It was worth a try

Forums

My Commando is popping out of first gear - not all the time but often enough to make a wet cheddar gorge tricky. I measured the kickshaft end float at 14 to 15 thou and decided to put a 5 thou shim in there and see how that went.

Whilst I had the outer cover off I thought I'd replace the mainspring and found that the pawl carrier pin was not located in the mainspring... meaning only the 'hairspring' on the pawl was engaging - a quick watch of the Hemmings video again and I thought this 'could be it' so I replaced the spring and made sure that the pin was in the main spring.

I only had one outer cover gasket and thought I'd chance putting it all together again in the hope that that was the issue.

Well it was worth a try... didn't work even though the gear change is much nicer as the spring is working properly.

on to Andover again for a couple outer cover gaskets!

I'll look at the dogs while I'm in there with a shim - hoping I don't need a new first gear.

Anyhow - share your advice and experience please!

The dogs on the layshaft 2nd…

The dogs on the layshaft 2nd gear and the corresponding layshaft first gear holes are probably worn. A first check is the index plunger spring, has it lost its springyness?
Whereabouts did you put the 5 thou shim?

Hello Peter, I didn't get…

Hello Peter,
I didn't get as far as using a shim, but was going to put it on the kickstart shaft up against the inner cover (so the inner cover has to come off) to make the kick start end float around 10 thou.

I haven't tried the index plunger spring - but (from the outside) it looks like a new one.

So the gears that may need replacing would be the layshaft second and layshaft first? Excuse my ignorance - new to all this.

cheers

Mick

First gear engagement is…

First gear engagement is between the layshaft second and first gears, The layshaft 2nd gear is moved by the selector fork to get the dogs on it engaged with the holes in the layshaft first gear. Worn dogs and holes cause jumping out of gear
Any engineer will tell you to replace gearsets in pairs, mating a part worn gear with a new one is a no no. That said, if the mainshaft gears teeth look ok and there isn't any other obviously worn components, just replacing the dodgy gears will work ok.
All this entails a gearbox strip to examine the cluster. It can be done with the box still in the bike and the primary drive intacted. Just that the mainshaft and sleeve gear will still be in the box. It will be a good idea to strip the box anyway, first to check the layshaft bearing is the roller type, if it is still the ball type bearing it needs changing. If this fails it can destroy the box and worse it could bring you off. Secondly check the sleeve gear bushes are still in place and havn't moved, they have a nasty habit of either moving outwards towards the clutch and the bush then gets milled away by the mainshaft clutch circlip or inwards and get munched up by the gears themselves. Check the box sump for ground up bronze.
The 850Mk3s have two circlips that stop this happening. Earlier machines will have no circlips or just one. The sleeve gear can be machined to fit the later circlips.

Thanks Peter - that's all…

Thanks Peter - that's all really good advice.

I'll strip the box in the frame and dive in. Haven't come across any bronze colour in the oil, only silver, but I was expecting a little.

Would you replace the gear bushes as I'll be looking in there anyhow? They seem to be designed to be a loose fit with oiler holes so it doesn't look like a big job.

I'll check that bearing too - I know that the box has been rebuilt, but given how the mainspring wasn't clipped on properly I don't know how well its been done. In the accompanying parts book I can suspect that 3rd was replaced as it has the part number against it. Such is the perils of buying at auction - but I'm still with my budget if I have to buy some gearsets. Was just hoping to get a fix with a 20p shim rather than £200 of gear!

Can't complain though - it was a 600mile round trip to the rally through a monsoon and she never missed a beat.

Strip, inspect, replace…

Strip, inspect, replace. Also look at the kickstart shaft, in the corner where the pawl sits, they have a nasty habit of cracking. Replace the kickstart pawl when your in there as well.
These bikes are 50yrs old now, Its a very rare thing to work on one that has not been apart before.
As i explain to all my clients, they weren't made very well and previous owners have had very variable skills, sometimes leading to allsorts of horrors lurking within.
A budget.... Good luck with that, there is always something needing attention......

Budget... yep laugh out…

Budget... yep laugh out loud moment there!

Will do - I'll keep you posted too

cheers

Mick

Accumulated Commando Wisdom

Norman White's Restoration book has a useful gearbox rebuild section (amongst other goodies), and with lots of photo's - much much better than a Haynes for example. He points out common wear points, and comes highly recommended.

If new to gearboxes …

… I'd very strongly recommend the Mick Hemmings video, available from the NOC shop. The John Hudson version is something of a museum piece, but has some points that Mick's doesn't cover.

p.s. videos highly recommended even if not a novice.

Thanks both

Been watching Mick Hemmings on a loop! All seems so easy... there's some good YouTube stuff too - hoping to get in for an inspection on Monday.

All making a bit more sense. Hoping at worst I can do 1st and 2nd without taking the box off the bike.

That seems to have worked....

I think I've found the culprit!

The old cam plate plunger spring on the left - new one on the right. Thought I'd change the spring and test that first before tearing into the gearbox, only costs a fill of gearbox oil.

The bike held on to first uphill until the indecent amount of 5000 rpm was reached. Trying different on and off throttle combinations and she feels a lot more solid. Gear change and neutral finding a lot more positive too. Shout out to Peter Shand for the suggestion as a job to do 'while I was in there'.

You can see the old spring on the left was not up to the job and had been stretched at some point.

All for the sake of a 90p spring...

As with all these things on an old bike I'll keep my fingers crossed and see how it goes.

Old spring on left

Definitely the wrong spring…

Definitely the wrong spring had been fitted. Reminds me of a tale from our club sec, He once came across a g/box not selecting properly, he found the pawl spring was made from a coat hanger!

conclusion

Mick,

thanks for the photo and update.

Good to learn the conclusion of your fault.

Also it's of general interest and possibly helpful to others on this forum.

Coathanger?

Crumbs - I knew they were good as car aerials - but there's no spring in one!

Given the obviously bodged plunger spring and the fact that the mainspring wasn't on the pawl points to what Peter described as: "previous owners have had very variable skills, sometimes leading to allsorts of horrors lurking within."

Oh well - we'll keep an eye on the box - but I've learnt plenty in the process!

Norton Owners Club