Gearbox Problems

Information relating to the Matchless G2 or AJS Model 14 250cc Lightweight
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Re: Gearbox Problems

Postby clanger9 » Sun Jan 24, 2021 7:00 pm

I'd love to know more detail about how they did that 19 tooth gear. Only the 19 tooth part is listed as different - the other 28 tooth gear is listed as unchanged (!)

This doesn't seem physically possible. :?
1989 Moto Morini Dart 350
1993 Ducati 750SS

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Re: Gearbox Problems

Postby IanAlexander » Mon Jan 25, 2021 11:38 pm

Can anyone confirm I have the gears in photo,in there order or are 2nd & 3rd the other way round ? Working from the selector it appears to be the top line ?. I am trying to find wich and why 3rd makes so much noise,so need to know how the power is driven though the gears... BSA box and Triumph drive as bottom line 4 2 3 1 hope this makes some sort of sence.
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Re: Gearbox Problems

Postby clanger9 » Tue Jan 26, 2021 8:09 am

The gears are in order (i.e. 4-3-2-1)
There's a photo of the gear set in my rebuild guide here: https://www.ifixit.com/Guide/AJS-Matchl ... 77#s171910
1989 Moto Morini Dart 350
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Re: Gearbox Problems

Postby g80csp11 » Tue Jan 26, 2021 9:49 am

Paul , great rebuild guide . perhaps you could send to the editor for inclusion in the Jampot . i'm sure it would be a welcome addition and to a wider audience
especially as the lightweights are becoming more popular

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Re: Gearbox Problems

Postby clanger9 » Tue Jan 26, 2021 10:04 am

Thank you!

That's a great idea. When I first put the guide together, I wasn't sure how useful it would be (and I was still figuring things out), but now that it's been "road tested" a bit, then it would be great to get it out to the Jampot readers. I'll give it a go...
1989 Moto Morini Dart 350
1993 Ducati 750SS

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Re: Gearbox Problems

Postby g80csp11 » Tue Jan 26, 2021 10:18 am

Ive been doing similar for our section Zoom theme nights on a smaller scale. usually a collection of data gathered form many sources into one document
I know when I was younger and new to AMC , I must have read every document i could while restoring my 46 G80L

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Re: Gearbox Problems

Postby Stan Palmer » Tue Jan 26, 2021 5:57 pm

Hi Clanger9,
I also thought that gears couldn't be played around with to the extent of adding a tooth. I looked into it a little, was initially put off by the mathematics and terminology, but eventually found a site that explained it better. How naive I was !

https://www.researchgate.net/publicatio ... s_Analysis

Basically the involute tooth form does tolerate a change of shaft centres, I estimated a change from 18 to 19 teeth is about 1mm on shaft centres. It seems from the tables in the article that such a change would be acceptable.
So I believe AMC would have designed on the 19:28 set, which means the 18:28 set would be 1mm out from the theoretical value, It seems it can be slightly optimised by change of tooth form, backlash etc. You have to admire the engineers of 60 to 100 years ago that did all this by hand and trial and error.
The downside is noise, vibration, increased tooth loading. I haven't got a gearbox of any kind in bits at the moment, it would have been interesting to measure some backlash to see if they put extra in as a matter of course. It could have some bearing on why old bike gears are noisy. Third gear seems to be an issue on nearly every make. I found other tables that indicated, for optimum conditions, center tolerances of about 2 thou, even for the lowest grade of gears !

One site I looked at described the early gears made of wood for windmills and the like, sometimes just pegs and slots, and went on to describe how the technology had developed as speeds, power transmission, wear issues and the like had arisen.

Again reminded me just how bloody clever some people are, and whether that brilliance will yet give us a route out of consumption, waste emissions, sustainability, global warming, loss of species and overpopulation. To name a few.
Stan

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Re: Gearbox Problems

Postby clanger9 » Tue Jan 26, 2021 7:49 pm

That is fascinating information, Stan. Thank you!

With my lack of engineering training, I didn't know it was even possible to change a 18:28 set to a 19:28 set while keeping the same centres. Given the rather "agricultural" clearances in these gearboxes, 1mm error on the shaft centre would neither be here nor there. Amazing.

It's an ingenious way to produce a close ratio box at minimal cost. Also entirely understandable, given the situation AMC found themselves in 1965/66...

The story of this one extra tooth alone could make for an interesting Jampot article!
1989 Moto Morini Dart 350
1993 Ducati 750SS

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