HOW TO, SPROCKETS & CHAINS

 

HOW TO, SPROCKETS & CHAINS

HOW TO, CHAINS & SPROCKETS

Another “Gem”, this one had the split link on backwards!

 Just about every machine that arrives for rebuild is in need of new sprockets and a chain. Never
in the world of sprockets and chains just change one item ….. change the LOT! Most 70’s
machines that I get are still on their original factory parts and therefore one way or another they
are shot.

The tools we need

Let’s look at all the usual problems going back in time to the 60’s when nearly all bikes were not
fitted with chain tensioners, and when they first arrived on the scene people were a little unsure
how tight to run the chain with this new fangled device. Then there were often huge chain guides
to try and keep the chain on the big sprocket and of course if they got bent on a rock the chain
would come off and invariably come tearing forward where it would “double up” and smash the
forward casing. Many machines of the 70’s were modified to facilitate getting the chain on the
engine sprocket and the Ossa stands out in my memory as being difficult especially with my
“watch makers” fingers. Many others were cut as rectification after chains had damaged the
forward cases. Nowadays we often see the engine sprocket running bare and in all my years
riding I have never seen anyone get their foot in the sprocket so I guess we really don’t need
that protection.

So what goes wrong in this area? old chains would always stretch and it was quite common to
have to take a link out after 3 months running on a new chain. The only ones that didn’t stretch
were Renold “Racing Chain” if you were lucky enough to get your hands on one. As the chain
stretches it will start to “hook” the rear sprocket and has a similar effect up front where the
grooves become elongated. An old test was always to take hold of the chain about midway
round the rear sprocket and pull back, if you could see the teeth easily then the chain is toast!

Just like Golf he “Hooked” it

Advanced Hooking, and now the teeth are breaking off and the chain will soon run round the
outside

Another way was when the chain was off, turn it on it’s side and see how much curvature from
the horizontal there was, again if it was a bit “grannyish” it was time to go.

Curvature on a “used” but not trash chain

Curvature on a new “Renold Racing” chain

Another false economy is the practice of reversing the sprocket after it has become hooked.
I have one in the workshop which is the worst case of “shade tree” I have ever seen. This came
off a 74 Yam TY250A and boy wonder had turned the hooked sprocket over and then managed
to rip off some of the teeth before the chain went whistling forward and smashed the timing side
cover. No surprizes there as it’s a dished sprocket and would have been running at least 1-2
inches out of line with the engine sprocket.

Some elongated engine sprockets…. soon they will make that “CLACK  CLACK” noise

Going back in time, in trials where they was traditionally a lot of mud and water it was essential
to have your chain well lubed and older bikes all had “chain oilers” fitted but they did however
make one hell of a mess! After 3 events it was necessary to boil up the “goop” and with an old
coat hanger wire through the last link let the chain sink into the hot liquid and then when the
grease had penetrated all the rollers you would hang it up and let the excess drip off. Bit messy
but it did a good job. There is a new product on the market which does just this in a spray can.
Other lubricants out there you might think twice about using, some are good while others do
little more than wet the chain and fly off at speed all over the bike. Others exacerbate the
problems by acting like flypaper and attracting all the fine grit and sand such that it sticks to the
chain and then acts like emery paper on the rollers and bearings. Since being in Arizona I have
now opted to run my chains on the drier side and have had less problems.

When changing sprockets it may be worth lowering the gearing to be in line with the modern
bike sections, and in most cases this will be one tooth less on the front or + 2 teeth on the rear.
Don’t go too small on the engine sprocket as the chain may start to hit the swinging arm. Also if
you are using a bigger chain , say 520, you may find that it won’t run smoothly around a 10
tooth engine sprocket….. so think before you leap. Changing the front sprocket can be simple or
difficult depending on the make. Yams are easy as they use a simple key tab and a nut. Use your
flywheel holder and then flatten the tab and undo the nut and slide the old sprocket off it’s keyed
shaft. Some Montesa’s run on a tapered shaft with a woodruff key and can be confusing when
the replacement sprocket is not slotted to take the key? Some have small screws while others
just use a circlip in a groove.  Use a chain guard where ever possible as the mud, if you are riding
in mud, coming off the rear tire will be deposited on the chain and eventually clog up the front of
the motor.

New Sprocket, new chain

Buy a chain breaker, 2 styles shown earlier, and when you fit the new chain take a little care to
ensure you cut it where it needs to be. Like everything else the split link can be fitted the wrong
way (I see a lot!) curved end faces forward, a bit like a comet with a firey tail.

So having gone to all the trouble and expense make sure everything lines up when you refit the
wheel, also I always fit a new tensioner block and spring and check the assembly is also in line
with the natural chain run.

This tensioner has been out of line and the chain has cut through the block and
the steel

Nice line up on the new block

Finally always carry a spare split link! No good having one at home or in the truck…. carry one!

TONY DOWN

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