Spondon G50

Hopefully you'll notice that this isn't any ordinary chassis. The rear suspension is fully adjustable rocker arm type, and the domain of GP bikes in 83 and is the same set up as used by Spondon framed RG500 GP bikes in the early 80s. The frame is made from 531 and all bronze welded.

Now i wasn't starting from scratch. Over the last 4 or 5 years i'd been slowly collecting parts for a Seeley G50 project, i'd source most of an engine, gearbox and primary. I had forks and wheels which where intended for a Zegers project that I abandon after loosing out to when trying to buy a frame, that was five years ago and he's still done nothing with it - it's unlikely that i'll ever find another.

In short the spec of the build at this point is;-
Matchless g50 engine refreshed.
Schaftleitner 5 speed gearbox in AMC magnesium shell.
Spondon 38mm forks
Spondon Yokes
Spondon hubs and discs - pretty trick as the disc carriers hold the wheel bearings saving quite a lot of unsprung weight.
AP Lockheed callipers and front master, Brembo rear master.

Trial fitting the engine, forks and wheel, about an hour after getting the chassis into my workshop.

A few days later.

One less thing to worry I can fit a belt .

Originally the bike use a chain primary which has a smaller envelope.
May not seem like a big issue but the chassis is so tight there’s very little room either way for the gearbox to rock over the lower mount, a total around 17mm only - the gearbox is either hard up against the engine or the belt fouls the frame. So I needed an almost perfect length belt and 880/8M x 30 is perfect. Phew……
In the photo the belt can be turned through 90deg so gearbox position is spot on for correct tension of the belt. A few things to do before I can button all up like fit a gearbox sprocket, wheel and chain alignment and I can tighten all up.

This one’s sprinting along.

A little progress!

It’s now on its wheels, getting tyres wasn’t easy but special thanks to Dennis Trollope. Gearbox and belt now fitted, a few mods to the primary guard also. Wheel and chain alignment sorted. Front suspension is sorted, brakes, all AP, stripped and rebuilt, just need to fit the front guard which is RS1000. Rear end similar but no brake line as yet, will sort tomorrow and fit the rear chain.

Have decided to use a 38mm mikuni VM.

Need to decide on exhaust, seat and fairing?

Forgot to post photos!

Seat and tank fitting.

No idea what the original seat was so with a bit of help and a beauty contest fitting different seats i opted for this. Its a Maxton TZ750 seat from around 1976.

Tank gets a light refresh too.

Also starting to think about an exhaust.

The exhaust.

After being quoted between £950 and £1250 plus VAT by 3 different exhaust specialists I thought that’s a lot of money for a single down pipe and silencer. So I considered my options for a 1/2 second - I’ll make my own system how difficult could it be?
As it turned out it wasn’t too difficult. Certainly not £1250 plus VAT difficult.

The down pipe is in two parts as there’s no way to fit a single header pipe inside the frame. Believe me I tried. Exit from the cyl head is tight so might make a new exit pipe at some point. Will see how it goes.




Hopefully with the exhaust under the engine I’ll be able to fit a fairing with a narrow pan.
The finished exhaust doesn’t look too bad IMO.

Well it’s running and running very well and just 7 weeks from start to finish.

Paint scheme is period and similar to how the bike was in 1984. Note the rear tank strap mount is redundant as the tank is held down by 4 Dzus fasteners.

Full spec.
Spondon frame and arm with adjustable rocker suspension (ratio and height), shock with adjustable preload, compression and rebound damping.
38mm Spondon Forks re-valved with air assistance.
Spondon Yokes.
Spondon Hubs laced to 2.5” alloy rim front and 3.5” alloy rear.
Brake are Spondon floating discs front and rear, AP CP2696 callipers. AP front master cylinder and Brembo rear.
Matchless G50 engine rebuilt with Al Gunter cam.
PAL magneto with external condenser and race PVL coil driving a Krober rev counter.
Mikuni VM38 carb bored to 39.25mm.
Magnesium gearbox with all roller bearing 5 speed gearbox.
Newby dry clutch and 32mm belt.
Spondon rear sets.
Works length exhaust 1 3/4” exhaust header and short reverse cone megaphone.
Fairing is Kirby flowline fairing with full belly pan made in carbon, slightly modified.
Seat is Maxton Yamaha TZ750.
Front guard is Honda RS1000.
Tanks are alloy.

kerb weight 278lbs with oil and a gallon of fuel and 56hp at the back wheel and a package good for just over 130mph.

woodsman said:

Beautiful Steve. It looks like it wants to dance.

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Dance! So far I’ve ridden it just once, about 14 miles only (about 6 laps).

1st impressions are positive, rides bolt straight and steers well.

Suspension up front was a little hard so changed to lighter springs and lighter damping oil 15 grade. Rear suspension I’m still working out, I’ve lowered the back end about 25mm and dropped the front end a bit also which has helped. The whole bike could be a little lower IMO although its stance is quite modern and suits it.

With the changes made there is no great drama changing direction mid corner, hooks up well, it doesn’t squat like a cantilever chassis or does itstand up too early as you feed the power in - I guess I got the lower chain length about right and my guess at rear suspension settings about right. I do, however, need to alter the chain run as it’s to close to the chassis.

Brakes are too much for the bike but I knew this when I fitted them but it’s nice to have a lot of stopping power in reserve.

Impressed with it so far, still wondering what’ll do in fault mode I.e. that’ll be me overriding and screwing up!

peter400four said:

Beautiful, as is all of your work Steve. Welcome back to Cafe Racer. Just one question. With the range of periods represented in the build, which class is it eligible to race in.

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A good question. Best I say what it cannot race in which is just about everything!

Its one of those bikes, like after market framed 350 TZ’s, Rotax etc in alloy spondon, DRS, Harris and so on which also don’t have a suitable home. Too modern for post Classic to old to be competitive in modern era. Especially if force to fit a 250 lump.

1980 to 1988 is a real odd era when it comes to classic racing today as period 750’s have to bash fairings with fj1100’s in xr69 chassis. Therefore Classic superbike isn’t as the eligibility criteria effectively makes many bikes uncompetitive pre 1984 was a 1000cc class, 84 to 88 was 750, 88 was production 750. Today there no point racing a period z1000 against 1300cc Yamahas and 1260 Suzukis. Which is sort of ironic as this bike was built for the UK Kenning series which was an single cylinder class all about getting the old big thumpers out of hibernation and back on track after 15 years of two stroke domination.

Also because the bike is GP based (g50 engine and rear suspension) it can’t race in UK classes like “air cooled 500” in which bikes have to be production road based.

That said classes are changing all the time.