Docking an F-frame Moulton

Many owners remove the rear rack of their F-frame and then cut off the “spike” of the main frame that supports it. This certainly makes the bike lighter and gives it a more modern look (possibly even more so than a spaceframe), but is it a good thing for the long-term health of the frame?

Alex Moulton never approved of docked frames, but didn’t give a reason for this. The record-winning Moulton Speed ridden by John Woodburn from Cardiff to London was docked, and Alex Moulton was reportedly not happy when he found out, possibly because he wanted to show what could be done with something looking like a bike that the public could buy; he was trying to sell them, after all.

This is more of an engineering examination rather than a marketing one but first, a little history. The very earliest 1963 F-frames had a rack with only a top strut, from the seat cluster to the front of the rack. These suffered from bent rear spikes if the rack was heavily loaded, so the lower, adjustable strut and “foot” were soon added. In this case it appears that the top strut was mainly intended to support the rack. The spike itself is hardly of a shape and size designed to help support the extended seat tube and prevent it from bending backwards. This means that the top strut was designed to act in tension, and the thin flattened ends and lightweight tubing used also bear this out.

The lower strut, when added, was clearly designed to act in compression to support the rack and transfer some of the load to the main frame. The lower strut is also of heavier tubing and with more substantial ends.

So the upper strut was not designed to act in compression, which is the only way that it can help support the seat tube. However, we need to answer two further questions: can it act in compression, and does it?

The answer to the first question is yes. The strut is not slender enough to suffer from Euler buckling (although the flattened ends complicate any accurate calculation of the critical buckling load) and even the light gauge mild steel tube used is strong enough in compression not to suffer from shear failure, even by a heavy rider pushing hard on an ascent. The safety factor is several times the likely load.

The answer to the second question is also yes. Although the top strut may have been designed to act in tension, a simple experiment shows that it is in compression when being ridden. Tap the strut with something non-marking, like a wooden spoon, and note the sound it makes. Now lean hard on the saddle, or have a friend sit on the bike, tap it again, and notice how the tone changes. The strut is clearly compressed by the seat tube trying to bend backwards.

The original bikes with only a top strut may not often have put the strut into compression with a heavy load on the rack, since the spike would have bent (hopefully elastically) away from the seat tube and the top strut would have started in tension, pulling on the seat tube rather than supporting it. Only when the seat tube bent substantially would the strut have gone into compression. Add the lower strut, however, and the spike cannot bend at all at its midpoint, meaning the top strut is pushing against something fixed.

So the final question is: does it matter? With no reinforcing struts, the seat tube will undoubtedly flex backwards to a greater extent if a rider sits in the saddle and pedals hard, for instance when climbing a steep hill in bottom gear. Does this increase the likelihood of a fatigue fracture at the pierced seat tube joint?

My view is that it does increase the risk but (as with all risks) it may be one worth taking, if there are mitigating factors such as:

• A well-built frame will have a better-brazed joint than a sloppily-built Kirkby special
• A low mileage frame will not have accumulated fatigue at the joint (steel, in theory, has a fatigue limit, but in practice it is of little use if the tubing is overheated in construction or the frame design is not very stiff)
• A light rider will cause less stress than a heavy rider
• A standing climbing style puts no stress on the joint
• Series 1 bikes have a seat tube which is stiffer fore-and-aft (the seat tube was turned through 90 degrees for series 2, presumably to increase bottom bracket stiffness) and therefore resists the weight of the rider better

If you do decide to dock the frame, I have two recommendations:

• Don’t cut off the whole spike – leave two inches of it in place. People who have cut the spike right up to the seat tube have experienced early failure of the frame, because the brazed joint is weakened. The joint must remain fully intact.
• Have the cut end capped with a brazed-in steel plate. This does three things: it keeps water and dirt out of the tube, it stiffens it by resisting squashing of the oval section, and it looks a lot better.

Oh, and don’t forget to replace the two self-tapping screws that used to hold the foot of the lower strut to the main frame spar; they also retain the rear suspension block!

Moulton F-frame racks and bags

Rear rack types

All Moulton series 1 and 2 F-frames originally came with a large rear rack which is removable but only for repair or replacement; the bike was never designed to be ridden without it. The rear “spike” that supports the rack cannot be removed on these bikes and, in most cases, the bracing struts for the rack may also brace the seat tube against bending backward (I’ll do a separate blog on this, and whether a frame can be “docked”).

Rear racks come in two types of which I am aware. Most bikes have a completely tubular rack that attaches to the frame in four ways:

• A one-piece clamp which is slid forwards along the spike and then tightened
• A small self-tapping screw under the very rear of the rack
• An bolt-in upper strut, the other end of which attaches to the seat clamp
• A bolt-in lower strut, the other end of which sits on the main frame spar just in front of the suspension block. The “foot” at this end is adjustable to ensure the strut is tight between the rack and the main spar.

Later bikes have upper and lower struts permanently brazed to the frame. The racks for these simply attach with a two-bolt clamp, not unlike a scaffolding clamp. The racks themselves are largely made from U-shaped steel channel sections, no doubt cheaper than the tubes previously used.

The carrying capacity of a rear rack is a substantial 50lb, provided it is securely fitted, with the struts helping to take a share of the load. This is enough for a weekend’s camping, if you can find space to fit that much gear onto it. Nevertheless, many are bent through careless handling or from use as a child seat; most children big enough to ride a Moulton had friends who weighed more than 50lb! The tubular ones can be straightened quite successfully by hand (a clamping workbench helps) if you have a feel for metal and a good eye. The U-channels are more difficult, although at least the outer parts, most likely to be bent, are still tubes.

Front rack types

There are two types of front rack. The first only fits early series 1 bikes made up to sometime in 1964:

The later, more common (but more desirable!) type fits series 2 and even series 3 bikes made from 1964 onwards:

All front racks fasten in the same way: a long bolt through the two lower mounting tubes and the two unthreaded bosses on the main spar of the frame, with a short bolt through the top mounting tube into the head tube of the bike. The threading of the long bolt doesn’t matter as long as it fits through the holes, and the length isn’t particularly critical either as long as it doesn’t snag your legs. The short bolt is 1/4″ BSF and must be exactly the right length to pass through a washer, the rack tube and the head tube boss of the frame without fouling the steerer tube inside. The correct length is 1″, assuming a 1/16″ washer is used.

The difference between early and late racks is because the head tube boss on earlier bikes is much further up the head tube (178mm from the bottom of the head tube). On later bikes this distance is only 110mm. I don’t know whether the design was changed for a neater appearance or whether there was a structural benefit to the lower top bolt. The “low bolt” type adds an extra vertical stay, which the “high bolt” type doesn’t need since the load is taken by straight diagonal tubes.

Front racks came as standard on the Deluxe and Safari models but were otherwise optional, so are somewhat rare and expensive. A reconditioned front rack like the ones in the photos above (sandblasted and powdercoated) will cost around £75, whereas rear racks are comparatively cheap.

Some reproduction front racks were made by a Moulton club member for a while. The only one of these I’ve seen had a slightly shorter tube for the top bolt; use the original bolt at your peril, as it will foul the steerer! The genuine racks have a tube 0.830″ long (53/64″).

Front racks have a capacity of 20lb. The bags are much smaller than at the rear, so this is quite reasonable.

Bags

Moulton offered front and rear bags made by Arrowsmith. Not many of these still exist in usable condition. They were made of a plastic material, probably PVC, stiffened internally with something not dissimilar to cardboard. If a good one ever does come up for sale, it will not be cheap. The original bags were designed to fill the available space by sloping towards the frame (following the line of the head tube and the upper rack strut respectively), so they are wider at the top than at the base.

A Carradice Super C rack bag, or most other rack bags that attach with velcro straps, can be used on the rear. The bags for Raleigh Twenties/ RSW do not fit well, although they are a superficially similar shape; the mounting straps are all in the wrong position. Some small rack packs will also fit the front rack, but you will need to carefully check mounting straps first.

The best solution involves making new bags using either an original design or an original Moulton bag (however knackered) as a pattern. My front bag is a copy, in black Halley Stevenson 18oz canvas (same as Carradice “cotton duck”), of a bag that was handmade by a Moulton club member some years ago. It has a pocket in the base which tightly slips over the rack, holding the bag very securely in place, and is prevented from coming off by two short straps at the head tube end. The rear bag is a copy of an actual Arrowsmith rear bag, again in the 18ox canvas material but stiffened with HDPE sheet so that it keeps its boxy shape, just as the originals were stiffened with card. The bags are far higher quality than the originals, are waterproof and can be repaired with a needle and thread.

Since my sewing skills only extend to sewing on buttons and (badly) darning old saddlebags, my bags were made by Jon at Mack Workshop. His rates are very reasonable and he no doubt still has the patterns he made for these bags.

Threading on Moulton F-frames

A blog on threading? Obsessive, or what?

Well, no. Take a Moulton F-frame to a well-equipped bike mechanic, or a framebuilder or repainter not familiar with them, and it could well end up ruined. The threads on these bikes are mostly archaic imperial standards, and three different standards to boot. Force a metric bolt into a hole, or run a metric tap through it, and the bike will not be the same again.

Imperial threads – yuck!

Well, not really. Metric threads are convenient and work well for most purposes. You can buy metric fasteners anywhere, and the sizing is very straightforward: M6 has a 6mm outside diameter (well, nominally; an M6 bolt will drop through a 6mm hole nicely), the thread angle is always 60 degrees with flattened crests, and the pitch varies according to diameter to keep things in proportion. For most applications, a metric thread will give good holding power, not be too prone to stripping, and won’t vibrate loose.

Imperial threads, on the other hand, come in a plethora of different standards depending on the intended use. BSC is for bicycles and motorcycles as it is more resistant to loosening through vibration. BSW is the standard coarse Whitworth thread, BSF is for smaller threads with a finer pitch, BSP is for pipework to give sealing properties, and there are still others, like British Brass. Then there is BA (British Association), a British metric thread (really: 0BA is M6 but with a different thread angle and shape), often used in small assemblies and scientific instruments.

In many cases, the imperial thread does a better job or is available in a more suitable size. Metric fasteners are rare in some odd-numbered sizes like M7 and M9. Nor is metric threading especially foolproof: just as we have BSW and BSF, metric fasteners often vary in pitch. An M6 bolt is usually 1mm pitch but it can be M6 (fine) which has a 0.75mm pitch. Generally, “M” then an integer means the thread is the “standard” pitch. If the thread is finer or coarser than this, it should be specified M6 x 0.75 (or whatever) but this isn’t always done. There are at least three pitches for M12, as I once found when trying to get a replacement Nyloc nut for a Mazda steering wheel, where the manual just said “12mm nut”. In the end I bought all three and used the one that fitted. So all that BSW and BSF stuff doesn’t look so silly now.

Nevertheless, imperial threads aren’t used on new bikes – except for some BSC threads, which have been adopted into ISO – and your average mechanic won’t come across them very often.

So here are the threads on a Moulton series 1 or 2 (and a cautionary note or two about series 3), based on my own research and measurement. Disclaimer: threads wear and corrode over the years and may measure up a little differently to specification. I have looked at all the likely candidates and these are the best possible matches. Where possible, I have tried a new bolt or nut of the size to confirm.

The threads

Headset threads: 1″ BSC/ISO, 24 threads per inch (tpi). Series 3 bikes may have Raleigh threading, which is 1″ 26tpi. Test first with an ISO adjustable race, carefully.

Fork rebound stop retaining screw (if you round it off or have to drill it out): 2BA. However, the only other use of a 2BA Philips head screw I know of is for the distributor mount on a Triumph motorcycle. You may have to settle for a slotted head, rendering your long Philips screwdriver redundant after taking the fork apart.

Mudguard eyelets and stay-to-blade fixings: 2BA. 2BA nuts have their own series of across-flat dimensions for hex heads and none of your AF or metric spanners will fit well on the backnuts. A 2BA socket is useful to have.

Front hub axle, if original, 5/16″ BSC.

Bottom bracket: BSC/ISO, 24 tpi. Often erroneously called BSA. Still used on most new bikes. Series 3 Moultons have Raleigh 26tpi threading which can be a real problem, since no new cups have been made in this threading since the 1980s.

Front rack head tube mounting bolt: 1/4″ BSF.

Rear hub axle (Sturmey-Archer), 13/32″, 26tpi.

Rear hub axle (Sachs Duomatic 102), FG10,5. This is a German bicycle thread (Fahrradgewinde), 10.5mm diameter with a 26tpi imperial pitch!

Rear hub axle (Sachs Duomatic R2110), FG9,5.

Seat pinch bolt and rack clamp bolt (where rack has an integral clamp that must be slid over the frame “spike”): 5/16″ BSC. An M8 seat pinchbolt will fit very nicely as a metric alternative, although you can usually only squeeze M7 into the rack clamp. The original bolt in the rack clamp was so tight a fit that it is usually found to be bent when removed.

Rack clamp (very late 2-bolt fixing using a separate clamp and a rack made from U-shaped pressings): 1/4″ BSF. It doesn’t appear that Philips head bolts are available in this threading any more, so you will need to settle for hex heads.

Rear rack light bracket boss: 1/4″ BSF.

Self-tapping screws for the “foot” of the lower rack strut (also attach the suspension block to the rear frame): No.10.

Self-tapping screw underneath the very rear of the rack, attaching it to the “spike”: I confess I’ve never been able to extract one in good enough condition. Possibly no.8, although I just run a drill through it to enlarge the hole enough for a no.10. It’s not as if it shows, and a bigger screw helps, as it is the only thing that positively locks the rack in a horizontal position.

A comparison of three rear pivots

Suspension on a road bike is difficult, as road bikes need to be light and need to be ridden up hills as well as down, quite fast. Nor do they need much travel, since even West Berkshire Council roads aren’t as rough as the sort of stuff mountain bikes have to cope with. Yet, scale down MTB suspension and you don’t really end up with anything lighter.

Moultons and Bromptons therefore use a very simple form of rear suspension, with a single pivot and a lump of rubber that gets squashed (Brompton) or squashed and sheared (Moulton) to provide shock absorption and some degree of inherent damping due to the hysteresis of rubber. In fact, Bromptons use it more as a method to maintain contact between main frame and rear triangle without it coming apart and clanking on bumps, which the very hard aftermarket suspension blocks do permit!

(Hysteresis, in this context, is when something returns to its original state but doesn’t return all the energy it absorbed in the first place. Something like a Super Ball has very low hysteresis and will bounce almost as high the distance it was dropped from, but rubber used in suspensions is designed to absorb far more energy, preventing the bike from bouncing more than once).

The pivot on an F-frame, TSR and a Brompton is of very similar design, with two bushes pressed into a tube in the main frame, a steel sleeve that can freely turn in the bushes, and a bolt (or bolts) to pinch the sleeve tightly between the “ears” of a rear frame assembly.

In service, the F-frame pivot gives very little trouble except being somewhat hard to overhaul. The Brompton pivot deteriorates in use but is surprisingly long-lived. The TSR pivot is a flawed design and can wear out quickly, causing poor derailleur gear indexing or noise as the rear end floats from side to side. This is especially unfortunate, since F-frame Moultons and Bromptons, normally fitted with hub gears, would be more tolerant of rear end play.

TSR rear pivot assembly. This one wore out in about a year of moderate use. The bush with the black finish was loose in the frame and has probably been rotating in use. Not very satisfactory. The frame tube is probably enlarged now, which means trying to have it fixed by a framebuilder, or fitting a new bush with a beer can shim. Not acceptable on a £2,500 bike only a year old.

Dimensions

The Brompton sleeve is 3/8″ diameter, the pivot tube is 15/32″ and the bushes are only 3/8″ deep. Total bearing area is therefore 0.88 square inches. The bushes are 06DX06 glacier bearings, nylon-faced with grease pockets on a brass carrier with a steel backing – quite complex! They cost about £1.50 each from a bearing supplier.

The TSR sleeve is 1/2″ diameter, the pivot tube is 3/4″ and the bushes are 0.475″ deep (they’re not a round fraction of an inch because they are a standard industrial part, machined a little thinner by Moulton). Total bearing area is therefore 1.49 square inches. The bushes are Oilite porous bronze. You can’t buy them off-the shelf due to the thinner machined flange, except as part of the Moulton pivot kit. TSRs have a grease nipple for the pivot, and it should be used quite frequently to exclude dirt. Oilite bushes are theoretically pre-lubricated for life but the bottom of a bike is a filthy environment.

The F-frame sleeve is 7/16″ diameter, the pivot tube is 5/8″ and the bushes are 7/8″ deep. Total bearing area is a stonking 2.40 square inches. The bushes are usually some kind of nylon, although early bikes used bronze.

Good pivot, bad pivot

So we can see that the F-frame pivot has the biggest surface area, and this partly explains why it lasts well. Another reason is that it is attached to the same main frame as the bottom bracket, so each lunge of the pedals doesn’t try to rip the pivot apart.

The tiny Brompton pivot lasts better than the TSR’s, though, so it’s not all about size. There are other differences:

• The Brompton pivot adds thin, slightly compressible, nylon washers between the rear frame and the main frame. This makes the length of the pivot sleeve less critical and helps to exclude dirt from the pivot.
• Despite the small size, the glacier bearings used have a huge load capacity.
• The Brompton pivot is more-or-less on the frame centreline. The TSR’s isn’t; it was offset to the side to provide space for a triple chainset to be used.
• Small manufacturing tolerances in the bushes and pivot tube of a TSR can make the sleeve too tight or too loose when new or, worse, the bushes a loose fit in the frame. Brompton get around this by using bushes that are somewhat undersize after press-fitting and require reaming in situ. The only hiccup here is that Brompton won’t sell you the special long-piloted reamer they specify must be used; it is a dealer-only tool and costs almost £200. You can do the job with a cheap long 3/8″ hand reamer but there is a slight risk of getting it wrong and over-reaming, or getting the two sides on different centres.
• The TSR bottom bracket is part of the rear frame, not the main frame. This is great for keeping a constant chain length (making fixies and singlespeeds easy) but it means all the force of pedalling goes through the poor little offset pivot.

The ideal pivot is therefore an F-frame one in size and location, with Brompton nylon washers and the TSR grease nipple. If only it existed. Moulton designers- you know what to do.

The cheapening of the Moulton F-frame

This is either a rant or a lament, or both. In an earlier post, I covered the decline of Moulton sales in the 1960s, and how Moulton ended up selling out to Raleigh. What I only realised last week, when stripping down a very late series 2 bike, was how much these bikes were cheapened, de-specified and generally made worse over the years. Continuous improvement was not an objective (except for addressing a few known warranty issues like cracking forks and seat tubes) but improving the bottom line certainly was.

Series 1 bikes are generally well-specified and you can see Alex Moulton, the engineer, in some of the design touches. The adjustable lower rack strut, the lightweight tubular racks, the curved rear swingarm that gives a good bottom bracket height, the high specification Deluxe model, the Dynohubs seen on so many early bikes.

All these gradually disappeared as the accountants took charge. The Deluxe became largely the same as the old Standard, losing its alloy components and eventually even its chromed mudguards. The Standard itself was dropped, probably because they couldn’t make it any cheaper. The rear rack was made from stamped U-section steel and no longer fine tubes. The rear rack stays were just brazed permanently to the frame, and the rack was only fastened by one clamp instead of at four points. The series 2 swingarm presented an opportunity to fit an ugly dynamo bracket at the rear for a cheap bottle dynamo. Unforgivably, the straight series 2 swingarm completely messes up the riding experience. Unless you are extremely tall, you can no longer get a toe down at traffic lights, and the frame angles are steepened, making the already-twitchy steering more so. If you change a curve to a straight line, the dropout ends up in a different place: 3/4″ lower, it happens. Couldn’t they have fixed that with a dog-leg or an offset pivot hole? In engineering terms, it’s a schoolboy error.

So the late series 2 is a sad relic of the bike that took the world by storm in 1963. What about the Mk3? Well, I’ve never ridden one, but its reputation is of a solid but stupendously heavy and slow bike. The rear triangle is a predecessor of most of the modern spaceframes, and avoids the bending loads that did for so many series 1 rear ends, but it’s not elegant and adds a lot more dead weight. Plus Raleigh, in their arrogance and desire to find cost synergies, switched to in-house components, meaning the dead-end, obsolete 26tpi threading for the bottom bracket. Good luck finding a NOS BB when that gets pitted or worn.

I don’t really talk about Moulton Minis, but Raleigh did something even worse there. The Moulton Minx was a well-brazed iteration of the Mini with the usual 7/8 scale front suspension. Then Raleigh changed it to the Moulton Midi, which was a hunk of junk. The front suspension was totally omitted, with a longer headtube below the main spar where the bellows would have been. Now, a “lazy F” frame design is not especially strong or stiff, so guess what happened? They mostly cracked or bent due to the unabsorbed shock loads from the front fork. If you see one for sale, run in the other direction.

Fortunately, the modern bike industry, at least at the “enthusiast” end of the market, does seem to have embraced continuous improvement in specification and performance, although maybe things aren’t built to last as long as they used to. I suppose that’s why we see price rises of 10-20% a year.

As a final thought, I recently bought a used bike from a trader who also works in procurement and product design for the airline industry. Out of interest, he costed out all the parts needed to assemble a low-end bike of the type sold in Halfords for around £200. The actual value of the frameset, wheels and components was less than £20. Goodness knows how low Raleigh could have gone with the Moulton, if they hadn’t given up on it in the early 1970s.

All about chrome

Sometimes an exciting box arrives in the post (well, FedEx in this case). Inside were four parts from a 1964 Moulton Speed that can’t easily be replaced, nor are better ones ever seen for sale. So, at some expense, these had been off to Chromefix in Birmingham to be stripped, polished and replated.

Probably better than when they were new; the chrome has a very “liquid” appearance and they are incredibly smooth.

Chrome plating isn’t as simple as throwing steel items into an electroplating bath. What you see is the top layer of chromium metal, which is mere microns thick. Beneath this is a fairly thick layer of nickel plating and, beneath that, copper. All of this is necessary to achieve good adhesion, perfect smoothness, and corrosion resistance.

In itself, three-layer chrome plating still wouldn’t be all that expensive, but the steel underneath it all needs to be polished by hand using abrasives to remove any pitting or scratching that would show on the final finish. Your rusty chrome items will have a lot of pitting to the base steel. All the old plating needs to be chemically and electrolytically stripped before a Brummie metal polisher (it is an actual job, and they’ve been doing it for hundreds of years) removes all the imperfections on a grinder or polishing wheel, then it goes through the 3-layer plating process. When you know that, and when you appreciate the toxicity of some of the chemical baths involved, it doesn’t seem quite such bad value.

So why are new chromed steel items as cheap as chips? Well, there is no pitting or scratching on a newly-made item straight from the foundry, so no polishing is needed. There’s no old plating to strip first, and standards aren’t as high as they are for one-off commissions like this. The original Moulton chrome varies depending on who did it; TDC headsets hold up pretty well (although my cups needed doing, as you can see), really good Nicklin chainsets are easy to find after 60 years, but it is rare to see good chrome mudguards, bars, rims or stems. Modern chrome done in the Far East probably doesn’t have the 3-layer plating and won’t last long at all. Things that are still steel on new bikes, like headset brake hangers and tracknuts, will look terrible after one winter on British roads, unless you smear on a barrier layer of vaseline or linseed oil/beeswax mixture.

The following rule still applies, though: rechroming is expensive. If you can find new parts (fulcrum clips, nuts and bolts, etc) or better-condition used parts, that should be your first option. It’s always cheaper, and you don’t have to pay postage both ways!

A ride on the restomodded F-frame

Firstly, this isn’t a Speed. It was a very neglected 1964 Standard that I bought for the front rack. However, after stripping it down, it became apparent that underneath was a very good Bradford-on-Avon series 1 frame with neatly brazed, uncracked rear forks.

The frameset was powdercoated in RAL 3001 red by a local powdercoater (Sunbase) with an extra layer of clear lacquer. They also did the rear rack and struts in white. The mudguards are the originals, powdercoated in faux chrome by a different powdercoater (Maldon Shot Blasting and Powdercoating).

The parts are a mix of new and used. The rims are cheap 349 alloy rims with Brompton stainless spokes. The rear wheel is actually from my Brompton, since that bike has been converted to a 2-speed. It has a Sturmey-Archer AM 3-speed medium-ratio mechanism in an alloy SRF3 shell. I did build an FW 4-speed wheel for this bike but it has a weak spring in it and second gear slips. I now have another mechanism to swap into it, which will hopefully cure the problem. The trigger shifter is a 3- or 4-speed type, which is very convenient for swapping wheels.

The brakes are Alhonga dual-pivot and frankly quite disappointing. The rear one needs to go on quite a tall standoff spacer to clear the suspension block and they are not very powerful with the Tektro levers. At least the levers have a quick release mechanism for fixing punctures – a luxury most Moultons don’t have. Brake choice is a bit limited on a Moulton, because you need calipers where the cable pulls on the right. Most new calipers now pull on the left, because they are designed for countries where the cabling and frame cable stops are the wrong way round for countries that drive/ride on the left. Back when Moulton F-frames were being made, there were plenty of British manufacturers making brakes that were correctly “handed” for our right-front, left-rear setup.

Anyway, this was its first serious outing, about three hours around local country lanes. The fork has freed off nicely (it was a bit tight on the splines when reassembled) and the suspension generally works well. There are a lot of rattles on these bikes, some of which are my fault; the front mudflap, for example. Metal mudguards are difficult to hush up, though, and there was a squeak from the Shimano BB-1055 bottom bracket because I adjusted it in a warm room and then cycled in nearly-freezing temperatures. It was fine on a 12 mile test ride earlier in the week, but it was much warmer then!

The bike climbs a little better than my TSR. It is undoubtedly not as stiff a frame, but the fork is less soft due to the extra 3/4″ of preload that I added. There are two sections of “washboard” tarmac near Castle Eaton, and the bike soaked them up pretty well, making a lot of light rattles but not shaking me much. Just before home, I gave it a full-on thrash up a slight hill at 20mph (there was a tailwind) where it picked up its skirts and flew along very well. It is a little heavier than the TSR but I didn’t notice the weight at any point. The AM hub suits any vaguely “sporty” bike well, having 15.55% steps between its three gears, and it is utterly smooth and reliable – I have five or six of them and I believe they are by far the best of all the SA hubs. Unless I’m heading for serious hills, I don’t see any particular rush to reinstall an FW hub.

Something I do need to sort out is the rear bag. I have a small Gilles Berthoud rack bag (bought for 1/3 the new price on eBay; I’m not made of money) but I’m having trouble strapping it on tightly enough with the supplied straps. So, this morning, everything had to go in my pockets, with the little Topeak 16 multitool (old enough to still have the essential 8mm and 10mm spanners) strapped to the saddle. I hear toestraps are good for attaching the GB bag.

The roads weren’t salted this morning as it was about 3 degrees C but I’ve already smeared the irreplaceable chromed steel parts with vaseline to protect them. It looks awful after a few months, being like flypaper for dirt, but you can wipe it off in spring and everything is perfect underneath. One of my dad’s old tips from when he cycled in the 1950s.

Rechroming – I must do a post on that.

F-frame front fork assembly

This isn’t a particularly difficult job but it is a greasy one. Buy two types of grease: molybdenum disulphide (CV grease) for the sliding bushes, and red rubber grease for the inner steerer. You will need the same tools as for disassembly. An M6 bolt at least as long as the front brake bolt, or even a nail, is useful to keep the assembly together, as you will run out of hands to fit the front brake.

The main risks to avoid are cross-threading and damage to the fragile bellows and bellows retaining ring, where fitted. If it feels like you’re doing it wrong, you probably are, so stop and think again!

Everything must be clean and free of grit or old lubricants. Firstly, slide the following parts onto the inner fork steerer: bellows retainer (if not integral with the fork) with holes facing downwards, lower bush retaining cup, lower (splined) bush with the wider end of its four steps upwards. Fit the top bush and check it is not a loose fit on the top of the inner steerer. If it can be rocked from side to side, try fitting it with a shim cut from a drinks can. Push the circlip on when you are happy.

With the black MoS grease, liberally grease the bushes, lightly grease the splines, and grease the inside of the outer (bare metal) steerer tube using a sponge on a stick or similar. Place this over the inner steerer. Find an orientation for the lower bush on the splines where there is no rotational play. Bring the outer steerer down and push the lower bush into its four slots as far as possible. Now bring up the lower bush retaining cup and, ensuring it is not cross-threaded, screw it to the outer steerer. If you cannot get the thread started straight, it is because the bush has not been pushed far enough into the outer steerer slots. Use a lockring spanner to tighten the retaining cup securely against the underside of the crown race seat.

Now turn the fork upside down, thickly grease the rebound spring and the rebound spring stop with red rubber grease (RRG) and drop them in together at the fork crown, spring first. If you use enough grease, this will slow their descent enough to ensure that the spring stop stays the right way up, with the flat screwdriver slot facing the fork crown.

Using a long flat-bladed screwdriver, jiggle the spring stop until it is seated in the fork “stool” and cannot rotate any more. Keep pressure on the screwdriver so the spring stop cannot move. Now lift up the fork, keeping it upside-down, put the little rebound stop retaining screw and anti-shake washer on the end of your long Philips no.2 screwdriver with some RRG, and feed the screwdriver up into the other end of the steerer, ensuring the screw finds its hole. Ensure it is not cross-threaded by turning it anti-clockwise until it skips, then carefully tighten it into the rebound spring stop. Do not overtighten, but ensure it is tight enough not to work loose.

Now thickly grease the main spring and the outside of the spring abutment with RRG and insert them at the fork crown, the closed end of the abutment towards the spring. If you want to add more preload to the fork, try adding half an inch of aluminium rod or wooden dowel between the two. Have the bolt or nail ready (in your mouth!) to drop into a brake hole as you hold the fork in one hand and push the abutment with your other thumb to compress the spring. I find this is less painful if I use the stopper from a port bottle (which has a cork and a wide plastic head) between my thumb and the spring abutment.

Once you have everything locked in place, you can fully insert the bolt or nail, ensuring it also goes through the holes of the bellows retainer (if not integrated). Replacing it with the real front brake bolt (and the brake bolt tube, if you have a very early bike) is easy enough later without allowing the spring to escape again.

Finally, refit the bellows with extreme care. The longer straight end goes upwards. It can be tricky to get it over the lower bush retaining cup, so add a little RRG to this first and ensure you don’t tear the bellows on the two cutouts. Ensure it is properly located in the groove between the crown race seat and the retaining cup at the top, and on the bellows retainer at the bottom. Try not to get MoS grease on the bellows as far as possible.

F-frame rear pivot assembly

This can be a frustrating job. Not because anything is seized – you’ll be fitting new parts with plenty of grease – but because the design of the rear suspension means that the rubber block is always in compression, and you will be fighting the rubber as you try to insert the pivot bolt.

Firstly, obtain a pivot bolt kit. There are a couple of suppliers on eBay and Moulton Preservation sell kits if and when they are operational again.

The critical dimensions are 7/16″ for the OD (outside diameter) of the sleeve and 5/8″ for the ID(inside diameter) of the pivot tube. The bushes must be just over 7/16″ ID when pressed in and just over 5/8″ OD before pressing in. Check the kit on arrival to ensure your bushes are slightly over 5/8″ OD, using calipers. 0.630″ is just about ideal. They must be a tight press fit into the pivot tube, which means they need to be larger than the tube itself. It is critical that the bushes are not loose in the tube.

In theory you could manufacture your own kit quite cheaply if you can’t obtain a good one from anywhere; the kit consists of two nylon bushes, a long M8 partly-threaded bolt (or an 8mm spindle with threaded ends), nut(s), washers, and a steel sleeve of precise length. The sleeve is easy, as 7/16″ OD steel tube costs next to nothing. The bushes are the tricky bit, as no-one seems to sell off-the-shelf nylon bushes in the correct size, although this type of bush costs peanuts from a bearing supplier. Bushes with a 16mm OD and a 10-11mm ID are available, and could potentially be reamed out to the correct ID in situ (16mm is an excellent press fit into a 5/8″ ID tube).

The tools you will need are as follows: the trusty mallet, a long fully-threaded M8 bolt (150mm is good) with three large washers and a nut, two 13mm spanners, a pop rivet gun with 4 x 3.2mm rivets, and a ratchet strap. Molybdenum disulphide grease (CV grease) is the usual lubricant. A long 7/16″ reamer is very useful when dealing with pivot kits of indifferent quality.

Rivet the suspension block to the rear triangle, top side first. You may need to carefully run a 3.2mm drill through the holes to remove any new paint from the inside of the holes. Now do the bottom rivets, carefully tapping the tab back into place with the mallet so that the holes line up. A suspension block from one frame will generally not fit a different frame without some metalwork; the holes were not drilled consistently at the factory.

I de-rusted, primed and painted the metal parts of this suspension block before re-riveting it. These were originally bare galvanised steel but they blend in with the rubber part better if they’re painted black.

Clean the inside of the pivot tube and lightly grease the bushes on the outside. Put one washer on your long M8 bolt, followed by the first bush, flange towards the bolt head. Put the threaded end through the pivot tube then, on the other side, add the second bush (flange outwards), two washers and the nut. Hold the bolt head with one 13mm spanner and wind the nut in with the other 13mm spanner, ensuring the bushes go in squarely. Ensure the bushes are fully seated, but don’t overtighten as this will deform the flanges.

Grease the sleeve liberally and check it for fit. It should go in under firm thumb pressure, or with very light taps from the mallet. If it is too tight, you have a number of options:

• Get a bush kit that fits correctly
• Run a reamer through both bushes to make the ID correct
• Remove the bushes and clean any thick paint from inside the pivot tube
• Reduce the size of the sleeve slightly with abrasive paper. Putting it in an electric drill as a makeshift lathe is a good way

Once you have a sleeve that is a good sliding fit, thoroughly grease it, insert it, and ensure it protrudes from the bushes slightly on both sides. This is essential. If it doesn’t, there may be thick paint on the faces of the pivot tube, or you have been supplied with a sleeve that is too short.

Offer up the rear swingarm to the frame, ensuring the “shoe” of the suspension block slips squarely into the main spar. You will notice that none of the holes quite line up, because the rubber block needs to be compressed.

To do this, get a ratchet strap and pass it around the base of the head tube and the brake bridge of the swingarm. Protect the paint with soft cloths before tightening the strap. You will be able to pull at least one hole into line. Insert the well-greased bolt or spindle from the kit (not forgetting the anti-turn washer, if you have the bolt type) and push or lightly tap it in. It will generally become stuck as it reaches the “ear” of the swingarm on the opposite side. Some manipulation of the triangle and tapping with the mallet will now be necessary to get the bolt to pop out of the other side.

If using a bolt type, tap the bolt fully home, add the other washer and nut to the other side, and tighten to about 30Nm while holding the bolt head steady with the other 13mm spanner. if it is the spindle type, centre it up in the frame, then add the washers and two nuts before tightening as above.

Now check that there is a sliver of daylight – it doesn’t matter how small – between the bush and the “ear” of the swingarm on at least one side. It is critical that the ears are pinching the sleeve and not the bushes. If there is zero clearance, you need a longer sleeve. This can happen due to a poor quality kit, or because a previous pivot has seized and allowed the old sleeve to chew into the ears.

You can see that the swingarm ears are not pinching the bushes in this shot

Fit the three no.10 self-tapping screws that secure the “shoe” of the rear suspension block to the frame. New stainless steel screws are strongly recommended, as for all small fasteners on the bike. The bottom one will benefit from threadlock at this point, and you can use threadlock on the two side screws when you come to fit the “foot” of the lower rack strut.

Some kits come with an over-length chamfered bolt, which is easier to encourage out of the opposite side of the swingarm. If you have one of these, you will need to hacksaw off the chamfer when installed, and smooth the end of the bolt with a file. Watch the paint when doing this.

Cleaning and checking it over

Cleaning components

White spirit removes oil and grease. Then remove the white spirit using detergent then rinse in water. Dispose of the white spirit responsibly, or strain it through a filter and use it for cleaning chains. The inside of the fork (the real steerer and the separate bare metal steerer) should be scrubbed clean with a long thin bottle brush, rinsed and dried quickly in a low oven.

Light rust on steel components, especially if chromed, comes off with Barkeeper’s Friend (oxalic acid-based) and a toothbrush. This cannot restore chrome, though, and badly-rusted parts will still be pitted afterwards.

Heavy rust can be removed by soaking the components in a strong solution of warm citric acid for an hour or three, followed by a light scrub with a toothbrush. Follow all the safety precautions on the container, and avoid getting it into your eyes or on your skin. It is non-toxic but can burn. I would avoid soaking the main spring or the rear suspension block in citric acid in case it damages the rubber.

The frame, fork and swingarm can be cleaned with a proprietary bike cleaning fluid or spray, rinsed, and dried indoors. Ensure the frame is dried upside-down so it can drain.

Rubber components – the bellows, main spring and rear suspension block – must be cleaned of any Plus Gas or oil-based lubricants with detergent, then rinsed.

Inspecting components

With a torch, inspect the inside of the frame tubes and fork steerers for serious rust that may be structural. This is unlikely as the steel is quite thick, being a low-strength alloy.

To check forks for straightness, place them face down on a known flat surface so they rest on the tips and the crown. Contact should be made at four points simultaneously, or very close to it. If the fork is bent, it will be obvious.

If the inside of the “inner” steerer is very rusty and rough, clean it with a roll of abrasive paper so it is reasonably smooth. It is not a real bearing surface but the metal coil spring does need to be free to move within it.

The inside of the “outer” steerer must be shiny and smooth. If this is seriously damaged by rust, you need to obtain a better one via the owners’ club or eBay.

Check the bushes for chipping or damage. The upper bush should measure about 26.0mm in diameter, preferably slightly more. Measure at several different orientations. Shiny patches indicate where it has worn in service. It doesn’t tend to rotate around the steerer, so it can be refitted with the least shiny parts fore and aft, which is where most of the wear takes place.

This is a top bush in good condition, with light wear. It measures over 26.0mm diameter all around. The shiny patch is the most worn area.

Check the headset races for bad pitting. These are normally in usable condition even if the outside is cosmetically challenged. The top races (a loose dark steel insert for the cup and the adjustable screwed race) can still be found on eBay as NOS spares at the time of writing – they were made by T D Cross (TDC) in Birmingham, and were used on other brands too. The bottom races are only obtainable from another Moulton F-frame. Tinkerers may consider fitting a 1 1/4″ headset bottom end, which requires reaming the lower head tube to accept a slightly larger cup. You would need to find a bike shop that has a 1 1/4″ head reamer, which could take time as it has never been a very popular size. The crown race is the same size as the Moulton one but swapping it is a challenge as the outer steerer is the same diameter all the way down; there is no true “crown race seat”.

Check the “ears” of the rear swingarm to ensure the old pivot hasn’t chewed into them. A seized pivot causes the swingarm to rotate on the bolt alone, and the sleeve erodes the ears. Remove any remains of the old rivets from the holes using a small drill or pliers.

Measure the internal diameter of the pivot tube, which should be 5/8″. If the old bushes were loose, they could have turned in the pivot tube along with road grit, and enlarged it.

Check the bellows for any splits. These really need to be intact and, if yours are damaged, try to obtain a new bellows from Moulton Preservation (postal contact only, closed at the time of writing) or through the Moulton Bicycle Club. Apply a good rubber conditioner/preservative to slow down any future drying.

If the frame is to be repainted, check a series 1 rear swingarm thoroughly before you commit to the cost of a respray/powdercoat. Using a drill and a rotary wire brush, clean the paint off the rear fork blades near the suspension block cup, and check the bare steel and braze (if brazed rather than welded) very carefully for cracks. Cracks that have not progressed much can be repaired through the owners’ club, along with additional strengthening of the swingarm. If there are no cracks, some people will still have the swingarm strengthened. My feeling on this is to leave alone and proceed to painting if there are no signs of cracking. There are plenty of unmodified series 1 forks still giving good service, and build quality is the differentiator.

These series 1 forks are not at all cracked after 57 years

Another job to do before painting (restomodders only) is to file out the front fork dropouts to accept a modern 9mm axle. Only file the back, lower, side of the dropout, ensure the end of the slot is well-rounded, and keep checking until the new wheel fits and sits centrally. This means you have to build the wheel first! A nasty surprise may be that the front spacing is not quite 100mm; more like 97 or 98mm. Most hubs have a washer between the cones and locknut that can be removed on both sides, or replaced with a thinner one, to make the hub Moulton-width without stretching the fork.