AJS Model 30 - the 'what bits are missing' dry build

 A few days after the Model 30 kit arrived in Norfolk, it's outside in the street for a degreasing session which will help us understand what we have, what we don't have and how it goes together.

The main frame parts are all there and most of the big studs as well.

Some of them are not in great shape and will need replacing or building up with weld and the threads recutting. And option would be to buy a complete new set at vast expense but we are not there yet!

The centre stand, it's bushes, stud and spacer are all there:

Footrest bars, footrests and side stand are also there as is the spindle for the swinging arm – but the cotter pins appear to be missing:

We have two sets of fork yokes but unfortunately the steering head races are a bit worn. We will see if they need replacing later on:

AJS Model 30 - a new bike joins the family

 Well, his has been a long time coming. A few months ago, son Thomas & I conceived a plan to buy a project we could build together with the kids - to give them some hands on experience and learn some new skills. I wanted Tom to buy something he really wanted, and we looked and bid on a Sunbeam S7, a BSA B50, an A65 and looked at an Ariel NH (which was a very good deal but wasn't a project).

I'm delighted that we ended up with this, a 1958 AJS Model 30 - Tom says there is a poetical symmetry to it, since I had a 1957 example when I was at university which we sold soon after we bought our first house.

It's an eBay find, described like this:

• AJS Model 30 Project rebuild or spares.
• Frame and engine are 1958 model 30
• Was going to rebuild, but will never happen, so must go.
• Engine fully rebuilt by local AJS Model 30 club specialists 15 years ago, still turns over fine. Comes with AMC gearbox and clutch etc. and majority of all major parts to rebuild, look at photo and you’ll see what’s included.

Obvious things that are missing are the silencers, mudguards, speedo and rear shocks but if we really have a properly rebuilt engine for less than £900 we will have done well!

Main frame and wheels above and most of the rest of the cycle parts below. Siamese exhausts - a sidecar bike? The rear mudguard stay looks like one from the CS model; there's a chainguard, brake pedal, battery carrier and lots of other bits:

A box of bits, including a new looking set of engine bolts:

Another view of the same curtain - there are two tanks in the kit that arrived and we see fork legs, some very high bars, a set of yokes (one of two), headlamp shrouds, one of two headlamp shells, centre stand, a head steady, footrests, frame rails, sidestand, oil pipes, engine plates and covers and the toolbox:

A tidy 58/30 engine with dynamo, gearbox, oil tank, primaries and clutch:

We can't wait to get stuck in!

FH - update

 The FH has been the go-to bike recently, and it is shaking down again after it's 500 mile service. I'm getting on top of the carburation helped by Hitchcock's (or Amal's?) guide to tuning the Mk1 Concentric, and now that I have it ticking over with a #30 pilot jet and the pilot air screw 1/4 turn out, I might go to a #25!

It's flying along and looks great:

Notice that the rear wheel is nicely off the ground in these pictures!

The only problem is - it's still burning oil. The head is going to have to come off again to inspect the guides which is a shame, because the leaks are cured...

Model A - carburetter needs some bits...

 The Model A uses an Amal 6/112 carburettor, often known as a pre-monobloc. The Type 6 carburettor has the pilot air inlet in holes around the body and is similar to the Type 76 - the difference is that the 76 is cast alloy and the 6 is cast brass; the later Type 276 has the pilot air inlet inside the bell mouth. The float chamber design associated with each of these carburettors is also quite different in that the earlier float chamber has the extension pipe banjo retained to the float chamber itself with a screwed joint - for the 276, the extension pipe banjo is a part of the float chamber casting.

Whilst the carburettor that arrived with the Model A is complete, it is also pretty tired. The slide is very bad, the main jet is missing and we know from experience that the needle jet and needle will be very worn as well. 

The specifications are listed here:

• Size: 1"
• Main Jet: 4/042-160 (still available new)
• Pilot Jet: none
• Needle Jet: 4/061-106 (still available new)
• Needle Position: 6/065, position not recorded
• Slide: 6/0524 - that's a #4 cutaway, or 1/4"
• Float chamber: 14/004

Folk with some experience of Amal carburettors will realize that these part numbers are used for the Type 76 and Type 276 as well - and are still available from Burlen Services, or Hitchcock's Motorcycles.

I put in an order to Hitchcock's for some bits and sent the body, jet block and jet block nut to Joe the Carb on the 23rd of July:

It came back from Joe on the 8th August with a cylindrical bore, a slide to match, and he has refaced the mounting flange so that it is nice and flat. It looks like it has been vapour blasted too:

Until I make up the cables there's not much else I can do with this carburettor (other than replace all the gaskets and fibre washers), so we'll fit it back on the bike and leave it for now.

Model A - brake plates

 There hasn't been much action on the Model A lately – I have been rebuilding the top end of the Huntmaster and doing a bit of travelling. However, here is a little interlude: some while back we painted the brake plates from the Model A ready for rebuild and last year I acquired a new set of brake cams from the Slovak Klub.

You can see from the picture how bad the originals were - there was an awful lot of movement in the bush on the brake plate. Karol at the Slovak Klub supplies his replacement cams with a diameter of 13 millimeters which I thought was a problem until I realized what he was doing – if you drill out the brake cam bush on the brake plate, 13 millimeters is enough to take out most of the wear and you can fit new brake cams without replacing the bush, which saves a bit of time.

They work very well, although the square section is a bit oversize too - probably intentionally!

I had also noticed that whilst Karol's cams were identical, the old ones were not. You can see from the picture of the rear brake plate as the bike arrived that the position of the brake lever is a long way forward - too far forward:

The new cam puts the brake lever in a more sensible position.

FH - reassembly

 Having checked the pistons, looked at the big ends, camshaft and followers I was ready to put the barrel back in place.

First step is to Wellseal the barrel flange and stick a new gasket in place. I decided it will be easier to have the gasket on the barrel with well seal both sides before introducing the barrel to the crankcase.

Attempting to refit the barrel over the pistons revealed something interesting and that I had not spotted before - there is no lead-in chamfer on the bottom of these barrels making it very difficult to get the rings into the barrels. I used a half round file to make a chamfer of maybe 1 mm, much smaller than is commonly found on cylinders but it made all the difference.

The cylinder head went back on with Wellseal on both sides of the head gasket. I put the bolts in with Copperease and tightened them down as tightly as I could with a 12 in ratchet drive.

I've fitted and removed the rocker box several times now, and I know the optimum way to do it. Fit the gaskets to the head and apply your chosen sealant to both sides, then fit the rocker box from the front right direction remembering to trap the two exhaust push rods either side of the web in the middle of the inlet side.

I hope no one sees this as an act of wanton vandalism but I have removed one of the vestigial fins from below the rocker box, because they are an absolute pain. When they are in position, you have to put these two nuts on before the rockerbox sits down on its gaskets, because the shape of the casting means that you can't get the half nut on with rocker box fully down. One of these things was missing when I got the bike and I have just removed the other one.

I must remember to clean up that area next time the head is off.

With a bit more spannering, the head steadies are in place and the oil lines are connected. We will end this blog post here as this concludes the work on the replacement of the cylinder head.

Model A - painting more bits

 A rewarding but seemingly never ending job is painting bits for the Model A. The wheels are off and the brakes are currently in pieces and here we are with two brake arms and the torque arm for the front brake.

These are the two brake plates, with the paint cleaned off with a Scotchbrite wheel and coated with primer:

These bits had their second coat of black on the 31st of July 2026.

FH - carburation

 For the record, at the 500 mile service I have changed the carburetter slide on the FH for one with a #4 cutaway.

A #3 1/2 was previously fitted, and the plugs were quite dark.

It's still got a size 30 pilot jet, and for the record, the pilot air screw is about one quarter of a turn out. Perhaps I'll go to a size 25 pilot jet? 

Model A - chainguard

 The latest in a long line of broken bits waiting repair before they are painted is the chain guard. 

This is a pretty simple bit of welding. Initially the mounting nut is missing so I have replaced it with a new un-plated 1/4" CEI nut welded in underneath and I've filled in the worn hole as well:

The next bit is this gap which is a piece of material worn away as the chain rubs away at the chainguard. This is a bit more complicated.

First job is to chop it out with the Wiss snips and the Dremel. Next we can make a repair patch from a scrap of 18 gauge steel sheet cut to roughly the right shape, folded in the vice and refined with the linisher.

If you're careful, you can get it close enough to weld in without any filler rod which saves clean up time and reduces the heat (and hence distortion) going into the work. This wasn't one of those occasions, as I needed a bit of filler to close the gap at one end.

It's not too bad though.

Next is the other side - a bit that had been rubbing against the rear mudguard and worn a chunk away. That's it for the welding now.

With the paint finished it looks a lot better!

Model A - magneto chain case

 The magneto has been sitting on its platform behind the engine for some while, ever since it came back from Tony Cooper. I'd left it off because I wanted some time to look at the seal between it and the back of the gear case, and I'd also posted some questions on the AOMCC Facebook page to try and learn about the two breathers that route out of the gear case and onto the chains. This post is about those two issues.

Let's start with some pictures. This is a page from the 1930 heavyweight parts book:

Club member Michael posted these three pictures on the FB page. This is a 28 bike which is not the same as 29 or 30 but gives you a flavour of what they would have used to implement these breathers.

Emerging from the crankcase, we have a breather emerging to oil the primary chain:

The equivalent pipe on '29 and '30 bikes appears from the back of the magneto chain case as shown here:

We will use the illustration in the parts book to invent something to head cross to the primary chain from here. It will have to have something to attach to though, to stop it wobbling about.

This is I think an S21/1 oil pipe union with its associated union nut and a broken nipple. The parts book identifies two of these unions and the other one fits into a hole right underneath the magneto chain run which is not visible in the picture above, but the hole is clear and the thread is good.

These next pictures shows the rear chain oiler on Michaels '28. Below, we see the pipe emerging from the timing gear case and disappearing in front of the gearbox - mine will be similar, but it comes from the bottom of the magneto chain case as I said.

What we are seeing in the picture below is the other end of the same tube emerging from a gap in front of the gearbox and running along the frame rail under the gearbox sprocket, flicking up and over onto the chain. This is shown in the 1930 parts book picture above as item A6/683, but just to confuse you the parts book picture is upside down.

This is the relevant page of the 1930 parts book. We can see here that there are two S21/1 unions called up so we can be confident that if we can replicate the one we've got, will be good for the other. The next puzzle is to work out what the A6/120 component does.

This last picture shows the three elements of the magneto to chaincase seal. Left to right we have the retaining washer, the Vellumoid washer, and the felt washer that pushes up against the chain case. The Vellumoid washer is basically a thick gasket that sits across the front of the Magneto - Vellumoid are actually still trading as gasket manufacturers. It's all in reasonable shape and I put it back in as I found it.

SQ4 - maintenance

 After a run to Norwich today, 55 miles at 27.4 mph average speed (according to my new Beeline sat-nav) the Square started making an odd noise on the way home, a bit of a squeak from the engine sounding perhaps like a leaky head gasket. I stopped for coffee at the lovely Itteringham community shop:

After going on to reserve on the way home, I thought I would have a look at the plugs and do a compression test and the picture shows the result. All four plugs are the same colour, dark chocolate, all dry, numbers two, three and four all gapped to 18 thou but number one was gapped to more like 25-28 thou, which I corrected.  

Compression figures are good and consistent at 130-140 psi.

Restarting the engine after I had put the plugs back in revealed that the squeak had gone. Now I am worrying about the oil pressure on the last part of the trip home...

FH - oil from the drive side cylinder

 I might have mentioned a few times that the Huntmaster has been burning oil from the drive side cylinder, manifested as an oily exhaust pipe, and oily spark plug, and smoke when pulling away. It's always done this ever since rebuild. I had been hoping that this was just really bedding in but after 550 odd miles I think I have to admit there's something wrong. Since it's back in the workshop for its 500 mile service the rocker box has to come off anyway to retorque the head and we can do some investigation.

I had hoped that the rocker box drain might be blocked and excess oil being sucked down the exhaust valve guide but a poke down the drilling with a bicycle spoke reveals the hole is completely open - as I had expected since I cleared the hole out during rebuild.

Removing the head revealed this - a bit of an oily mess on the drive side (that's on the right of the picture) and a fairly normal looking though dark combustion chamber on the timing side.

And then this! That bare piston crown is the drive side, the one that is smoking. There is barely any carbon deposit there at all compared to the other side which looks quite normal to me. It should be noted that the mixture is quite rich at the moment as the mileage is not really high enough to do any proper plug chops.

This is the timing side exhaust valve.

And the drive side exhaust valve, looking a lot hotter.

Here is the upper side of the head gasket - that is the side that touches the head itself. The area within the red ring shows I think a leak from the cylinder into the head bolt drilling and possibly into the drive side exhaust valve drain. Perhaps this explains both the smoke and the oil coming from the cylinder head joint and dripping onto the primary drive case.

It pays to be careful when removing the cylinder. I released all the nuts and made sure that I collected them all with their washers and put them aside. Next we used the leather mallet to loosen the cylinder joint which was quite straightforward - not forgetting that the forward magneto pickup has to come out to remove the cylinder. 

It's wise to lift the cylinder with the pistons in their uppermost position so that you can lift the skirts above the crankcase mouth to get a couple of pieces of wood into the joint to support the weight of the cylinder. You can then introduce a suitable cloth into the gap to prevent any broken bits of ring or circlip falling into the crankcase. 

Once you have lifted off the cylinder the wooden battens can support the pistons.

Removing the cylinder very carefully reveals two pistons in very good shape - to be expected since they have only done 550 miles. The purpose of this exercise of course is to check that the rings are sound and indeed they are so we can take some comfort in the knowledge that the results of the compression test we did months ago are supported by rings which appear to be in very good condition.

Investigating the head gasket sealing area and the bolt holes reveals a couple of interesting points. Well, one main point really and that is that most of the cylinder head bolts open into a gap between the fins, a few fins below the head joint and secondly that one of the front middle two bolts doesn't pull down properly as the thread appears to be very tight. This is in the area where we suspect the leak to have been.

We will leave this for now as I have a day on the railway tomorrow and some other bits to do. I've made a post on the FH Facebook group to make sure that I've selected the right tap to clean these threads out!