bent mainshaft

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htown16

htown16

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Looks like I have a bent mainshaft. Starting to pull things apart. Want to leave the gearbox in the bike. Shoud I dismantle the gearbox first or the primary. Will I need to maintain the primary intact to keep things from spinning when I do the gear box?
 
htown16 said:
Shoud I dismantle the gearbox first or the primary.
Click to expand...

You have to remove the clutch assembly and clutch location circlip before you can remove the mainshaft so primary before gearbox.

htown16 said:
Will I need to maintain the primary intact to keep things from spinning when I do the gear box?
Click to expand...

Loosen the mainshaft nut at the gearbox end first.
 
Thanks LAB. First outer gearbox down to main shaft nut loose, then primary, then rest of gearbox. I'm getting my head around stripping all these parts I just recently assembled but the dial gauge says 50 thou runout on the clutch hub.
 
You could remove the gearbox inner cover, various gears and selector forks first but ultimately the clutch and location circlip (also the location spacer and shims) must be removed in order to release the main shaft although the inner primary cover can remain in place.
 
i assume your runout is side to side? what kind of bearing is in the clutch hub? did you put a new bearing in the clutchhub, if it has a c3 clearance bearing it may contribute to the wobble, although i'm not sure how much runout that would represent, these days it more difficult to find a c0 clearance bearing for the clutch hub, but a c0 has way less clearance than a c3, needs a bit more research and chat with a bearing supplier.
in my opinion, you can only verify a bent shaft once you have it out and spin it ( v-blocks or lathe)

PS: opinions are like @$$holes, everybody has one...
 
850commando said:
i assume your runout is side to side? what kind of bearing is in the clutch hub? did you put a new bearing in the clutchhub, if it has a c3 clearance bearing it may contribute to the wobble, although i'm not sure how much runout that would represent, these days it more difficult to find a c0 clearance bearing for the clutch hub, but a c0 has way less clearance than a c3, needs a bit more research and chat with a bearing supplier.
in my opinion, you can only verify a bent shaft once you have it out and spin it ( v-blocks or lathe)

PS: opinions are like @$$holes, everybody has one...
Click to expand...
Or roll it about on any piece of plate glass and observe. Sleeve gear bushes need to be checked for wear.
 
You need a lathe.
I don't know if it is possible to straighten a bent shaft.
If straight ( or a new one..) : install the clutch centre with the shaft still in the lathe and spin it.
Try different positions of the centre on the shaft.
If it spins perfectly true in only one position ( not impossible..), mark it.
Then assemble the complete clutch and check again.
 
htown16 said:
Looks like I have a bent mainshaft. Starting to pull things apart. Want to leave the gearbox in the bike. Shoud I dismantle the gearbox first or the primary. Will I need to maintain the primary intact to keep things from spinning when I do the gear box?
Click to expand...
Htown,
How did you discover that you have a bent main shaft?
Mike
 
If it is bent, at least you have the option of a new one. It isn't beyond the reach (cost) of most of us.
 
You don't need to pull half the bike to bits or buy a lathe.
Just remove the clutch centre hub and clock the actual shaft and the end of the sleeve gear.
The shaft is fixed at its T/S bearing and centred on the sleeve gears bushes at the D/S so you already have fixed centres unless the bushes are worn out.
That would make for an easy check, if that is found to be OK then the shaft ring clip and hub would need to be checked.
Check for a cause (the shaft) not a symptom (at the hub) which is easily done with minimal disassembly.

With the hub removed even a simple fixed whatever close to the end of the shaft would show wobble or oscillation by eye.

gb.jpg
 
htown16 said:
Looks like I have a bent mainshaft. Starting to pull things apart. Want to leave the gearbox in the bike. Should I dismantle the gearbox first or the primary. Will I need to maintain the primary intact to keep things from spinning when I do the gear box?
Click to expand...

You would disassemble the minimal but in order the primary first if anything.
You should be able to check the shaft with just the centre hub removed and drum/basket still in place.

The catch with that is only service tools to do so make it easy (primary removal) and some of the generic tools strain the primary by default. (Which is why I made a specialised rotor holding tool (stator removed) to isolate the nut removal and retorquing)
 
Time Warp said:
You don't need to pull half the bike to bits or buy a lathe.
Just remove the clutch centre hub and clock the actual shaft and the end of the sleeve gear.
The shaft is fixed at its T/S bearing and centred on the sleeve gears bushes at the D/S so you already have fixed centres unless the bushes are worn out.
That would make for an easy check, if that is found to be OK then the shaft ring clip and hub would need to be checked.
Check for a cause (the shaft) not a symptom (at the hub) which is easily done with minimal disassembly.

With the hub removed even a simple fixed whatever close to the end of the shaft would show wobble or oscillation by eye.

View attachment 83744
Click to expand...
Looking at this pic made me wonder, is micro-plating the gears and shafts etc still being done? I remember ads for this process stating the plating was so thin, no clearances were reduced and (supposedly) everything runs with less friction.
 
Danno said:
Looking at this pic made me wonder, is micro-plating the gears and shafts etc still being done? I remember ads for this process stating the plating was so thin, no clearances were reduced and (supposedly) everything runs with less friction.
Click to expand...

I don't know about micro plating but when I sent my DR650SE gearbox to those noddy's at Nova Racing (to get the 3rd billet set made) they were doing micro polishing of the gears which sounded more like getting an acceptable finish not an improvement.

The gearbox internals are not that bad (on a Commando) but the oddball inboard sprocket makes the near unsupported parts outboard a potential problem by design (unless some mechanical empathy is shown)

Oddly enough, 1970's/80's bevel drive Ducati's have a very similar sleeve gear/sprocket to the Norton but the shaft stops at the outer end of the sleeve gear and the clutch is mounted on the other end of the shaft.
 
I have stripped the gearbox down to loosening the bolt on the main shaft. I have also stripped the primary. When I put my dial gauge on the primary end of the shaft I get the same 50 thou runout that I was getting on the clutch hub. Will pull the inner GB cover and remove the main shaft today. Will also inspect the bushes. As mentioned, while not cheap a new mainshaft won't break the bank. No lathe and finding a machinist that will do small jobs is difficult. This bike had been in a pretty bad accident. Hit hard in the front and I had to replace the frame as it was pretty bent. Not sure if that had anything to do with the bent main shaft.
 
In my (limited) experience, the mainshaft gets bent if you have catastrophic failure in the primary. Something gets caught between the chain and clutch basket teeth. In my case it was pieces of an exploded alternator. Broken chain, bent shaft.
 
There are posts where folk recommend jamming things under the primary chain in some attempt to tighten or loosen the rotor nut so no surprise the gearbox shaft gets a hard time when that nut gets 70 ft/lbs.
Then there is standing on the rear brake pedal to address the clutch centre nut (That might even be in the workshop manual) over a clutch locking tool.
If something doesn't break it must be OK ?

Who knows what has happened in someone's shed in the last 50 years with home mechanics and 'just get it done.

As per the picture up the page, from the gearbox bearing out to the hubs spline is a reasonable distance (unsupported bending leverage ?) so reefing on the primary parts is not a good idea (imho) and a prime reason I make tools for service jobs, one of those reasons is to not risk self generated damage. ($$$)

If the shaft is being replaced that in turn raises replacement of the sleeve gear bushes. (and the wear parts on the clutch actuating system while there along with shimming the kick start shaft / first gear etc etc )

I bet a few simple parts replacement jobs in the past turned into major tear downs (from personal experience)
 
Andover has rebuilt kit Bearings ,Bushings and clips I think 131 pounds can't beat it 5-7 day delivery!
 
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