Clacking noise

[I6V8]

Does anyone know what could be causing this clacking noise:

https://youtu.be/QeOLmfR0dy0?feature=shared

It takes a full 10 seconds at cold start before the knocking even begins so I'm not sure how this could be either piston slap or the valve train. It gets quieter as the engine warms up but never fully goes away.

Engine has 30K on a complete rebuild. Fresh oil change didn't make a difference. I haven't checked valve clearances yet, waiting for parts

Thanks

[TobyB]

It's the valve train.
Check your lash.

If that's all ok,
then use a stethoscope to figure out which one it might be,
and lash it 0.005" tighter and
see if that quiets it.

Flat eccentrics make it harder to quiet things.

The 10 seconds is the pooled oil being squeezed out of the rocker.

t

[I6V8]

Valves were way too tight. Adjusted them to .008 and .009. Idles a little better, slightly more torque down low but the clacking noise is still there. The rocker arms have some side play when they're not under tension from the cam lobe. That's the noise I'm getting so I think you're right. There's play. Wondering if there's wear because of the tight specs it was set to for more top end power.

[I6V8]

It's the valve train.
Check your lash.

If that's all ok,
then use a stethoscope to figure out which one it might be,
and lash it 0.005" tighter and
see if that quiets it.

Flat eccentrics make it harder to quiet things.

The 10 seconds is the pooled oil being squeezed out of the rocker.

t

Alright, resurrecting this thread as I'm prepping to pull the rocker cover off again next week. I'm beginning to think I might have some premature wear on one of the cam lobes on cylinder 1.

At first, what you wrote didn't make sense to me because I'd very carefully set & twice checked all valves at the eccentric to a tighter than spec clearance with multiple cold engine turnovers in between. The head had 30K on it on it at the time, all new hardware so how could the rocker have vertical play and still clack? All retaining clips were properly in place and I guess a small amount of lateral play is supposed to be normal.

So what's going on here? Did a bunch more research and found out the following:

(1) The rockers are made of aluminum alloy that expands more than steel. Explains the quieting after warm-up. Alloy cools off fast, that explains the initial clacking after a warm-start.

(2) So perhaps I need to check clearance at the cam on that rocker? - Yes, but why is there wear at 30K miles in the first place?

(3) Came across several "oil spray bar" threads on here and Reddit where people reported issues with cam wear from poor oil supply to the cam lobes. Dirt blocking the flow, loose banjo bolts or poor pressure (no oil at idle) from old pumps, pickup screen blockages or debris blocking oil lines after a rebuild.

That's when I remembered talking to a German BMW Master Tech 25 years ago who mentioned to me that M20s had "undersized" oil supply passages causing cam wear. Well, now I understand what exactly he meant. Apparently M10, M30 and M40 are plagued by this too, to varying degree.

So in addition to figuring out the proper clearance, I need to address to root cause. There's no "upgrade" of sorts, the only sensible mod / fix is:

(1) Pull, drill out the holes to 2mm, clean with carb cleaner and compressed air. (Crimping the bar at the center is no longer advised)
(2) Inspect the area where the banjo bolts are tightened down. Over-tightening them can apparently cause damage to the line and create a blockage point?
(3) Ensure nothing else is restricting flow in the head. Once the clearance is adjusted, I'll run the motor with the cover to see if there's flow at idle.
(4) Do an engine flush and change oil change

I'll post an update once after I'm done but thought I'd share this here in a post connecting the symptom and different findings together.

[digger]

what oil and rockers were used? there are no banjo bolts presumably you mean oil sprayer tube nuts (it is different to the m30 and you seem to be confusing the two e.g. crimping the sprayer bar)

[I6V8]

what oil and rockers were used? there are no banjo bolts presumably you mean oil sprayer tube nuts (it is different to the m30 and you seem to be confusing the two e.g. crimping the sprayer bar)

Not sure on the rockers. I got the cover off now and snapped a pic. Oil is Mobil 1 5W-50.

Drilled the spray bar holes out to 2mm, cleaned and blew out with compressed air.

Re-checked the valve clearances on cylinders 1 and 2 and found the intake valve too loose on cylinder 2. The eccentric bolt wasn't loose and I'm certain I was anal about the last adjustment 4K miles ago so that's odd.

Ran the motor with with the cover off and the vacuum line plugged and I'm still getting the clacking noise after 5 to 8 seconds. It stands out in between the tickling.

The thing is: when I put my ear close to the rockers I can't locate any of them making the noise.

https://youtube.com/shorts/hb7YomEWoPE?feature=share

Starting to wonder if this is piston slap. I had that once on a Lincoln Navigator with 2 bad injectors but I'm not confident the tone of the noise is the same.

The whole motor was professionally rebuilt 35K miles ago, deck to pan, fresh bearings, wrist pins etc. so that would be a bummer. I'll let it cool down over night and check all valves one more time, after that I guess I have to pull the plugs and check the cylinders with my borescope camera.

[I6V8]

UPDATE:

I thought the clacking was gone after doing another round of adjustments tightening clearances slightly to the tighter end of 0.008 and 0.009 but 2 cold starts later we're back to square one after about 15-20 seconds of idling...

The noise disappears after temperature is starting to build so next step is to pull the plugs and scope the bores.