Boring & Pistons & Rings

To date I have never had any of my Lambretta bored out. Mainly because I have enough spares (not for sale) to aid with replacements. However, it’s something that people may need to do.

If I needed to do it, I would take the cylinder to a specialist and ask them to bore it out and also if it was possible, I would ask them to supply the replacement piston, rings & gudgeon pin.

The information below may aid you in this area. I would also encourage, that unless you already have a good understanding of Cylinder Heads & Piston Rings (including gudgeon pin circlip installs), you view the You Tube video clips below to aid in further understanding in this area.

Reboring

Reboring is required when the piston, piston rings and cylinder are damaged, either after wear or tear or excessive usage (continuous high speed use, or usage without proper lubrication). When the cylinder wall is damaged, it may sometimes be rebored to a larger size and larger size pistons are used.

Hair line crack at the bottom area of the cylinder, that locates into the engine / crankcase

In my experience early Lambretta C; D; LC; LD models are know to also have hair line cracks at the bottom of the cylinder and this may therefore need repairing prior to a rebore taking place and if it is possible to do so.

Here are some of your options in this area, along with information

Option One

Find a company that is willing to re-bore the old cylinder. Note: A warranty may not be possible and damage may occur during the process, or may prompt a hair line crack to occur at the bottom of the cylinder.

If you go down this route, you may want to ask the company that is reboring to fit one of the standard LD piston rings, piston and gudgeon pin, rather than supply them yourself, as dealers may supply something that may not fit after the bore. See the comments below on a standard 125 & 150 part numbers and available parts.

Option Two

Wait for a second hand engine and purchase (& take the risk of the head being damaged)

or use Facebook and one of the Lambretta Groups to publish your needs and dsicuss costs and delivery. Ask the supplier / person to check for hair line cracks before you purchase it from them.

Option Three

Lambretta LD Top End Replacements – In July 2020 of this year, (Facebook Reference) “Gran turismo performance” informed members of the the Facebook group known as Lambretta Shaft Riders, that they had finished producing Lambretta D / LD Cylinders; Heads and Manifolds and were waiting for Japanese pistons (Due in before the end of July 2020). Should you require a replacement in this area, read up about it on their Facebook page and consider reaching out to them and deciding if it’s right for you, along with prices.

Question – I have a 125 engine. Can I install a 150 top end instead?

Although I have not completed this task myself, I see no reason why you can not install a 150LD engine top end onto a 125LD engine. The engine case is the same part number (Lambretta 12111012). Required parts would include: Cylinder Head + gasket; Manifold + gasket; Piston; Gudgeon Pin; Piston Rings.[/vc_column_text][vc_column_text]

Lambretta Engine Basics Including Boring & Should I bore a 125 to a 150?

If you were looking at boring the cylinder to improve performance, there is no point in doing so in my opinion, as little to nothing can be gained in this area.

The following link covers a number of basics and although not specifically aimed at LD’s, it will aid in understanding a number of engine basics, including boring