Strange Vibration

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Sleeve gear bushing okay?

Easy test, keep a feel on primary chain tension while putting tension on drive chain with foot or assistant. If primary chain tightens up when pressure put on drive chain, replace sleeve gear bushing (easier said than done, sometimes).

Probably NOT this but so easy to check, why not? :?
 
The rotor inner and outer seem to be in good order and I can't feel, or see, any movement between them.

The primary chain doesn't move or tighten when I put pressure on the rear chain.

The clutch hub does have some "wobble in its bearing, about 3-4mm max.

There are no signs that the primary chain is touching anything it shouldn't.

The primary chain tensioner seem to be keeping the chain tensioned.

The primary chain seems OK, if it were a rear drive chain I would say it was in usable condition. There isn't excess wear.

Anyone in Brisbane who can look at this and give an experianced opinion? (FREE BEER !)

Any ideas???????

Graeme
 
The wobble is in every plane, not much, 3-4mm max.

by holding the clutch hub / drum I can move it by a small amount in any plane, 3 mm to 4 mm.

As the bearing is only small compared to the clutch it must have some movement, but how much is too much?

If it was a Ducati, which I know, it would be stuffed. But they are a gear drive primary.

graeme
 
GRM 450 said:
The wobble is in every plane, not much, 3-4mm max.

by holding the clutch hub / drum I can move it by a small amount in any plane, 3 mm to 4 mm.

As the bearing is only small compared to the clutch it must have some movement, but how much is too much?

If it was a Ducati, which I know, it would be stuffed. But they are a gear drive primary.

graeme
Click to expand...

1/8in? I'd pull it and make sure the circlip is still intact.
 
Clutch 3-4mm wobble is way out of spec and could well be
the source of the harmonic random vibration.
That implies a gearbox -bearing and sleeve gear issue and maybe
even bent twisted main shaft, to some degree.

Bottom ends decaying are reported to buzz-vibe in mystery
patterns before that source lets go.

Hope its just a bad link in the triplex chain and you don't
go though my learning curve with tantrums to face tough tasks

hobot
 
With regard to wear, the Mk111 primary chain needs replacing when the chain comes into contact with the case. At this point, it is only about 'half-stretched' in terms of the earlier models with adjustable gearbox position and I can remember cheapskates years ago who used to scrounge primary chains from Mk111 owners to use on their 750s.

If your primary set up had been run with the substantial misalignment that you referred to in the first post then it's really not possible that the chainwheels and chain aren't damaged. By altering the alignment, you will have altered the contact between the chain and the damaged teeth. Does the chain have polishing on the inside of the side plates ? Did it go back on the same way round ?

I can't understand the impossibility of obtaining alignment. The crank mainshaft should be OK. It may be that the problem lies with the taper on the engine sprocket (never heard of it though) and that a new part will bring it back to spec. It is normal to have to shim the clutch outwards to obtain alignment. Do you have the correct spacer with the circlip retaining groove ?

Alignment of the chain is important. With the chaincase removed and a straight edge along the outside of the teeth, it needs to be set so that there is absolutely no mis-alignment visible. There will always in my experience be a small amount of 'rock' on the clutch outer due to the internal clearance in the centre bearing.

All Mk111s should have the later welded magnet rotor. I'd be surprised if one of those was falling apart. It's easy enough to check the date of manufacture. The NOC Service Notes suggest that there should be a small 'W' on the welded rotors ans part number 54202275 or 54201143
 
Thank you gentlemen for your time,
Nothing looks suspect to my untrained eye,
Here is a picture

Strange Vibration


Can you see anything wrong ?

The chain doesn't touch the case anywhere and the tensioner appears to be working.

Graeme
 
Thank you LAB, there are no signs of the chain hitting anywhere in the case.
Maybe I will just keep riding it until it shows me what is causing the vibration in no uncertain terms? (with teeth and sphincter clenched)

graeme
 
Graeme, the rear of your inner chaincase looks to be very close to the 'Z' plate. is that just due to the camera angle ? If not then I can imagine it contacting under some conditions (hard acceleration ?)

I'm intrigued by your clutch spring centre boss. Has it been lightened or relieved in some way ?
 
This is the only Commando clutch I've seen and it is how I found it before rebuilding the bike.

The gap is large enough not to touch and if it could the frame would have to be cracked, it rides well apart from ground clearence issues.

A pic of the alloy I removed from the inner chaincase to allow the clutch drum to move inward to get it to align as close as possible to the crank sprocket.

Strange Vibration


And a pic of the gear box side of the clutch drum with its new bearing.
I had to remove the 3mm spacer that packed the clutch drum out to get the drum inward more. The best I could get it was 3mm proud.

Strange Vibration


graeme
 
79x100 said:
I'm intrigued by your clutch spring centre boss. Has it been lightened or relieved in some way ?
Click to expand...


I think what may have caught your attention is an additional slotted ring or washer around the boss? I noticed that too, as my MkIII's spring doesn't have that, and I've no idea what it's purpose is?

A portion of what looks to be an identical washer can be seen in this Old Britts photo:
Strange Vibration


http://www.oldbritts.com/ob_clutch_info.html
 
That's the bit I was looking at L.A.B. . Do you suppose that it's some sort of helper spring ? I've never heard of it.

Graeme, I really think there is something fundamentally wrong with your set-up because it shouldn't be necessary to remove that amount of material. Furthermore, it looks as if you have removed the clutch location spacer and replaced it with a plain shim. This means that there is nothing to prevent the circlip from being squeezed out of its groove (and they can do that anyway).

I'm trying to work out where the problem lies. The gearbox is located by the rear cradle and unless that is badly bent, the lugs should be in line with the crankcase lugs. There was mention in an earlier post to the top lug spacer 03-0023. The parts book doesn't make it clear but this goes between the gearbox top lug and the inside of the cradle. It is often missing. This could cause some alignment oddities but I don't see how it can result in the inner chaincase clearance problem.

If your inner chaincase is mounted squarely on the crankcase and is straight and if the clutch when mounted with the proper spacer (and usually additional shims) is not contacting the chaincase then I would think that these parts are correct and this must mean that the problem lies with the crank or engine sprocket.

Could it be that a previous owner has damaged the taper on the crank and had it machined or lapped so that the sprocket now sits too far inboard ? It's a huge amount though. Did you shim your crank, and if so at which place ? Again, your problem seems too great to be caused by crank shimming.
 
Hi there, just my two cents: if engine sprockets too much inwards , why not a 750/85O mk2 crank instead of an 850 MK3 , thus the earlier crank beeing less wide the taper is at least 1,5mm inwards...................
 
The electric tart gear is all installed so the drive side cheek at least must be Mk 111.

This is a really odd one.
 
79x100, thanks for your time with this.
The gearbox spacer is in position between the cradle and the box. The same as it came apart.
When I checked the sprocket alignment it was out by over 6mm with the clutch outward.
The crankshaft sprocket can't move as it sits on a taper, so the clutch must move inward. I removed the 3mm spacer behind the clutch, that made the clutch rub slightly on the chaincase.
I removed some alloy and all tightened up ok but the clutch was still 3mm outward from perfect. (better than 6 mm plus)
I had 3 people look at this, none of which were Norton savy, but motorcycle restorers and all were mechanically minded.
None could see any alternative.
The chaincase is flat on the crankcase and I installed as per the manual
Graeme.
 
Try checking the transmission main shaft nut to make sure its tight. I drove around for a while with a loose nut held in place by the tranny cover.Every thing seemd to work fine!
I only discovered it when changing to a 520 chain.
 
Bruce is referring to the nut inside the gearbox under the clutch actuator, this would also explain the vibration as the mainshaft moved over 3mm will affect the position of the gears on the mainshaft and possibly be causing gears to be out of position.
 
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