My recent messages regarding gear ratios etc have lead me to discover some poor Norton engineering practice as regards chain life.
On many bikes with a larger (650 and 750) size engines there is a primary drive set up with a ratio of exactly 2:1. This is comprised of a 21T engine sprocket and a 42T clutch drum.
You can see straight away that there will only ever be just TWO chain to sprocket combinations. Any one chain link will only ever see two teeth of the engine and clutch sprockets. This is considered poor engineering practice, although it also occurs in the camdrive set up too, but there is far better lubrication here.
If the engine sprocket is not a direct multiple of the clutch sprocket the chain wear will be more uniform. For example if the engine sprocket is increased by one tooth to 22 or dropped to 20 there will be around 80 (or is over 900?...I do not have time to work it out)engine revolutions before the same chain teeth engage on the same sprocket teeth. What ever thecombination number you can see the benefit, and you can see that a chain drive (and gears) should avoid direct multiples of ratios to even out the wear and a possible exageration of ovalityoccuring on the sprockets and chains.
As a footnote, Velocette introduced an idler cog in their gear train with an one extra "hunter tooth"for the very same reason.
Les.
Oh Dear, just jumped out o…
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Oh Dear, just jumped out of bed realizing that the message I had written above is completely WRONG....OH Dear, sorry for that. Itâs a pity that I didnât write it on April the first, but no excuse Iâm completely wrong Iâm afraid. I was forgetting the chain itselfâ?doh! Yes as long as the chain is also not a multiple of the driving sprocket you will have many teeth to link combinations before you get a repeat of the meshing.
So with primary chains of typical length of 76 links and rear chains of around 97 links you are not easily going to get a sprocket that will divide into that number.
If the primary chain was say, 84 links and you had an engine clutch set up with 21T and 42T you can see this would be create a problem, but it isnât, and Iâm sorry for wasting your time on that oneâ?.whereâs my coat?
Les