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FERCing final drive chain

Posted: Mon May 06, 2019 9:00 pm
by robjameson
I purchased a new final drive chain at stafford as my old one has got to the end of its adjustment.
100 links as quoted, and when I fit the new chain, it is towards the end of its adjustment!

When I counted the links on the old chain, I discovered that I had a half link in the chain, so I was running 99 links!

So, my question is - as I run a 22t engine sprocket, is this enough to cock the final drive chain length up?

Re: FERCing final drive chain

Posted: Thu May 09, 2019 10:00 pm
by paul.jameson
The engine sprocket size can affect the number of links needed in the primary chain but all that does is alter where the gearbox mainshaft ends up in terms of the range of gearbox adjustment. With 22T instead of 23T and the standard size primary chain the mainshaft will be closer to the back of the range of adjustment than the front if we assume (and this is by no means a safe assumption) that the standard 23T puts the mainshaft midway along the adjustment range. Hence the rear chain appearing to be close to fully adjusted. The manuals of the era generally give suitable instructions for shortening or lengthening a chain which suggests that this was often necessary. So expect to remove a half link in due course when the new rear chain has worn a bit.

Chains these days tend to have an easier life than they did 60 or 70 years ago. The FERC helps massively but perhaps not as much as the option to use alternative transport (the car) when the weather is wet. Using the bike in all weathers in the early 1970s I went through chains and sprockets maybe slowly but surely. In the past 20 years or so, when I have been out in poor weather due to chance rather than necessity, chain and sprocket wear has fallen drastically.