Despite using nothing but semi-synthetic oils, my clutch started slipping again around the 15,000 mile mark. By 16,000 miles it was not at all enjoyable to ride, so I once again replaced it. This time, I had a choice. There was the updated stock clutch, which might provide better life (Aprilia has never said there was an issue with clutch life so it's hard to tell). And for the aftermarket, Barnett has stepped up and offered a replacement. Barnett clutches usually come with stiffer springs, but people often use them with the stock springs, or a mix of half stock, half Barnett springs. Also, the kevlar construction of a Barnett clutch seems to make it hang on a little longer, but I've been told it's degradation is greater when it starts to slip. In the end, I chose to give the updated stock clutch a try.
Measurements for the New Aprilia clutch (comparing my third clutch I'm about to install to measurements taken from my second clutch before I installed it):
| Item | Avg, New design |
Avg, Original design when new |
Aprilia Spec |
| Spring | 1.73 in | 1.72 in | > 1.69 in |
| Steel plate | 0.058 in | 0.059 in | |
| Friction plate (new measured dry) |
0.137 in | 0.137 in | |
| Stack height (steels+frictions) |
1.82 in | 1.82 in | > 1.77 in |
As you can see, Aprilia has not made any dimensional changes to the clutch pack.
It might be interesting to compare the measurements of the clutch I removed (my second clutch) to its measurements before installation. I didn't keep individual component identities, so we can only compare averages.
| Item | Avg, Original design before installation |
Avg, Original design after 9,000 miles |
Aprilia Spec |
| Spring | 1.72 in | 1.73 in | > 1.69 in |
| Steel plate | 0.059 in | 0.058 in | |
| Friction plate (before use was measured dry) |
0.137 in | 0.137 in | |
| Stack height (steels+frictions) |
1.82 in | 1.82 in | > 1.77 in |
As you can see, again there was no wearing of the clutch materials. Suggesting again that another mechanism is at fault for the clutch failiure.
The steels did not look blued this time, probably because I was quicker to recognize the slipping clutch and babied the bike a little. There were three steels with very minor warpage, perhaps 0.010 inches deflection when held against a flat surface. The steels were definitely polished smooth.
Continue to installation of new clutch...
Go back to first clutch page...
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