Early 500 Pantah sprocket seal???

[GRM 450]

Hi all, a 4/81 500 Pantah that has just had a major rebuild and the sprocket shaft seal is not sealing on the round shaft but is running on the splines.

It would seem that the shaft is too far inboard the cases?
Unles they use a different seal to later belts?

When we bought the bike it hadn't run since 1986 and the gearbox wouldn't select gears.
After stripping the engine we found some welding in the cases on the opposite end bearing houseing where it appeared that the bearing had broken the right side case. This had been repaired.

So replace all bearings and shim the gearbox so that it did select gears and reassemble the motor.

Now the last seal in is the sprocket shaft and it doesn't rub on the round section of shaft but the splines. Obviously this won't hold oil.

The manual shows 2 seperate drawings for this area and I would like to know how the early 500's seal was installed.

Might save me splitting the cases again.
It seems about 5mm in too far, and there isn't 5mm of shims in there.

Graeme

[Duccout]

Hi Graeme. The seal was changed to a different type early in the 500 Pantah's production run. The early seal had part no. 0660. 49. 265 and the later one was 0660.49. 268. I don't think that there is a step in the seal though.

On the left-hand side of the output shaft there is a 3.8mm spacer and on the right side a 4.6mm spacer, so if they were both fitted on the left side this would cause the problem.

[GRM 450]

Thanks Duccout,

There is witness marks on the output shaft splines where the inner and outer seal lips have been rubbing.
This Can Not seal oil.
It seems the shaft is too far inboard.

So I split the cases and looked.
The 2 spacers are in the correct position either side of the shaft.
The shaft can not move outboard, to the left, the 5mm it would need to to get the non splined section to line up with the seal.
If it did, the other end would only be sitting in its bearing by about 5mm, and not the full 10mm it should. (5mm and 10mm are approximate)

I have a mates 3 dog box which I put next to the early 6 dog box, and the output shaft is 7mm longer (on the 3 dog) than the 6 dog box output shaft.
If the 3 dog box was installed the seal would be correct.

What seals the early 6 dog output shaft??????

Also the 3 dog shaft places the sprocket out board approx 7mm further than the 6 dog shaft, meaning the rear sprocket on the wheel would be approx 7mm out of line.

?????????????????????????????????????? and ?

Graeme

[Duccout]

Graeme, is there room in front of the bearing for the seal to fit and bear on the plain section of shaft? I'm wondering if the earlier seal was stepped, so that it was running further in. I have some early seals somewhere, if I get time I'll try to find them.

[GRM 450]

There is about 2 to 3 mm of un splined shaft out board of the bearing, then splines. The seal recess is 7mm deep.

In the manuals there is 2 different gear box's, one has what is described as a seal ring and the other is called a gasket. with different no. and different sprocket no.s also.

I have a feeling that I split the cases for nothing? (I needed to see anyway)

I still can't see how the shaft is sealed?
Unless the bearing seal iss left in,? but it would not seal well around the shaft.

graeme

[DesmoDog]

Originally Posted by GRM 450

I have a feeling that I split the cases for nothing? (I needed to see anyway)

Nope. Now you know the spacers are correct so it wasn't for nothing.

[wdietz186]

Is It possibly set up like the bevels with a spacer that the seal rides on that goes between the sprocket and the bearing? Or maybe you have the wrong output shaft? I ran into some problems trying to fix a friends TT1 with some gears from an earlier trans that turned out to be different diameters so an odd shaft wouldn't be out of the question.

[Duccout]

Hi Graeme, I might have it sussed, but I'm no expert.... I think that the seal that you refer to is an 'o' ring that goes in front of the sprocket and seals the output shaft, then the outer oil seal, which has an i.d. of 35mm (the later seal is 25mm i.d.) fits over the sprocket boss. What do you think?

[GRM 450]

That would work if the early 500s' had a different shaped sprocket?
I have one on order from Ian Gowanlock, so I'll give him a call and ask.
The gears are thinner on the 6 dog box than the 3 dog set

graeme

[Duccout]

The early sprocket is definitely different. The early one has a large boss on the crankcase side, whereas the later type is flat. If this is the problem, hopefully you can sort it by changing to the later sprocket and seal.