Bulldozer

Hi everyone. I originally posted this on d-series but I guess it won't hurt to grab some more thoughts here I hope it's OK with you all and thanks for any help in advance.

So, just did a rebuild on my D16Z6 (which was burning a lot of oil). New rings, valve/seat job, head surfaced, new valve seals, etc. Rod bearings were inspected for wear and everything looked good.

Engine is still on the break-in period (it only has about 1000 miles on it), running strong and no more oil burning!

Thing is: looks like a new unknown noise is growing up there...I didn't notice it on the first 500 miles and now it is becoming real annoying.

It is more noticeable during warm up (not exactly right after cold start) but even after warmed up I can hear it...very faintly though. The weird thing on this is that I can only hear it on low rpm and light acceleration (knock pitch varies with throttle position). On WOT or no throttle at all there is no noise!

What I already tried: valve adjustment; ignition timing (it was 2 degrees off but didn't solve anything)

Now the real important detail which hopefully will give you a clue:

http://www.youtube.com/watch?v=HZ9JL...layer_embedded

This video is not mine but it is EXACTLY the same sound (maybe not that loud) and I can reproduce it the same way (on cold starts...after warmed up hand trick doesn't work anymore, only on road with light acceleration).

Any clue or hint is highly appreciated. It may be nothing but since the engine was just rebuilt I'm a little concerned...
Click here to find out more!

Bulldozer

In the meantime, these are the updates:

- valves were adjusted more than once
- mechanical timing and ignition timing is spot on
- oil and filter changed after 1500 miles; no metal shavings on oil or filter element
- the guy who originally posted that video told me that he never had an issue with the engine, only regular maintenance (he is the first and only owner). The knock never got worse and tends to disappear on warm weather (don't know if my symptom fits this...for the time being weather here is quite cold). A long time has passed since he posted the video and the engine keeps running fine
- did a compression test on the engine and the output is very good in all 4 cylinders: 182-180-180-185
- one of the spark plugs shows a bit of shiny fouling on the ground electrode; it is the only cylinder that shows black soot on top of the piston

Bulldozer

Last but not least, here are the news as of yesterday:

I finally had the car parked at the shop for inspection (not the original mechanic who did the rebuild, as I don't really trust the guy anymore). Oil pan was removed and rods were checked for excessive clearance. Rod bolts torque was also checked and they were fine. Everything was OK on this chapter according to the mechanic who did the inspection.

Now, for the oil pump screen chapter...it was a real nightmare! It was gunked up pretty badly with what seemed to be paper rag and engine silicone (yes, the one used on gaskets...). Oil light never came up though, despite the brief "shhwwooosshh" noise I began to notice on cold startups...

No metal shavings were found either, not even on the gunked up screen. Honestly, this was a relief.

So, either way the mechanic who did the rebuild screwed up pretty bad...I'm glad I had the oil pan removed and found this before starving the engine for real.

Anyway, my hope is that this episode didn't cause any harm to the bearings...the downside of this story is that the knock is still there...even after replacing exhaust manifold gasket.

Thing is: if this noise is the result of bad lubrication due to the clogged oil screen, then there's nothing I can do now...it is there and I only hope it doesn't get any worse (assuming it is not a bearing...otherwise it will definitely get worse).
Not, if the noise is a fortunate coincidence and a sign from above for rescuing the engine from a death foretold, then I give thanks to the Lord for it but I still have this stupid annoying knock going on...

What are your thoughts?