The Horstman FX-100 TaG clutch is a replacement clutch for the poorly designed PRD shoe clutch. It is distributed by Grand Products, the North American importer of the PRD Fireball. My understanding is that new Fireballs are being shipped to GP without any clutch and GP is installing the FX-100 before sending to the end-user.

The PRD shoe clutch was patterned very closely after the Rotax clutch design that has been adapted and modified by numerous other TaG engine manufacturers (Vortex, Motori and others). Unfortunately, PRD's shoe design allows the spring to extend under centrifugal force to an extreme and results in a very high number of spring failures.

Although as of this writing the FX-100 does not appear on TaGUSA's web site as an alternative clutch for the PRD, Grand Products has repeatedly said that the FX-100 was approved for the Fireball by TaGUSA back in March. The homologation papers on the GP website show both clutches.

In installing these new clutches we have come across a few considerations that were not mentioned or documented well in the manual that came with the clutch. We offer some suggestions here to compliment the instructions Horstman provides.

Also, we've listed the torque specs and conversions at the bottom of this document since the manual lists all values in Newton Meters.

Checking the air gap: The air gap (the space between the fiction disk and the pressure plate) on the FX-100 should be .025" to .030".

One of the clutches we received had a air gap of only .010, too tight for when the clutch heats up.

Should be no gap between Pressure Plate and Drive Hub: We traced the tight air gap to the Pressure Plate not setting down completely on the Drive Hub. We were able to put a .015" feeler gauge between the Pressure Plate and the Drive Hub, a condition that had Gary of Horstman request the clutch be sent back to him.

It is possible we received an isolated case but it is more likely, we feel, that a manufacturing flaw could be responsible. At any rate, it is worthwhile to closely inspect the air gap and where the Pressure Plate meets the Drive Hub.

Roller bearing should spin freely: The manual that is included with the FX-100 cautions that the drum (read: bearing) should spin freely when assembled and that the washer "Item #7" should be ground to allow this. We've verified with Gary at Horstman that the reference to "Item #7" is a typo. The washer that would need to be ground is Item #5, Internal Thrust Washer, in the exploded parts diagram.

Ours did not spin freely and we had to modify the inner thrust washer (Item #5). The reason for this seems to be the .010" manufacturing tolerance on the PRD crankshaft end. However, when we measured the

distance between the two washers in question (.763) and the length of the bearing (.775) we found more than a .010 difference. According to Gary we should also look for .005 - .010 of play so we needed to shave in the neighborhood of .017 off the inner washer.

Note that both washers have a chamfered side to the bore so, naturally, care should be taken to orient these properly before measuring.

If material is to be removed, machining or grinding should be done only to the non-chamferred side of the Internal Thrust Washer (Item #5).

Lapping not a bad idea: Since the PRD crankshafts are not keyed we felt lapping the Drive Hub to the taper it mates to on the crankshaft was a good idea and Gary at Horstman seemed to agree.

Doing a keyless crankshaft certainly lowers manufacturing costs but isn't necessarily a bad thing. :Lapping a clutch to a crankshaft is a fairly common

practice in karting. In fact, many Yamaha builders leave the key out to reduce the risk of it breaking and then destroying the end of the crankshaft. In those cases they carefully lap the clutch hub to the crankshaft and rely on perfect fit of the tapered surfaces to hold them in place once tightened.

Careful with the 290 Loctite®: The FX-100 guide directs the user to use "one drop" of 290 Loctite between the crankshaft and the clutch Drive Hub. Very special care needs to be taken here since 290 Loctite is designed to "wick" or seep into anywhere it

can and bond those surfaces. We're concerned about the possibility of the 290 wicking into the threads the Jam Nut tightens on just outside of the mating surfaces or, worse yet, wicking into the crankcase seal and bearing just behind it.

Fastener/Diagram #

Newton Meters