First gear in my Honda RS125 is good for around 106km/hr. The engine only really starts to think about producing real power around 9,500rpm, which means you really only start moving once you can get the bike rolling to around 77 km/hr give or take. In comes the most undervalued part of most bikes, the humble clutch.
When I got my NX4 RS125, it was fairly clear to me quite quickly that the clutch needed some attention. Like the 10th round against Mike Tyson, it was unresponsive, unstable and didn't help me land any punches. When I finally took the scared up clutch cover off to check out the damage, the doc concluded terminal brain damage and that was it. On the phone, on the internet and some burning plastic later a box of beautiful parts arrived on my doorstep.
I went for the highly rated Talon clutch basket and replaced all other components with genuine Honda HRC. Due to the overall lack of information on Honda RS125's on the internet I took photos as I went along so that others may learn from the process (or potential mistakes). That and the Talon clutch basket came with minimal instructions and does actually require a bit of machine time.
What you need:
- Torque wrench
- 27mm socket
- Clutch hub holding tool
- Thread locker
- Talon clutch basket
- Original HRC NX4 clutch basket - you will salvage the primary drive gear from the rear of it
- Drill press or vertical milling machine
- New clutch plates
- New clutch hub
- New clutch pressure plate
Follow along these instructions with the photos above, left to right, top to bottom.
Drain the clutch oil. Remove the clutch cover. Remove the pressure plate bolts and springs. Remove the clutch plates. Remove the pressure plate needle bearing (don't lose this slippery bugger). Break out the clutch hub holding tool and the 27mm socket. Quick tip: some clutch centre nuts (which hold the hub and basket onto the gearbox input shaft) are left hand threads. In this case, the RS125 has a special washer behind it which provides tension that stops it undoing itself. The nut therefore is a normal right hand thread so turn it anti-clockwise to undo it. Once that nut is off you can remove the hub and factory basket from the input shaft. Your bench will look like photo 1 above.
Use a hole punch and a hammer on a flat surface to mark the heads of the pins on the back of the factory basket. These pins hold the basket onto the primary drive gear. Using a drill press with a large drill bit, drill into the centre of the pin heads until they come loose from the thread part of the pin (photo 2). Drill out each pin until you can remove the backing plate, seeing the gear and drive rubbers (photo 3). Remove all of these items and inspect the drive rubbers if you intend on using them again.
Move everything from the machining area to a clean workspace (photo 5). I used kerosene and a fresh rag to clean the cut metal and oil off the parts I needed. These then got the air hose on them to make sure no filing would get near the bike. Reassemble the rubbers and gear to the new Talon basket including the fresh backing plate provided (photo 6). Apply thread lock to the screws and tight using a torque wrench and a no.3 hex bit. The Talon basket unfortunately did not provide a torque setting but thankfully standard torque settings are available. They are 10.9 grade M5 x 0.8 screws and such 9 Nm (6.5 lb ft) is the listed standard torque setting.
Once the basket is all together, reassemble the clutch in reverse order to when you disassembled it. Take note of the importance of the placement of washers and ensure key components have a layer of fresh gearbox oil on them to prevent a dry start up. I topped mine off with a new clutch cover to replace the torn up one that was on the bike. Racing the bike over the last weekend proved that a) the old clutch definitely was on the verge of a K.O b) a new clutch improves lap times tremendously and c) I still haven't learnt to get a 125GP bike off the line satisfactorily. Sigh.