Engine rebuild, LI Series 4-speed

If you’re having a Lambretta LI series scooter, it maybe time for a general overhaul or engine rebuild as all Innocenti Lambretta engine blocks are over 40 years old now. Despite the good and reliable design and manufacture. Although a good maintained engine can last for more than 40.000km with minimal intervention, maybe some new piston rings and some gaskets.

Engine rebuild cutout

Here underneath you’ll find some photos about a complete engine rebuild. Especially if you thinking to add some extra power to the engine you better be sure all parts are in excellent conditions.
This section doesn’t pretend to be complete but you will have a good idea of the work evolved. Beware before you begin this isn’t a job for beginners, you will need several specialized and good quality tools.

Steps needed for an engine rebuild:

It’s logical that such a rebuild job can’t be done while the engine is still in the scooter so prepare to remove the engine from the frame:

  1. Remove both footboards left and right
  2. Remove rear shock and black rubber engine end buffer
  3. Remove the flywheel and cylinder cover
  4. Remove the silencer
  5. Disconnect throttle cable and air filter and remove the carb
  6. Disconnect the flywheel leads from the connector block
  7. Disconnect clutch, rear brake and gear change (2) cables
  8. Remove the engine bolt. Sometimes it can be rusted inside so use some WD40. The washer-method can help to remove the bolt bit by bit. Add some washer and span the nut until end of the thread, add some more washers and again span the nut.
  9. Once the engine is removed start to give it a thorough cleaning.

Before starting with the real stuff in the engine rebuild process, begin to remove all the auxiliary parts like kick starter, gear, rear brake and cloth engager, finally the head, barrel and piston.

See also the gearbox pages and torque settings page.

Here’s a list of replacement parts you will need for doing the engine rebuild.

Complete gasket set:
Different types available for 125/150/175/200 engines including:
gaskets for: engine casing, cylinder, cylinder head, bearing plate (drive side, round), inlet and outlet manifold, mag flange, ignition cable outlet.

on rear brake, clutch and gear arm, 3 O-rings: 12(inner diam.)x2.5(ring thickness)
on main shaft 22×1.8

Engine mounts:
Standard and wide types available. When using the wide type you will need 290mm long engine bolt with two M16 step 1.5 threads.

16 x 20 x 20 Small end needle roller. (same as P200E)
gudgeon circlips (2) 16mm internal

Drive side:
6305 Bearing (high performance bearing by SKF part# 6305 C3 or 6305 000 retail: € 27.
Make sure though that the drive side bearing is a “C3” grade – this grade of bearing has a radial internal clearance greater than a normal bearing to allow for the additional heat build up.
There is also a “high load” version of the drive side bearing – the standard bearing has seven balls in it and the “high load” version has eight. RS or 2RS means it has a 1 or 2 rubber seals, remove at least the drive side one for lubrication with gearbox oil.)
33 x 50 x 6 Oil seal (retail: € 7) make sure it is a double lip model (DIN 3760 AS or R23), recognisable by a AS or RP suffix (A=single lip). 5when a FPM prefix is used then it is high resistant to unleaded fuel Viton seal.
4x M6x16 flathead countersunk screws to hold the bearing plate, preferable hex type.
Maybe when the old crank’s sealing surface is damaged by wear, Speedisleeves can be used to compensate.
Most common are seals made of Nitrile (prefix: NBR) which can resist a continues use at 105°C. Seals made of Viton (Prefix:FPM, colour: brown) are about 50% more expensive an can be use up to 200°C.
i.e. Nitrile seal with double lip: NBR33x50x6AS

Ignition side:
NU 2205 Bearing (GP200 only) or NU 205 Bearing (all others).
part#  SKF GP200 = nu2205ecp all others nu205ecp (extra capacity polymide)
33 x 52 x 6  (retail: € 9,5) and 25 x 42 x 6 (retail: € 5,8) Oilseal
Circlip of 55mm (52mm internal)
Points and condenser

Rear wheel:
The bearing is special made for Innocenti (for example by SKF part# 440029, but unknown now or 2062)
32 x 45 x 6 Oilseal  (retail: € 2,2)

Gear box (endplate):
6004 Bearing
circlip 42mm internal
small tie rod circlip gear arm 6mm external

Kick start shaft:
22 x 32 x 5,5 Oil seal (5,5 not easy to find) (retail: € 6)
shaft circlip 20mm external, piston circlip 18mm internal

Layshaft (X-mas tree):
20 x 24 x 10  inner race (retail: € 4,5)

16 x 22 x 12 inner needle roller (retail: € 6)

24 x 28 x10 clutch needle roller bearings (2x) (retail: € 5,6 /piece) or bronz bush on some models
clutch arm circlips: 10mm (external) for lower and 12mm for upper