Peugeot GT10

Out of a cellar, indicators included

In the early 2000s, my father picked up a Peugeot GT10 from one of his customers. It had sat for years at the back of a cellar without running, complete right down to its indicators. The original engine, with its contact breaker points, had lived a full life: my parents bought me a brand-new 103 SP engine. Under its frame and small wheels, the GT10 shares its mechanics with the 103 SP.

As a teenager, of course I wanted to modify it. Enough to make purists shudder, but that's part of the fun of modifying. Back then, I also rode a black and yellow Peugeot 103.

• Cellar find
• 103 SP engine
• The black and yellow 103

My only way to get to work

Since September 2010, the GT10 has taken me to work every day, rain, wind or snow, because it's more fun than the car. An engine that had only run now and then wears out: it gets a fresh start. Airsal T6 cylinder with 6 transfer ports and a single-ring piston, crankcase transfers filed, 15 SHA carburettor, Polini reed valve block for a straight, centred intake, NGK 7HS spark plug. The workshop is a badly lit cellar, and the home-made kick-start pedal has held up for ten years.

• Airsal T6
• SHA 15
• Polini reed valve block
• NGK 7HS

The Ninja G3 exhaust meets the welder

To fit a Ninja G3 onto my Gianelli swivel joint, I cut the fitting off the Gianelli and weld it onto the G3. A messy first weld, the joint redone, the rear bracket shortened, and in the end 2 cm gained. After the Ninja silencer mount broke, I fitted a Gianelli silencer instead. The Polini spring arrives and replaces my home-made kick-start pedal. And, by luck, I get the original speedometer mount back from the neighbour who had kept my 103.

• Modified Ninja G3
• Gianelli silencer
• Polini spring
• Original speedometer mount

Doppler exhaust and a first ER3 variator

The Doppler exhaust and the Doppler ER3 variator arrive. Problem: the belt is slack, because the ER3 is a wide-range variator. After a belt that turned out too short, I cut the engine mount again to move the engine forward. A proper kick-start pedal and new footpegs round it all off. First ride: "the variator changes everything, it feels like riding a scooter".

• Doppler exhaust
• Doppler ER3 variator
• Kick-start pedal
• Footpegs

The day my bank account hated the GT10

It all starts with a vintage-looking Polini Sport exhaust. It's made for a 70 cc with a W outlet, so the engine follows: Polini 70 cc cylinder and piston, matching cylinder head and a 21 mm Dell'Orto PHBG. As I wrote that year on the MobCustom forum: "my passion for this moped never goes out of style!"

• Polini Sport
• Polini 70 cc
• PHBG 21

A real heart and a fine seat

MVT Premium ignition for a proper spark, Malossi Variotop wide-range variator. On the looks side: headlight brackets, a fuel tank with chrome sides, new side panels, and the original seat redone in black leatherette with stitching and red piping.

How I refitted the seat, step by step, is on the page Restoring a GT10.

• MVT Premium
• Malossi Variotop
• BLG-Sellerie

A flea-market meter, an aquarium sensor

An old exercise bike meter found at a flea market now houses a Sigma MC10, with its connectors rewired at the back. In the original speedometer, a temperature sensor meant for an aquarium keeps an eye on the engine.

• Sigma MC10
• Temperature sensor

Saving the GT10's special fork

The GT10's fork has dimensions all its own, impossible to find anywhere else. Rust at the bottom of the tubes: dismantling, cleaning the tubes and springs, fresh oil and new gaiters.

Taking the fork apart and putting it back together, step by step, is on the page Restoring a GT10.

• Fresh oil
• Gaiters

Indicators and alarm, without touching the wiring

Wireless indicators and a vibration alarm, together in a housing I designed and 3D-printed, hidden under the seat. It all runs on a 3.7 V 3000 mAh battery, rechargeable over USB-C, with adapted bicycle components. The original wiring harness stays untouched.

• Alarm
• Wireless indicators
• USB-C
• 3D printing

A mount for the speedometer and the rev counter

A new speedometer mount on the handlebar, designed and 3D-printed in TPU, a flexible material: it holds the round speedometer and, just below it, a Runleader. This multifunction meter replaces my 2019 aquarium temperature sensor, which topped out at 120 °C. Its probe, fitted on the cylinder head, gives the engine temperature, and a simple wire wrapped around the spark plug lead gives it the revs per minute.

The mount files are available further down, in the 3D-printed parts.

• TPU mount
• Runleader
• Cylinder head temperature
• Rev counter

The Doppler ER3 optimised across its whole range

After a lot of trouble setting up the wide range of the Malossi Variotop variator, I switch to the Doppler ER3: easy to set up, but not optimised straight out of the box. I enlarge the sleeve with a 2 mm washer, so that at rest the belt sits as low as possible without touching it: you gain at pull-away. I lightly grind the pulley faces so that at full opening the belt climbs right to the top. Finally, I shift the engine 4 mm to the left for perfect alignment with the clutch pulley.

The setup: Doppler ER3 variator, Doppler ER2 11-tooth clutch, Malossi 617233 belt, 15x8x853 at 32°, 38-tooth rear sprocket. The whole range is finally used, with no rider on board: the road tests are still to come.

• Doppler ER3
• Enlarged sleeve
• Ground pulley faces
• Engine shifted 4 mm
• Malossi 617233

Read the step-by-step guide: optimising a Doppler ER3 →

Watch the test video ↗

The transmission, to the millimetre

With the range sorted, I move to a 13-tooth sprocket thanks to an Omega Revo clutch pulley. When it arrived, a machinist turned it to 32° to take the 15 mm Malossi belt. Switching to 13x38, because on 10-inch wheels the engine spins like mad. The variator still only uses two thirds of its travel: there's room to spare. To stop the engine over-revving, the Doppler ER3 weights make way for better-quality CBE ones, at the maximum weight. The only downside: the bracket of the Polini V1 exhaust snapped clean off, a classic on this model. A Polini Sport V2 takes over.

• Omega Revo
• 13-tooth sprocket
• 13 x 38
• CBE weights
• Polini Sport V2

The side panels get their GT 10 decals back

The side panels, which I had cut open with a Dremel back in the day, start again from scratch: filling, primer and paint. My neighbour recreated the GT 10 stickers by vectorising the old ones, in a real bright red, and I 3D-printed new fixing knobs.

All the steps in detail are on the page Restoring a GT10.

• Filling
• Primer and paint
• Stickers remade
• 3D-printed knobs

All rolling, except one bearing

New side panels, transmission set up, Polini Sport V2 fitted. I also put back more standard headlight brackets, closer to the fork. Latest snag: a rear wheel bearing developed play, and I had to change the rim. I'm going to see a machinist to find out whether the original loose ball bearings can be replaced with 30 mm bearings.

Alongside that, I'm testing a forced-air cooling system I designed and 3D-printed: a fan spins with the ignition inside a shroud fixed to the casing with a 100 mm hose clamp, and a duct blows air onto the cylinder fins. It only matters when standing still with the engine running: on the move the airflow is enough, but at a standstill the engine still gets a minimum of cooling. The first attempt taught me a lesson: the base of the blades was too thin, the PETG deformed as it spun and rubbed against the ignition just behind it. Hence the 0.5 mm washer, which now spaces the fan away. It's still a PETG prototype, to be reprinted in at least PETG-CF to last; the files are in my 3D parts. That's the GT10 as it rides today.

• Headlight brackets
• Rear rim replaced
• Cooling fan
• Ongoing project

Watch the cooling test video ↗