Street Twin lost downshifting, bent internal shift mechanism DIY walk-through - Page 7 - Triumph Forum: Triumph Rat Motorcycle Forums
Water Cooled Twins Technical Talk Technical Talk for water cooled Triumph Twins.

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post #61 of 104 (permalink) Old 02-13-2019, 05:48 AM
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Quote:
Originally Posted by Singlin View Post
Did you just bore a 14mm hole in a 25mm dia piece of delrin rod?
Pretty much. Ideally wants doing on a lathe (unless you’re much better with a hacksaw than I am - not difficult ).

Don’t obsess over the material too much. Aluminium would work fine, so would brass, anything you have lying around the shop really. @StreetTwin ’s stack of washers will work just as well.
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post #62 of 104 (permalink) Old 02-13-2019, 09:47 AM
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Quote:
Originally Posted by Simon64ds View Post
Pretty much. Ideally wants doing on a lathe (unless you’re much better with a hacksaw than I am - not difficult ).

Don’t obsess over the material too much. Aluminium would work fine, so would brass, anything you have lying around the shop really. @StreetTwin ’s stack of washers will work just as well.
The type of material used to make the spacer may not be critical, but the size is important. Don't forget, there is a 23 mm diameter hole under the spacer where the oil seal and needle bearing lives.

The contact area between your spacer and the engine side cover is calculated as follows :

22/7 x 25/2 x 25/2 - 22/7 x 23/2 x 23/2 = 75.43 sq. mm.

Where as the contact area between my simple washers and the engine side cover is calculated to be :

22/7 x 28/2 x 28/2 - 22/7 x 23/2 x 23/2 = 200.35 sq. mm.

Don't have to be an engineer but grade 10 math and a bit of simple logic could save you an expensive repair bill down the road.
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post #63 of 104 (permalink) Old 02-13-2019, 01:16 PM
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Not that it is all that important, but I don't understand the math you presented. (I am an engineer) The area of a round area used to go something like Area = Pi times Radius squared. So Simon's contact patch is the area of the OD minus the area of the ID which is roughly {3.14 * (25 mm/2)*(25 mm/2)}-{3.14 *(14 mm/2)*14 mm/2)} = 491 sq mm-154 sq mm =337 sq mm. Perhaps you are describing something else?
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post #64 of 104 (permalink) Old 02-13-2019, 01:18 PM
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Then amend my statement to read @StreetTwin ‘s stack of washers would work even better..

It’s going to take a hell of a whack to move the shaft inward on my bike (and yours). So much so that plenty of other damage would be sustained. It’s about as much as we can hope to achieve.
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post #65 of 104 (permalink) Old 02-13-2019, 02:04 PM
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StreetTwin / geb The plate does look bent in the photo. I did check it and the rod itself with a metal square/straightedge and it's fine. It's funny because I almost included that in the pic post as a disclaimer. I did take the bike out for about an hour yesterday in stop and go traffic and it performed just fine. I believe I am going to do the cat delete to get rid of the heat that it generates.

Last edited by Sharkguy; 02-13-2019 at 02:07 PM. Reason: added to post
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post #66 of 104 (permalink) Old 02-13-2019, 02:15 PM
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Originally Posted by cougsfan View Post
Not that it is all that important, but I don't understand the math you presented. (I am an engineer) The area of a round area used to go something like Area = Pi times Radius squared. So Simon's contact patch is the area of the OD minus the area of the ID which is roughly {3.14 * (25 mm/2)*(25 mm/2)}-{3.14 *(14 mm/2)*14 mm/2)} = 491 sq mm-154 sq mm =337 sq mm. Perhaps you are describing something else?
Simon's spacer has an od of 25 mm.. It is in contact with the engine side cover. Under the spacer is a 23 mm od hole in which the oil seal and needle bearings for the shift shaft can be found. Since the hole containing the oil seal is recessed, only a 1 mm wide ring is in actual contact between the spacer and the engine cover. If Simon was to spread a light film of grease on the face of his spacer that is in contact with the engine cover and would bring it in contact with the side cover, he would see, upon removal of the spacer that a 1 mm wide ring along the outer edge of the spacer has made an actual contact with the engine cover.

Please see attached photo. Enlarge it and you will see the recessed oil seal. The bright aluminum around the inside circumference of the 23 mm od hole in the engine cover shows the depth of the recess. Nothing but air between the spacer and the 23 mm od hole containing the oil seal. (Not that we would even like to have pressure on that seal.)

You could repeat this experiment for yourself using a suitably sized washer or bottle cap.

Feel free to message me if I was not clear in the above description.
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Last edited by StreetTwin; 02-13-2019 at 03:53 PM.
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post #67 of 104 (permalink) Old 02-13-2019, 03:12 PM
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Don't want to beat this topic to death, but I thought I would include Simon's first go at this problem - he sure does take good pictures.

You can see that his first spacer makes direct contact with the recessed oil seal. His revised spacer that measures 25 mm od would contact the outer edge of the 23 mm od hole containing the oil seal, leaving a 1 mm gap between the oil seal and the face of the new 25 mm od spacer.
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post #68 of 104 (permalink) Old 02-13-2019, 05:08 PM
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it came to my mind two options why this shifter was enginered this way:
1) In a event of a crash where the throttle is active after the fall, this transference of force from floor to the rod, would disengage the mechanism avoiding an uncontrolled behaviour
2) transference of force to a small part would avoid damage to the clutch system as a whole.

exhibit a:. i had a crash on thursday. the bike went to left side and after sliding 20m it didnt turn off. i turned it off manually after recovering my head, 10-15 min

exhibit b.: on the shop we started with lever pressed as normally to check it. we are not able to select gear as supposed. however a gear is selected because the bike starts to move forward probably 3rd.

rock & roll baby

been there, done that.

Last edited by cosmetik; 02-13-2019 at 05:23 PM.
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post #69 of 104 (permalink) Old 02-13-2019, 05:48 PM
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I don’t believe it was engineered in deliberately (“Hey! Let’s make it so if the bike falls off it’s side stand it does $600 damage to the shifter..”) and suspect it was just an oversight. I think they designed an acceptable shift system WITHOUT thinking what’s going to happen if it falls over.

The bike shows many nice touches and has, quite clearly, been designed for a long service life and minimum hassle. It’s a clean, robust design. Well, maybe not the shifter..

The valve gear, for example, really impressed me and changing valve shims is an absolute doddle. Thanks Mr Bloor!

Y’know, I bought this bike partly because my first new bike was a Bonneville (1970) and I had this vaguely romantic notion that it would be nice if my last one was also a Bonnie. And now I find that it might actually be my last (it’s the third ‘last bike’so far) but it’s growing on me. And the more I tinker with it and make it ‘my own’ the more it continues to grow on me. Identifying potential weak points and making improvements is really quite satisfying, far more so than just buying something that’s ‘perfect’ straight off the showroom floor. Where’s the fun in that?
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post #70 of 104 (permalink) Old 02-13-2019, 05:58 PM
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Quote:
Originally Posted by Simon64ds View Post
I don’t believe it was engineered in deliberately (“Hey! Let’s make it so if the bike falls off it’s side stand it does $600 damage to the shifter..”) and suspect it was just an oversight. I think they designed an acceptable shift system WITHOUT thinking what’s going to happen if it falls over.

The bike shows many nice touches and has, quite clearly, been designed for a long service life and minimum hassle. It’s a clean, robust design. Well, maybe not the shifter..

The valve gear, for example, really impressed me and changing valve shims is an absolute doddle. Thanks Mr Bloor!

Y’know, I bought this bike partly because my first new bike was a Bonneville (1970) and I had this vaguely romantic notion that it would be nice if my last one was also a Bonnie. And now I find that it might actually be my last (it’s the third ‘last bike’so far) but it’s growing on me. And the more I tinker with it and make it ‘my own’ the more it continues to grow on me. Identifying potential weak points and making improvements is really quite satisfying, far more so than just buying something that’s ‘perfect’ straight off the showroom floor. Where’s the fun in that?
Ditto ! (I had a 1968 T100S, bought used in 1970 - First bike was a 1968 Sears 125 cc Puch)
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