Friday, 12 February 2016

Unchained Malady!

The last time I wrote about chains was in January 2012. That was to do with renovations, now it's time to actually fit them to Sentinel 7109.

After some discussion, I concluded that to fit these heavy items safely in an awkward situation was not going to be easy and required the preparation of some special tools to assist. It was going to be quite a complicated process to be able to get the chains into position mid-way between the sprockets and then get the chains over the sprocket teeth so that the two ends could be joined.

The first tool is a trolley to carry the chain under the loco.
Chain trolley
The centre of the chain is placed in the centre of the trolley with each end piled up to allow it to be pulled over its respective sprocket.
Trolley with chain in position
The trolley and chain are then put on a plank to wheel the chain into position. The upright support piece of wood is to prevent the trolley drifting off the plank and on to my lap whilst underneath!
Ready to go under
The next tool is, as Sentinel called it, a chain 'slipper' to allow the chain to be dragged over the sprocket teeth. One is needed for each sprocket.
Chain 'slippers' in place
I made the slippers from Aluminium strip left over from another job. I drilled a hole at each end and put in a bolt and nut to enable a strap to pull the ends together.
Axle sprocket with slipper
For the second slipper, I used two bolts so that a ratchet strap could be used to tighten the slipper with static straps to hold it once tight (I only have two ratchet straps so limited resources!).
Ratchet & static straps on drive sprocket
The chain was then wheeled into place...
Ready to drag chain over slippers
...and dragged over the drive sprocket.
...and over
The chain was then secured to prevent it from slipping back over.
Secured from slipping back
Then the slipper was pulled out after removing the bolts from one end to allow it to pass under the chain. (It had to be pulled quite hard!).

The same process was then applied to the axle sprocket and the two ends pulled together with a light duty lorry strap.
Ends pulled together from afar...
...and from anear with both slippers removed
At this stage, I came to the conclusion that the light duty ratchet strap was not strong enough to pull the ends together and that a heavier duty type might do the trick.
This photo shows that even that was not going to solve the problem.
So near yet so far!
I had assumed all along that the axles would be in the same position as when the chains were removed. However, clearly that is not the case and the axles and brakes will all have to be adjusted to get the sprockets the right distance apart for the chains to fit with the correct tension (+/- 2" movement mid way between sprockets).

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