Awful noises coming out of my Miata - help me diagnose

Yesterday I noticed that there is an awful racket coming out of the engine in my 96 Miata. It has been running great and all of a sudden the squeaking belt and the can of marbles noises came up out of the blue. I've posted a video as well - the rattling sounds like it's coming from inside the engine and isn;t a loose heat shield or anything like that. It still runs fine, except for the rattling. Sounds okay at higher revs and under load, but is most pronounced while decelerating with lower revs.

What do the experts think? Is this the end of this engine? It only has 130k miles on it, but a few hundred autocross runs on it as well.

edit: the embed tag didn't work - here's a link to the video. http://youtu.be/YDPT7fFwpZg

I cant tell from the video, but this is what I would do:

1. Make sure it is not an exhaust leak at the manifold.

2. Remove the valve cover and take a peak inside.

Hopefully it is not rod knock.

Yeah, it's hard to tell from a video because I can't localize the noise, but it sounds like what I've heard when a flywheel/flexplate bolt walks out. I'd pull the serp belt off and see if it's a FEAD issue. If it's not FEAD, pull the cam cover and have a look-see down the timing drive area.

Squeak sounds like a spun rod or main bearing to me. It could also be a cam bearing. Use a stethoscope to really nail down the location. If it has a cam position sensor look into that too. I know on a Ford they can make a horrible sound with the engine still running fine.

Obviously that sound indicates serious trouble if you continue to drive the car. You basically have no choice and need to address this issue now. If that sound is internal (bottom end) then engine is already gone.

The good news is it may be a simple problem.

Start with removing the power steering belt then start car..

then remove the alternator belt and try again..

Hopefully the trouble is something on the front of the engine.

I'll take it apart a bit tomorrow and see if I can figure it out. I listened around quite a bit and it doesn't sound like it's coming from anything hanging off the front of the engine. It sounds like there's something banging around deep within. After listening to a bunch of other videos on youtube, I am also leaning towards a spun bearing.

Is it unusual that it would happen out of the blue like that? Car is full of oil and didn't have any warning signs. Just fired it up one morning and it sounded like hell.

If the engine is toast I'll either sell the car as it sits, part it out, or put it away until the spring and deal with a new engine then.

I'd say too fast for a rod knock, and it doesn't get a lot louder when you rev the engine. Sounds more like a ball or roller bearing piling up, although not being able to localise the noise makes it tough.

To me, it sounds like a bad pulley that is covering up some major internal engine rattling.

I had a terrible knock develop shortly after replacing the timing belt on my '02 Miata. Long story short, the trouble turned out to be loose bolts on the water pump pulley.. forgot to tighten them when I did the timing belt.

I lean strongly toward a timing belt tensioner or idler pulley failure, Isuzu V6's would sound like that if the hydraulic plunger went bad. The Miata doesn't have the hydraulic plunger but the sound changes about the same way the Isuzu would, i.e. rattle like hell on decel. This of course won't fix itself, disassembly to the point of failure will be necessary. But don't do it haphazardly, as each part is removed inspect carefully before going to the next.

So i started digging in today and found this...

Three of the four bolts on the crankshaft pulley are missing. Do I just replace this pulley and be done with it, or is this a sign of a catastrophic problem?

That's good news, looks like you found it. First: be sure the crank center bolt is tight, remember the problems Miatae seem to have along those lines. Then be sure the small bolt holes are in good shape, if they are get another pulley and some NEW bolts (don't even try to recycle any of the old bolts or pulley) and reinstall. Now, if the holes in the balancer are wallowed out or have sloppy threads, replace it too; you'll save yourself a lot of aggravation that way.

Took another layer apart and found that three of the bolts sheared off into the pulley behind it. The center bolt doesn't budge at all. If I'm reading this diagram correctly, I think this is the Boss Pulley, right?

I obviously need a new one of those plus four of the little bolts. I'd get a new 21mm crankshaft bolt as well since its only a few bucks. Would I need to replace the big crankshaft pulley that I took off first? It looks to be in good order and it'd save me $100. Anything else while I'm in there?

Whoa.

I would be curious as to why this happened in the first place.

Take no shortcuts.

I fired it up last night for a second with the belts and pulleys off - no more death noises. I placed an order for all of the offending parts and will put it back together this weekend.

I'm not looking forward to getting that big crank bolt off, but otherwise I may have dodged a bullet here. No idea why it happened, but it looks like this is fairly common when digging through miata.net.

The big crank pulley bolt will zip right off with a good impact. (ie, dual piston like the Harbor Freight Earthquake ones will work fine)

Torquing it back to spec though isn't possible with an impact. I wish it was!