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Starting a chain reaction
The Final Drive Chain is possibly the least thought about,
most abused and neglected highly stressed mechanical component on
the average motorcycle.
"Mechanical?" I hear you say - "Certainly" I reply. Each link comprises
two precision ground pins peened at each end as a rivet, two bushes,
two rollers and two side plates. A further pair of outer
side plates join each link to the next link, so every inch or so of
your chain has ten moving components.
The chain is measured by the number of pitches, which is the
gap between each pin or rivet, so the gap formed by the outer plates
connecting the actual links is also a pitch. When giving a chain length
also include the "split" or joining link as a pitch. An average
chain for a six-fifty twin therefore, has about one thousand moving
parts.
Imagine then, the friction and heat build up from an unlubricated
chain. This friction and heat is helping to destroy the sprockets
on which it runs too. All in all, potentially a very costly exercise,
for the sake of a little oil on a regular basis. A wide variety of
specialist chain lubricants is available. After giving a useable old
chain a good scrub in paraffin, I use the Linklife "boil in the box"
type as it ensures total penetration into the bushes. Thereafter I
use an aerosol spray on type for routine oiling.
It is no less important to keep the chain tension correctly
adjusted. Primarily to promote minimal wear, but just as important,
to eliminate the "snatch" effect a loose chain has on taking
up the slack after a gear change or in throttle on/off situations,
in traffic for instance.
This makes uncomfortable riding and promotes stress in the transmission.
Just because the primary chain is enclosed and running in an
oilbath, doesn't mean you can forget it, he same advice applies. Remember
also that over tight chains will impose undue stress on bearings as
well as themselves.
Speaking of stress on bearings, this time the bearing bushes of the
chain itself, I have on a couple of occasions, opened a primary drive
case to find a selection of broken rollers and bushes in the bottom.
The chain should have been replaced thousands of miles ago it was
running partly on rollers and partly on the pins. No wonder the owner
complained about harsh transmission!
Finally, because chains and sprockets do not wear evenly all around,
before adjusting, rotate the chainwheels bit by bit, checking
for "tight" spots. Adjust for recommended "free play" at the
tightest spot.
Is my chain worn out yet?
After cleaning, the simplest way to see how worn the chain is, is
to lay it along the ground, turn it onto its side plates and pick
it up by one end only. A good chain will droop by no more than 30-50
degrees at the other end, beyond that and you're beginning to accept
excessive wear on both chain and sprockets.
If the chain droops vertically, or you can pull the far end
back towards you beginning to form a loop, it still has a use. You
can keep it in the workshop to use as a "dummy" to join to
a good chain, pulling it into place on the sprockets while you service
your good chain. Alternatively, use it to reinforce concrete.
Chain sizes
Most imperial and metric sized chain is interchangeable, the "metric"
sizes being direct equivalents of the imperial sizes, eg 5/8 X 3/8
= 530. Here is a handy conversion chart
Renold 110044 = ½ "X 3/16" = 420
* (see below for exception)
Renold 110046 = ½" X5/16" = 428
Renold 110054 = 5/8" X ¼" = 520
Renold 110056 = 5/8" X 3/8" = 530 or 50
* BSA/Triumph Bantam/Cub and similar earlier lightweight British motorcycles
must use Renold ½" X 3/16" chain. This is because metric equivalents,
although having the same pitch and width, have slightly larger rollers,
which of course will not seat into the sprockets and will very quickly
knock the tops off the sprocket teeth. - I found this out the hard
way, stranded in moorland miles from anywhere on a Bantam trail bike
with nothing more than bumps on a gearbox sprocket I'd only fitted
three months previously.
Where you must also be careful is if choosing a modern heavy-duty
chain, ensure that there is sufficient side clearance, as the side
plates of these chains are thicker and some models have barely sufficient
clearance for the standard chain.
"A Stitch In Time"
There is a more serious consequence of ignoring chain maintenance,
as a young friend found, to his great cost. 'MV' rode a T120 Bonneville,
a good-looking bike in nice overall condition. It was his daily transport
and he was to be seen "caning" it all over the locality, often with
his girlfriend, Augusta, on the pillion.
I'd pointed out to him over a period of some weeks that he really
should adjust his rear chain, which was hanging very slack indeed.
I'd ridden close to him on more than one occasion and watched with
alarm as the lower run of the chain snaked not only up and down, but
sideways too. "You'll hit a bump when you're well leaned over one
day and that chain will run clean past the rear sprocket" I warned
him, but he was always too busy to attend to it.
The inevitable did happen, just as I had predicted, but the result
was far worse than I had foreseen. Augusta had a spell in hospital
with a broken leg, they were both torn and bruised, MV was devastated,
"Oh how I wish - - - "
As for the Bonneville, the chain had indeed missed the rear sprocket
and run around the outside of it, jamming between the brake plate
and the swing arm. The rear wheel locked up and down they went. MV
got off lightly, with scratches and bruises, and Augusta's leg repaired
itself in due course.
The Bonneville however needed more than just routine maintenance.
The swing arm was twisted, brake plate warped, left silencer flattened,
footrests and handlebar bent, seat cover torn and paintwork scratched.
Quite a bill for the want of five minutes no-cost attention.
| Comments |
| Ton Up 8th June 01 | great story, i get the feeling that spannerman is a tad on the smug side here!!
| | Spannerman 16th November 01 | Not at all! I was fond of both the young characters described (names changed - protect innocents & all that) and was genuinely upset when I heard of their (avoidable)accident.
| | Shadow Shack 12th April 02 | Too true. I have a friend who rides a CBR1000, his chain snaps and dangles although not quite as bad as your story describes. I kept telling him to fix it, and he claims the bike has a self tightening chain (self tightening valves maybe, but I never heard of a chain...).
He had a spill one day, took a turn too hot and went off the road to lay the bike down. Not chain related in any way shape or form, but I had the bike in my possesion for a time bending it back into shape. I also tightened his chain tension, unbeknownst to him, to Honda specs on the CBR1000.
from the Shadow Shack
| | Sophie 10th December 02 | Good information...thank you
| | george goddard 24th April 03 | first time on your site i have sent it to all my friends can you please tell me the renold chain details that will fit my yamaha R6 many thanks George
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