Wednesday, 7 August 2019

Improved Oiling for the inter-axle Chain

Whilst I've written extensively about Sentinel 7109's front drive chains, I've said very little about the chain which links the two axles. It does the job more conventionally performed by connecting rods. The chain was in place when Joyce arrived in 2004 and I've largely just left it to get on with its job.
Highlighted original oil pot and down-pipe with wipe-rag
Oiling the chain was originally done by gravity. A pot fed oil down a tube to the chain via a rag which wiped oil on the links as they moved past.

The oil pot was another example from Joyce's missing items portfolio so I had to construct a new one. I used the end section of a small argon gas cylinder and added a valve to turn the flow on and off.

These items are hidden in the photo below beneath an upturned metal cover (OK, it's a bean can but it was a perfect fit!). The down-pipe is original but the new rag was a hem extracted from an old pair of jeans.
Gravity-fed oil feed
In so far as it went, it could do the job just about adequately but I was forever either forgetting to turn it on before moving off or leaving it on when stopped so one link got deluged and the rest left dry. (Perhaps the original pot used a wick?). What was really needed was a similar system to the front drive chains such that oil would only be provided when moving.
Being driven by the engines, the mechanical lubricator was an ideal candidate but its four pump barrels were already allocated.
Mechanical Lubricator (before restoration)
In the above view, the right hand pump feeds the near-side drive gear bearing and the next one feeds the off-side drive gear bearing. The third from right feeds the steam supply and the left hand one feeds the front chains via a pair of drip trays.
Drip trays and drip feed tubes
Initially I thought that the mechanical lubricator was out of bounds but experience showed that a good supply of oil was already being fed through the drive gear bearings into the drip trays without any additional oil required from a dedicated pump. Thus the left-most pump was effectively a spare.

In the back of my mind has always been the thought that 7109 was a prototype and thus some parts/methods of operation were possibly experimental and not well tried and tested; they could thus be improved.
Oil from the gear bearings into the drip tray
I set out to construct a feed from the mechanical lubricator to the inter-axle chain. My plan was to suspend a three-drip device above the chain and connect it by a pipe to the lubricator.

A number of parts needed to be made:

1. An adaptor to connect a pipe to the lubricator pump.
2. The pipe itself (I chose to cheat and use rubber fuel hose).
3. The three-drip device.
4. Rigid support for the feeder so it wouldn't shake it all about.

The adaptor seemed an easy task: it would be needing BSP threads obviously? No it wouldn't! To cut a long story short, it needed a rare British Standard Cycle thread as used on push-bikes and motor bikes. The thread was actually 3/4" 20tpi and taps and dies were surprisingly easy to obtain (Ebay).
The rubber hose adaptor rightmost
The adaptor consists of a coupling with a female 3/4" BSC thread end to end and a plug screwed into the top. The plug is tapped for a standard 1/8" BSP hose adaptor. The coupling is screwed on to the pump first. The plug seals against the top of the pump with a fibre washer. Heldite was used to seal the hose adaptor.
Three-drip device
I wanted to be able to set the three-drip device so that it would dribble on the left and right links of the chain as well as centrally on the rollers. Thus it would be required to be able to be rotated to get the drippers the right distance apart and in the right place.

Any resemblance in the body of the device to a Lidl compressed-air adaptor are purely coincidence of course (but it saved a lot of work for very little cost!).
The dripper attached to an angle-iron support
The complete dripper support
I made the rigid support using a pair of Stauff clamps to fix a vertical piece of 1.25" steel pipe (same as used for the vacuum braking pipework) to the front of the water tank inside the engine compartment.
Pipe clamped to the water tank
I then attached the angle iron support bracket to the pipe with another Stauff clamp.
Viewed from underneath
Stauff clamps grip the pipe very tightly and the dripper is held very robustly in place.
Not an easy photo so take (apologies for low quality)
The rubber pipe is supported in a fairly low-tech manner.
Rubber pipe routing
After a lengthy non-trivial design and installation task, I tried it out on a passenger operations day. It certainly works and there is now no shortage of oil for the drive and inter-axle chains and one less job to do when preparing to steam. There is still a good deal of fiddling about to do yet to get the flow rates right, not helped by the newly sorted central heating for the mechanical lubricator. The oil is now warmer and thinner as a result and the pumps provide more oil than before.

One question I don't have the answer to is how much oil does a chain need? I haven't oiled my mountain bike's chain for years and it is still happy; however, these chains work a little harder than my bike's so sufficient will be enough.

I'm also hoping to reduce the oil consumption. 7109 uses about 3 pints of cylinder oil a day - that seems a lot to me.

I'll remove the old gravity-feed oiler when all is set up satisfactorily.

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