On the Lambretta, power is transmitted from the crankshaft to the transmission via a duplex chain (simplex on Junior and Lui models). This primary chain is one of the components under the most stress and affects smooth operation, power transmission, and the service life of the sprockets and clutch.
At Scooter Center, we carry only high-quality IWIS chains
made in Germany, continuously riveted, and suitable for all engine variants of:
Recommendation: Check the chain after the first approximately 1,000 km and adjust it, if necessary. After that, our IWIS chains remain extremely stable, and no further stretching and associated chain alignment should happen.
The correct chain length and suitable chain guides / chain tensioners
The required chain length depends on the combination of the front and rear sprockets. Thanks to the new generation of chain tensioners, which allow the chain to be tensioned downward as well, it is no longer necessary to search for used—and thus elongated—chains from old original engines. A classic example from the past is the TS1 engine with a Li 150 gear box and a 16/46 sprocket combination, which used to require a stretched 80-link chain. Today, this is simply achieved by using an 81-link chain and tensioning it downward.
Here is an overview of the possible combinations:
|
Sprocket Combination |
Chain links |
Chain tensioned to |
|
15/46 |
80 |
top |
|
16/46 |
81 |
below |
|
17/46 |
81 |
top |
|
18/46 |
82 |
below |
|
19/46 |
82 |
top |
|
20/46 |
83 |
below |
|
21/46 |
83 |
top |
|
15/47 |
81 |
below |
|
16/47 |
81 |
top |
|
17/47 |
82 |
below |
|
18/47 |
82 |
top |
|
19/47 |
83 |
below |
|
20/47 |
83 |
below |
|
21/47 |
84 |
below |
Incorrect alignment causes side-to-side pull, increased wear, and rough running.
When assembling the motor or replacing sprockets, check the alignment and correct it with shims if necessary—this is especially important for tuned motors and aftermarket sprockets.
The rear sprocket may be 0.25 mm lower than the front sprocket, but no more than 0.05 mm higher.
Measurements can be taken using a steel ruler and caliper or the MB tool:
Oil thrower plates
Casa Lambretta MB Developments
When replacing the chain, always check the sprockets as well and replace them if worn.
Conclusion
An original IWIS chain + a one-time tension adjustment after 1,000 km + proper chain alignment = maximum service life and smooth operation—for every Lambretta engine.
If you have any questions about the correct length or adjustment, we’re happy to help: [email protected]
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