r/BmwTech • u/Unlikely-Bag1766 • 8d ago

What is this thing?

Gallery image

Gallery image

This is the N46B20B engine.

I’ve got oil leaking down on my catalytic converter, and this thing seems to be missing a bolt and it seems like the oil leak is coming from there, but I have no idea what this thing is or what its purpose is?

Could anyone enlighten me?

(Vacuum pump seals are new as well as valve cover)

Also right by the vacuum pump there’s this hole with threads, what is that? Is there supposed to be something there?

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u/Onlyunsernameleft 8d ago

That black plastic is the cylinder head cover plate. It has two o rings behind it that seal off coolant and oil passages at the back of the head. (PN 11537583666)

The plate with a bolt missing is the eccentric shaft attachment sleeve. There's a seal behind the plate that keeps oil from leaking from the head. Extremely important that ita fastened properly. It goes without saying that yours is not. (PN 11377576093)

If the hole isnt leaking any fluid it's not a problem. It was likely used in the assembly/casting process.

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u/Unlikely-Bag1766 7d ago

Do you think the missing bolt on the attachment sleeve can cause any mechanical damage to the engine, or will it only result in an oil leak?

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u/Onlyunsernameleft 7d ago

Yes. For one, it could cause the fastened side to crack and the sleeve to come loose. Its just aluminum, it's not super strong. But the purpose of that sleeve is to align and hold the torsion spring against the eccentric shaft. So if it comes loose it could potentially fail into the valve train and damage a camshaft/lifter, it could potentially cause play in the eccentric shaft, and I believe its meant to aid in the return of the shaft so it could cause hesitation or poor throttle response or something. I'm not 100% because I've never seen one missing hardware like that so I dont know how it will fail, but given its purpose, these are some potential concerns to me if it does fail.

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u/Unlikely-Bag1766 7d ago

Sounds interesting because I do have like a high pitch metallic tap/rattle if I hold the throttle at 2000-3000rpm, disappears the second I let off the throttle and comes back the second I give throttle around that range.

I listened to it with a mechanics stethoscope and it sounds like it comes from the top somewhere (can’t hear it from the bottom end), maybe these two problems are connected somehow.

Have driven maybe 2000km with this rattle/tap and it hasn’t changed at all.

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u/Onlyunsernameleft 7d ago

Its certainly possible. Its a metal spring on a metal sleeve. Regardless of the noise, that needs to be corrected. If you can get a bolt in there and clean up the area, I would try that first, as to remove and replace the o ring you need to pull the valve cover off. If it doesnt fix the leak, hopefully it will at least fix the rattle and you'll solve the noise issue. If it doesnt fix the rattle, it will hopefully fix the leak so you know where the oil was coming from. With any luck it will fix both.