Real Classic

ROYAL ENFIELD CLIPPER PROJECT

Enfield enthusiast Stephen Herbert had an inclinatio­n to build a trials special and, rather than start from scratch, he purchased a part-completed pre-unit 250 project. And then the fun began…

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Enfield enthusiast Stephen Herbert had an inclinatio­n to build a trials special and, rather than start from scratch, he purchased a partcomple­ted pre-unit 250 project. And then the fun began…

I’ve never had a trials bike and I had a sudden hankering for one. Don’t misunderst­and; I have no intention of going trials riding and getting muddy. I just liked the look of a Royal Enfield pre-unit Clipper which popped up one day on my fuzzy laptop screen when in eBay mode. I’d been thinking about my next rebuild (cos we gentlemen cannot exist without a project on the bench, can we?) and taking an unhealthy interest in that great shoppe in the skye. An Enfield made perfect sense, because I’m a creature of habit and most RE designs didn’t change much from the late 1940s onward. Also, being lazy, I knew that Hitchcocks stock

parts for most REs so there’s no need to go scouring bike jumbles!

I spotted ‘ Tribulatio­n’ on eBay in September last year. The vendor was honest enough to warn me that he was a bitza (the bike, not the man) and that he’d hung most of the bits loosely together so that he could see what it would look like. And then he (the man, not the bike) lost interest. This suited me well. I could see that most of the parts were there and that a complete rebuild would be needed. That’s what projects are all about, aren’t they?

So a deal was struck. I was the only bidder and I paid a little extra for the spare engine, swinging arm, plus various bits of tinware, etc, just in case they were needed. It turned out that they were…

Tribulatio­n arrived on my drive one day, together with the box of bits. My wife came out to see what all the commotion was about and immediatel­y dismissed the whole project as a pile of junk (they all do that, sir). To the cursory glance the machine might’ve looked ready to ride, but touch a few vital components (like the engine for instance) and it all took on a much wobblier aura. I smiled and started to make a list.

Why name this motorcycle ‘ Tribulatio­n’? Because it was a trials bike and caused me

endless trials and tribulatio­n until it burst into life again, and then caused me yet more T&T…

When Tribulatio­n left the Royal Enfield factory in Redditch (in separate bits, spread over the mid-1950s) it was a 250cc iron-head ohv pre-unit Royal Enfield Clipper. Bit of a mouthful, but loosely related to the Model G 350 and early Bullets, and not to be confused with the late-1950s RE Clipper which was unit constructi­on and the cooking version of the sporty little Crusader.

The pre-unit Clipper’s frame is massive and heavy and full of now-redundant lugs, similar to a Redditch Bullet frame. Where tubes join there are huge forgings for strength, and the engine is a stressed member forming part of the bike’s integrity, as can be seen even more starkly here than on a Bullet. The swinging arm is equally sturdy but the bearings are subject to wear (more on this later). Tribulatio­n’s frame is from 1955 while the engine is from 1954 – as am I, so I can confirm it was a good year!

The Clipper’s engine is a 250cc developmen­t of an early sidevalve single jobby, sporting overhead valves in a hemispheri­cal combustion chamber within the cast-iron head. The barrel is also cast-iron and the crankcases contain the oil tank in a similar way to Bullets, Meteors, Connies, etc, but with a difference. As with the Model G, Tribulatio­n’s oil tank is a split affair, half behind and half in front of the crank. The timing gear is all gear driven á la Bullet, and sparkles are provided by coil and points. Other elecricker­y is magically delivered by a feeble alternator on the driveside end of the crank. The gearbox is a separate item originally courtesy of Messrs Albion and the two are joined together within the primary case by a wet and frail clutch.

So that’s what I was dealing with, and here’s the nub of what needed doing:

But first I needed to source a centre stand (only a prop stand was fitted) in order to work on the bike. This was the first item bought from Hitchcocks – a good secondhand one which I didn’t bother painting as it was going to be a removable maintenanc­e item. So, once on its stand on the hydraulic bench, I proceeded to remove and strip the engine, gearbox and the rear end. I adopted my normal approach to the rebuild of painting the rear part of the frame while these components were out, and then moving steadily forward.

Stripping things down was an easy job as most fasteners were only finger tight. One of the first problems I encountere­d was with the main bearings. I’m used to roller-and-or-ball combinatio­ns which are complete (as in outer race, balls/rollers in a cage, inner race all as a unit). This engine’s main bearings were of

the roller variety but, as I split the crankcase, the rollers made a bid for freedom – they were uncaged and entirely separate from their races. This made for an interestin­g time collecting all the rollers together, counting them, checking they were unworn (they were OK) and bagging them with their respective inner and outer races. I was half-expecting something like this after looking at the parts and workshop manuals, but even so it was a whole new experience for me.

The bottom end of the engine was fine – no play at all in the big end, the mains were fine and there was no damage to be seen. The only issue was with one of the two oil drain plugs. These engines have two oil chambers connected by a channel in the castings, and each chamber has its own drain plug. Except one of these was a cork glued into the hole (I kid you not – check the photos) presumably because someone in the past had snapped the stud to which the plug should screw. Fortunatel­y I was able to extract the broken stud from its tunnel and replace it with a new one, otherwise Tribulatio­n would have been a real Royal Oilfield…

The barrel, piston and head on the bike were less good. All were a bit sloppy,

especially the valvegear, and the head had a broken fin. So I turned to the spare engine and selected the best of each component. The best barrel and piston were on +20 thou so went together with new rings, and the best head was treated to new valve guides and valves. Interestin­gly, the best head had been ‘ported’ at some stage in the past – the inlet tract had been opened up to a slightly larger diameter and metal had been removed from the throats of both ports where they entered the combustion chamber. I thought this could be a good thing. Unfortunat­ely there were no valve guides in the best head so that was the next task.

I’d never replaced valve guides before, so I resorted to my trusty B&Q blowlamp to heat the head up, and then drifted the new guides into the holes. Even with a lot of heat transferre­d to the head it was quite a job with the hammer, but they went in eventually. I then recut the valve seats; I had to buy a new set of cutters as the ones I’d borrowed from Theo in our VMCC section (Cheshire Cats) were either too large or too small for the small combustion chamber. Not much metal was removed from the seats as the new guides proved to be pretty concentric to the seats, so after that and a quick lapping I was able to fit the new valves and the original springs. Theo asked if I’d reamed the new guides – I hadn’t as it all seemed to fit well together. I should have heeded his advice as I discovered much later…

That done, it was time to tackle the petrol tank. As mentioned, I didn’t like Tribulatio­n’s tank. Fortunatel­y I found one on eBay from one of Royal Enfield’s smaller, 2-stroke offerings – an Ensign or Prince I think.

Not only was this a pleasing shape, it had previously stored an oily petroil mix so wasn’t rusty inside.

Before I did anything else, I needed to remove all the exterior paint as it was very thick, soft and uneven. B&Q’s gel paint stripper did a great job and very soon I ended up with a bare tank and loads of gloop on the floor. This revealed a surprising­ly undamaged tank which needed very little filling, just lots of rubbing down, primer and paint.

One of the problems with building a bitza is that things don’t always fit together properly. This was the case with Tribulatio­n’s new tank. It was a bit short and designed for a bike with a steeper slope on the frame main tube, presumably to fit a rigid rear end. I ended up fabricatin­g brackets for the front end of the tank to lift and stretch it to suit the bike.

?? ?? This almost looks like a motorcycle, but in fact it’s a collection of components, loosely hung together, and the start of Stephen’s tribulatio­ns
This almost looks like a motorcycle, but in fact it’s a collection of components, loosely hung together, and the start of Stephen’s tribulatio­ns
?? ?? This Enfield engine has two chambers inside the main crankcase casting, connected by a gallery, to hold its oil so of course it requires two sump plugs. Which are located in the other crankcase half, of course
This Enfield engine has two chambers inside the main crankcase casting, connected by a gallery, to hold its oil so of course it requires two sump plugs. Which are located in the other crankcase half, of course
?? ?? Left: Royal Enfield built a unit-constructi­on Clipper at the end of the 1950s, but this is the earlier pre-preunit versionver­sion mademade fromfrom 1953 to 1957
Left: Royal Enfield built a unit-constructi­on Clipper at the end of the 1950s, but this is the earlier pre-preunit versionver­sion mademade fromfrom 1953 to 1957
?? ?? One joy of RE singles is that most bits from most bikes might mostly fit. Observe the faintly glorious elderly rectifier and the Indian carb. No Amal here!
One joy of RE singles is that most bits from most bikes might mostly fit. Observe the faintly glorious elderly rectifier and the Indian carb. No Amal here!
?? ?? Classic RE single. The crankshaft drives the exhaust camwheel, which in turn drives the inlet camwheel, which in turn drives a train of gears to the ignition device – whatever that might be
Classic RE single. The crankshaft drives the exhaust camwheel, which in turn drives the inlet camwheel, which in turn drives a train of gears to the ignition device – whatever that might be
?? ?? Above: What to do when you’ve lost the original drain plug? Glue a cork in the hole, of course…
Above: What to do when you’ve lost the original drain plug? Glue a cork in the hole, of course…
?? ?? Complete engine rebuild. Nothing was tightened up so it all needed to be taken apart, inspected and rebuilt Complete gearbox rebuild. My last project, an Indian Bullet, didn’t have the box rebuilt, as it looked OK. This proved to be a big mistake and I wasn’t going to repeat it! Frame re-paint. The previous owner had rubbed down and Hammerited the frame, but it was a bit rough so it needed doing again Rear wheel rebuild. The rim and spokes were rusty and tarnished respective­ly and the hub needed a good clean and paint. Both the front and rear wheels are off an early Bullet as Clippers had 6” half-width hubs whereas Tribulatio­n wore full width 7” ones Steering races. These were the only things The bottom end comes back together again. This truly is a monster crankcase for such a simple single, and a very complicate­d casting, too
Complete engine rebuild. Nothing was tightened up so it all needed to be taken apart, inspected and rebuilt Complete gearbox rebuild. My last project, an Indian Bullet, didn’t have the box rebuilt, as it looked OK. This proved to be a big mistake and I wasn’t going to repeat it! Frame re-paint. The previous owner had rubbed down and Hammerited the frame, but it was a bit rough so it needed doing again Rear wheel rebuild. The rim and spokes were rusty and tarnished respective­ly and the hub needed a good clean and paint. Both the front and rear wheels are off an early Bullet as Clippers had 6” half-width hubs whereas Tribulatio­n wore full width 7” ones Steering races. These were the only things The bottom end comes back together again. This truly is a monster crankcase for such a simple single, and a very complicate­d casting, too
?? ?? The Clipper’s main roller bearings can get a bit frisky once they’re let loose. Which is of course one reason why research is a good idea before stripping an engine that were missing – well actually there were races in place but they were Indian Bullet ones and didn’t fit properly. PO had warned me of this Tinware. Oh dear. The tank and toolboxes as-supplied were ex-Indian Bullet too and looked very wrong on a trials bike. The tank was very large and bulbous and only one toolbox was installed as the trials exhaust prevented the right toolbox fitting. I resolved to source a smaller, neater tank and ditched the toolboxes in favour of the minimalist look
The Clipper’s main roller bearings can get a bit frisky once they’re let loose. Which is of course one reason why research is a good idea before stripping an engine that were missing – well actually there were races in place but they were Indian Bullet ones and didn’t fit properly. PO had warned me of this Tinware. Oh dear. The tank and toolboxes as-supplied were ex-Indian Bullet too and looked very wrong on a trials bike. The tank was very large and bulbous and only one toolbox was installed as the trials exhaust prevented the right toolbox fitting. I resolved to source a smaller, neater tank and ditched the toolboxes in favour of the minimalist look
?? ?? RE’s primary chaincase was one of the best in the business. Secured by a single bolt and sealed by a vast O-ring. Shamelessl­y copied by Norton for the Commando
RE’s primary chaincase was one of the best in the business. Secured by a single bolt and sealed by a vast O-ring. Shamelessl­y copied by Norton for the Commando
?? ?? Removing the timing pinions and the cams reveals the cam followers, neatly stepped because of their unusual way of operating
Removing the timing pinions and the cams reveals the cam followers, neatly stepped because of their unusual way of operating
?? ?? Where the oil goes. It seems strange, carrying the oil in two linked compartmen­ts, but it plainly worked
Where the oil goes. It seems strange, carrying the oil in two linked compartmen­ts, but it plainly worked
?? ?? Priming the crank’s oilways. This reduces the lag between the engine starting and oil reaching vital parts Ignition is controlled by a nice, simple, neat distributo­r, complete with a mechanical advance mechanism
Priming the crank’s oilways. This reduces the lag between the engine starting and oil reaching vital parts Ignition is controlled by a nice, simple, neat distributo­r, complete with a mechanical advance mechanism
?? ?? The camwheels are back in place, and the timing marks are aligned. Valve timing is easy when the manufactur­er marks things up for us. Less so if not
The camwheels are back in place, and the timing marks are aligned. Valve timing is easy when the manufactur­er marks things up for us. Less so if not
?? ?? RE engines have an entertaini­ng approach to oil pumps, and it pays to understand them in the interests of long engine life
RE engines have an entertaini­ng approach to oil pumps, and it pays to understand them in the interests of long engine life
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?? ?? NEXT TIME: the gearbox, primary drive and the bike’s back end…
NEXT TIME: the gearbox, primary drive and the bike’s back end…
?? ?? Heating the head, ready to drift new valve guides into place One engine, awaiting the replacemen­t of its head
Heating the head, ready to drift new valve guides into place One engine, awaiting the replacemen­t of its head
?? ?? The new petrol tank didn’t quite fit the Clipper’s frame, so Stephen fabricated brackets to bridge the gap
The new petrol tank didn’t quite fit the Clipper’s frame, so Stephen fabricated brackets to bridge the gap
?? ?? Stephen wasn’t wild about the Bullet-type petrol tank which came with his project, so sourced one from a smaller two-stroke
Stephen wasn’t wild about the Bullet-type petrol tank which came with his project, so sourced one from a smaller two-stroke
?? ?? The cylinder head which was attached to the engine had broken fins, but happily there was a spare in the big stack of bits
The cylinder head which was attached to the engine had broken fins, but happily there was a spare in the big stack of bits
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