Knock from bellhousing (I think)

[Neilbsg]

Hi, I have a loud knocking sound which you can hear and feel when sat in the car and turning the engine over. As soon as the engine fires, the noise goes away and the engine runs well. The oil pressure light goes out but my pressure gauge does not work (have a new sender to fit). The strange thing is, the longer you turn the engine over with the king lead removed, the quieter the noise gets but never fully goes away. I can’t see any obvious damage to the flywheel or starter. Here’s a link to a video on YouTube of me cranking the engine.
Has anyone had these symptoms before?
It’s a 3.5 engine.
https://m.youtube.com/@neilbeetham5035

[BlueWedgy]

My silly ten penneth, I take it the starter motor is secure and tight?

[Neilbsg]

Yeah the starter is bolted up correctly and no movement

[Wedg1e]

How about a sluggish cam follower taking a while to pump up?

[Neilbsg]

I can feel the vibration/noise on the bellhousing casing and you can also feel the vibration when sat in the car and turning the engine over. I ve had the rockers off and the lifters are all quiet starting, I do get a slight tick from one with it warms up.

[SLB]

It sounds familiar to me. I wonder if it's some kind of backlash noise as the starter is working against compression, then the release of compression helps it and so on. It's not a consistent force.
I do get a different "ting" noise when changing gear sometimes which I think is the clutch fulcrum leaver wearing thin. I'm waiting for the clutch to go before fixing that.

[BlueWedgy]

You could prtobably take the starter motor out and see if the flywheel seems loose at 90 deg increments, accessing through the starter hole?
Mine kind of clonks for want of a better word until it catches, I kind of think perhaps it is near locking-up with unspent fuel?

[oakdale]

Sounds like a slightly worn/noisy starter motor in conjunction with low compression on one or more cylinders to me.

[Neilbsg]

Thanks for the replies. I’ve not removed the starter yet so will have a close look at that and check compression too.

[Neilbsg]

Here’s another link to a shorter video with rockers removed.
https://youtube.com/shorts/VGvRbUqw2T8

[oakdale]

Neilbsg said:

Here s another link to a shorter video with rockers removed.
https://youtube.com/shorts/VGvRbUqw2T8

Having heard this, I'm going to say I dunno now.
I think you need to remove the starter to have a look at it though.

[keynsham]

Sounds like the exhaust hitting the chassis to me. I have had plenty of that in the past!!!

[oakdale]

Having had another listen to this, my internet guess is that the starter bushes are worn which is causing the armature to catch on the stator, it's only a guess though.

[Neilbsg]

I’m pretty sure it’s not the exhaust but will treble check this. Will remove the starter to examine

[keynsham]

Neilbsg said:

I m pretty sure it s not the exhaust but will treble check this. Will remove the starter to examine

The exhaust on my 350i is very close to the gearbox, and I mean a few mm! Also the pipe going through the chassis and over the driveshaft at the back has virtually no clearance and can clonk a bit sometimes.

[Neilbsg]

Yeah mine seems very close to the gearbox as well with just a few mm clearance but didn’t seem to be knocking in that area when I checked

[BlueWedgy]

I assume that you have disconnected the fuel pump in some way prior to running the starter? If not the injectors will continue pumping fuel in and not igniting. This will pottential bore wash the cylinders and thin the oil?
If not, then let the fuel evaoporate (Spark plugs out), disconnect the pump and try again see if it improves, other than that it will take a bit of stripping down i guess.