Aluminium 'dust' in oil - should I worry?
 

My engine has always made an occasional annoying 'whine' at idle. Like a low volume belt squeal. It's always mystified me, even the location of the source, although the CAS area seemed most likely. The clutch, flywheel, bearings, cambelt, accessory belts etc have all been changed without success. So today, to eliminate any chance of noise from cavitation around the not so small coolant sensor, I pulled the Electromotive GM sensor (spliced into the heater in pipe below the CAS) and moved the TECgt signal back to the OEM sensor.

Now the worry bit. I also pulled the Mk1 cam sensor, to give access to the coolant pipe, by removing the 'bearing cap' that holds it in place. The oil there was black with a shiny metallic appearance, could feel very fine 'dust' in it. Much was definitely on the engine side of the 'O' ring and must be getting into the engine. So perhaps I have found the reason for my mystery noise, but could the finely ground aluminium cause any engine/bearing wear? I am desperately hoping that, being aluminium, it should be too soft to cause much, if any, wear but I can't help having a real bad feeling about it. Should I be worrying?

I would definitely be concerned about it and send the oil in for analysis immediately to find out for sure.

+1, Means something is misaligned or wore out causeing excess wear and "dust" is the result of that.

Pull your cam caps, starting with the front caps on the exhaust side. That usually shows signs of wear from metal impregnated oil first. It collects on the surface of the cap, looks like it's pasted or smeared on.

cam bearing failure.

Thanks for the input, you've all confirmed my concerns. The guy at my local machine/race shop who did a lot of the final assembly is stopping by my place tomorrow evening after work to have a look.

I've not removed any of the cam bearing caps, so as to let him take a look tomorrow, but the cams themselves show no free play whatsoever and the oil remaining in the head appears aluminium free. Everything smooth, shiny and un-scoured. I know it doesn't really mean anything but, right now, it's making me feel a little better. Hopefully it'll just turn out to be an issue with the fit/balance of the Mk1 CAS which I am in the process of junking for an alternative cam sync'ing idea.

BTW the CAS I used was off my original Mk1 1.6L engine, my understanding is that all Mk1 CASs are interchangeable and therefore it should not matter which CAS I used for the sequential signal on my Mk2 head?

You'll see the opposite of free play. Since the cam "bearings" are loading up with the metal particles they're actually consuming the bearing tolerance. It just gets worse from there.

Did your recently jack with the timing belt tension? If there's too much tension the bearings will whine.

No, not since I had the head gasket replaced just 500 miles, probably less, after turning the new engine over for the first time (head gasket had a coolant passage or two missing on inlet side..).

Are you referring to the cambelt pulley guide bearings?

Your not helping that feel good factor I was working on ;)

Seriously though thanks for the input. Do you (or anyone else) have any pictures of a cambearing that has suffered this fate? The chap taking a look at it tomorrow evening has a lot of experience (from building classic race cars to Nissan works cars), but I'd like as much information about what we're looking for as possible.

Well, the good news is that the cam caps make for an easy check. And odds are if you don't see evidence of scarring/accumulation on the caps, the bottom end is ok.

I got a few of the 99 thrust bearing TSB engines way back and I know one of them had bad cam caps only on the exhaust side and the crank and rods were fine.

The caps are the first to show evidence - if the journals in the head are ok, you can use cams from another engine. Of course you'd have to get lucky and find some caps that fit the bore axis good enough for tolerance/spec, or at least meet tolerance/spec with a hone.

After a big sigh of relief I have uploaded a couple of images of my bearings. It looks as if the fine aluminium dust has not done any damage. The stock CAS is going to be replaced with a new setup (I'll post images when it's done in a couple of days) and I'll just have to keep an eye on things. The bearings appear to be OK, no reason to be unduly concerned?
http://rockbeareweather.co.uk/cambearing1.jpg
http://rockbeareweather.co.uk/cambearing2.jpg

I had a better image showing honing marks still on he bearing face. I'll try and upload it.

Guess I had better put the car back together now.

It's hard to tell the photos. It's more about a feel thing. Drag your finger nail across the surface (perpendicular), both cam and head - does it catch? No? Lucky you. :D If you feel any bumps there's a problem. Bearing surfaces should be pretty close to the lobe surface. You can get your cam surfaces micro polished for relatively cheap (I got two cams done for <$20 US). That process will dramatically smooth out the cam w/o removing a significant amount of material- providing there's not a lot of damage to the surface.

Think I've been lucky or caught it early enough. Time will tell. The stock CAS is now gone and hopefully so will the problem (both the noise and the fine aluminum debris).

If you can feel scoring on the cam surface, I'd get it micropolished. Then fresh filter and oil, and drive on.