Ok to reach advice in a quicker fashion, I'll start from the current state and then fill in background information after. I'd like to apologize for the wall'o'text as I'm trying to be as thorough as possible. Also, thanks in advance for any help/advice on the matter!


The crankshaft pulley with the key appropriately aligned does not seem to reflect top dead center as it is marked on the plastic cover. Using a straw in the #1 cylinder to determine movement and top dead center it appears to be TDC when the key is at about 11:00 on a clock. How could the key possibly be off?

In addition the camshaft to crankshaft timing seems to change over time. The timing belt is in good condition, the teeth seemed to be aligned correctly and the tension seems at least as tight as the specified tension.

So now, on to the run down of events I've gone through thus far in regards to the timing....

I received this truck from my uncle and when I got it it seemed to be lacking in power. It would run steadily just significantly weaker than the engine should be. So I:
replaced the spark plugs,
spark plug wires,
check the distributor which seemed nearly brand new,
ran some seafoam through the gas tank and some into the intake,
replaced the fuel filter

All of these changes seemed to make no change to it....
Then I acquired a compression tester. When I checked the compression it seemed significantly low, ~120-130psi per cylinder. This lead me to check to make sure the camshaft to crankshaft timing was correct. I used a straw to determine where TDC was and the pulley marking was considerably off. Using this method I think aligned the camshaft to be with the #1 marking at top. This got the compression to about 165, then removing the valve cover and checking the tension on the springs determined that one more tooth would be correct for TDC. With this additional tooth change the compression was at ~175-180 per cylinder, which is very close to the manufacturers specs.

The water pump went out so I replaced that which meant reseating the timing belt.

At this point the engine was back to the power you would expect a vehicle to be at. Although the ignition timing was still not 100% as the pulley marking isn't viable and doesn't align with the TDC markings on the flashing. It was running good during this time.

I was driving the truck basically back and forth to school everyday during summer school and it was running great for a few months.

Then one day I was running low on gas and decided I could make it to school and then to the gas station easily, so I did just that. Filled up on gas at the costco, then parked the car to go in and do some shopping. Came back out and on the drive home from here I was back to the car slugging, barely capable of doing 60-65mph on the freeway due to the lack of power. I was thinking that it was from the gas getting so low that sediment had clogged the fuel system, so I again replaced the fuel filter and seafoamed the gas tank. This made no change.

So I again today did a compression test to find that the compression was back to ~120psi.

This leads me to where I am now, trying to figure out how the compression could change like this. I was thinking maybe the belt skipping but the belt is in perfect condition, and seems to have been seated correctly with adequate tension.

 

Found this, Hope it helps!

How do I replace my timing belt tensioner?
This really is a loaded question that we get from many of our customers. We always recommend for our customers to reference our car forum. There are two main types of timing belt tensioners, a roller type, and a hydraulic type. The hydraulic tensioner requires more effort to install, and is usually done at the same time as a timing belt replacement. You need to remove the old tensioner, and put in the new tensioner in it's place, adjust the tension accordingly, and then remove the pin to have the tensioner take over the tension. Obviously, there is more involved, and we recommend discussing this in our forum.

So what does a timing belt tensioner do?
As the name implies, it ensures that the timing belt has the right amount of tension, so your timing belt doesn't skip, slip, or jump off of track, causing catastrophic engine damage. It is absolutely recommended to replace this tensioner everytime you release tension, or replace your belt.

How do you replace the different types of tensioners?
If your tensioner is the type of automatic hydraulic, all you need to to do is use a wrench, and turn the tensioner in a direction that allows the timing belt to slide right off. Sometimes you might need to loosen the tensioner pulley adjustment bolt, and the tension on the belt should slack off right away. If your belt is non automatic hydraulic, then you will need to go through more steps to replace it, and might require professional installation.

 

Aqua seems to think the belt skipped a tooth because the tensioner wasn't set correctly. I agree with aqua. Check the timing marks agin. Also you need to find out why the timing marks at the crank pully are off.

 

Thanks for the reply guys, I tore it down and came to find out that the woodruff key on the crankshaft was broken. This was causing the timing belt gear on the crankshaft to intermittently rotate a small amount, likely only on starting the engine.

 

Good job!
little things make can make a big difference!

 

Hopefully the recess on the crankshaft will be OK so you can just use a new woodruff key. Apparently there are instruction manuals for these that list a far too low torque value for that big bolt (21mm socket), why this can happen The service manual lists 130 - 145 ft lbs.

 

I think I know what's wrong with your Mazda, cause I just went through it on my B2200. The crankshaft snout is likely broken. I had to use an impact to remove the center crank bolt, and when I did, the gear - and the end of the crank fell off on the ground.
I am now searching for a crank kit. I think it'll be about $250. Or, I could buy a new crank from Mazda for $505, plus tax.
JT