Clutch and Fluid
My concern about the clutch requiring frequent adjustment was unfounded. My friend Mike has more than 200 hours on his first ePure and the original clutch is still working fine. I think part of the credit should go to the electric motor which makes life easy on a clutch compared to an ICE. The peak versus average torque is numerically much smaller for an electric motor than for an internal combustion engine (4-strokes being worse in this regard than 2-strokes). Although electric motors do exhibit “torque ripple,” it is small compared to an ICE.
I specifically mentioned the clutch working for my level of riding because it most certainly did not work for Ryan Young. For the unfamiliar, Ryan was at one time the top trials rider in the USA and an importer for Electric Motion in the early days of the 5.7. He now conducts a trials school that the prior owner of my bike was fortunate enough to attend. Ryan rode the bike I now own but quickly returned it when he realized the clutch was not going to behave anywhere near his needs/expectations. Knowing what I do about the OSSA clutch setup – that pack thickness, spring force, lever adjustment, and even oil have a huge influence on behavior – I'd be keen to try setting up an EM clutch for a rider with Ryan Young's ability.
Flywheel removed exposing clutch primary gear
A flywheel puller is required to service the clutch. In the ePure Race, the flywheel is mounted on a tapered shaft as it would be in an ICE motorcycle.
The required tool is a standard M35 x 1.5 right-hand external puller. EM offers this tool for about $70, but more economical solutions can be found. It appears Motion Pro's $37 08-0349 would work. No-name pullers are even less expensive.
Flywheel weight and primary gear shown with both removable disks installed
Clutch Service Notes
Ferrous material found adhering to my pressure plate
Clutch Pack Access Procedure
XiU-rdi Clutch Pack
Although EM does not mention any of this in their clutch video, following these steps will ensure optimal performance and minimize the time needed for the clutch pack to “adapt” itself. The following information comes by way of XiU-rdi Engineering (the designer of EM's clutch) for their aftermarket OSSA clutch components.
New friction plates are not perfectly uniform in thickness. Slight variations can make the clutch grabby, and increase initial wear.
Using a vernier caliper to measure, find the thickest point of each friction disk. We will call it point “T”.
Mark point “T” on each disc.
Prepare a clutch pack with the disks aligned so the “T” marks are 90 degrees from one another.
Measure the total thickness of the pack at many locations around the disc pack.
If the pack thickness variation exceeds 0.03mm, the process must be repeated from the first step.
Webmaster's notes: To further elaborate, let's say one of your discs is perfect with no deviation in thickness. This disk could have any orientation relative to the other three, which would have their “T” marks placed 120 degrees apart. Likewise, two perfect disks would require the remaining “T” marks placed 180 degrees apart.
I always soak new friction plates in gearbox fluid at least overnight, preferably longer.
Close-up of the XiU-rdi Spring Support Plate
XiU-rdi Spring Support Plate
This information also comes by way of XiU-rdi Engineering for the OSSA. The Spring Support Plate is also called the Clutch Control Ring.
The spring support plate has 3 mounting positions, numbered 1, 2, and 3. The higher the number, the greater the spring preload. Number 1 is like the original clutch support. Each number supposedly represents a 0.1mm change in preload (however, measurements on my OSSA indicate a delta of 0.15mm).
With new plates, you can start with position number 1 or 2, depending on your preference. After some working time, the plates will “adapt” and be thinner. Then you can choose a higher number until position 3.