RX-125 clutch help needed

**Muzzab** · 27th July 2009, 13:02

Hi,

I have a 1980 Yamaha RX-125 Bucket. Under load the clutch slips some times.
I was wanting to replace the clutch plates and springs. I don't have a workshop manual, so was hoping someone may be able to tell me the part numbers needed. Or, recommend other suitable parts that may make it better for racing i.e stiffer springs. I asked a local bike shop, but they were unable to help due to the age of the bike.

Also, what sort of gear box oil should I use? It had valvoline semi-synethic in it. Which was what I use in my road bike, and since I had enough left over from an oil change, and being budget conscious I put it in the RX. This may not have helped.

Any advice appreciated.

Cheers
Muzza

**R6_kid:Me** · 27th July 2009, 15:41

I have a parts book for the RX at home, will have a look tonight and let you know.

**Buddha#81:Me** · 27th July 2009, 16:29

Originally Posted by Muzzab

Also, what sort of gear box oil should I use? It had valvoline semi-synethic in it. Which was what I use in my road bike, and since I had enough left over from an oil change, and being budget conscious I put it in the RX. This may not have helped.

Any advice appreciated.

Cheers
Muzza

The oil should be fine......Try getting the steel plates bead blasted, this could be all you need to stop it from slipping. I had the same problem with a Honda single and after new springs and less worn (within spec) fibres it still slipped untill I did the steels. Worth a go and cheap/free to do.

**F5 Dave** · 27th July 2009, 18:24

another steel plate or some spark plug washers under the springs can preload them enough to help.

**TZ350** · 27th July 2009, 19:21

One of the things we do with our GP125's is de-glaze the friction plates with a sheet of 120 wet & dry spread on an old mirror. We wet it down with kero or CRC and then wipe the plates around a couple of times both sides and then wash them off. The steels get this treatment too but more vigorously and we run ATF in the box.

.

**TerraRoot** · 27th July 2009, 21:14

Wouldn't really thick oil like ATF rob you of a bit of horse power (like .5, but you get what i'm getting at)

**Muzzab** · 27th July 2009, 21:54

Thanks for the tips. I'll try the washer under the springs and the sanding the plates for a kick off, as I can do this myself.
The oil I had in was 10-40, I had it suggested to me to use Castrol GTX 20-50i.e old style oil for an old style motor and change it after each meeting.
I am giving some thought to the ATF (Auto Trans Fluid? right?), any particular grade?

Cheers
Muzza

**F5 Dave** · 28th July 2009, 10:34

Just buy 2 stroke gearbox oil & change it once a season, it's not an MX bike, don't stuff around with ATF.

Scuff the steel plates on smooooth concrete in fig 8.

**Muzzab** · 28th July 2009, 10:58

Originally Posted by F5 Dave

Just buy 2 stroke gearbox oil & change it once a season, it's not an MX bike, don't stuff around with ATF.

Scuff the steel plates on smooooth concrete in fig 8.

Thanks, will give that a go too.

Cheers
Muzza

**bucketracer** · 28th July 2009, 12:21

Originally Posted by TerraRoot

Wouldn't really thick oil like ATF rob you of a bit of horse power (like .5, but you get what i'm getting at)

ATF (Auto Transmission Oil) is usually thin and red. I use it in my bike A. because Dad does and B. there is plenty of it around the garage. Doesn’t mean its the best though, Using ATF is a bit old school, pay to research it, there are probably better purpose made oils for 2-Stroke gearboxes with wet clutches.

**SHELRACING** · 28th July 2009, 13:12

Clutch slip is quite common in the RX125's. Although my clutch is good at the moment.

Adding another plate as suggested by F5 Dave alleviates the problem. It does make the clutch a bit heavy tho.

I could probably find you an extra steel plate if you want one.

**Muzzab** · 28th July 2009, 14:52

Originally Posted by SHELRACING

Clutch slip is quite common in the RX125's. Although my clutch is good at the moment.

Adding another plate as suggested by F5 Dave alleviates the problem. It does make the clutch a bit heavy tho.

I could probably find you an extra steel plate if you want one.

I have two sets already, although the ones from my parts bike don't look as good as the ones from the race bike. It was seized when I brought it so things probably got pretty hot in there. I could pick out the one best of them
give it a bit of a rough up and add it in. Where about in amongst the fibre and steel plates do you put the extra steel one?

I have managed to order some new fibre plates and springs, but will keep those in case the quick fix doesn't quite do the job.

Cheers
Muzza

**Muzzab** · 10th August 2009, 17:02

Clutch seems to be fixed

I gave the fibre plates a quick rub with some wet fine sand paper.
Gave the metal plates a couple of figure 8's on concrete.
Put some Castrol GST 20-50 in the gear box and a couple of washers under the bolts that hold the springs on.

Raced at Ruapuna yeaterday, no clutch slip, bike seems to have much more get up and go. Will have to work on take offs as the front wheel comes up easily.

I fell off coming out of the hairpin, opened the throttle up as usual and lost the back end

Cheers
Muzza

**F5 Dave** · 10th August 2009, 17:29

Originally Posted by Muzzab

. . Will have to work on take offs as the front wheel comes up easily. . .

Glad it worked out.

Try sitting on the tank for starts if it is really bad, I used to do that with my old H100. On low gearing it could wheelie into 3rd whilst on the tank.