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I'm in the process of having the gearbox out to fix some leaks and want to make sure I have the taper pin in the clutch shaft fitted correctly,

The pin in the photo with the fork, fits right thru the shaft with no taper, I have also reduced the boss in the fork so the pin goes right to the top of the fork.  There is also a roll pin fitted thru the fork and shaft on the left. This pin appears to be a different colour so perhaps a pin hardened. This pin has already be installed and has done some 8000 miles no problem.....

Second picture with pin on its own is a new pin not already fitted, tight in the taper fit at this point, I feel if I tighten it more it may break, but doesn't go fully into the hole at the top of the fork.

So which one would be the best pin to fit,  picture one or picture 2?

John

Picture 1

TR5 taper pin1.JPG

Picture  2

TR5 Taper pin.JPG

Edited by John L
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I think the reason these pins break is that the small end is not supported by the fork casting.  The hole it extends into is oversized.  This means that all of the stress on the pin is concentrated in one place near the end of the threads. 

This is why the most common fix is to add a supplementary pin through the fork and shaft--either a through straight pin or, better yet, a through taper pin.

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11 hours ago, John L said:

I'm in the process of having the gearbox out to fix some leaks and want to make sure I have the taper pin in the clutch shaft fitted correctly,

The pin in the photo with the fork, fits right thru the shaft with no taper, I have also reduced the boss in the fork so the pin goes right to the top of the fork.  There is also a roll pin fitted thru the fork and shaft on the left. This pin appears to be a different colour so perhaps a pin hardened. This pin has already be installed and has done some 8000 miles no problem.....

Second picture with pin on its own is a new pin not already fitted, tight in the taper fit at this point, I feel if I tighten it more it may break, but doesn't go fully into the hole at the top of the fork.

So which one would be the best pin to fit,  picture one or picture 2?

John

Picture 1

TR5 taper pin1.JPG

Picture  2

TR5 Taper pin.JPG

Hi John,

Your pins do not look original design to me or the holes in which they are fitted? In my view the best re-enforcement a an Unbrako socket cap tapped and fitted right through the whole assembly with a nut wire locked.  Mine did 35years of service with out any problems and was re-fitted when my gearbox was re-built in 2016.

Bruce.

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1 hour ago, astontr6 said:

Hi John,

Your pins do not look original design to me or the holes in which they are fitted? In my view the best re-enforcement a an Unbrako socket cap tapped and fitted right through the whole assembly with a nut wire locked.  Mine did 35years of service with out any problems and was re-fitted when my gearbox was re-built in 2016.

Bruce.

The pin in the first picture is better in my opinion, as it will be better placed to take the torsional load, once engaged into the hole in the back of the fork. Are you certain the second pin actually fits into the hole in the fork?

Kevin

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A pin which is not tight in the shaft will fail. So picture 2 is better, however... the head of the pin should be chamfered on its underside to allow it to go further into the yoke. Pins lacking this tend to bottom on the head and not the taper, a recipe for failure as in the first sentence above. You can file off the corners if need be.

 

Tom

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I agree with the comments from Kevin and Tom.

I though a bit about it...

Would below method make sense (I’m open for correction off course)?

1. First measure how deep the pin screws in the yoke with a vernier calliper but without the shaft installed. Measure how high the head of the pin sticks out.

2. Then check that the taper of the both bore in the shaft and the pin are the same, very important, otherwise failure will likely occur. You can check  this by using a permanent marker or similar on the pin and check the pattern rubbing / contact.

3. If this is ok, now install the shaft in the yoke, install the pin and use the vernier calliper again. The pin should sit a bit higher now because it is seating in the shaft. If it does, it’s ready for installing in the GB.

4. If it does not, grind the pin off a bit as Tom indicates and start over again at 1.

By doing this, the pin will sink a bit deeper, and if sufficient, have an intimate contact with the shaft-taper.

The devil is in the detail.

I think it is still a weak design, which could be worsened by the use of 50 year old components and new pins that are not dimensionally correct, so I have also installed an additional roll pin, which I think does a better job than this original pin.

Waldi

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Matching tapers are important, and that's the problem.  Tht bore in the shaft is tapered, but the one in the yoke is not. It's a design flaw that  leaves the small end of the pin unsupported. It contributes to these pins being prone to breaking.

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Hi Ed,

yes, but it would be hard to match the taper diameters of yoke and shaft in serial production, only if they were made it pairs.

I think the pin would either fit in the yoke or the shaft, if not “paired”.

Waldi

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I agree with that, Waldi. Creating a tapered bore "in situ" would be expensive, and the shaft and yoke would effectively be a matched set.  The next best solution that many have applied is to install a supplementary pin that doesnt suffer from the single sided loading.

Ed

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For the more anal among us, there is a type of taper pin that is threaded on the small end, so  the pin is pulled into its tapered bore.  Still requires taper reaming with the parts assembled.  I really believe that this pin eliminates the need for the stock one, but I have both installed anyway.

Ed

SDC10743a.JPG

 

 

Edited by ed_h
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Very nice Ed, your design ensures there is no bending on the pin, just shear, and equally important: on two cross-sections.

Waldi

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