Sprocket height and chain alignment

[dickie]

I changed my front sprocket from 18 to 17 tooth last night.

I knew that I'd aligned front and rear sprockets well so I compared new and hold heights i.e. from the machined Base to the upper flat surface of the teeth.

There was 0.8mm difference. Easily sorted by fitting a new shim under the clutch sprocket that was 0.8mm thinner that I had.

Anyway, it made me wonder if it really matters as I hear of folk changing sprockets ad hoc but don't get the impression that they're aligning the sprockets when they do.........

Also was I just unlucky in having such a big difference? I can't remember where I got the 17 from but the 18 tooth is from 'a reputable SIL dealer'.

Does it matter?

[Digger]

Does it matter? - depends on who you ask.

Some of these machines have been pottering around for several decades without going anywhere near a skilled or knowledgeable Lambretta mechanic and at the end of the day they are pretty agricultural.

[Knowledge]

I must admit, I have never checked the heights of the two sprockets in all my years. It is just one of those jobs I never remember to do. I have not suffered any drive chain failures and I have never heard of anyone who has had a drive chain failure as a result of misaligned sprockets.

I figure that if you hold a chain at each end and turn it on it side, there is always some sag, and this would be more than enough to cope with a misalignment of 0.5 - 1mm.

Let's hear your stories.