I just changed the timing belt and water pump on my 98 Mazda 626.
After I got everything reassembled I started up the engine. I had been running the engine for a few minutes, revved it up to around 3k rpms a few times and started and stopped it a few times. At some point I noticed a strange sound which seemed to be coming from the timing belt area. If I had to guess, I would guess it was the sound of the timing belt flopping around due to it being loose. I never heard such a sound from that area before. I reused the tensioner, the spring and the idler pulley as they all seemed to be in good condition, although I've never done this before so what do I know.
The things that somewhat stood out to me where that it was fairly easy to get the new belt on ( most people said it was a real PITA ), I simply used the allen wrench to turn the tensioner left until the allen wrench hole was exactly to the left of the tensioner bolt. I put the belt just a little bit over the cam sprockets first, then worked it fairly easily a little onto the crank sprockets, then went around with a rubber mallet gently tapping it into place, a little at a time. It took under five minutes.
The other thing I noticed was that after I removed the zip tie, the tensioner moved back quite a bit, and the tensioner spring was maybe stretched to 2.5 times it's resting length. I don't know what's normal here, I don't have any basis for comparison.
I'm thinking that if the noise really is the belt flopping around, then maybe even though there was 100% no noise like this before, and even though the tensioner spring looked fine, maybe it's just not strong enough to deal with a brand new belt?
I'd really like to hear what people think as I'm a bit afraid to drive it till I figure out what this noise is and I don't want to just throw parts at it.
Here's a picture of how I got the tensioner spring on by holding the tensioner with a zip tie:
EDIT Nov. 13th 2016
So I pulled off the valve cover and upper timing cover and took a look at the belt:
I've run the belt maybe ten minutes total, and the outside part which contacts the tensioner and idler pulley already has this kind of smudged look to it ( don't know if that shows up so well in the picture ).
I also took an approximately one minute video of the belt with the engine running and there is no wobble in the belt and no noticeable movement of the tensioner or tensioner spring. However you can hear the noise very clearly in the video.
So here is my theory at the moment. When I tested the tensioner and idler I spun them and listened for any noise. I didn't hear any noise so I figured they were good. However, when I spun them they only turned a few times before stopping, which is in contrast to what I'm seeing in this video in which the guy spins a t-belt pulley and it spins freely for quite a while.
So I'm wondering if the bearings in my tensioner and idler pulleys are somewhat worn out to the point that the the pressure from a brand new belt is sufficiently greater than the pressure from the old belt and that's making them make noise where they didn't make noise before.
However, I ran across this other post which says the bearings should not spin freely and in fact should stop almost immediately.
So now I'm completely confused. As a side question, can I safely drive this thing around till I get this noise figured out?
EDIT Nov. 14th 2016
OK, so now I'm onto something. Only had about twenty minutes to mess with this today, but I noticed before starting the engine up that the t-belt was hanging about a millimeter off the edge of the idler pulley:
So before starting the engine up I pushed the belt toward the engine a bit both at the idler pulley and at the cam sprocket. So there was no noise until about ten minutes after I started the engine, when I could start to slightly hear the same click clacky knocking kind of noise, which seemed to be coming from the bottom end. At that point I noticed that the t-belt was slightly oscillating back and forth on the idler pulley ( video ) in the plane tangential to it's point of contact. After another five minutes or so ( 15m total since starting the engine ) the noise was again very distinct.
It may be that I didn't get the crank pulley quit on as far as I should, and that there is a little back and forth play in the crank sprocket which only shows up after the belt warms up and loosens a little bit.
So I'll probably test that theory out tomorrow.
EDIT Nov. 17th 2016
OK, so the noise is still there ( although not as bad ), and here's what I found and did.
When I pulled off the lower timing cover I noticed a few things:
The first thing I noticed which I didn't really pay attention to before is that the t-belt cover is severely warped. So much so, that it's contacting the back of the crank pulley body and the crank timing teeth and has burnished them silver.
The second thing I noticed was that the belt was sitting at the very edge of the sprocket and the edge of the belt had been rubbed off enough that you could see the copper strands in the belt itself. You can see it clearly here after I pushed the belt as far onto the sprocket as it would go:
After I pushed the t-belt all the way onto the crank sprocket it also automatically lined up properly right in the middle of the idler pulley:
I also noticed similar wear ( although not as bad ) on the back of the belt:
So remember what I said about the timing cover being severely warped? Well it looks like both the belt and the tensioner pulley have at some point been rubbing against the inside of the timing cover:
The thing is of course that I don't know when this happened, as I didn't pay any attention to the inside of the cover when I originally took it off, and the size of the circular scratch is about half a centimeter smaller than the diameter of the tensioner pulley.
This just gets more and more confusing. I'm thinking that maybe my first course of action should be to replace the timing cover, since it's clearly warped and has contacted the belt and tensioner at some time, either in the present or the past.
EDIT Nov. 22nd 2016
OK, now this gets really interesting and goes off in a direction that I think no one expected.
I decided to see if I could improve a little on Zack's truly excellent answer with some more exact measurements and data. So I took the video and loaded it into Audacity audio software, and zoomed in a bit to look more closely at the audio data:
As can be seen in the highlighted area, the clicking noise heard in the video is extremely uniform and occurs at a rate of exactly 16 clicks per second, or 16 Hertz. Looking through the entire audio file confirms this rate, even if an occasional click is muffled or missed here and there.
Now the question is what's making a clicking noise at a rate of 16 Hertz? Here is where I'll differ a little in my approach. In order to determine the RPM's of any gear or pulley in the system, it is sufficient to know the RPM's of any one gear, and the diameter of that gear and any gear whose RPM's you want to find. The calculation is:
(Driving Gear Diameter / Driven Gear Diameter) * Driving Gear RPM's
This works because the timing belt and accessory belts cause any gears or pulleys they are connected to to behave as if they had a direct physical connection. If gear A moves through an arc measuring one centimeter, the belt moves one centimeter and gear B also moves through an arc measuring one centimeter. How much faster or slower the driven gear turns is determined by the ratio of the gears circumferences, which is the same as the ratio of their diameters since you can simply factor out PI from 2*PI*R. You could factor the 2 out as well and just be left with the ratio of the radius', but I think it's easier to work with the diameters.
So anyways, I went ahead and measured or looked up the diameters for everything in the system and did the calculations. There are two groups, the first group is the things driven by the crankshaft sprocket, and the second group is the thing driven by the crankshaft pulley / harmonic balancer:
+-------------------------------------------------+ |Gear / Pulley |Diameter in Cm.|RPM |Hz | +-------------------------------------------------+ |Camshaft | 10 |375 |6.25 | |Tensioner | 6.2 |604.84 |10.08 | |Idler | 5.2 |721.15 |12.02 | |Crank Sprocket | 5 |750.00 |12.5 | |Ball Bearings ?? | 0.5 |7500.00 |125.00| | | | | | |Harmonic Balancer| 14.11 |750 |12.5 | |Air Conditioner | 12 |881.88 |14.70 | |Power Steering | 12 |881.88 |14.70 | |Water Pump | 11 |962.05 |16.03 | |Alternator | 5.5 |1924.09 |32.07 | |Ball Bearings ?? | 0.5 |21165.00|352.75| +-------------------------------------------------+
So what jumped out at me was that the Water Pump pulley is rotating at almost exactly 16 Hertz, the exact frequency at which the click was occurring.
Why was my brand new GMB water pump making noise?
I say was, because the sound has since disappeared for no apparent reason I can think of. Maybe the bearings in the new water pump just needed a breaking in period?
Anyways, I'll wait for people's comments, but I think Zach definitely deserves the the bounty on this one even if it turns out the conclusion was slightly off.