gearbox question

I have been asked to do some repairs on a friends commando. He has had trouble with the gearbox slipping out of 1st gear, I understand it is under load whrn as you do, accelerating . He has been holding the shift lever up to hold it in gear. Now to add to this the clutch has been dragging and slipping. And the lever is very hard to pull.
I am going to inspect the clutch first, I suspect the clutch stack height need rectifying to get the diaphragm spring in it's sweet spot. Also I will naturally check the plates for oil contamination and thickness.

But I was after some experienced thoughts on the 1st gear slipping, (jumping out). Would it be a safwe bet to expect the gear dogs to be worn and rounded? So in theory the box wil need at the least 1st mainshaft and layshaft replaced?
Can these gears be replaced with the box in situ? I have studied the manual and it appears this can be done, anyone done this? Next question, I wanted to replace the layshaft bearing, for peace of mind, the outer one is the problem one isn't it?
Thanks in advance, I just want to help this guy without going nuts and puling the hole box and dice apart.

Cheers Richard

Yes you can but the dogs for 1st laygear gear are on the 2nd laygear and engage through 4 holes in the large laygear. It would have to be seruiusly worn to slip out of gear IME. Check the large laygear bush as they are very thin and do wear heavily IME. Could be rocking so badly it's not engaging properly? Bit unlikely though. Check the detent and spring in lower front of box (external acorn nut). Will be very tight. May be badly worn quadrant where it indexes on the above detent. Of course the mainshaft must be pulled up tight in the inner cover. That failure prone bearing (if it's not been upgraded) is unfortunately one of the last parts removed from the box. You will need to pull all the gears (and primary, clutch etc), heat the casing and the layshaft may/should come out with the bearing. If not it's gearbox removal time.

It's excellent advice to get the first-gear layshaft bush checked out--that tall gear can rock around. You should probably have that bush on hand when you open the gearbox.

The jumping-out-of-gear problem is likely to be caused by too much end float of the kickstart stub. You simply use a rear Isolastic shim between the inner gearbox cover and the stub to force the pawl end deeper into the layshaft first gear. This keeps first gear properly located and engaged when selected. Old Britts has a superb article on this on their website.

Good luck


Tim Kraakevik
kraakevik@voyager.net
Three Commandos

The detent spring and plunger should be checked before going into major dismantaling. This spring loses its gumption. With me, first gear would jump out under load when showing off. NOT COOL! Could not live with that. Went to my man to get a first gear lay suspecting rounded edges. He sold it to me and said under his breath, " it's probably just the detent spring". I said "What?. He said "oh nothing".

Just undo the thing from under the gear box (it will drain it) and measure it. It should be 38 mm or 1.5" and the plunger should well rounded, not be worn flat. For around $3 for a new spring, I could show off with confidence.
The detent was $22 but my pride is worth it.
First gear lay is on the bench waiting for an unsuspecting sucker, I mean potential buyer who didn't know about the detent spring and plunger fix.

Here is the exert for Capt. Norton notes.
28.5 Jumping Out of Gear

From: Gregg Kricorissian
Date: Fri, 21 Apr 95 14:53:01 EDT

> Speaking of gearboxes, my Norton has just developed a problem--it's
> jumping out of first gear. This happened for a third time coming home
> from the Easter Ride and I'm now convinced it's not my imagination...
> sigh.

Afraid that my mind went into autopilot too quickly, and I scoped out the worst-case scenario in my earlier reply. After my original post, I realized that a simple cause of the ' jumping out of first gear' could be the shifter detent. It's under the gearbox, and its cover looks like large domed nut. Especially suspect this if you've suddenly sprung a new oil leak under the bike. Best of all, the detent mechanism is accessible without taking else anything apart!

If you're really lucky, it's just the detent mechanism that's come loose ...
simply screw the thing back in. Otherwise, remove the assembly, consisting of a stout coil spring, and a steel plunger which should drop right out. If they don't just drop out, that may be the problem: if water has gotten into the box, the plunger may rust and begin sticking.

Now check the spring to see that it hasn't compressed or become weak. It should be 1.5" (38 mm) long, and have a spring rate of 21 lbs/in, (for those of you endowed with suitable apparatus). Second, check the plunger, to see that it's end hasn't worn flat ... it needs to be spherical in order to prevent the shifter camplate inside the box from rotating under load.

Hope this helps in sorting out the problem,
...Gregg

I too, hope this helps with your problem.
Peter

Worth checking out the detent spring, if for no other reason than it's easy to do.

Then again, I recall Mick Hemmings on his gearbox servicing video referring to the "myth" that it's the detent plunger that holds the box in gear, when all it really does is provide a positive stop for the cam plate as it rotates from gear position to gear position. That's pretty close to a direct quote IIRC.

FWIW/YMMV

Boy what a list. In my jumping out of 1st events it turned out to be the 1st gear bush on the layshaft. Its the thinest of the bush but does require digging in deeper to check. If one thing badly worn very likely other stuff not far behind which implies full renewal for lasting joy. Loss of engine power or drag even in easy leans can be upsetting.

hobot

If it is 1st gear bush then it'll need reaming to size/good fit. It's a very thinwall bush unlike the thicker main and layshaft bushes which size themselves after pressing in. If you buy a gear then it should already be installed and sized. Good points about the kickstart movement and the quadrant. Could be a combination of things though.

in my experiance jumping out of 1st is a worn selector fork an you can normally get away with swapping it for the 3rd gear selector forkas they are the same.
Al

Well thanks guys,

I will try the detent first as this is the most accessable and by the replies a common malady!

Then sound like the bush on the gear followed by checking layshaft gear endfloat.

Many thanks for the learned replies. This inquiry was generated by me offering to fix a mates bike, and I would have assumed gear dogs first off, so I would say you guys have saved me some embarassment?

Funny thing, last ride on my own CMD I noticed a she jumped out of first a couple of times, I assumed I was getting lazy on properely selecting first, feet getting cold and lift up for first instead of down action for other gears to up shift. May need to get two springs?

Many thanx will advise when I get into it

If it is just too thinly worn 1st cog bush, it only came out of 1st when loads removed on letting off gas and just beginning to coast. Likely a few things to diddle as ya find em.