M54 Chain replacement interval?

[yg54sg]

Hi All, I had always been told that these chains last the lifetime of the engine, I would like to believe that up until I purchased a 320d 03 plate with 160k miles on it at christmas as the family car. Also chain driven it was great for a couple of months until one day it just wouldn't start, after hooking it up to INPA i was getting a camshaft signal sensor issue, changed that out and still had the same problem. The engine in it is the M47N which is supposed to be pretty bullet proof apart from turbo and injector issues (lol) which I was fine with sorting every 30-40k. After putting a torch in the oil filler hole cranking it and looking about the air inlet camshaft had snapped clean off the cog that drives it which means that timing will have been out and a piston has hit a valve breaking the camshaft :x

Rather than scrapping the car or sourcing perhaps another knackered engine as all these 320d are high miles... being the complete nut case I am I followed all procedures on BMW TIS stripped the engine down and sourced a reconditioned head from the E90 M47N2 (same block) many nights and weekends later she is back up and running. The cause of the issue was a sprocket that had worn down to almost nothing on the injector pump causing the chain to slip that day when i went to start the engine. This altered the timing causing a valve which are made of hardened steel to punch up and snap the camshaft. Luckily no piston damage! Aside replacing the head i replaced both chains (they looked stretched by a few mm to the originals) and also the other sprockets, guides and tensioners the chains run on. Engine back together and wow very smooth and powerful but of course no where near as nice to drive as the M54.. I will say nothing beats that M54 engine, its not until you own something else you realise the true magic of an inline 6!

My questions is.... on my Z4 which I have had from new in 2004 now done 110,000 (intend keeping it forever) always followed the recommended oil changes is there a chain replacement interval? I assume when they replace the chain they replace everything the chain runs on like I did? I have no idea how the 320d was treated in its past life but I didn't find an excessive amount of sludge in the camshaft cover there was a little here and there but not a huge amount to suggest few oil changes. Service history shows bmw oil changes up to about 120k after that there is no history.

This was the first time id ever stripped an engine so I guess it has me a bit worried as to what might be going on as the miles increase on the Z4 :driving:

thanks in advance!

 

[Midhurstman]

Sounds like you did a great job on the rebuild, hope you are rewarded with a trouble free engine now. My own opinion on the timing chains on these engines is that I would be happier replacing them around the 100,000 mile mark, regardless of what everyone seems to say about no need to do this. I would venture the opinion that the stretching of yours over all of those miles, then led to enough slack on the sprocket to increase wear rapidly. I feel the same about the auto gearbox which they say is sealed for life and that the fluid & filter does not require changing. I have just had this done on my 3.0i Z4 E85 ( tiptronic with my own design paddle shift fitted) and there is a noticeable improvement in gearchange and smoothness. My own indie, who is ex BMW and has years of experience agrees with this fluid change and usually recommends it at 100,000 miles. It's all about personal preference for peace of mind really and I'm sure many will have different views on it.