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You are here: Home > Lambretta > Lambretta tuning > Tuning options for 125/150/175cc engines using cast iron barrels
    

125, 150 and 175 ENGINE BASICS

Li 125, 150 Series 1
Li 125, 150 Series 2
Li / Sx / 125 Series 3
Tuning to the original cylinder is not really recommended because much work is involved for very little improvement (Except 150 Series 2, these are OK).
Boring the 125 cylinder beyond 150 cannot be done so MB Developments would prefer to convert to a series 3 150 cylinder or a 175 cylinder and then use a 2 ring 175-conversion piston.
We recommend that the original con-rod or crankshaft be replaced for a series three type or upgrade to a GP standard or race crankshaft. If upgrading the crankshaft then upgrade the flywheel and stator to a later type, or better still upgrade to GP electronic ignition. MB Developments don’t recommend SX electronic ignitions the flywheel weight is too heavy for the crankshaft and snapping of the taper or crank pin can occur, it is also prone for the cam to split!
If upgrading to a GP crankshaft high load bearings are required. (Series ones require a later type magneto housing.)

GP 125
Tuning to the original cylinder is not really recommended because much work is involved for very little improvement.
Boring the 125 cylinder beyond 150 can not be done so MB Developments would prefer to convert to a Series 3 150 cylinder or a 175 cylinder and then use a 2 ring 175-conversion piston.
The original crankshaft and ignition can be used but MB Developments recommend converting to GP200 standard or race type crankshafts, upgrade bearings and convert to GP electronic ignitions.
We recommend that the crankshaft be replaced as the original crankshaft uses an SX type crank pin and has been know to snap!

Li / Sx / Special / Pacemaker 150, Series 3
GP 150
Tuning to any type of cylinder can be done, MB Developments recommend boring out to 175 then use a conversion 2-ring piston.
The original crankshaft and ignition can be used but MB Developments recommend converting to GP standard or race type crankshafts, upgrade bearings and convert to GP electronic ignitions.

Tv 175 Series 2
Tv 175 Series 3
Tuning is no problem but the original piston is not very good for other than a mild tune. Converting to a Suzuki 190 piston is a better option. Ideally MB Developments would convert the crankshaft to a Li / Sx with the shorter rod or better still convert to GP standard or race type crankshafts, then use the better quality 2 ring 175 conversion pistons.

125cc = Bore 52mm X Stroke 58mm
150cc = Bore 57mm X Stroke 58mm
175cc = Bore 62mm X Stroke 58mm

MB DEVELOPMENTS TUNED KIT RECOMMENDATIONS

125, 150 engines

Tuning and boring 125 and 150 engines is usually a waste of time, it is more beneficial to jump to the 150 - 175 conversions.
MB Developments recommend a number of conversions that have proved to be the best set-up for all round performance.

1, 150 – 175 conversion.

150 cylinders bored to 175cc (or use 175 cylinders) then use either Vertex or SRP 2 ring performance conversion pistons starting at 62mm.

PROS: Good quality piston kits with a good selection of oversizes, from 62 to 63mm for Vertex pistons and 62 to 64.5mm when using the SRP pistons. A good kit to do either Stage 2, 3, 4 or a mild stage 5 kit when using a Vertex piston, full stage 5 is ideal with the SRP piston. A cheap conversion and can use existing crankshaft / ignition set up. No cylinder machining is required.
CONS: None really, the Vertex piston is not really suited to full stage 5 race conversions but still works fine.

2, 150 / 175 – 190 Suzuki conversion.

150 cylinders bored to 190cc or better still 175 cylinders bored to 190cc using a Japanese Suzuki piston starting at 64mm.

A Use the original crankshaft (107mm) and ignition set up or convert to standard or race type GP crankshafts.

PROS: Excellent quality piston kits with a good selection of oversizes 64 to 65mm (Japanese) then 65.5 to 66mm (Wiseco) Good kit to do Stage 5 or 6.
CONS: Because of the layout of 150 cylinder castings lower tunes are difficult to do. Expensive, as it requires a new crankshaft, bearings and ignition, requires a lot of machining work to be carried out to the cylinder. Extra machining to the cylinder base makes exhausts difficult to fit.

B Change the crankshaft to GP then use a Yamaha con rod (110mm).

PROS: Excellent strong kit good piston and rod set up ideal for stage 2, 3, 4, 5 and 6 tunes.
CONS: Expensive requires crankshaft, bearings and ignition change. Could need exhaust modifying to suit the machined cylinder.

C Change the crankshaft to GP then use a Yamaha con rod (115mm) this then requires a cylinder packing plate.

PROS: Excellent quality piston kits with a good selection of oversizes 64 to 66mm. Good kit to do Stage 2, 3, 4, 5 or 6.
CONS: A little more expensive due to the piston, extra machining or con rod swap required.

3, 175 – 200 conversions

175 cylinders bored to 200cc using either Asso or SR 2 ring pistons at 66mm then ceramic plated.

PROS: Good quality piston kits, no oversizes required, good kit to do Stage 2, 3, 4, 5 or 6. Ceramic plated in theory means less friction and is harder wearing and longer lasting. The largest safest cast kit available. No cylinder machining is required.
CONS: The kit requires the expense of normal tuning work but then requires ceramic plating (a chrome plating method) this makes the kit expensive.

175 engines

MB Developments recommend a number of conversions that have proved to be the best set-up for all round performance.

1, 175 tune

Mild tune using the original crankshaft and piston set up.

PROS: Cheap kit uses existing parts. Has a number of oversizes. OK for Stage 2, or 3.
CONS: Only mild tuning should be done to look after the original piston. Uses old parts and technology. Pistons are be coming hard to find.

175 cylinders converted to use Series 3 type crankshafts - see 1, 150 - 175 conversions above

2, 175 – 190 Suzuki conversion.

175 cylinders bored to 190cc using a Japanese Suzuki piston starting at 64mm. This can be done in a number of ways.

A Use the original crankshaft and con rod (116mm) convert the cylinder and head to Suzuki, this then requires a cylinder packing plate.

PROS: Cheapest 175 – 190 kit and uses existing parts. Excellent quality piston kits with a good selection of oversizes 64 to 65mm (Japanese) then 65.5 and 66mm (Wiseco).
CONS: Uses existing old parts. Because of this there could be a limitation with tuning spec.

B Change the crankshaft to GP or (Li / Sx) then use a standard or race type con rod (107mm) then convert the cylinder and head to Suzuki.

PROS: Excellent quality piston kits with a good selection of oversizes 64 to 65mm (Japanese) then 65.5 and 66mm (Wiseco) Good kit to do Stage 5 or 6.
CONS: Because of 175 cylinder casings lower tunes are difficult to do. Expensive, as it requires a new crankshaft, bearings and ignition, requires more work to be carried out to the cylinder. Extra machining to the cylinder makes exhausts difficult to fit.

C Change the crankshaft to GP then use a Yamaha con rod (110mm) then convert the cylinder and head to Suzuki.

PROS: Excellent strong kit good piston and rod set up ideal for stage 2, 3, 4, 5 and 6 tunes.
CONS: Expensive - requires crankshaft, bearings and ignition change. Could need exhaust modifying to suit the machined cylinder.

D Change the crankshaft to GP then use a Yamaha con rod (115mm) convert the cylinder and head to Suzuki this then requires a cylinder packing plate.

PROS: Excellent strong kit good piston and rod set up ideal for stage 2, 3, 4, 5 and 6 tunes.
CONS: Expensive requires crankshaft, bearings and ignition change.

CYLINDER BARREL DIFFERENCES

There are many differences between cylinders of different models, manufacturers and production runs, it is nearly impossible to know all these differences and as time goes on we will probably never find out!
Whatever the differences it makes very little difference when tuning or converting to a modern tune!
In terms of modernising a Lambretta with this article we are ignoring all 125cc cylinders and early 150 cylinders.
This leaves us with SX150, LI150, Pacemaker and GP150 cylinders. There are differences between these but are basically the same to look at.
An easy way to find out if a cylinder is a 150 type is to measure the bore (57+mm) and then measure the diameter between the 3rd and 4th fins, a 150 cylinder should measure 69.5mm. The major differences with 150 type cylinders are cylinder heights, it is critical to check squish clearances on rebuilding a 150-type tune. These differences can be over come by using a fat base gasket.
The TV175 to look at is different with transfer, inlet and exhaust port sizes, but done correctly affects nothing.
A TV 175 cylinder would have a bore of 62+mm and would measure 80mm between 3rd and 4th fins.
The differences show up when doing an old style Suzuki 190 tune. 5mm has to be taken from the base of the cylinder, the piston needs shortening to clear the casing at bottom dead centre. Then when setting up the tune and checking the port timings you find that inlet ports are abnormally small or too large and transfer timings can be spot on or far to big making the barrel slower than standard! For this reason I stay clear of this set up tune!
Considering this information if we used the same different cylinders with a Vertex piston the problem doesn’t effect the tune, because of the length of the piston skirt. This is the reason why Suzuki tunes work better with 110 and 115mm Yamaha con rods.
Spanish 150 cylinders have different port heights and tend to be slower as standard, but once tuned are fine.
Indian 150 cylinders tend to have smaller ports but once tuned are fine.
There has been over the years a number of pattern cylinders for 150 and 175 engines, some worked most didn’t. Most were very badly cast, machined and were soft, these didn’t last very long, these kits are still around today beware! There are also barrels from Lambretta 3 wheelers on the market. These barrels do not work well on Lambretta 2 wheelers!

PISTONS

In the above list MB Developments recommends three types of pistons: These are used for their reliability of the piston and ring and availability.
They are as follows:

Vertex 150 to 200cc conversion pistons, available sizes are: 62, 62.4, 62.6, 62.8, 63 and 66mm.
Suzuki 190 to 195cc genuine pistons, available sizes are 64, 64.5 and 65mm.
Suzuki 190 to 200cc pattern pistons, available sizes are 64, 64.5, 65, 65.5 and 66mm.
Suzuki 190 to 200cc Wiseco pistons, available sizes are 64, 64.5, 65, 65.5 and 66mm.
Yamaha 190 to 200cc genuine pistons, available sizes are 64, 64.5 and 65mm.
Yamaha 190 to 200cc pattern pistons, available sizes are 64, 64.5, 65, 65.5 and 66mm.
Yamaha 190 to 200cc genuine pistons, available sizes are 64, 64.5, 65, 65.5 and 66mm.
Other piston kits are available some are good some are not.

These makes are available. They all use cast iron rings.
Borgo, Heporlite, Diamond, Mahle, GOL, (2 ring) Asso, Vertex, (3 ring) These we would use as an alternative.

GPM, Meteor, Speed, Siam, Comec, Dinamin. These we would try to avoid. These sizes could be available 62, 62.2, 62.4, 62.6, 62.8, 63, 65 and 66mm.

Please E-mail us with any questions or comments.