Lambretta GP 200 Flywheel Side Bearing & Seal Upgrade

The Lambretta, a true icon of scooter engineering, often calls for a bit of fettling and upgrading to keep it running at its best. One area that can significantly impact the smooth operation and longevity of your engine is the flywheel side bearing and oil seal assembly. While many Lambretta models share similar components, the GP 200 presents a slight variation due to its wider crank shoulder. However, with the right guidance, adapting this crucial area is well within reach, even for those new to Lambretta mechanics. This article will guide you through the process of installing new flywheel side bearings and oil seals, focusing on the GP 200 but providing insights applicable to a range of Lambretta models, from the early Series I bikes through to the LI, SX, and TV variants.

Understanding the GP 200 Flywheel Side Assembly

The flywheel side of a Lambretta engine is a complex yet vital component. It houses the main bearing that supports the crankshaft and oil seals that prevent gearbox oil from entering the crankcase and vice-versa. For the GP 200, the crank shoulder is wider, necessitating a specific bearing (NU2205E) compared to the NU205E used in LI, SX, and TV models. Despite this difference, the magnetic (mag) side flange casting remains the same across these models. This allows for a degree of interchangeability and adaptation, making the process achievable with careful attention to detail.

Essential Components and Tools

Before embarking on this task, gathering the correct parts and tools is paramount. This will not only ensure a smoother installation but also the correct functioning of your engine. Here’s a breakdown of what you’ll typically need:

Tools Required:

• Blowtorch (propane or similar)
• Mallet and drift (or a large socket of appropriate size)
• Circlip pliers
• Screwdriver (for heating inner race)
• Vice grips (optional, for stubborn races)
• Cutting tools (optional, as a last resort for old races)
• Freezer (for cooling bearings)

Step-by-Step Installation Guide

With all your components and tools ready, you can begin the installation. Patience and precision are key throughout this process.

1. Removing the Old Crankshaft Inner Race

This is often the most challenging part. If a previous bearing race is still on the crankshaft, it needs to be removed. While specialist tools are ideal, a careful approach can also work. Heating the old race with a torch can expand it slightly, allowing it to be gripped with vice grips. Alternatively, it can be very carefully cut off, but this carries a risk of damaging the crankshaft. If you’re unsure, professional help from a scooter shop is recommended.

2. Preparing the New Inner Race

Once the old race is off, you’ll need to fit the new inner race onto the crankshaft. A useful trick is to use the mag flange as a base to hold the crankshaft steady. Heat the new inner race using a propane torch on the end of a screwdriver. The heat will cause the race to expand slightly, allowing it to slide easily onto the crankshaft taper. Aim to heat it sufficiently so it drops down to the crank web oil seal lip without force. If it doesn't seat fully, support the crankshaft web securely and use a long tube and hammer to gently tap the race into its final position. Crucially, never tap the race down without supporting the crank web, as this can lead to crankshaft damage.

3. Installing the Outboard Oil Seal

Moving back to the mag flange, the first seal to be installed is the outboard oil seal. This is fitted from the inside face of the mag flange. Note the small circular spring around the lip of the oil seal; this spring must face towards the crank once installed. To ease fitting, you can gently warm the mag flange. However, avoid overheating, especially near the seal, as you’ll likely need to handle the flange with your bare fingers. Ensure the seal seats perfectly flat against the lip within the mag flange.

4. Fitting the Spacer Washer

Next, the spacer washer is installed. This component maintains the correct gap between the outboard oil seal and the main bearing. It should be positioned with its flat side facing the oil seal and its lip towards where the bearing will sit.

5. Installing the Main Bearing Outer Race

Now it’s time to fit the outer race of the main bearing into the mag housing. Heat the mag flange again using your blowtorch. Again, keep the flame away from the recently fitted oil seal and limit the casing temperature to around 200°F (93°C) to prevent seal damage. For an even easier installation, you can freeze the bearing beforehand. Use a suitable drift or a large socket that contacts only the outer rim of the bearing to carefully tap it into place. You'll often hear a subtle change in sound when the bearing is fully seated.

6. The LI/SX/TV Spacer (If Applicable)

For LI, SX, and TV models, which use a thinner flywheel side bearing, an additional spacer is required between the inboard oil seal and the bearing. This compensates for the difference in bearing width. This spacer can typically be fitted in either orientation.

7. Installing the Inboard Oil Seal

The inboard oil seal is fitted next, again ensuring the spring and lip face towards the crank. This seal can be notoriously tricky to fit. Patience is key; slowly force it in by hand. If necessary, a flat piece of wood can be used to gently tap it into its final position.

8. Final Touches: Circlip and Grease

The final steps involve fitting the circlip retaining ring to secure the bearing assembly. Ensure the circlip does not catch on the oil seal. Finally, and critically important, liberally smear high melting point grease all around the bearing. This bearing is not lubricated by the fuel/oil mixture, so the grease provides its sole lubrication. Without adequate grease, premature bearing failure is almost guaranteed.

Adapting for Different Models

As highlighted, the core principles of this installation apply across many Lambretta models. The primary differences lie in the specific bearing size and the potential need for an additional spacer in earlier Series models (LI/SX/TV) due to their thinner flywheel side bearings. Always double-check the part numbers for your specific scooter model to ensure compatibility. The GP 200’s wider crank shoulder means its bearing is dimensionally different, but the mag flange itself is designed to accommodate it, along with the appropriate seals and spacers.

Troubleshooting and Tips

• Stubborn Races: If the old inner race is proving impossible to remove without damage, consider using a Dremel or angle grinder with a cutting disc to carefully cut a slot into the race, being extremely cautious not to nick the crankshaft.
• Seal Installation: For tight seals, a small amount of grease on the seal lip can help it slide into place without damage. Ensure the seal remains perfectly square during installation.
• Bearing Seating: A common mistake is not fully seating the bearing. Listen for the change in sound and visually inspect that the bearing is flush within the housing.
• Lubrication is Key: Do not underestimate the importance of greasing the bearing. Use a good quality, high-temperature grease designed for bearings.

Frequently Asked Questions

Q1: Can I use a standard bearing instead of the specific Lambretta ones?
A: No, it is highly recommended to use the correct bearing numbers (NU2205E for GP 200, NU205E for others) as they are designed for the specific loads and dimensions within the Lambretta engine.

Q2: How do I know if my GP 200 crank is different?
A: The GP 200 crank has a wider shoulder where the flywheel attaches. This is the primary reason for the different bearing size.

Q3: Is it safe to heat the engine casing components?
A: Yes, gentle heating with a blowtorch is a common and safe practice to aid in the installation of bearings and seals, provided you do not overheat the aluminium or the rubber seals.

Q4: What happens if the oil seals are installed incorrectly?
A: Incorrectly installed oil seals can lead to oil leaks, potentially contaminating the clutch or gearbox, or allowing gearbox oil into the crankcase, which can cause engine damage.

Q5: How often should these bearings and seals be replaced?
A: It's good practice to replace these components during a full engine rebuild or if you suspect any play or noise from the flywheel side.

By following these detailed steps, you can successfully adapt and install new flywheel side bearings and oil seals on your Lambretta GP 200, or indeed most other Lambretta models. This maintenance task is crucial for engine health and will contribute to a more reliable and enjoyable riding experience. Remember to work carefully, use the right parts, and your classic scooter will thank you for it.