The faulty part in Powertune package. Delivered with incorrect wire clips. Too wide to fit into the release arm.

Original bearing width = 3.075 Original shim clip thickness = 0.015 x 2 Original arm inside space = 3.108 Net clearance in assembly = 0.003 New Power Tune bearing width = 3.090 Need to increase arm space by 0.015

Photos and notes above from the August 2022 installation of the faulty part.

Also see FT-092 CLUTCH RELEASE BEARING Bad When New
That 2018 report was for an MGA release bearing (another Powertune part) that fell apart right out of the box before installation, and was also soft carbon. Please Do Not Buy Or Install A Powertune Carbon Release Bearing. Until proven otherwise, you should assume they are all bad with sub-standard soft carbon.

Saturday, January 21, 2023:
I just finished replacing all of the parts of the MGB clutch assembly in my MGA. Pardon the primer paint, as the car was in the middle of a nose repair when the clutch failed and took precedent. These clutch parts were all new issue at end of August 2022 with installation of freshly rebuilt engine. 4-1/2 months and 8500 miles later, complete clutch failure due to failure of the Moss Motors 190-300 carbon release bearing (made by Powertune). This also destroyed the new Borg & Beck pressure plate, the clutch release arm, and the early MGB (1962-1967) gearbox front cover, about $300 in replacement parts, and one very long day of labor to R&R the engine to replace the clutch parts (and gearbox front cover). Click on picture below right for a 5-second video of the damaged pressure plate that had to be replaced.

There is the culprit (pictures below) that caused all this damage, the failed carbon release bearing. Again 4-1/2 months and 8500 miles to total failure of the release bearing. The obvious primary problem is soft carbon with very fast wear and premature failure. But that is not the only fault here. This release bearing was too wide across the trunnion thrust surfaces, requiring modifying the release arm to make it fit. It really rubs me the wrong way to have to modify a perfectly good original part to accommodate a faulty replacement part. Now that we have a better original style release bearing, we have to throw out the modified release arm and replace it with another original style arm (good money after bad).
That failed release bearing was also delivered with MGA style wire spring slips, which cannot be used with the MGB release arm, because the MGB arm does not have the divot detent depressions in back side of the arm (the MGA clips would fall off with first vibration). And the faulty bearing is also too wide across the thrust surfaces at the trunnions, so it cannot be installed with MGB Tinnerman style spring clips. The only way to install the faulty bearing is to grind the inboard sides of the MGB release arm forked ends to allow the faulty bearing to fit in between with the MGB clips.

Failed release bearing and modified release arm on the left (with some of the tailings that came out of the bellhousing). Replacement original style release bearing and another original (not modified) release arm on the right. There was some minor shrapnel damage inside the bellhousing, not enough to put it out of service. The gearbox front cover suffered some with the release arm wobbling significantly sideways, so it was prudent to replace the front cover along with the arm (and new pivot bushing and bolt). The low mileage clutch friction disc is being put back in service, but otherwise everything between the flywheel and face of the gearbox was replaced. That's about $300 in parts and a full day of labor to fix damage caused by a faulty $25 release bearing.

The new 3-piece clutch kit this time is Moss Motors 190-807 Clutch Kit (MGB) premium aftermarket (with apparently good release bearing). Time will tell. The new pressure plate has absolutely no identifying markings on it. Will have to take a look at packaging materials to see if there may be a clue to origin.