BSA M20 - How to Measure Wear in a Motor Cycle Chain

the chain has located on the sprocket teeth, engage
a gear and gently turn gearbox over with the
kickstarter. This will feed chain round gearbox
sprocket. When sufficient length of chain is hanging
below sprocket, disengage gear and chain can then
be pulled round until both runs can be fed inside rear
chainguard and engaged on rear wheel sprocket.
HOW TO MEASURE WEAR IN A MOTOR CYCLE
CHAIN.
First carefully clean off all oil, etc., from the bearing
surfaces of the joints, i.e., from the bush bores and
bearing pins. Next, place the chain on a flat surface
and exert a pull on the ends. (Actually measurement
should be made under a load of 28lb. For .5in. pitch,
or 44lb. For .625in. pitch chain, but a sufficiently
accurate measurement can be obtained providing the
chain is pulled enough to take up all joint
clearances).
Having extended the chain to its maximum, measure
the distance between the bearing pin centres over a
pre-determined length; the measurement so obtained
can then be compared with the nominal length, the
difference being, the amount of wear that has taken
place. For example, if it is decided to measure the
distance over 20 pitches of a .5in. pitch chain, the
measurement should normally be 10in. If in the case
of the worn chain the same number of pitches
measure 10.20in. the elongation is of course .20in.
This amount, expressed on a percentage basis is:
.20
It is possible to measure the whole chain, but it is
preferable to measure successive sections as this
will show whether wear is varied or equally
distributed. If the whole chain or any section shows
the equivalent of 2.0% wear the chain should be
replaced. It is incorrect to try to measure chain wear
by checking the difference in length when the chain is
pushed together against its length when pulled out,
as this makes no allowance for the small clearances
which are present even in a new chain.
”
10 x 100 – 2.0%
31