Friday, 29 April 2016

Glandular Diversion

My recent article, 'Glandular Fervour', showed the gland packing replacement task ahead. However, prior to that, I had a little idea to temporarily prevent the leaked water ending up in the crankcase.
Grommet
By wiring a grommet around the pump shaft to just the right tightness, hopefully, with the shaft well greased, any leakage should be diverted away from the lower gland and out to the drain.

Fingers crossed!

Thursday, 28 April 2016

Being a Dipstick

In an August 2013 article, I was left with a mystery. Why did the rear engine require so much less crankcase oil than the front engine to reach the dipstick half-full mark?

At the time, I'd assumed there was something lodged in the rear crankcase but didn't investigate further. Some three years or so later, while preparing to clean out the rear engine's oil sump, the actual reason has become apparent.

Take a look at the following photo with the two dipstick heads highlighted.
A new slant on dipsticks
Although the photo is taken from slightly above the level of the dipstick heads, it is clear that the far one is not only at an angle but considerably lower than the nearer one, about 3" in fact. I'd not taken any notice of this before and assumed that the dipsticks told the truth. When I checked the two dipsticks together, I found they were identical in length and markings. Thus the lower one dipped 3" further into its oil bath registering full rather in advance of actual fullness!

This answers the mystery of the differing oil requirements for each engine. What worries me is how long has it been like this and why are the two engines different?

Of course, the rear engine will have been running with two fewer gallons of crankcase oil than the front one. Hmm...

At some time in the future, the rear dipstick will need fixing. In the meantime, yet another mystery has also been solved.

In this photo, there is a drain cock to let water out of the sump and another highlighted in the top right.
Extra drain cock, top right
I'd wondered what this extra drain cock was for but now I know. Examining the front engine's dipstick for where the oil level would actually be in the sump, it is clear that this drain cock would let out any oil above the full dipstick level. Thus it is an alternative way of checking for sufficient oil without a dipstick.

The rear engine had a blanking plug instead of a drain cock so I swapped the two. The rear engine oil level can now be checked using the drain cock while the front engine's dipstick can still be relied upon.

The mystery has been solved but why the two engines are not identical remains an unknown.

Tuesday, 26 April 2016

Glandular Fervour

In February 2016, when Sentinel 7109 took its first self powered trip in decades, it was clear that there were a few problems. One being that the various glands which seal piston rods and pump plunger shafts have gone hard or have been overtightened in ignorance recently or in the past.

There are 18 of these associated with the two engines and their boiler feed pumps. Some are worse than others, particularly the pump glands which are letting water out and down into the crank cases. Whilst crankcase oil is designed to allow the water to separate out from the oil and be drained, I'm not sure it was designed to cope with gallons of water!

These photos are from April 2009 and show the state as found of the front engine pump glands.
Glands within the pump assembly
There is an upper and lower gland, one should prevent water leaking downwards from the pump, the other to prevent water that did leak from entering the crankcase below.
A bit Rusty?
It's difficult to tell whether the rust had accumulated during use 50 years ago or subsequently.
No better from this angle!
After much restoration, the front engine pump glands are shown operating in this video clip on YouTube. (Sorry, it's too big to include here).

Clearly there is work to do! I took apart the rear engine's upper pump gland and poked in the camera to see how it was.
Rear engine's upper pump gland
The gland material looks pretty hard with a small gap around the plunger. This will have to be dug out and replaced before it will work well. Fortunately the shaft seems to be fairly parallel so it may not need replacing. Anyway, it's easier to try a simple fix before a complicated one so I'll do the packing only to begin with.

I've been recommended greased hemp rather than graphite or PTFE for water pump applications. It needs to be 3/8" square section. Sentinel used to have an off-the-shelf item for this but it doesn't seem to be available any more for some strange reason...!

Tuesday, 19 April 2016

Front Engine Sludge

Vertical Sentinel locomotive engines were designed to allow for water to accumulate in the crankcase sump, the lowest part of the engine itself.

The water comes from condensation and leakage in the boiler feed pump piston glands. It's dealt with by using special 'Crank case oil' which is formulated to enable water to separate out from the oil quickly and sink to the bottom below the oil itself. A drain valve is provided to enable the water to be let out periodically.
Front engine sump cover in place showing the water drain valve
I'd noticed when draining the water that it seemed to drain out intermittently as if there was something not quite right in the front engine's crank case. Additionally, the dipstick did not seem to register whenever I added some more oil.

The only way to find what was happening was to remove the crank case cover and have a look. It wasn't a difficult job but required the oil to be drained first (about 11 gallons of it!).

There was at least 1/2" of thick sludge in the sump.
Nice! Gungy viscous mess about 1/2" deep or more
I drained the sludge and put the crank case cover through the parts washer to produces something a little more serviceable.
Even nicer!
The crank case cover is sealed by a gasket containing a perforated metal coarse filter.
Coarse filter as found
I tried to remove the filter but it did not want to come off easily. I also didn't want to break the filter in case I couldn't get another. I took the easy way out by blowing compressed air through it to remove the remaining oil and any potential blockages.
Coarse filter after (it's not from a beehive!)
The cover is now back in place awaiting the oil to be replaced, hopefully without any gasket leakage!

Friday, 15 April 2016

Re-Chained Malady

Last time I wrote about fitting the two drive chains, I'd been concerned that one chain seemed much slacker than the other. I counted the number of links on each chain and checked that the corresponding sprockets had the same numbers of teeth. All were present and correct. 

Fellow member of the Sentinel Drivers Club Keith Reynolds visited the Midsomer Norton station open day at the end of February 2016. He explained that chains can stretch and that this was probably the cause. The stretch can be detected by laying the chain on its side and lifting one end. The curvature of the chain indicates the level of wear in the link roller bearings. The greater the curve, the greater the wear.

Although I could not do this while the slack chain was in situ, kicking it showed that it had a lot of sideways play.

So I decided that the best option was to simply replace it with another of the spare chains and take a chance on the result.

I was lucky as can be seen below. The two chains are very similar in tension now and I didn't have to do any axle adjustment.
Nearside chain replaced (the less shiny one)
The two chains are now similarly tensioned.
So a day well spent.


My apologies for the lack of blog material lately. Actually operating 7109 is great fun but without a 30ft selfie stick, it's very difficult for the driver to get any of his own photos!
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