Miata belt frustrations

Hey all,

So I had to replace the thermostat on my 99 NB awhile back. When I did so, I used one of those sticky gaskets and no gasket-maker. Maybe I did something wrong (some say use gasket-maker even with the sticky gasket), but the stupid thing developed a massive coolant leak. I finally got around and redid that, this time with gasket-maker, and I've had zero issues.

During the time when it was leaking, my belts would squeak pretty bad when coolant dripped on them. I figured now that I wasn't leaking, the belt squeak would go away. Wrong!

Aside from this, I had a nasty rattle at 3k rpms. I figured it was heat shield, as I've seen this problem personally many times on many different cars. False!

It turns out my lower alternator pivot bolt has completely backed out. I loosened the belt and tried to screw it back in. It screws in until it reaches a certain point, then it just spins. So, obviously stripped.

I jumped online thinking I could just find a similar bolt and run it through with a nut on the end, call it a day. Well, surprisingly nobody had measurements for the bolt (at least that I could find). I bought one that I think might work, but I wondered if anyone here by chance new of the correct size, or maybe a more simple fix to this issue. From what I've read, its not exactly uncommon.

The bolt doesnt necissarily need to be tight, right? It just serves as a pivot point, so it simply needs to never back out again...or is this wrong? If I could get a drill under there, I could put a hole through the end of the bolt and put a cotter pin through it to prevent it from backing out.

"Keith, cleanup on isle 5..."

the alternator pivot bolt needs to be fully tightened after the belt is tensioned. Any allowance for movement can change the tension on the belt and cause squealing.

-Henry

I lost the alternator tensioner bolt on my 90 Miata in an exciting fashion while 600 miles from home, and had to find a replacement - unfortunately, not the pivot bolt! I remember hearing a clunk that sounded an awful lot like a bolt rattling around in the engine bay then falling on the ground, and then the belt got pushed around on pulleys and shredded before I could pull over.

If you can't find the size/type, I can pull mine off and take it to the hardware store and find out :-)

Wish I could help but when this happened to me I just rooted through an entire garage full of old standard hardware, found one the right length, powered it through the remaining threads, stripping them out of course, and put a nut in the back of it. There. Fixed it! Probably not the solution you were looking for but it did work for over a year til I sold the car.

I hate that alternator bottom bolt.

Brokeback wrote: I lost the alternator tensioner bolt on my 90 Miata in an exciting fashion while 600 miles from home, and had to find a replacement - unfortunately, not the pivot bolt! I remember hearing a clunk that sounded an awful lot like a bolt rattling around in the engine bay then falling on the ground, and then the belt got pushed around on pulleys and shredded before I could pull over. If you can't find the size/type, I can pull mine off and take it to the hardware store and find out :-)

IIRC, its the same pitch and diameter as the spare tire and jack holddown. Just measure for length.

(I sheared one awhile back...)

Apexcarver wrote:

Brokeback wrote: I lost the alternator tensioner bolt on my 90 Miata in an exciting fashion while 600 miles from home, and had to find a replacement - unfortunately, not the pivot bolt! I remember hearing a clunk that sounded an awful lot like a bolt rattling around in the engine bay then falling on the ground, and then the belt got pushed around on pulleys and shredded before I could pull over. If you can't find the size/type, I can pull mine off and take it to the hardware store and find out :-)

IIRC, its the same pitch and diameter as the spare tire and jack holddown. Just measure for length. (I sheared one awhile back...)

That is brilliant. This is the reason I love GRM

Belts squeak forever once coolant soaked.

Apexcarver wrote: IIRC, its the same pitch and diameter as the spare tire and jack holddown. Just measure for length. (I sheared one awhile back...)

I'll bust out the ruler when I get home! My spare is underneath the car, and my jack is no longer there - AAA is much easier, plus weight savings!

Earlier Miatas used a nut and bolt on that pivot. It's less convenient to use, but an easy fix.

99% sure that bolt is a 10x1.25.

3/8" allthread and a pair of nuts is pretty easy to find, too.

Yeah, but then you're That Guy to the next owner.

I was thinking that there was a nut and bolt combination too. I do remember stopping in Pikeville Tn on an afternoon drive in my Ex's Yellow to tighten up the bolt when it had come loose. I had to buy a complete set of metric wrenches to get the 12 or 14mm that was needed. Quite an interesting place!