Lightweight gearbox removal & overhaul

Information relating to the Matchless G2 or AJS Model 14 250cc Lightweight
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clanger9
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Lightweight gearbox removal & overhaul

Post by clanger9 »

My gearbox has started to make scary noises, so I've finally embarked on a rebuild. I'll post questions and progress in this thread.

To get things going, I posted a guide on how to remove the gearbox on iFixit:
https://www.ifixit.com/Guide/AJS-Matchl ... oval/91263

Please let me know what you think. Useful? If so, I'll try to cover the rebuild in the same style...

Wish me luck! :D
1989 Moto Morini Dart 350
1993 Ducati 750SS
Steve S
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Re: Lightweight gearbox removal & overhaul

Post by Steve S »

Really good Clanger!

I'm finally ready to re-assemble my box after its rebuild, so will be watching closely!

Steve S.
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clanger9
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Re: Lightweight gearbox removal & overhaul

Post by clanger9 »

Excellent - we can compare notes!! :)

I'm currently compiling a list of the weird and interesting things that can go wrong with a Lightweight gearbox. So far, on a sample size of (1) i.e. the gearbox I just dismantled, I found:

- clutch actuator retaining ring loose
- gear selector pivot shaft not screwed fully home <- possibly the source of my chronic oil leak
- layshaft bearing so loose it just dropped out onto the bench <- which made me feel a bit better about my decision to dismantle it even though it was working OK

Other highlights included a weird bodge involving what looks like a nail to try and stop the layshaft bush from spinning in the casing [edit: it's got the same mystery 2mm hole that Chris859 found on his gearbox in this thread] and the plunger pin retaining bolt that was stupidly tight/stuck fast. That was an almighty pain to undo...

Surprisingly, the output sleeve gear and bearing look serviceable (if a little grumbly).
Last edited by clanger9 on Wed May 31, 2017 7:56 pm, edited 1 time in total.
1989 Moto Morini Dart 350
1993 Ducati 750SS
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Ozmadman
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Re: Lightweight gearbox removal & overhaul

Post by Ozmadman »

That's a neat guide! Didn't even know something like this even existed, excellent well done.... All those issues mentioned above are common issues..
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed
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BultacoBen
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Re: Lightweight gearbox removal & overhaul

Post by BultacoBen »

Looks great Clanger, looking forwards to following you on this journey...
http://www.ben-eddings.com
1966 Matchless G2 CSR scrambler
1986 Suzuki DR600 long-range explorer
1971 BSA B50T street tracker
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clanger9
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Re: Lightweight gearbox removal & overhaul

Post by clanger9 »

The gearbox rebuild guide is taking shape:
https://www.ifixit.com/Guide/AJS-Matchl ... haul/91777

Not complete yet, but I figured I'd publish it anyway as there are a few questions kicking around regarding the variety of parts used in the Lightweight boxes. I've done my best to address these in the guide, but I'm bound to have missed something important.

Feedback welcome!
1989 Moto Morini Dart 350
1993 Ducati 750SS
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Ozmadman
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Re: Lightweight gearbox removal & overhaul

Post by Ozmadman »

This is mega excellent Paul.... nothing like this was available before you did it and even more so for a lightweight where decent, well explained info along with clear pictures regarding our bikes are few and far between. very well done and definitely one for all lightweight owners to keep.. :beer:
Paul
1960 Model 8
1974 Yamaha RD250B US Model 6 speed
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clanger9
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Re: Lightweight gearbox removal & overhaul

Post by clanger9 »

I'm glad you like it! :D

The ifixit.com website makes it very easy to pull a guide together - I guess they've already figured out a format that works really well.

Apart from the photos, what I've written is just a summary of what I've learned from the incredibly helpful people on this forum. Without that help, I think I'd still be staring at a pile of bits and a confusing workshop manual(!).

Anyway, the end is in sight so hopefully I'll have the bike back on the road this weekend...
1989 Moto Morini Dart 350
1993 Ducati 750SS
Steve S
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Location: Hertfordshire United Kingdom

Re: Lightweight gearbox removal & overhaul

Post by Steve S »

I'm sure this will be the definitive re-build guide!

Getting near to final re-assembly of my G5 box and noticed the 2 thrust washers 041389 and 01390 and the washer under the nut 041325 were all missing. Russell Motors could supply 2 of them and the result is a much improved camplate spindle action.

Also bought a kickstart spring which resolved my problem of not being able to re-fit the outer cover.

However fitting one of the oilseals 040006X (later square section type) on the kickstart spindle was OK but on the footchange spindle it causes the selector part to fail to engage properly with the spring (see photo). I'm therefore thinking that I can't use a seal in this position (there isn't one shown in the exploded diagram) and just rely on the 2 O rings 040079. What do you think?

Steve S.
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clanger9
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Re: Lightweight gearbox removal & overhaul

Post by clanger9 »

Hi Steve,

You don't want to put an o-ring there. As far as I can tell, it goes in the recess between the outer case and the bronze bush:
IMG_1302.jpg
Some people fit another o-ring between the two bronze bushes to improve the seal.

Good point on checking the thrust washers on the selector mechanism. I didn't dismantle this part of the gearbox because it all looked OK, but I will add a note to the guide.

PS: I just put my bike back together, all seems good. The sun is shining, so I'm just about to take it out for a test ride... :)
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1989 Moto Morini Dart 350
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