential consequences are of an extended timing chain with the N47 engine?

 

[dukedkt442]

Worst case? You'll need a new motor.

It's not something you can get by with not attending to.

 

[rnp57]

So does this mean there could be valve to piston crown contact? If the timing chains are replaced should the cylinder head be taken off to check if the extended timing chains have done any damage?

 

[russella]

Don't bother. The problems occur when it snaps. In the UK BMW had a recall to change the timing chain in N47 engines about 2 years ago. What's the situation in your locale?

 

[rnp57]

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.

 

[swampX3]

some US failures too/timing chain info and links

slapping sounds from bad chains......also ....left for long the chain wreaks havoc on the teeth

https://www.youtube.com/watch?v=3xm-YYmtkFY#t=41.149941299

the front installed chains do well BUT ....they do fail sometimes

https://www.google.com/search?clien...iming+chain+in+N47+engines+&ie=UTF-8&oe=UTF-8

 

[dukedkt442]

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.

 

[swampX3]

N 20 timing chain assembly etc

https://www.youtube.com/watch?v=dsMyT2iJjS8

 

[rnp57]

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?

 

[dukedkt442]

If there's piston valve contact the will barely run and a simple compression test will show it.

As stated earlier, there will be catastrophic engine damage when it snaps. A chain won't stretch enough to let the engine get out of time enough for interference to occur before it snaps.