This is the Allett C34 and we're going to look at the final drive chain tension on this machine.
First thing we need to do is to remove the guard. The final drive is made up of two chains and three
sprockets. The drive comes effectively from the engine crankshaft through a belt system to
this intermediate pulley which does a large speed reduction so we can change engine speed rotations
to rear roller rotations and it's important that we check the tension on these two chains. There is
the lower chain and the upper chain. The lower chain is thicker and more substantial than the
top chain because the top chain is turning more quickly therefore there is less torque after the
speed reduction the chain is now going much more slowly and therefore the torques are higher. We're
going to look at the tensions of these. It's important they're tensioned correctly so they
don't come off or are damaged and also keeps the noise levels reduced as much as possible. When
looking at the chain tensions we check the lower tension first make the adjustment of the position
of this sprocket and then once we're happy with the tension of the lower chain then we can adjust
the tension of the upper chain. So we can see that these chains are too loose and I'm going
to increase the tension on them. So if we look at the tensioning of the lower chain first we need
to do this one first and the top chain second. So the lower chain is going to be tensioned by moving
this intermediate sprocket. The intermediate sprocket is retained within the chassis within
a slot so by using a 17 millimetre spanner at the bolt behind the spindle of this sprocket
and also this 30 millimetre spanner on the front I'm able to release the spindle from the chassis
and I just need to release that enough so that then I can move this sprocket
away increase the distance and therefore increase the tension on the drive. Once
I know the location where I want to go then I can then tighten this back up.
Once I'm happy with that location I'm going to tighten that up and I'm just going to do
a check on this by using a straightedge rule and just looking at the amount of tension and
I expect to see deflection here of about three millimetres to know that I'm at the
right tension. Once the intermediate sprocket has been moved in order to increase the distance
and tighten this chain then of course it will slacken even more even if this top chain was
at the right tension before this will now become loose because we've decreased the
distance between these two centres. This chain simply tensions by using this small idler. To
change the tension in this chain I'm just going to move that idler two 17 millimetre combination
spanners inside/outside I just need to do that enough so that I've got the movement here and
then I can pull this into a location where my tension is actually where I need it to be. So
I use the inside spanner to push the bolt head through and then I just need to tighten this up.
By using a straightedge again just here then I can check that I've got the tension that I
require here and again I'm going to go for roughly about six millimetres movement. So now that we're
happy with the tensions of the chain we will also look at whether these need lubricating so
either use some chain oil or some grease on these chains before we then put the side guard back on.