As you would imagine, the IMS Retrofit kit went through many iterations during development, including forced oiling of the ball bearing prior to switching to a ceramic ball for it’s performance in environments with poor lubrication.

We did develop a version that utilized a cylindrical roller bearing with thrust ring, but it never made it from testing to production for the primary reason that Porsche chose a ball bearing originally, not a roller.


  • A deep groove ball bearing as currently used in the IMS Retrofit can take up to 50% of the dynamic load in thrust.
  • A traditional cylindrical roller bearing with thrust control can only take up to 10% of the dynamic load in thrust.
  • The factory single row 6204 bearing a dynamic load capacity of 2900# with thrust max load rating of 1450#
  • The NJ or NU204 cylindrical bearing has a dynamic load capacity of 3750# with thrust max load rating of 375#
  • The custom dual row ceramic hybrid bearings used in both the Single Row Pro and Classic Dual Row IMS Retrofit has a dynamic load capacity of 4000# w/ Thrust or 2000#.

Although the cylindrical bearing has 29% higher load capacity, in thrust it has only 26% of the capacity of the deep groove 6204 bearing. The special roller bearing supplied exclusively by RND Engines to SSF have integrated thrust control in both directions and 5800# dynamic load capacity with thrust 580# and no additional forced lubrication is required with the RND Roller kit.

Other considerations:

  • Porsche used a ball bearing because there was no way to internally lubricate a plain bearing.
  • Ball bearing was used as it provides thrust control as the other end of the intermediate shaft uses a plain bearing that does not have any thrust control.
  • Cylindrical bearings are used for crankshafts BUT they are typically paired with a ball bearing for thrust control OR two cylindrical bearings (i.e. NJ204) with thrust rings are installed together to provide thrust control.
  • Roller bearings are higher friction than ceramic hybrid bearings.
  • Roller bearings are susceptible to skidding which will lead to bearing wear and failure and deep groove ball bearings are considered superior to roller bearings in this respect.
  • The RND Roller bearing uses an expanded load capacity bearing with more rollers to increase load rating and also increase the # of loaded rollers at any one time.

A deep groove ball bearing was the most cost effective solution to control thrust by the factory. The RND roller bearing kit sold by SSF Auto Parts use a custom expanded load capacity cylindrical roller bearing with integrated thrust control in both directions but costs dozens of times more than a common ball or roller bearing.

Additionally, in the case of the IMS Solution, thrust control is built into the design with two thrust surfaces and endplay set during manufacturing of each kit individually.

Source, Timken NJ, NU 204.

*Quoted load capacities vary by manufacturer and testing method used to evaluate bearing load. All these figures can be found in from any manufacturer’s catalogs including Timken or SKF.

Decided you want a roller bearing rather than a ball bearing? Choose the only roller bearing IMS replacement sold and backed by SSF Auto Parts.

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