Ajs 16 Trials Project

[tyrefryer]

Hi everyone, I've just bought my first AMC bike which is an AJS 16 that's been built as a trials (style) bike. A fair bit has been done to it but there is also a lot I need to sort out and improve upon. The plan is to use it for some road trials like the Arbuthnot, some rides out with my local VMCC sections and a bit of playing around at my trials club's local practice ground. I'm not looking to use it for serious pre-65 competition use.

From what I can tell so far, it's quite a bit of a bitsa. I believe the frame is a 1959 but the engine may be earlier as it has a pressed steel primary chaincase and magneto with manual retard control. I was also told that the crankcases are from a G80. I'd be happy if anyone can shed further light on what I have.

I've started sorting through all the immediate problems I can, I've adjusted the primary chain tension, re-assembled the gearbox adjuster the right way around, corrected the timing and adjusted the carburetor so that it will run. However there is one major problem I need to sort out before I can start using the bike.

The rear chain is way too loose and the rear wheel is adjusted as far back as it will go but before I shorten the chain I need to sort out why the rear chain is rubbing on top of the swing arm where it pivots in the frame. This has obviously been happening for some time as there are shallow grooves worn in the swingarm by the chain. The cause for this amy be due to any of the following or a combination of more than one:

1. The gearbox sprocket is 16 teeth.

2. The rear wheel sprocket is 42 teeth.

3. The frame and swingarm are from a road bike as far as I'm aware.

4. Girling gas shocks have been fitted.

5. Aluminium engine plates have been made up and fitted.

The pivot point of the swingarm seems too high compared to the gearbox and rear sprocket. I've looked at pictures of other AMC trials bikes and the angle of the swingarm and length of the rear shocks look the same as mine? Also the mounting of the gearbox on my bike doesn't look any lower? Also I understand that the gearbox and rear wheel sprocket sizes I have are the same as was standard for trials bikes?

If anyone can advise me on what could be wrong I'd be really grateful because at the moment I'm stumped!

Thanks for reading, Martin.

[totalshell]

blimy apart from jampots and the oil tank i thought it was my 16.. the chain rub on the swing arm is simply because the rear sprocket front sprocket sizes, shock length means the chain is having to go up and over the swinging arm,, get a piece of nirte and fix iit to the top as a 'slipper' my jampots are very short compared to your modern shocks..i believe my bike is a 53 off the top of my head.

[tyrefryer]

Thanks for that, I did wonder if something like what I've got on my Sherco swingarm might be the answer. Is "nirte" what it's really called or is that a typo and where can I pick some up?

Cheers, Martin.

[tyrefryer]

Just found these on Ebay, are they the sort of thing you mean?

http://www.ebay.co.uk/itm/UNIVERSAL-CHAIN-SLIPPER-PRE-65-TRIALS-PROJECT-BIKE-TIGER-CUB-ARIEL-HT-C15-b-/400584932464?pt=UK_Motorcycle_Parts&hash=item5d44b8fc70

http://www.ebay.co.uk/itm/UNIVERSAL-CHAIN-SLIPPER-PRE-65-TRIALS-PROJECT-BIKE-TIGER-CUB-ARIEL-HT-C15-/161194768070?pt=UK_Motorcycle_Parts&hash=item2587f4f6c6

Cheers.

[totalshell]

ys looks like they ll do the job. remember that the original trials bikes had 19 inch rear wheels and the road bikes even bigger so with the 18 inch rim you ve lowered the height of the top edge of the rear sprocket.. a bigger sprokect would not only make the bike more usable but give more clearance.

.nitrite is the plastics proper name.. not a typo sadly.. following a little 'episode' words can look right to me but to you they are plainly bonkers!

[laird387]

Hi,

The use of the rubbing blocks will stop the chain from eventually cutting through the swinging arm pivot - so I would go for that every time.

The nub of the problem is because the 16C was fitted with a 4.00 x 19 Trials Universal from new - but the all the two-strokes went to 4.00 x 18 so now none of the tyre manufacturers make a trials 4.00 x 19.

The not so clever solution (as seen on your bike) is to fit a slightly longer rear suspension unit to try and get ground clearance better that way........

Now let's look at the practicalities, when Ian Rennie and myself recreated the Arbuthnot (it had disappeared from the trials calendar in 1929) we made it for rigid machines, and the sections were selected accordingly - and your machine, even as it stands today should give you a very good day out, similarly in the Talmag next January and quite a few of the Sammy Miller series. I agree it would be a handful, compared to most, in one of the 'so-called' pre-65 trials these days, because they have thrown away the eligibility rules that worked so well for the first twelve years after John Smith, Derek Lord and myself created the first ever pre-65 trial, the Shawforth Shake - and now they have created a sport for men with very deep pockets....

Sadly far too many are drawn into the sport without realising that if you have not got the necessary riding ability, whether you are riding an old nail or a multi-thousand pound fiddle replica, you still won't win.........

You can't buy ability.

So ride your bike purely for the fun and meeting people and getting to many places you might never think of going to otherwise. If you want a correct fully illustrated breakdown of all the popular British trials models produced by AMC, BSA, Ariel, Norton, Triumph, DOT, Greeves, Cotton, etc., with plenty of technical detail then watch developments in ORRe - because we did just that in Off-Road Review years ago - and now it is being revised, brought up to date and extended with hundreds of photographs never seen before.

Enjoy - and in the meantime, here is an image that you might enjoy - taken from a recent issue of ORRe. I'm afraid if you want to see it without the watermark - or even would like a free copy - then you'll have to subscribe.

[tyrefryer]

Thanks totalshell and Derek that's all interesting stuff, I'm beginning to get a much better understanding now. I initially thought that the problem was due to the swingarm angle being pushed down by the shocks being too long but I have a copy of Classic Bike from January 1982 featuring the Gordon Jackson AJS. In the pictures that has what I thought were the same rear shocks and the swingarm angle looked the same as mine (parallel with the bolted on tube under the seat) but there isn't a picture of the drive side of the bike. However it's now apparent (thanks to a member on the AJS and Matchless forum) that the Gordon Jackson shocks are 12 coils and mine are longer at 14. And possibly the rear wheel was a 19" in 1982?

I'll start with a slipper for the swingarm and then consider a larger rear sprocket and maybe shorter rear shocks. I have to check but I thought the rear sprocket was part of the brake drum and not separate? (A member on the AJS forum was running a 50 tooth rear sprocket).

Cheers.

Edited September 17, 2014 by tyrefryer

[jon v8]

"You cant buy ability" - Truest statement ever made in reference to trials ! I would go for the shorter rear shocks,never mind about ground clearance,lift the front wheel if necessary.I've ridden a few jacked up pre 65 bikes that are horrible,they are massively top heavy and just want to fall over as soon as they get a couple of degrees off vertical.Then you are fighting the weight and not concentrating on steering/where you are going.Plus when it starts to get out of control in a sticky situation you have much less chance of getting it back.

You simply cant get past the fact that all the pre unit engines are very tall and very heavy - with little chance to reduce either.I'd rather keep the weight down low and spend time,effort and if necessary money on getting the engine to run sweetly and reliably.Then attend to gearing,clutch action and making the brakes work.

With practice its suprising where you can get heavy old bikes to go,and its VERY satisfying to get lower scores than riders of lightweights - its a good challenge.Whatever you do with it,dont give up,it will be another old bike out being used .

[tyrefryer]

Thanks Jon, I've ordered the slipper and am now making a list of the cables I need to replace and sorting out the controls while I'm waiting for it to arrive. The choke is missing, the valve lifter was in the wrong place and the cable was broken and I've moved the mag retard control to the left instead of the right where the choke lever is going.

[laird387]

Thanks totalshell and Derek that's all interesting stuff, I'm beginning to get a much better understanding now. I initially thought that the problem was due to the swingarm angle being pushed down by the shocks being too long but I have a copy of Classic Bike from January 1982 featuring the Gordon Jackson AJS. In the pictures that has what I thought were the same rear shocks and the swingarm angle looked the same as mine (parallel with the bolted on tube under the seat) but there isn't a picture of the drive side of the bike. However it's now apparent (thanks to a member on the AJS and Matchless forum) that the Gordon Jackson shocks are 12 coils and mine are longer at 14. And possibly the rear wheel was a 19" in 1982?

I'll start with a slipper for the swingarm and then consider a larger rear sprocket and maybe shorter rear shocks. I have to check but I thought the rear sprocket was part of the brake drum and not separate? (A member on the AJS forum was running a 50 tooth rear sprocket).

Cheers.

Hi Tyrefryer,

Please don't use that Classic Bike picture, I promise you that I know what happened to Gordon's 1961 winning bike, (the one that is depicted in its new colour scheme before the start of the 1962 SSDT in the image that I used). The model shown on the cover of the other magazine is not the actual model.......

Look at the rear mudguard stay - and, by the way, the number of coils on the rear suspension is determined by the required spring poundage and the diameter or gauge of wire used in creating the spring - you could always check with Norman Blakemore at NBG - I know he knows.

Jon is spot on with his advice on using shorter shocks.

Deryk.

Edited September 17, 2014 by laird387

[tyrefryer]

Thanks again for the info and advice Deryk, I'll have a search for some shorter shocks.

Is it best to stick with Girling gas shocks and how should I determine the best length?

Thanks, Martin.

[laird387]

Thanks again for the info and advice Deryk, I'll have a search for some shorter shocks.

Is it best to stick with Girling gas shocks and how should I determine the best length?

Thanks, Martin.

Hi,

I have no preference for type of shock these days but to determine length balance bike on box so that wheels are clear of the ground, disconnect rear shock then raise wheel until chain just clears the rear spindle housing, support it there then measure distance between top and bottom shock mounts. That gives you the length - then speak to someone who knows - here I would seriously recommend Norman Blakemore at NBG shocks - who used to work for Girlings and he will ask your weight, bike's weight and make a calculation for you for the optimum spring poundage.

Cheers

Deryk

[tyrefryer]

Thanks Deryk that's excellent info, I'll have a measure up tomorrow and give Norman a call.

[scramblebike]

hi tyrefryer when all said and done you have a nice looking bike. enjoy.

[tyrefryer]

Thanks scramblebike, I'm enjoying learning about the marque and tinkering and I can't wait to start using it.