Rear Chain Adjustmnt

Hello Roger. On Featherbed framed bikes the centre of the rims are perfectly aligned with the centre-line  of the hubs.  The front wheel with the brake-plate and bearing cover should be equidistant to the sliders in the front forks.  Similarly the rear wheel with the sprocket, brake-plate, spacers and speedo drive should be equidistant from both sides of the swinging arm.  So technically, if both rear wheel adjusters are the same length then with the wheels aligned they should both have the same amount of thread showing.   Get your string on the front wheel and ensure that it is not fouling the stand or frame parts and get the rear wheel perfectly aligned with the front.  When this is complete you should be able to measure the distance of each side of the rear tyre to the swinging arm lhs and rhs.  There are many bent featherbed frames. swinging arms, fork yokes and fork tubes around so make sure your wheel alignment is sound before you ride.  Regards, howard 

Hi Roger ,As Howard said , everything should be central ,but there are a lot of variables that the years have wrought . On my slimline I can either have the sprockets (and chain ) nicely aligned or the wheels . But not both !.  I compromise and go for both a bit out. Once the frame is bent or twisted  its not that easy to get it back. I have consulted the experts who were not confident .It would appear that they cannot  fix a small descrepancy only large ones and not to the level of accuracy that i would need.

The "odd"  non threaded locator stud ? is not recognised by me .  My new hub drum is not like that at all. Is it a Commando item ? How many teeth on the sprocket?.

Hello again Roger and Bob - I fear that the so-called odd spacer is not a spacer but part of the rivet that is hammered into the brake-drum to mount the rear wheel.  It looks as if the original snapped or got damaged and was replaced with a different type perhaps from a Commando or a Hybrid Atlas.  Good luck, Howard

From memory I believe the Commando has 42 teeth on the rear sprocket + the cush in the hub,

Earlier models have 43 teeth, But the point I really want to make is to leave the chain slacker than what might otherwise be. This is because if the chain pulls slightly tight it will pull the primary chain tight with unintended  consequences. 

As for alignment: Twisted & bent frames etc, use the statistical method: Line of best fit if not, put it on a jig. 

Hello again Roger - The previous owner didn't drill the hub oversize, at one of the mounting holes, to fit the extra room needed for the bigger stud, did he?  It would be a bit naughty to do so but I've seen worse bodges in my time.  Are the threads on the rivet/studs BS Cycle or UNF ?  Howard

Roger,

You need to align the front and rear wheels to the frame centre line, which is very difficult to do to any degree of accuracy with out access to fixed horizontal and vertical planes used as datums to which the frame and wheel assembly can be referred to. Straight edges don't work because one is using a 2-dimensional tool (e.g string/laser/straight edge) to check a 3-dimensional object and there is no fixed datum.

P.S I should have said the front wheel should be centred on the steering head axis by using a pointed bar through the steering column. With the bare wheel assembled in the forks minus springs and the the rim centre line marked all around the rim adjust the spokes as required to centre the rim to the pointer. Thus the front wheel (when in the straight ahead position) is now aligned to the frame centre line. The rear wheel needs aligning to the known frame centre line. A common mis-conception is thinking if the two wheels are in line with a straight edge then every thing is fine. Unfortunately it's not that simple as it's possible to achieve straight edge alignment even when the rear wheel is off centre to the frame centre-line.  

Simon.

I an thinking you have something very odd.  The three studs are not supposed to be all the same . One stud has a slightly bigger base part . This stud can normally fit in any of the three holes in the alloy hub. Its a bit confusing as you might think it needed its own special hole, it does not. It may be that a Po has made up something special for whatever reason. Its possible that you can replace the stud with the correct item if the cast iron drum has not been altered . On my hub the studs used to unscrew themselves . It might be helpfull if you were to give us some good photos of the alloy hub holes and the cast iron drum. Spare studs used to be availiable.

I find the easiest and most accurate way to line wheels up, is to get someone to ride a short way behind you, and ask them to advise if the back tyre/ wheel is equal with the front tyre /wheel. By moving slightly to the left and the right it is possible to tell if the rear wheel is lined up correctly, and if not which way to move it. 

My explanation may not seem very clear, but in practice it is very easy to do ( on a quiet road !) and from the rear looking at the wheels it is very easy to see if the bike is 'crabbing' one side or the other slightly.

Far more accurate than any other method I have used!

Regards John O

If only it was that simple. I mentioned before the priority is for the rear wheel to be in-line with the frame centre line. You can get the rear wheel in-line with the front whilst the rear wheel is off set to the frame centre-line. The result of that when ridden is a steering bias caused by the rear wheel being offset and not parallel to the frame centre line. The steering bias is counteracted by the rider turning the steering accordingly. This shows up as asymmetric  front tyre wear. Frame and rolling chassis tolerances were all over the place when new let alone what frame and wheel alignment is like 50 years down the road.

Hi Simon, I find your explanation of finding the frame centre line a bit complicated. In practice ( assuming that the front wheel is not 'twisted' in the front fork),  all we need is the rear wheel to follow the front without 'crabbing ' to ensure the bike tracks well. Quite often the various bits in the frame ( i.e. Engine/gearbox ) are not on the frame centre i.e. a Velo final drive sprocket is outboard of the clutch, the opposite of most Nortons, but it doesn't make the Velo a poor handling bike, ( but not as good a my M 50   I own both bikes so I am unbiased !)

IMHO the best way to line the front wheel to the fork pivot is to use a pair of straight edges on the stancions and fork legs, and check that no 'twist' is apparent.

Regards John O

My wheel /chain alignment issues are caused by a slight  corkscrew !  twist in the frame top rails . that sends the whole of the fork assembly off to one side and the error can be measured at the front tyre/road contact point  where it is 3/16 " out. If spirit levels are used on the frame the twist can also  be seen. Apparently many beds have this and its thought it was built in !. The bike handles well despite it,  however if you line the wheels up carefully  the chain line suffers a little.It has been suggested by a famous Triton builder that it would be better to "adjust the swinging arm pivot point on one side of the frame to compensate as getting the twist out will be very difficult. I used steel straight edges to determine the issue. Somehow the 99 still manages to leave most other bikes around the bends. 

John,

The crabbing occurs when the rear wheel is 1) not parallel to the frame centre-line  and 2) the rim centre is not in-line with the frame centre line. Achieving this state to any useful degree of accuracy with out the use of  fixed horizontal and vertical planes is virtually impossible. The engine and gearbox do not have to be on the frame centre line because they do not affect the dynamics of steering. (extreme cases excepted).

P.S I should define what the frame centre-line is. It is a line (in the plan view) projected from the steering axis which bi-sects the swinging arm axis at 90 degrees. As I mentioned before, manufacturing tolerances are all over the place.