Clackety Engine Noise - Source?
 

So I have a pronounced noise in the engine bay or from the underside, at idle. It sounds almost like diesel valve train noise. In the video, there is a higher pitched whine of the belts, but a much lower pitched clanking noise as well.

Any thoughts on what this could be?

Clakety noise 944 - YouTube

Car is at 83k, '86 turbo.

Bruce

Very hard to tell but I would eliminate it being an accessory buy pulling off one belt at a time, Ac, alt, ect and see if the noise goes away. If all the belts are off and you still have the noise you can start looking into the engine. I was curious why your boost gauge isn't moving?

sounds like a loose alt bracket or something, as noted remove the acc belts and go from there. I dont think it sounds internal, but hard to tell. underr hood sound bite might help/

I am having a similar problem myself that I am currently in the process of diagnosing. I think my problem is a header leak.

Here's another soundbite from under the hood.
Bad 944 sound - YouTube
It's dark, but basically I put the camera under the hood, then under the front lip, then walk around to the driver's door.

It sounds really bad to me - very mechanical. Two other clues:
1) I checked the oil for the first time in a couple 100 miles, and it was below minimum - I don't have any visible oil leaks.

2) When I drove it tonight (last time for a while I think), the temperature gauge was edging higher than normal to the second hash mark, on a reasonably cool 18C night. That said, she drove fine - not halting on power generally.

Header leak is an interesting thought - will feel around. However, when I had a header leak in the past on a 944 NA, it sounded different - like an exhaust leak.

Pete - Haven't had a chance to remove the belts / alt bracket, but would be surprised if that was it, i.e. why would it produce higher temps.

Re: boost - the gauge does move, not sure if it should have moved under very slow pedal pressure. Under heavy load it tops out at 1.4bar, which I have listed as another item to look into.

Sounds like rod knock to me. I definitely would not be driving it.

Might be time for new bottom end bearings.

I would get a mechanics stethoscope and poke around to rule out alternator and such.

That being said, it does sound "bad", like a rod. If you do take it apart and find something, make sure you mic up journal, as if it's a rod bearing likely your crankshaft is bad too.

That sounds nasty. Does it have a lower pitch tan what is on the playback? I am listening to it on my laptop speaker and it does not reproduce sound very well. Rod knock sounds like a small ball lien hammer hitting the inside of the block. Valvetrain noises are usually higher pitched and at half the speed of the motors rpm. Kind of hard to explain but if the rapping is in synk with RPM then it is something connected to the crank. If the noise is at half engine speed then it is a valve train problem.

If you want any help diagnosing it let me know.

I drained the oil this weekend to see if I could determine if the engine was producing metal shavings. Could not find any metal - dropped a strong magnet in the used oil, moved it around, did not get a spiky magnet. Filtered the first 2 cups to come out, no shavings. The method is at risk of false negatives (ex. the shavings could be in the bottom of the oil pan but not draining).

I also rotated the engine by hand, to listen and check timing. Timing is fine. There were several squeaks in the rotation, which sounded different from belt / pulley squeaks, but it did not sound 'horrible' metal on metal. Not really a clear signal.

Wondering what the next step on diagnosis is? I've been a little hesitant to start the engine again, but sounds like from the above, I should re-fill with oil and start again, then listen with stethescope and pull a belt off at a time.

In other news, my PS rack is leaking, so if it does come to rod bearings, I can merge the two steps.

A final (stupid) question: If the crankshaft was damaged, I presume that the engine has to be pulled to replace / rework it?

You have options depending on you ability's and time and obviously $$$

First thing is to see if you can locate the noise (top or bottom of the motor) then chase it accordingly) Top end remove the head. Bottom end the pan. Ohya does the noise change at all when you engage or disengage the clutch?

If it is a top end problem best bet is to fix the motor in the car unless there is some sort of damage to a piston or the block that precludes this.

If it is a bottom end problem you have options but it is almost certain that the motor is coming out at that point.

Had an interesting development today. Was getting the car ready to start up again (goal: chase the noise), so I refilled with oil. Noticed that the coolant was almost non-existant in the reservoir (always hard to see through the old plastic). Filled it back up to min (maybe 750ml!), then started the car. Noticed there is a slow coolant leak coming down the front of the engine, with coolant also pooling in the bottom of the belt covers.

So clearly I need to get in and take a look at the waterpump.

Is it possible that a waterpump that was failing could make the terrible noise I heard? Seizing bearing in the waterpump drive?

Anyone think that it may be a heat shield?

I've been wrong before, but I'd be very surprised if it was a heat shield. The noise was more complex than a heat shield vibration.

I'll know more in a week, but for the moment the lead hypothesis is the waterpump. I turned it by hand last night and it made some noise. It was not difficult to turn (ie. not seized).

Any update on this? Chasing a similar problem. Will try the belt removal idea this weekend.

It was the waterpump bearings, blown from over-tightened timing belt. Phew!

that's still a major pain, but far less painful than a motor rebuild. :) i never thought i'd say congrats on having to replace the waterpump! :)

Update on the noise. I had the engine all back together yesterday and started it up, with the new waterpump. Same noise re-emerged ! Not present at first startup, then louder as engine got warmer.

So either:
1) It was the waterpump originally, and now its the new (rebuilt) waterpump again. The company that received the old core confirmed that the impeller on the old one had contacted the housing. Apparently it is rare that the off-axis rotation that causes this impeller-housing contact would also damage the block somehow.

If this is the case, it would mean there was damage to the block which is now banging up my new waterpump. I took a picture of the block - waterpump interface when I had it apart:
http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/783653-waterpump-impeller-contacted-block.html

2) The waterpump was an unrelated failure, and something is still wrong, so we're back to top end vs. bottom end (?). I guess I need to do some more listening.

Looking back at the pictures from the block, I was so focused on the little nick / crack, I didn't notice the rubbing spot on the block.

This suggest that I once again tensioned the belt too tight, forcing the impeller over to the side? Alternatively, the previous rubbing could have left a high spot.

I'll try loosening the timing belt to see if that makes a difference.http://forums.pelicanparts.com/uploa...1387125921.jpg

how are you confirming the correct belt tension?