Created 5/12/03 Updated 6/7/03

In the install of the D/A supercharger a pair of idler pulleys are added for the belt run to the blower. A few people have had these pulleys sieze up which leaves you stranded when this happens. At one point D/A upgraded the bearings in the pulleys to try to correct for this.

The Sebring Miata guys have a similiar problem. Their solution to the problem is switching out the plastic idler pulleys for the timing belt idler pulleys from the Miata engine. See their info here. From what I've read these pulleys have solved siezing problems for them.

I was curious to see if this might be helpful to D/Aed 1.9ls. Our idler pulleys are 2.5" diameter compared to about 2" for the Miata pulleys. However, unlike the Miata setup, we have a dynamic tensioner so belt size and pulley size isn't as critical. The Miata guys use the slotted pulley to make it easier to adjust belt tension, with the dynamic tensioner this isn't an issue for us. The non-slotted timing belt idler pulley is about $45 at a Miata dealership but can be had for around $18 online.
I bought mine here.

It turns out we can replace one of the two plastic pulleys easily using the plain Miata idler pulley. After taking out the pulley mounting bracket the new pulley will just bolt in place and it can be reassembled following the torque recommendations in the D/A install manual.

The pulleys alignment looks pretty good without any additional work. The red band on the pulley mount is the outline of the original D/A supplied pulley.

The belt itself runs right up against the leading edge of the pulley.

Because the pulley is smaller the position of the dynamic tensioner has moved slightly but there isn't a clearance problem.

With the change in positon of the dynamic tensioner the tension on the belt also seems to have been lowered a little. I'm not sure yet if that is going to cause any problems with belt slipage under boost. If the tension really is lower that might help with bearing life too.

Unfortunatly the mounting of the other idle pulley is such that it can not be as easily changed over to the Miata pulley as there is a spacer that needs to be positioned to move the pulley out to the proper distance. I'm going to see what it would take to change this pulley too. I am also looking to see if I can find larger timing belt idler pulleys to get back closer to the stock D/A pulley setup size.

For now this is still a work in progress to see how everything fits together and the get some miles on the new pulley.


Made a little change to the position of the pulley to get the belt a little better centered on it. I used a 0.075" stainless steel washer (from West Marine) between the pulley and the plate to move the pulley a little further out.

I also used a little thinner washer between the nut and the pulley to make up for some of the lost length of the bolt from the spacer washer.

Now the belt isn't running on either edge, it is now closer to the rear of the pulley.

So far the pulley has a few hundred miles on it so far. No problem with throwing the belt. It might be slipping ever so slightly up high WOT though as my boost seems to be slightly down. My belt is a few years old though so I'm going to replace it with a new one to see how it works. The old one may have stretched a little over time.

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