Clutch Modification to fix "Grabbing" problem under load:

The stock Yamaha clutch is not the best clutch in the industry and some people, including me, have had to deal with it. I have had the problems detailed in this letter and after an unsuccessful attempt to get it fixed under warranty (they just could not fix it), I undertook to fix it myself.
The chattering problem is a result of insufficient quantities of oil being delivered to the clutch plates, although some riders have not had any problems....this is a bit of a mystery. I performed the 6 hole mod here, but did not have much improvement. So recently I performed this mod and also undertook to add a custom 'expansion ring' that sits over the basket fingers, which I found out is used on other bikes and on the YZF750, so no inventive points there!. This expansion ring is aimed at increasing strength and rigidity and will hopefully result in something close to a billet basket. I have also purchased some Barnett springs to possibly help, but I may remove them later as they are a little heavy. (I decided to leave them in, they are not too bad at all).

*I have inspected the plates 5000km’s later and found that lubrication is good except the outer 2 plates have much less oil than the rest so if you do this mod you might want to pay more attention to more oil getting to these plates. But they are not over-heating so all should be ok.

Here is a link to a doc I wrote about the problem and sent to Yamaha.

These are photos of the clutch and mods I have done:


| Clutch complete before mod  |
|Channel to lubrication holes/plates |
| Large holes in backing plate and previous small holes mod |
| One of three long channels |
| Screws though fingers to hold ring on ( lots of Locktite ;) ) |
| New expansion ring |
| Though holes in boss, three are newly drilled |
| Difference between standard and special plates sent from yamaha |
| Counter balance comes within 2 mm of Expansion ring! |

Links to info on clutch:

| Basic mod - 6 small holes |
| Oil flow mod described at Factory Pro |

Initial Results:

5/99: One word: Awesome! (compared to what it was like), The problem with the clutch has completely been cured and I have peace of mind too, with the expansion ring holding things together. The cost of the ring? more than it should have been due to R&D but very nice result. With the right machinist and a source of good, cheap billet (I used 7079 T561 40 mm plate alloy), you should be able to do it for less than 50USD. The cost of the oil flow mod? the cost of the Dremel bit, a couple of dollars!

I can now clutch a wheel stand in second with no adverse effects or strange noises!...rather, smooth strong take-up :)
(Though power to get it up is lacking, but that may be my technique).

To my mind, the results observed are as a result of the oil flow modification, but unfortunately I won't know for sure what effects each mod had on the problem (I was too impatient to do each mod separately ;))

Updates:

11/6/99: No problems yet with the clutch, Others had ridden it and commented on its general positive and smooth feel. It is still very strong and smooth.

12/8/99: Going to change the oil this weekend. But actually got the dreaded ‘graunch’ L off the lights – the 3100 Motul is now 6000km’s old so I will change it this W/E.

17/8/99: Well, it has been a while now and I just changed the oil to Mobil 1 4T for motorcycles this weekend and went for a nice ride – I pulled the clutch to bits to inspect it too and am please to say that it looks as good as it did when I put it together.! (Awesome!), the plates look good, there are no signs of burn marks or wear, so there is plenty of oil getting through there now. Also note that I still have the Yamaha special plates that I got the second time round, they seem to be holding up well. No slippage yet with the plates as is sometimes experienced with fully syn, and with the new oil it smooth and positive. Pulled 2nd gear, 1 second clutched wheelie with not problem. (I don't really like to stress the clutch too much, regardless of the mod work on it!

16/8/2000: Well  into the new millennium  (though not technically!) and the clutch is still going strong, All is well and I am please with the strength of the clutch, still smooth and strong. Also I am back to Motul 5100 semi-syn.

Some interesting news - I recently ordered a new boss from Yamaha and, guess what?, it has almost exactlythe exact same modification that I did that originally came from Factory Pro Racing in the States! So Yamaha do listen to their customers :). I don't know whether it was me or Factory Pro themselves, but I doubt many other customers will have spoken to Yamaha!, I like to think it was my complaints and report of the problem that moved them....hehe :).......this'll be the last on I want to get an Aprilia RSV1000 Mille or pay off some debts!

18/10/2000: Finally install the new boss and pressure plate and am please to say that it is still as good as ever even though I have not modified this one at all, though of course it has the yamaha (similar to my mod) mod unlike the orig. one which had half the number of oil holes.