Engine rattle in the morning. Like rod knock

[Chuckcruzin1986]

Hi,
1986 325es 220,000 miles
I have a rattle in the morning and it sounds like a rod knock.
I used a factory bmw oil filter.
20 w 50w oil
40 lbs pressure idle with engine at 80 degrees (start up in morning).
60 lbs pressure at 2000 rpm
I heard the check valve in the oil pump might be stuck so we pulled the pan and pump. Cleaned and inspected it........nice. Put it together and this morning I had a slight rattle, like two slaps.

What could this be???

Thanks, Chuck

[nando]

timing belt tensioner? trying to think of things that might rattle in an M20..

[James Crivellone]

My M20 ETA back in the day did that around 210k miles.

Cold oil was the major issue, the rod bearings looked fine, although one was a little tired. I got a stethoscope and determined it was simply rod knock at startup.

[Liam]

Piston Slap is common on high mileage m20's... Goes away warm right?

Also the wrong (or cheaply made) oil filter can drain back... This could fit your symptom better. I recommend Mahle (OC49 is the correct number for all M20s)