Sounds like a slight rod knock

[CptPhilmeister]

Any more news? lol Don't mean to be a bother, but this mystery with my own car is really getting to me now.

One shop quoted me pretty high and wants to look at my clutch and trans when I'm CERTAIN the noise is coming from down low but towards the front/center of the engine bay.
[Mine is an S52 from a M roadster (Z3]

Further verified that nothing affects the noise aside from acceleration. Nothing changes when clutch in/out or in gear. Only goes away when hammering down on the power.

Getting a bit more persistent as well, topping off or changing oil viscosity doesn't seem to subside it much like it did.

[m3boost]

Any more news? lol Don't mean to be a bother, but this mystery with my own car is really getting to me now.

One shop quoted me pretty high and wants to look at my clutch and trans when I'm CERTAIN the noise is coming from down low but towards the front/center of the engine bay.
[Mine is an S52 from a M roadster (Z3]

Further verified that nothing affects the noise aside from acceleration. Nothing changes when clutch in/out or in gear. Only goes away when hammering down on the power.

Getting a bit more persistent as well, topping off or changing oil viscosity doesn't seem to subside it much like it did.

The engine was take apart by the machine shop and found no visual wear.. Every single piece was checked, nothing found. They put the short block back together and all tolerance are within spec just as I had checked it..I'm trying a different head and a new southbend clutch, pressure and another flywheel and see if the noise is still there. I just mated the engine and transmission together last night. It should be going back into the car by the weekend.. I'll keep you updated.

[m3boost]

Update, I finally put the engine back in, and that knock sound is gone..The changes I did, was put a new clutch, pressure plate, flywheel, and another head. The reason I replaced the head, was because the head I had initially installed had the non-tapered valve springs while using the s50 cam trays which use the lifters made for the tapered springs..So since I had another head ready, I went ahead put another head.. So in the end, I don't know what was causing that rod knock sounding noise..

[NotJesus]

What viscosity oil were you running?

[m3boost]

What viscosity oil were you running?

the first time around, I tried different thickness and at the end I went thicker to 20/50'' but the sound was there no matter thickness I used..

[CptPhilmeister]

Thanks for keeping us updated!

Seems at least one stop had a pretty good idea of where to look. Will definitely investigate the clutch first, if it's still heard I'll make the call to do a full engine sweep.

::Beers::

[CptPhilmeister]

Fixed!

Turned out to be definite Rod Knock, thankfully fixed by a new set of Rod Bearings. Back to smooth running for now!

:mrgreen: