Expert opinions required on the plate behind the clutch...

[daveo]

So, years ago when I was young and rash I decided that the crescent shaped plate behind the clutch basket (part number 4L0-17471-00) did nothing more than make it impossible to split the crankcases without removing the clutch basket from the input shaft (so that said plate could be removed). I haven't fitted one for years. Now I am older and more cautious I am wondering if it does indeed serve a useful purpose.

It is described as 'plate, cover' in the microfiche. The bearing it seems to be 'retaining' by fitting close to its outer race also has a retaining circlip (93440 52009) on its outer race that fits into a groove in the upper and lower crankcase halves, which will do a pretty good job of preventing the input shaft moving about anyway.

So, is this thing an important component, or just a device to prevent you from stripping the engine then remembering that you really should've removed the clutch basket before you split the cases?

[kostas]

Should do more than to prevent splitting the cases.
Maybe it aids in keeping the cases tight together as there must be some strain in the area due to engine torque.

Having said that mine was cut in half when I split my cases as I was missing a socket for the clutch so did not remove it.

Kostas

[kostas]

I'm not an expect, just to make it clear!

Kostas

[arrow]

My opinion is this;
The clutch basket has the biggest gear in the motor, its teeth being furthest away from the bolts which restrain the bearing, and more importantly the cases behind it. If either the chain snaps or the motor seizes up then the highest moment arm in the motor will be at the point where the teeth of the basket meet the teeth of the crank gear. That's a decent length lever between the basket teeth and the centre of the main gearbox shaft. It looks to me like the angle of the bracket is in the same plain as where that force would be. Therefore extra re-enforcing where it's needed most, if anything goes pop.

[dusty350]

Hi,
Yamaha put it there for a reason ! I found one in two pieces when I stripped the Yamasaki engine. Granby's had one in stock, not expensive.

Dusty

[rich]

I can entirely see the point that the clutch gear could potentially 'climb up' the primary if the motor locked but having said that I have suffered a couple of seizures that locked the back wheel and never had an issue or the slightest sign of the cases being forced apart and I never fit the plate. Personally I reckon it's a belt and braces thing as there are crankcase bolts quite close either side of the clutch bearing.

[daveo]

Hmm. Isn't it the wrong shape to be strong in that regard?

[higgsy]

I never fit them on a race bike, it makes splitting the crankases so much quicker, I too think it's belt and braces, I cant really see what the piece of flimsy metal is trying to achieve, the gearbox bearing is held tight by the locating ring, it isn't going to go anywhere and if anything did go wrong it's more likely to spin in the case. Even if the bearing decided to come out sideways I think the noise from the box would be horrendous well before that happened.

If it's a customers bike for the road then I fit them (if it's there), if it's a race bike then they are normally missing.

[daveo]

higgsy - the voice of reason. Thanks!

[yamark]

I'm pretty sure it's a bearing retainer. Yamaha fitted these  plates to engines without the grooved retainers to stop bearings from moving. Don't know why they have 2 parts doing the same job though.  HTH

[Tone]

In the Genuine Yamaha workshop manual they call it a "Bearing stopper plate". Perhaps Yamaha fitted it just to aid the circlip around the clutch bearing to stop the bearing from moving as yamark has said.

[daveo]

Thanks for all the input - I'm pretty much decided that it is surplus to requirements as it is duplicating the function of the circlip retainer on the input shaft bearing. It will remain not fitted.