RCM Dual Bearing Eccentric Adjustable Idler Set (EJ20/EJ25)

Roger Clark Motorsport has released a set of Dual Bearing Eccentric Idler Pulleys to correct cam pulley alignment issues.

Whether you want the ability to precisely align your cam gears, or you just need some additional ability to adjust your cam gears from thicker head gaskets or machining of your heads and block, the best way to get this is to use an adjustable eccentric cam pulley.

For the most part, there is just a single bearing used in these eccentric pulleys, which is fine for stock or street cars. But if your engine is making a good deal of power, or if it is for race use, the single bearing design is not ideal from a durability standpoint.

The Subaru community asked about the possibility of a Dual Bearing eccentric idler that would be better able to stand up to high-power, high rpm or race use.  Roger Clark Motorsports heard that request, and set about making just that.

The result are these new RCM Dual Bearing eccentric idler bearings.

Under most circumstances, the best timing belt idler pulleys to use are the ones that your car originally came with.  However, on a Subaru Turbo EJ engine, from time to time, you can run into a unique circumstance where this is not the case.  Because there are two cylinder heads, one on either side of the engine, sometimes when machining is required to re-surface a head or block the over-all height of the engine can change slightly.  Because the length of the timing belt is a constant, this small change in engine height can cause a small mis-alignment of the cam pulleys that are driven by the timing belt.

This can also occur when using a thicker than stock headgasket.

In those circumstances, it is more ideal to use an eccentric idler pulley which will allow you to properly align all of your cam pulleys to ensure that the engine is running with correct timing.

Roger Clark Motorsport has just released a set of eccentric pulleys just for this purpose.

These are not designed to modify timing belt tension in any way, and are only designed to correct a timing issue when it comes up.  They are single race bearings, so they are designed for a service life or roughly 60,000 miles, or one race season.

If these are used for high power or race application, it is recommended that these bearings be checked a couple of times a year.