knocking sound in s50 - causes?

[scooper]

Hi everyone,

I installed a s54 oil pump and s54 pan onto a s50 motor and maybe 6 months afterwards I start to hear to knocking. Furthermore, I see some coolant weeping from the rear of the motor (and onto the mid pipes), leading me to believe that the head gasket needs replacing. 160k miles. I had an oil analysis done and nothing seemed out of the ordinary.

I removed the valve cover and nothing seemed amiss. Then I removed the oil pan and thought that the 4 bolts I replaced (to install the s54 oil pump) were loose, but they are not. I did not however, torque them but installed them dry. I have another 4 new bolts ready to go, however. I have not actually checked the torque yet but the bearing caps are flush against the block like the other caps are. Might the knocking be coming from the top end somewhere?

When the motor is not running I cannot hand turn the cooling fan and the fan did not seem to be hitting anything. I also installed a 3 row radiator. Can a seized fan make knocking sounds? Any thoughts? I still think the knocking emanates from the motor somewhere. Thanks...

[UsernaM3]

Does the knock speed up with the rpms? How loud is it? Does it continue if you put some pressure on the vanos unit?

[bluptgm3]

Hmmmm. The main bearing caps are attached with ‘torque to yield’/‘torque + angle’ bolts.
You installed them how?

Use an auto stethoscope to attempt to isolate the sound....Look at the cam lobes.

There are various opinions about using the S54 oil pump/pan. The M/S5X hydraulic lifters can use more oil than the S54 pump can provide.
VAC has answered the concern of low volume S54 pump by fitting it with S52 internals.

My sons 328 threw a code for a miss-fire, so we started by changing the plugs. The miss-fire was not solved, turned out to be a coil. Couple of days later it developed a knock. One of the new Bosch plugs was defective. Ceramic insulator was loose in the metal base allowing compression pressure pasted the insulator creating the knock sound.

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[scooper]

knocking speeds up with higher rpms. As for knocking volume...it is for sure louder than your usual ticking. Not sure how to describe knocking volume. How do I put pressure on the vanos unit?

Yes I know... I installed those torque to yield bolts...dry. I understand that they are supposed to be installed wet with oil. but the bearing caps are still firmly against the block and the bolts are not loose (which was what I was hoping for ironically). I torqued to 20nm then turned the bolts 50 degrees. Since the oil pan is off I'll replace them again and install them wet.

I will look at the top end again and see if any coils or plugs are bad. The knocking seems to be different from the misfire noise in our m52 which I am also currently diagnosing (probably a bad injector).

I have a VAC modified s54 oil pump for s50/s52 motors. What did the knocking sound like? Klunking? Metallic? or more Bassy? Muffled?

Thanks guys please keep thoughts coming!

[bluptgm3]

I initially though rod bearing and I am back to that.


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[scooper]

I pulled my fan clutch, and it's seized. Could a seized fan clutch make these knocking sounds? I tried to listen to where the knocking sound was coming from, and it kind of sounded like it was coming from the front. However, I really couldn't say for sure. I will put this fan on another e36 we have and see if I hear this knocking sound. What does a seized fan clutch sound like in operation?

Before I reinstall the oil pan I'll have a look at those 2 rod bearings that may have been affected. Oil analysis seemed normal.

[bluptgm3]

If not excess metal in oil, it probably is not a rod bearing.
Good call on the oil analysis.


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[scooper]

So I inspected the fan clutch, and it is so busted that it froze off axis 2-3 mm. And since I installed a 3 row radiator with the fan shroud sitting 2 cm? closer to the motor that is what probably caused the knocking sound. I won't know for sure until I button up the motor and replace the fan clutch.

If anyone has further thoughts please share. Else I will update as I make progress.

On a tangent how long do un-boosted motor head gaskets last? That may be what I undertake next as I see some weeping from the rear of the head, but I'll need to pressure test the cooling system first. Thanks...

[bluptgm3]

That is good news that it was the fan clutch.
S50 is different than a S52...I have 284,XXX on my original HG on a S52. It seems like S50s have issues on cylinder 5/6.

BMW added (machined) more coolant passages in later “400” castings.
4 additional passages in the later heads at cylinder 1/2 and 5 additional passages at cylinders 4/5/6.




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[MauiM3Mania]

If you have the sound located, congrats. If the fan clutch turns out not to be the cause, share a video with us so that we can hear the knock.

[das borgen]

So I inspected the fan clutch, and it is so busted that it froze off axis 2-3 mm. And since I installed a 3 row radiator with the fan shroud sitting 2 cm? closer to the motor that is what probably caused the knocking sound. I won't know for sure until I button up the motor and replace the fan clutch.

If anyone has further thoughts please share. Else I will update as I make progress.

You can try running the car without the engine-mounted fan and fan clutch to confirm the knock is gone in that case. Running it without that fan is OK if you're doing a diagnostic test from cold for about 10-15mn

[bmwstephen]

That is good news that it was the fan clutch.
S50 is different than a S52...I have 284,XXX on my original HG on a S52. It seems like S50s have issues on cylinder 5/6.

BMW added (machined) more coolant passages in later “400” castings.
4 additional passages in the later heads at cylinder 1/2 and 5 additional passages at cylinders 4/5/6.




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Were the revision specific for s52 only? Or were they later revised for s50 as well?