944-turbo

It sound like 7-8 knocks every second at idle = 450 knocks / minute (once every second revolution)
Could be a bad valve lifter, but it sounds like it is coming from lower down in the rear of the engine (difficult to hear exactly where the sound comes from).
Rod bearing?

When I start the engine cold, I first do not hear the sound much. After a couple of minutes at idle, the knock is much worse (it sounds like what you hear on the video).

Any suggestions....?

Thanks!

xschop

No, not one of the 951 bullet-proof engines?

Spun bearing or lifter lost it's prime and is giving your cam the beat-down.

jeffrsmith

I would use a long screwdriver like a stethoscope - i.e. hold the handle to your ear and use the tip to listen to the spots where the sound seems to be is coming from, should help to pinpoint where the noise is coming from.

Carlsbergas

Check your timing belt, sounds like car is out of timing
Both videos my car was out of timing, first video I had mangled woodruf key and keyways on cam.
2nd video my timing belt tensioner roller was broke my car was by 1.5teeth out of timing.

http://www.youtube.com/watch?v=PeM-I...e_gdata_player

944-turbo

Update:

I did an oil analysis test. No traces of lead in the oil, which means my bearings should be ok (if I have a spun / worn bearing, there shold have been signs of lead in the oil).
I tried another set (8) lifters. The knocking sound is still the same.

Any other suggestions how I can find out what is causing this knocking?

Van

Sounds like rod knock to me... What's your oil pressure?

mytrplseven

You may have a broken valve spring. This is a solid sound and I agree with timing check and using a stethescope or screwdriver to see if the noise is upper or lower in origin. A compression check would identify if it's valve related. From the video, it does sound like a rod noise, though.

JimV8

Yup rod noise. Broken big end.

xschop

Spun rod bearing sound this way on 944 engine?
What is the cost of rebuild nowadays?

HICKS

Sounds like spun rod bearing.

lart951

Where are you located?

xschop

Somewhere up **** creek without a rod bearing. Snapped rod bolt perhaps.

944-turbo

Thank you for trying to help me!

My oil pressure at is as good (or better?) as before I got this knocking sound, 3-4 bar at idle when the engine is hot.
If a rod bearing was bad, I really should get lower oil pressure at idle, shouldn't I ? And since the oil analysis say no traces of lead, I think that means I do not have a bearing problem.

I have taken the cam box off to try another set of lifters (did not make a difference). The timing was/is correct, and everything I can see in the valvetrain looks perfect (no "wear" I can see / no broken valve spring I can see).

When I start the engine cold, it is difficult to hear the knocking sound. As the engine warms up, the sound is a lot worse (like you hear on the video). When the engine is hot, it is not so bad.

I can hear the knocking best at idle/low rpm.

I tried listening with a stethoscope. It is very difficult to hear where the knocking is coming from (I can hear the knocking in front/rear/left/right/under/over the engine....).

Thanks again for tying to help!

HICKS

Did you cut open the oil filter and check inside the pleats? Why do you keep saying you're checking for lead, they're not made of lead.... What oil weight do you use? When was the last time the rod bearing were changed? Does your oil pressure gauge bounce at idle? When you turn on AC does the oil pressure drop?

xschop

OK just listened to vid on home comp w/ good speakers. That actually sounds like a worn can lobe and/or tappet. If at some point a lifter (these are flat tappet design) has lost its prime for a long period of time, it can frag a cam lobe.