M42 TIMING CHAINS
Generally speaking, BMW engines are pretty reliable, but if you have an E46 3 Series fitted with an N42 four-cylinder you'd better read on.
As BMW engines go the N42 four-cylinder had a fairly short life span of just four years, but as it was fitted to two of the companies best selling models
(E46 316i and E46 318i/318ci) there are still a lot of them on the road.
While it was pretty advanced for its day, it’s not without it Achilles heels which can be hugely costly to repair.
The good news is that in the majority of cases there's a remarkably cheap fix, but the consequences of missing out of this simple piece of preventative maintenance could leave you with a big bill to pay.
The main problem is that the timing chain tensioner was not really up to the job,
so after a bit of time and wear it can stop working properly. This can be compounded by owners using cheap oil, the wrong grade of oil.
Or simply by trying to stretch, the distance between oil changes.
Once it became clear that the failure rate among these tensioners was high BMW redesigned it and as you can see from the picture (below), the revised tensioner is a bit longer.
So it certainly pays to check your cam chain tensioner. Externally, you can tell if it's been replaced with the modified part as the redesigned item has a smaller head.
The part costs around £28 and will take half an hour's labour to fit.
However, if you have the old style tensioner still fitted, the risk is that the chain starts to jump one tooth at a time making the exhaust cam timing incorrect.
Diagnostics will often lead to the camshaft sensor showing as having a fault, as the reference plate on the end of the cam moves incorrectly so the sensor can't read it properly.
This, in turn, can lead to the top chain guide breaking (the red plastic section in the image below and the bottom guide can also break which can allow bits of broken plastic to drop down into the sump .
To replace the top chain guide is a fairly hefty repair that requires special tools, so you will defienatly need to take it to a specialist that knows what it is doing.
We spoke to BM Bitz in Essex and it reckoned that the cost of replacing a broken guide would be in the region of £600-£700,
and while it carries out the repair, it will also rectify oil leaks these engines are prone to - rocker cover gaskets, vanos solenoid seals and top profile gaskets, all of which would be changed when doing the rebuild.
Tel: 01268 683790
BMW Car Magazine November 2011 Issue.