Friday 31 December 2021

The AJS V-Twin: First Road Test

It is now the 31st December and definitely my last blog post of 2021. Unfortunately, the weather where I live on the South Coast of England has rained for most of the past month and although I managed a first road test a few weeks ago, it has not been possible to continue testing.

The first road test was reasonably successful. Various "issues" arose but nothing that could not be easily remedied. There are a couple of videos, shown below and taken by my buddy Ian, warming up the engine and a few adjustments prior to the road test:


and then the first foray up and down my road.


This highlighted a few problems that would need fixing; in no particular order:

1)   Clutch slip

2)   Still too much oil coming out of the cambox on the rear cylinder

3)   The rear brake didn’t work too well

4)   It’s a bit loud (!!) and mufflers are needed to take the “crack” out of the exhausts if I’m going to avoid unwanted attention from Mr Plod (a good friend of mine in Japan has just asked me who Mr Plod is..... he is a fictional policeman in childrens books in the UK - this short movie gives the general flavour).

The Clutch

I had been making continual adjustments to the clutch prior to the road test and simply assumed it was all the new components bedding in. This was not the case and when I stripped the clutch I found that the entire clutch basket + bearing was about to fall off the back of the clutch inner. Why? Well, there was a fundamental design flaw in my clutch – easily remedied but could have been catastrophic.

I had made the clutch with a backplate that was fixed to the clutch basket with 3x ¼” set screws that was intended to both keep out road dirt and to prevent any axial movement between the bearing and the basket, shown in the picture below with the backplate removed.

Whilst the backplate successfully prevented any movement between the bearing outer and the basket I had not provided any means of preventing movement between the clutch centre and the bearing inner. A consequence of this was that the pressure from the clutch springs was forcing the basket + bearing away from the inner towards the final drive chain.

A straightforward modification was to tap 3 additional holes in the clutch inner and attach a second backplate as shown below.

I have also now lockwired the set screws as the consequence of any of these coming lose would have a bad outcome.

Rear Cylinder Cambox Oiling

It took me some time to sort out the cambox oiling on the AJcette and I have been expecting the same issues on the V-Twin – but worse because of the +/- 25 degrees of the cylinders. It had already become apparent that I needed to dump most of the oil from the oil pump into the crankcase to reduce the pressure upstream of the cambox flow restrictors but the 0 – 80 psi pressure gauge that I had fitted was now nearly useless as it needed to operate at around 5 psi. The pressure gauge was therefore changed to one giving 30 psi Full Scale Deflection.

As the pump can easily deliver more than 60 psi oil pressure I will have to be careful never to close the dump valve too far to avoid damaging the pressure gauge. Although 5 psi is still close to the bottom of the measurement range at least I can now see the needle move away from zero.

The other and more significant modification is that the rear cylinder oil drain that previously connected one of the cambox oil gutters to the inlet valve/guide, shown in the picture below

has now been connected with the oil drain pipes from the other cambox gutters to feed into the rear cylinder cambox scavenge pump.

I am hoping that this will positively scavenge the excess oil that currently cascades out of the slot for the inlet tappet in the cambox.


The Rear Brake

The Royal Enfield rear hub that I have fitted to the AJS was used on a number of bikes in the 1920, most notably Nortons and Broughs. Two of my Model 18 Nortons have this hub (the 1928 and the 1929) and the brake on both is excellent and I had no reason to think that the one fitted to this bike would be any different. However, on its brief first foray up and down the road I had difficulty in stopping and it was clear that a bit of attention was needed.

I re-examined the setup that I had put on the 1928 Norton and concluded that the AJS did not have sufficient leverage as a result of using a brake arm that was too long. The one that I had fitted was an eBay item from a BSA C15 and so another was bought and fitted with the distance between centres reduced from 3” to 2”, seen below.

This, together with a positive stop for the brake made to fit on the brake rod

has provided a much better “feel” to the brake with the bike on the bench and I am optimistic that it might actually stop the bike on the next road test.



I don’t really want to attract undue attention when riding the bike and, although I can avoid riding through built-up areas, with open exhausts it is really a bit too loud for road use.

I run with a straight pipe on a number of my other vintage bikes and the easiest way to make them (nearly) acceptably quiet without changing the appearance is to weld a clamp to an exhaust muffler and insert that into the end of the pipe.

It is painted black because, although the clamp itself is made of stainless steel, the muffler is mild steel and would otherwise quickly go rusty after welding.

The muffler, shown in the picture below together with the brake stop, can be inserted/removed in about 20 seconds

Further testing will now have to wait until the weather improves – I live on top of a hill and our road is again shrouded in low cloud and raining; I’ll report on the next test when the weather improves.

In the meantime, there are plenty of other things to get on with in the workshop. I have just done one job that I had put off for a long time, namely recommissioning a Velocette Thruxton that I restored many years ago and then dumped in the garage because it lost compression; it still has a UK Road Tax disk from 2011!

After stripping the top-end of the engine it was clear that there was too much piston/bore clearance and, as the barrel was on the upper limit of rebores I fitted a new barrel and piston from Grove Classics.

I had been using a Mk 2 Amal Concentric on the bike and as I had acquired the correct 1 3/8” Amal T5GP2 carburettor in the intervening years, decided that I would fit that at the same time. After fitting the correct slide and jets and a remote Type 510 Matchbox Float Chamber (the fuel level has to be set precisely with the carburettor using this type of float chamber – it’s hidden on the other side of the carb in the picture below)

and some other basic recommissioning the bike was ready for its first start after more than 10 years.

I’m pleased to report that it started first time on the rollers and sounded pretty good; plenty of compression, as one would expect with a new barrel and piston, and very responsive on the throttle. And so I now have 2 bikes waiting for better weather for road testing.

And so, what to do in the workshop for the rest of the winter? As I believe I mentioned in a previous blog I have plenty (too many?) more project bikes awaiting restoration – 5 early cammy Velos, including KTT 55 and KTT 305, a 1933 AJS OHC 33/7 Trophy model and 2x early AJS Big Ports. I acquired these during my working life for my retirement; the challenge now is to live long enough to get them done!

Anyway, I’ve decided that my next project will be to bring the AJS 33/7 back to life and it’s already up on the bench for a first assessment.

I’ll start reporting on this restoration in the New Year.

In the meantime, I wish everyone that reads my blog a Happy and Safe 2022

Friday 12 November 2021

The AJS V-Twin: First Start

One of the first jobs to do before wheeling the bike out of the workshop for the first start was to make a detachable prop stand. I did not want a stand as a permanent fixture on the bike as it would be somewhat out of place, even if it is a replica, of a bike intended for an attempt on the World Speed Record. There is also not much space to fit a stand.

Although I had a paddock stand, seen in pictures in my last blog posting, this needs 2 people to be used safely and is not ideal if I am alone. It’s also not feasible to carry a paddock stand around if out for a ride! I therefore constructed a prop stand to go onto the nearside footrest that can be easily detached and carried in a rucksack. The bike stands well on this.

The stand itself consists of 2 pieces of aluminium, shown in the pictures below with the bike on the ramp and before chamfering the top and bottom surfaces.


Time to start the bike!

My good buddy John Taylor came round to help (John has been a constant source of encouragement throughout the project – Thanks Mate) and we put the bike on the starting rollers …and, with my wife on the phone camera, the bike fired up for the first time.

Well, it was a great relief that it actually runs! …and with no discernible vibration (the effort on the crankshaft design and manufacture has paid off). However, that was the one and only run; the bike would not start for a second time. It’s not difficult to see that the engine was somewhat reluctant to start at all and would only run on 2 cylinders at higher engine speeds and with full ignition advance.

Now, it is well known (at least, if you have a V-Twin) that V-Twin magnetos can be problematical in the respect that you can get one good spark and one considerably weaker spark (see eg for an explanation in the context of K2F magnetos on Vincent twins). There was certainly evidence of this here in the respect of only wanting to run on one cylinder at lower speeds and with the ignition in the fully advanced position.

As I am now 70 years old, my days of push starting a substantial motorcycle by running alongside, dropping the clutch (or valve lifter) and jumping on are over! The bike has to be able to start using the kick-start. I owned a Vincent Black Shadow for many years and had the same issue with starting in the respect that the bike would only fire on one cylinder at low speeds. I replaced the original Lucas K2F magneto with a new BTH self-generating magneto and this absolutely transformed starting – one lazy kick on the kick-start and the engine would fire instantly.  I therefore decided to fit one of these on the AJS. BTH make magnetos in a variety of shapes and sizes and I ordered a 50 degree, base-mounted, anti-clockwise rotation, 45mm spindle height self-generating magneto to replace the 50 degree BTH magneto that I had originally fitted

The new magneto, on the left in the above picture, is slightly larger than the original but the important dimensions – distance of spindle taper to flange, securing bolt threads and location on the base and spindle height are identical and the new magneto bolted straight on.

with perfect chain alignment. It is extremely easy to set up: the magneto is locked with the 6mm spindle (seen inserted in the hole – the brass blanking screw has been temporarily removed) and the crankshaft position set to give the desired fully-advanced timing (36 BTDC) on the rear cylinder. As I had made Vernier adjusters to set both the valve and ignition timings all that was now needed was to make sure the upper run of the chain was in tension and to insert the pinned washer through both sets of aligned holes. Job done. The electronics takes care of the ignition advance vs rpm with a pre-programmed curve .

The magneto uses external coils and a small junction box which need to be packaged neatly – yet to be done.

After reassembling the timing cases, oil pumps etc.. it was time for another start. The 2nd start is not captured on film (the Chief Photographer had gone shopping) but I can report that the bike fired instantly on the rollers and we were able to check the oil return to the tank and to play around with the tap that controls the oil pressure in the line that supplies oil to the camboxes and the crankshaft via the crankcase drilling.

With the tap fully open, there is free flow to the pipe that delivers oil directly into the crankcase between the cylinders and the pressure gauge registered at the bottom of the scale at about 5 psi.

With the tap fully closed, all oil from the feed pump goes into both the vertical drilling that connects with the crankshaft and the supply to the camboxes (the pipe on the right side in the above picture delivers oil to the flow restrictors at the camboxes) and there is substantial oil pressure at around 60 psi.

It didn’t take long to realize that the tap-closed position delivered far too much oil to the camboxes and it came cascading out of the gap between the rocker and the cambox on the front exhaust and the rear inlet. This was not really surprising for 2 reasons: firstly, I had only inserted a single 0.6mm diameter orifice into each flow restrictor (the AJcette has 2 orifices in series) and, secondly, a consequence of the orientation of a 50 degree V-Twin means that the oil can more easily exit the cambox because of the orientation at +/- 25 degrees of the rear cylinder inlet and the front cylinder exhaust .

The single flow restrictor was therefore replaced with 2x 0.6mm orifices in series, shown below at the far left of the picture. These have been drilled at different radii to ensure that the upstream hole cannot feed directly into the downstream hole. The fibre washers provide both sealing and, in the case of the restrictor plates, allow a small, narrow plenum to exist between the holes.

With the new BTH magneto fitted and the revised flow restrictors in place it was time for the next test.

The bike would now start on the kickstart, I have balanced the carbs, the engine will idle and oil no longer pours out of the camboxes, although this will require some further calibration and checks.

Overall, a successful set of test runs and it shouldn’t be too long before I can start road testing.