Gearbox rebuild problems (2014)

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timsha said:
What is the difference between the Late and early Type Mainshaft 2nd Gear and which should my 1973 750 have?

It's a higher ratio gear set, but fitted to later 850 models although it can be fitted to earlier boxes.

This later 2nd. gear pair has the circular 'groove' mark on the dogs as shown on the one in the ebay link*, and the corresponding layshaft 2nd. gear should also have the groove mark.
*(Edit: He says it's the "late" gear but "04-0418" is the early part number)
 
Thanks LAB,

My RS85 has the groove on the dogs just like in the ebay photo.
The corresponding lay gear does not have the groove. In fact it has no markings whatsoever.

Does that mean i will need a new 2nd Gear Main, a new 2nd Gear Lay or both?

Another Gear which is a possible cause for concern is my 4th gear Lay. This has no markings whatsoever except for a "6" or "9" depending on which way you look at it. Should this gear be marked "AH" like the rest?
 
Is this the Mk2a second gear set ?
I have plenty of photo's of those gears.
 
I was quoting the 2nd gear ratio change as detailed in Roy Bacons book 'Norton Twin Restoration', obviously from The AN parts description this is incorrect.

Regarding my measurements, I do apologise, I wrote the layshaft second gear dimensions down wrong, it is actually 2.595 inches, all the others are correct and consistent with both gear sets I checked.

It looks like we might be on the right track with mismatched gears on 2nd.

The fact that the later ratio actually has one fewer teeth on the layshaft almost certainly means it is a smaller diameter, hence the larger dimentions of the matching mainshaft gear, although the tooth count is the same.
 
timsha said:
My RS85 has the groove on the dogs just like in the ebay photo.
The corresponding lay gear does not have the groove. In fact it has no markings whatsoever.

Does that mean i will need a new 2nd Gear Main, a new 2nd Gear Lay or both?

It's always better to fit gears as a "new pair" whenever possible, rather than run a new gear with an old part-worn one.Edit: A gear marked "RS" is not a genuine Norton part.

timsha said:
Another Gear which is a possible cause for concern is my 4th gear Lay. This has no markings whatsoever except for a "6" or "9" depending on which way you look at it. Should this gear be marked "AH" like the rest?

I just pulled out a late 4th. gear pair from my spares stock, the sleeve gear is marked "AH" but the lay gear only has the "6" (or "9") marking.
 
Time Warp said:
Is this the Mk2a second gear set ?
I have plenty of photo's of those gears.

Thats a good question....the bike is a 1973 MkV 750. These last few 750 Commandos (prefix 235) were to a certain extent a mish-mash affair, already utilizing the 850 Frame. Correct me if I'm wrong, but i would still assume, that the gearbox would originally have the old 750 Ratios.
 
L.A.B. said:
timsha said:
I just pulled out a late 4th. gear pair from my spares stock, the sleeve gear is marked "AH" but the lay gear only has the "6" (or "9") marking.

My sleeve gear also has AH on it. Could you possibly measure both gears diameter for me to compare against mine?

Sleeve Gear (23 Teeth)...69.2mm (2.724 Inches)
4th Gear Layshaft (18 Teeth)...57 mm (2.244 Inches)

I need to identify wether the majority of my components are late or early style.


Wouldn't putting an 850 box on a 750 have adverse affects on performance?
 
There is no way that should be tight on assembly something is wrong maybe a pair of gears in wrong it should turn free with no stiffness before inner cover is fitted. I've not done many boxes (four) and they were all free.

J
Gearbox rebuild problems (2014)


These gear came out a 69 lay 4 is an old gear as I blew the arse out two years ago it's done about 3.5 k and no probs.
 
timsha said:
My sleeve gear also has AH on it. Could you possibly measure both gears diameter for me to compare against mine?

Sleeve Gear (23 Teeth)...69.2mm (2.724 Inches)
4th Gear Layshaft (18 Teeth)...57 mm (2.244 Inches)

Something odd there?
I measured:
Sleeve gear (23T) = 64.45mm (2.537")
4th lay (18T) = 52.25mm (2.057")
 
oh yes....just seen I've been reading this antiquated non digital ruler wrongly all along..... :oops:

Correct measurements are:

4th Lay....52.25mm
sleeve gear...64.45mm

:lol:
 
timsha said:
Wouldn't putting an 850 box on a 750 have adverse affects on performance?

2nd. gear will be slightly higher with the later gear set, but that's all.
 
timsha said:
Hi Dave,

Mainshaft 1st (14 teeth).....45 mm (1.772 Inches) 1.696 inches
Layshaft 1st (28 teeth) ....80.05 mm (3.152 Inches) 2.995 inches
Mainshaft 2nd (18 teeth) ....63 mm (2.480 Inches) 1.975 inches
Layshaft 2nd (24 teeth)....70.8 mm (2.787 Inches) 1.595 inches
Mainshaft 3rd Gear (21 teeth)....63.4mm (2.496 Inches)
Layshaft 3rd Gear (20 teeth)...62.9mm (2.476 Inches)
4th Gear Main Countershaft (23 Teeth)...69.2mm (2.724 Inches)
4th Gear Layshaft (18 Teeth)...57 mm (2.244 Inches)

Sorry....my measurements were wrong

Here are the correct measurements:

Mainshaft 1st ....1.696 inches
Layshaft 1st ...2.995 inches
Mainshaft 2nd ... 2.055 inches
Layshaft 2nd ....2.598 inches

All exactly the same as yours, Dave

continuing:

Mainshaft 3rd...2.283inches
Layshaft 3rd...2.303 inches
Sleeve Gear...2.537 inches
Layshaft 4th...2.057 inches

Once again sorry for any confusion.
 
So my gears 1 and 2 match up with those from dave, and my sleeve gear and 4th lay match up with yours, LAB, which leaves only third gears. Could my third gears be the culprit (both have AH on them)?

I am starting to think i am barking up the wrong tree.
 
timsha said:
So my gears 1 and 2 match up with those from dave, and my sleeve gear and 4th lay match up with yours, LAB, which leaves only third gears. Could my third gears be the culprit (both have AH on them)?

I am starting to think i am barking up the wrong tree.

But if, as it seems, you have a high ratio 18T mainshaft 2nd. gear, and a standard ratio 24T layshaft 2nd. gear, then they will not be compatible and should not be run together-as the high ratio 18T mainshaft gear must be paired with the high ratio 23T layshaft gear.
 
Don't worry about the wrong measurements, you are in good company as I did likewise on one of my masurements. Your mainshaft 2nd gear appears to be the problem, it is the same size as the one that gave me trouble, if you look at my original measurements you will see that on the two standard 750 gearsets I measured that 2nd gear was a bit smaller and the overize one corresponds with what you have measured, I have just checked my overized one and indeed it has the groove machined into the dogs.

Your best options are to either get a new pair of gears, or else if you are trying to do this on a budget get a second hand set. The least good choice would be to simply replace one of the two gears with either new or second hand, although my experience is that Norton gearboxes are quite robust and dont't seem to mind a bit of chopping and changing.

Please keep us informed.
 
Thanks Dave, thats great information.

Would you buy both gears even when the 2nd gear lay is what one would describe as almost unused condition...i personally don't think these gears have seen much action at all...my suspicion is that were dealing with an aborted rebuild...and since then the bike has just sat there.

I will get on to Andover Norton tomorrow and get dimensions of the 2nd gears that they're selling before i order anything.

Will update this post when i have anything new...

At least i have plenty of other things to get on with in the meantime.....am putting on a new wiring harness...no big deal one might think, only the old harness was not color coded so just swapping old connections for new corresponding ones isn't possible!! To make things a little more complex it has a 3Phase Conversion. Ill be posting about the connections at the rectifier very soon i expect.
 
Honestly, if the 2nd gear layshaft looks almost new I would buy only the mainshaft gear. I'm sure some will disagree, but I have built up a box with unknown and non matching gears and it worked just fine.

Regarding the wiring loom, there are a number of colur coded wiring diagrams on the net, simply start by connecting those wires that you can easily identify like the battery terminals and the zener diode with the large spade connector and eyelet for the earth and before you know it you will be left with fewer and fewer unidentified wires. The wiring loom goes through the hole in the frame plate under the rear of the backbone with a rubber grommet and the later looms without the ameter connections require a separate sub loom for the headlight and other connections within the headlight itself. For things like three phase alternator, electronic ignition etc You can modify the loom after working out where all the wires go.
 
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