Timing belt pics and questions, and more!
 

I've had a scuffing-ish noise coming from the front of the motor for the last couple of weeks. It seems to be coming from the middle to upper area of the TB covers but I have not gotten as picky as grabbing a stethoscope to pinpoint it. I only hear it when the engine is hot, not at startup or even after a quick 5-10 min drive, only after running around for 20+ minutes, but not every time. It's frequency is less than that of the engine rpms, but increases with rpms.

It's not metallic in any way, no clanking/clattering/grinding, so I figured I'd start with the belts. The alternator belt looks great, and I finally pulled the valve cover today to have a look at the TB. I rotated it around and found the spot shown in the photos. It's not actually delaminating, as I can't pull the belt apart or even get a fingernail in there, but the nylon is fraying a bit for about 6" on one edge. There are not any actual scuffs/scratches anywhere on the edge or the top of the belt that would suggest it's making contact with something, no missing teeth, no cracks, it's not dried out looking, not oily, etc. I did not pull off the lower covers to see if there were any scuff marks on the inside of them, but again the belt looks unmolested aside from the frayed section and they stayed centered on the cam gears as it moved. Car has 109K and my best guess is that it's not the original TB (no receipts from the PO).

So it seems to me like the belt should not be making any noise, but prove me wrong. Or suggest something else that can be making this intermittent scuffing/chuffing sound up front.

Thanks ya'll

Edit: also, if the belt looks too worn/old to be reliable, even if it's not the cause of the sound, let me know that, too.

https://www.miataturbo.net/attachmen...1&d=1330992138

https://www.miataturbo.net/attachmen...1&d=1330992138

https://www.miataturbo.net/attachmen...1&d=1330992138

Have a look at the lower covers and tensioner pulleys.
Beg/ borrow/steal or cut your own cam cover and see if anything is wobbling around with the covers off.

Definitely looks like the belt has been rubbing.

Check the small hose from the t/stat to the mixing valve. It, or the thin bracket holding it back, may heat up enough to rub on the P/S-AC belt

Frayed timing belt is a no go and there are probably other wear items that have contributed (or, it could just be that a cord in the TB let go and the TB is no longer true). Buy this and install:

http://parts.arlingtonmazda.com/prod...KMK002%29.html

Note: Obviously, get the one that matches your AC/PS configuration.

My lowest cover has been machined by the pulley. Might want take off those four bolts and take a look.

Thanks guys.

I have not had a chance to pull off the covers yet, but upon quick inspection of the mixing valve lines I saw that the cover behind the water pump pulley is cracked and that there has been some contact between the pulley and cover. Next time I hear the sound I'll have a look there.

Hornetball, thanks for the link to the OEM parts. That's on the short list now I guess.

Rosenthal has covers too. They're pretty cheap if you need them. My covers have had some contact in the past too, but I haven't replaced them. As long as the rotating components are running true, you should be OK.

OK great. Now I just need to coordinate some warm temps with a day off. Thanks again.