[_Mars98_]

Hi all,

I've been having a bit of a nightmare diagnosing the rattle coming from my engine, it very much sounds like a top-end, higher pitched rattle coming from the rear of the engine as if a spring is pinging out of place while under tension (the video makes it sound more like rod knock than it does in person).

When it first happened, the car had dropped into limp mode but was still running smoothly although with reduced power, then all of a sudden a loud rattling noise combined with engine hunting led me to pull the car over within about 60 seconds and shut it off - I had it recovered and it hasn't been driven since. Read the codes and had several valvetronic codes which led me to replace the actuator and eccentric shaft with all new bearings etc - that cleared the codes but the engine still rattles like hell when started. There are no more relevant codes for vanos or anything and the adjusters and bolts are all in good nick.

I have unplugged each injector in turn and run the engine which didn't change anything at all and done a compression test which came back with the following:

Cylinder 1 - 155psi
Cylinder 2 - 150psi
Cylinder 3 - 150psi
Cylinder 4 - 155psi
Cylinder 5 - 120psi
Cylinder 6 - 160psi

I have since stripped the inlet camshaft off and replaced all the hydraulic lifters on that side as that seemed to be where the rattle was coming from but no joy unfortunately. The cam itself was a bit worn as were the outer bearings but I polished them up a bit and the cam was rotating freely once reinstalled. I couldn't see any damage to any of the cylinder head suggesting something had broken and all the springs were seated correctly so I am at a loss now as to what is making the noise.

The car is a 2013 M135i with 90k on the clock, I know all of the owners since it was first purchased and the oil has been changed every 6000 miles for the last 7 years, the car has also never been tracked or done donuts or anything like that so I find it hard to believe it was starved of oil at any point.

I never took the exhaust cam off as it requires yet more daft BMW special tools, but I believe the next step is to drain the oil and check it for metal shavings and maybe take the cylinder head off but before I crack on I just wanted to check if there are any wizards on here that recognise this bloody noise straight away and could give me a bit of advice.

Here's a link to the video, but it does make it sound more rod knockey than it sounds in person:

Many thanks

[IJO]

You need to investigate cylinder 5 as there will be a reason for the low pressure.
Could be a leaking valve, or broken ring. (which could explain the light rattling)

[_Mars98_]

Originally Posted by IJO

You need to investigate cylinder 5 as there will be a reason for the low pressure.
Could be a leaking valve, or broken ring. (which could explain the light rattling)

Will be pulling the oil filter and probably draining it in the next few days, next step after that I reckon will be trying to get the cylinder head off so I can check all the valves but maybe easier said than done.

[V8cylinder]

Hello did you manage to find out what the problem was? I also have a very similar rattle on mine and it gets more audible as you rev. Would be good to know if you were able to resolve it

[_Mars98_]

Originally Posted by V8cylinder

Hello did you manage to find out what the problem was? I also have a very similar rattle on mine and it gets more audible as you rev. Would be good to know if you were able to resolve it

Got to the bottom of it eventually yeah, it was a spun bearing on cylinder 5 so had to rebuild the engine to sort it out unfortunately.