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Offline 2Bears

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Re: Larger sprocket.
« Reply #10 on: November 28, 2019, 02:25:43 PM »
Looking at the Winger photo does show that space around the pinion sprocket is tight.  What makes it really tight is the chain drop guard.  If you could live without the chain drop guard and use spacers to install the cover, you would have more room.

Just eye balling and using a marked Popsicle stick (the best I could do Thanksgiving morning):

center of the pinion to outer edge of chain = 31/16 inches radius
18 tooth pinion outer edge of chain = 31/16(18/17) = 33/16 inches

An 18 tooth pinion results in an increased radius of about 1/8 inches; assuming my guesses are close.  It looks like you might (maybe) have about an 1/8 inch of clearance left to the case?  One downside is that you would have to live without the chain drop guard.  A broken chain event could result in a damaged case.  How often do chains break?


« Last Edit: November 28, 2019, 07:20:08 PM by 2Bears »

Offline smithy

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Re: Larger sprocket.
« Reply #11 on: November 28, 2019, 07:52:07 PM »
*Originally Posted by 2Bears [+]
Looking at the Winger photo does show that space around the pinion sprocket is tight.  What makes it really tight is the chain drop guard.  If you could live without the chain drop guard and use spacers to install the cover, you would have more room.

Just eye balling and using a marked Popsicle stick (the best I could do Thanksgiving morning):

center of the pinion to outer edge of chain = 31/16 inches radius
18 tooth pinion outer edge of chain = 31/16(18/17) = 33/16 inches

An 18 tooth pinion results in an increased radius of about 1/8 inches; assuming my guesses are close.  It looks like you might (maybe) have about an 1/8 inch of clearance left to the case?  One downside is that you would have to live without the chain drop guard.  A broken chain event could result in a damaged case.  How often do chains break?




Moot point really, the fact is you just can't buy an 18t front sprocket to fit the S series engine....unless you get one specially made for it.

Smithy.
When I die, I want to go peacefully in my sleep like my Grandfather....not screaming like the passengers in his car..!

Offline 2Bears

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Re: Larger sprocket.
« Reply #12 on: November 30, 2019, 01:11:10 PM »
This is my first chain driven bike in quite a few years.  The beauty of a chain drive is that it is simple and efficient in load transfer.

This is a XR replacement sprocket out of the JT Sprocket catalog:



This is a Triumph sprocket out of the JT Sprocket catalog, available in 17 and 18 tooth versions:



It looks like it could fit.  One could find out for about $20.  You would have to shim it out a little to line it up.

https://sprocketcenter.com/jt-1183-525-pitch-oem-replacement-steel-front-sprocket.html

Offline jskene

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Re: Larger sprocket.
« Reply #13 on: November 30, 2019, 07:02:46 PM »
Very nice find, but it looks like the spline contact area on the Triumph sprocket is half that on the BMW one. That might be a problem.

Offline smithy

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Re: Larger sprocket.
« Reply #14 on: November 30, 2019, 07:50:56 PM »
*Originally Posted by 2Bears [+]
This is my first chain driven bike in quite a few years.  The beauty of a chain drive is that it is simple and efficient in load transfer.

This is a XR replacement sprocket out of the JT Sprocket catalog:



This is a Triumph sprocket out of the JT Sprocket catalog, available in 17 and 18 tooth versions:



It looks like it could fit.  One could find out for about $20.  You would have to shim it out a little to line it up.

https://sprocketcenter.com/jt-1183-525-pitch-oem-replacement-steel-front-sprocket.html

What part of "lt won't fit" do you not understand"..??

Have you ever had the front sprocket cover off.??

Smithy.
When I die, I want to go peacefully in my sleep like my Grandfather....not screaming like the passengers in his car..!

Offline Mareng1

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Re: Larger sprocket.
« Reply #15 on: November 30, 2019, 09:31:47 PM »
A 525 17tooth sprocket has a predefined diameter- there are no variations of that.

Similarly, an 18tooth sprocket has a predefined diameter.

There is no method of cramming 18 teeth into the required diameter.  Not even Esther Rantzen managed that!  :182:

Offline 2Bears

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Re: Larger sprocket.
« Reply #16 on: December 01, 2019, 12:27:40 PM »


I don’t have a good way to make precise measurements in this location at the moment.  It is a tight spot.  I agree that an 18 tooth sprocket would have to be a certain diameter to meet a specific pitch requirement.  I don’t know who Esther is.

This was my thinking.  The following assumes that chain drop guard is removed and not reinstalled.

Measured radial dimension of 17 tooth sprocket with chain:  1 15/16 in = 31/16 in.

Assumed radial dimension of 18 tooth sprocket with chain = (18/17)(31/16) = 33/16 in.

According to the above assumptions, the 18 tooth sprocket is about 1/8 in larger, radially, than the 17 tooth sprocket.  The radial increase in size of 1/8 inches is less than the ¼ inch of clearance to the case.

I’m assuming that the system remains dimensionally stable even when running at high RPMs or during changes in acceleration.  When I inspected my chain drop guard I found no chain strikes or wear, even though the chain drop guard rides very close to the chain.

Disclaimer:  The above is conjecture and information sharing on my part.  I haven’t tried fitting anything or have looked at this in enough detail.
« Last Edit: December 01, 2019, 11:33:14 PM by 2Bears »

Offline 2Bears

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Re: Larger sprocket.
« Reply #17 on: December 01, 2019, 12:31:18 PM »
*Originally Posted by jskene [+]
Very nice find, but it looks like the spline contact area on the Triumph sprocket is half that on the BMW one. That might be a problem.

I had thought about that and you are right, it could be a problem, I don’t know.  I would hope that the shaft material would be stronger / harder than the sprocket and that the sprocket would fail before the shaft.

When you subtract out the end chamfers, the Triumph sprocket’s effective spline engagement length looks pretty short.
« Last Edit: December 09, 2019, 07:18:55 AM by 2Bears »

Offline smithy

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Re: Larger sprocket.
« Reply #18 on: December 02, 2019, 02:57:40 AM »
*Originally Posted by 2Bears [+]
I had thought about that and you are right, it could be a problem, I don’t know.  I would hope that the shaft material would be stronger / harder than the sprocket and that the sprocket would fail before the shaft.

Removing the "chain drop guard" is essentially committing engine suicide, granted the chance of the chain snapping/breaking is indeed rare.... but it does happen occasionally, and if/when it does, you can basically write off your engine.
Honestly...it's so much easier just to fit a smaller sprocket on the rear rather faff about doing what is essentially impossible to start with.  :084 Takes less than 1/2 hour to swap out the rear sprocket.

Smithy.
« Last Edit: December 02, 2019, 02:58:36 AM by smithy »
When I die, I want to go peacefully in my sleep like my Grandfather....not screaming like the passengers in his car..!

Offline bazzer

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Re: Larger sprocket.
« Reply #19 on: December 04, 2019, 01:22:49 PM »
*Originally Posted by smithy [+]
Honestly...it's so much easier just to fit a smaller sprocket on the rear rather faff about doing what is essentially impossible to start with.  :084 Takes less than 1/2 hour to swap out the rear sprocket.

Its much easier to not try and fix a problem that does not exist :-)

I know everyone is different, but I really can't see how making the gearing taller will do anything but make the bike worse.

I do loads of miles on mine and long days and I just don't see the problem. If you really want a low revving bike at cruise get a GS :-D