Timing Belt Pulley Adds Better Belt Adjustment

After I heard that some Sebring supercharger owners were using the Mazda timing gear idler pulleys for the supercharger belt, I decided to try it out.

Front and back view of the slotted idler pulley. There is also a second idler pulley that has a conventional round shaft. Some Sebring owners use both pulleys. With Trussville Mazda asking around $65 for each pulley, I only bought the adjustable pulley. Update 1-7-2004: You can get these pulleys for about $22-40 at www.bestforeignparts.com
Notice the brackets on the pulley. I thought about cutting off them off, but found they don't get in the way.

I wondered how to mount the new pulley. Recall how the Jackson Racing pulleys are mounted on bushings. Those are too short for this application. Then I realized that the slotted pulley's inner race is designed to rest against the mounting surface, so no bushings are needed. I did anchor the bolt that serves as the shaft with a nut and used a jam nut.

Here's the final setup. Following the advice of those who have done this before me, I put it on the side nearest the center of the engine.
With this pulley, it's possible to roll on the belt with the pulley unmounted. Then it's not hard to slip the pulley onto the shaft and lock it in place.

Advantages

I found adjustments to be far easier with the slotted pulley. One still has to get the overall alignment of the pulleys set up to match the length of your belt, but the slot allows far more freedom of motion.
Once the general alignment is done, belt changes away from your garage are simpler. I only need one wrench to remove the slotted pulley. Then it's not as hard to roll on a belt because there is less tension. Then I slip on the slotted pulley on and tighten things up. I don't have to remove the cross over tube or loosen any other bolts. Granted, it won't be as tight as if you readjusted everything at home, but it gets you back on the road with your air conditioner and power steering working. While I have never had to replace a belt on the road for mt car, I have helped someone else do it in a parking lot. It took three people and a box of tools!
The slotted pulley is steel and won't wear down like the Moss Pulleys. See this link. Since I still have one aluminum idler pulley, that can still wear.

Update - 5 days later

About 20 miles after I initially installed the pulley, I shredded a belt. Now I had not had any belt problems in 15K miles with the supercharger before this. So I figured I had nicked the belt when installing it and put on my spare.

The four rib pulley becomes a two ribber

Another 50 miles later, belt #2 went slap-slap-slap and I lost it. By the way, a power steering miata will drive pretty well without the belt, although there is no fast handling when you drive around a mall. But you can get home without a belt. You could even probably drive across the USA. Anyway, I figured something was wrong.

I checked my alignment with a straight edge and found that the S/C pulley was not lined up with the other three pulleys.

I also saw that the bolt for the slotted pulley was bent.

So I straightened everything out, thinking that the alignment was causing the belt to jump off track. I wondered how this could happen, because the tension is so high. I finally concluded that the belt must have been riding off the slotted flangeless pulley becasue its shaft was crooked. Being a paranoid sort, I swapped the two idler pulleys.

No way for the belt to slip off a pulley now.

With the flange on the left, I now have to loosen two bolts to install a new belt.

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	I checked my alignment with a straight edge and found that the S/C pulley was not lined up with the other three pulleys.
	I also saw that the bolt for the slotted pulley was bent.
So I straightened everything out, thinking that the alignment was causing the belt to jump off track. I wondered how this could happen, because the tension is so high. I finally concluded that the belt must have been riding off the slotted flangeless pulley becasue its shaft was crooked. Being a paranoid sort, I swapped the two idler pulleys.