Friday, 3 August 2018

Vacuum Exhauster

Images by Rob Bishop 

If you go back to the blog entry for 21 January 2017 the acquisition of a 4HP, 500cc Blackburne side valve engine for use as the vacuum exhauster was described.

Kerr Stuart Drawing 33728 illustrates the components needed to convert a Blackburne engine into a vacuum pump (and also, incidentally, how to convert the vacuum pump into an air pump for the subsequent trial on the Castlederg & Victoria Bridge Tramway).

The drawing was issued for the vacuum brake components on 8.2.29, with the air brake modifications being dated 19.11.29. Thanks to Blackburne engine enthusiast Martin Shelley, we have been able to obtain new pistons for both the pump and the starting engine. Rob Collins pointed us in the direction of vintage engine reconditioning specialists T&L Engineering to bore out and tidy up the cylinders to suit the new pistons.

Test fitting the new pistons in the bored out Blackburne engines for the starter engine and vacuum pump:

Inevitably the engines do have some other signs of age. A broken valve guide has been removed and replaced:


To convert one of the engines into a vacuum pump, one of the valves is plugged off, while an air release valve is fitted to the other. In the drawing below the release valve is shown on the left and the plug on the right:

These are the manufacturing details from the same drawing. Interesting use of the word ‘key’ to describe what we now call a spanner.

Rick has lovingly crafted these bits (including the spring, which we also have a drawing of), and they have subsequently been fitted to the cylinder head of one of the two Blackburne engines:


One of the things we do not have a dimensioned drawing of is the cradle to mount the exhauster, but this cradle was supported on a cast iron block with two keyway slots machined in it:

Cutting cast iron is not easy so the resourceful Mr Bishop resorted to good old fashioned chain drilling:

I’m sure there is a freemason analogy to what happened next on the milling machine:


While we don’t have a drawing for the engine mount cradle there more than a whiff of what is going on in the other drawings, so Will High has been drafting up some bits for laser cutting.

This is the modified engine, with one valve removed (and blanked off), no magneto and no carburettor, ready for its new role as a vacuum pump:

Will it make vacuum?...

Fit pump in lathe, stick vacuum hose out of window: 

Connect to train:


Whether this can be achieved in field conditions only time will tell.

Tuesday, 31 July 2018

Sump, block and camshaft

Images by Rob Bishop
More McLaren Progress

If you are holding your breath for the crankshaft replacement/repair you will go blue in the face. But we do have progress to report (unless you’ve been on the Facebook page, in which case this is old news). 

If we go back to the beginning, this is the sheared crankshaft and associated damage to the sump. Before…

And after Cast Iron Welding Services worked their patient magic...

Both the sump and the block have now had their faces skimmed in the horizontal borer at Boston Lodge...

The view below shows the repaired end of the sump after machining:

While the block was in the borer the top of the block was also skimmed:

Back in November 2016 the cam shaft was dismantled. While repair was an option, the cost for replacement was not significantly greater and while we are very keen to retain original components, there is quite a lot of pitting on the old shaft so we decided that replacement in this instance was a better option. 

This is what Christmas looks like in the Bishop household:

An object so beautiful it could be in the Tate Modern:

The cam followers are the refurbished originals:

Monday, 5 March 2018

Mclaren MDB4 engine update

Photos by Rob Bishop.

The current state of the Mclaren MDB4 engine, after return from Cast Iron Welding Services

The damage to the crank case has now been made good:

This shows the case before repair 

(Not the best set of pictures to illustrate the repair; we do not appear to have a good picture of the damage, but comparison of the above photo and the next photo shows the missing bit which has been replaced)

Crankcase after repair
The next task on the crank case and engine block is to skim the two mating surfaces to ensure that they are both true and oil tight. There is a large milling machine at Dinas so this is a task that can be carried out in-house. 

The repaired area of the crankcase can be seen in more detail in this view.  The damaged crankshaft can also be seen.
Flaw detection has confirmed that the damage is confined to the shaft itself and there is no cracking in the adjacent crank. 

In addition to the dye penetration test the crankshaft was set up in some ‘V’ blocks
 to allow the main bearings to be checked with a clock gauge. 
This confirmed that the shaft is not bent. The jury is still out on whether we repair or replace the crankshaft.
The pinion on the left drives a chain of gears to the camshaft and also the oil pump (see below).

While decisions are pondered on the big bits, progress continues on the ancillaries: 

This is the oil pump assembly, driven by the gear on the crankshaft as seen in the previous photo. 
For this photo, the pump has been placed on the line of the crankshaft. It is normally located in the engine inside the large hole seen directly below it. There is an idler gear on the spindle visible here below the pump, so the crankshaft gear drives the idler, which in turn drives the pump itself (see the lubrication diagram below)

This diagram illustrates the lubrication system, showing the pump and the gear train.

In the diagram there appear to be a number of pipes which lead to the crank shaft bearings. In practice these ‘pipes’ are formed of a series of interconnected oilways drilled into the crank case and engine block. 
The routes of these oilways have been marked up on the block in the photo below. At the end of each run there is a plug. There is an oil way from one end of the block to the other, with individual branches leading to each crank shaft bearing location.

The lozenge shaped cover is to the oil strainer and the fitting behind it is the oil pressure relief valve (the diagram is very diagrammatic!).

If you look carefully at the lubrication diagram you can see that there is also an oilway in the crankshaft itself, which takes oil from each bearing and feeds the big end - and in turn the little end on the adjacent con rod. 
The set screw in this photo of the damaged crankshaft is the plug on the end of one of these oilways.

Two more shots of the oil pump to close with:

This is the pump body

This photo shows the pump in place inside the crankcase
The banjo connection is on the oil line from the pump to the strainer.

Gearbox Repairs

Images by Will High

In the 6th December 2017 blog update the damage to the saddles which mount the gearbox on the layshaft was described. These screen dumps illustrate the proposed repair. We are currently waiting delivery of a kit of parts from a laser cutting supplier to move this aspect of the project forward.

The left hand (driver's side) plate will be located in the tight gap 
between the gearbox and the frame stretcher.

There is more space on the right hand side, so the plate will be outside the stretcher. 
This repair does not require any further holes drilling in the frame stretchers, 
in line with the conservation ethos of the project.

An overall view showing how the plates bear on the layshaft and
span the existing saddles, which will be left in their present (damaged) form

Wednesday, 6 December 2017

Assessing the gearbox

Photos by Rob Bishop
This is the story of the gearbox so far; it is like the rest of the project a mix of good and bad news.

45 years after it was taken out of use the interior of the gearbox is a beautiful thing, and once the bell cranks which operate the selector have been freed off, it performs beautifully.
How it works is very simple. It is a two speed box, with both speeds being available in forwards & reverse. The drive from the engine comes in on a bevel gear behind the forward/reverse selector. This meshes with one of the two bevel gears on the upper shaft. The upper shaft is splined, so depending on which direction is selected the upper shaft rotates either clockwise or anticlockwise. 
Also on the upper shaft are two chain wheels. The larger one on the left in the photo is for top gear, while the smaller wheel on the right is the low speed gear. Both wheels & chains are rotated by the upper shaft.
The lower chain wheels are mounted on roller bearings which rotate around the lower shaft. The central section of the shaft is splined, and drives a small external pinion which engages with the large gear wheel on the lay shaft. 
The drive from the high/low chain wheels to the splined shaft is via dog clutches, operated by the high/low selector.  

The photo below shows the high ratio gear, with the chain removed. The dog clutch is engaged and the chain wheel is driving the output shaft. The use of a dog clutch to change speed on the move is very crude and it accounts for a lot of the problems which exist and also places some of the historic stories into context. In a wonderful first-hand account published in FRM26 Bill Willans, who accompanied the loco on a lot of the trials states ‘On one occasion we broke some slates; she took a little care to start a train gently. On another occasion a drawbar was broken…’ 

It is easy to see why such things may occur. There are 2 ways to get a dog clutch to engage while the loco is moving; you can either be brutal or gentle. If you are brutal it may cause a snatch, if you are gentle the train can lose momentum, the couplings on a loose coupled train relax and when you let the clutch out, you can cause a snatch, particularly if the train has lost a lot of speed. It a nutshell it is never going to be good.

One of Bill Willans' other little snippets suggests that the brutal gear change was the order of the day. He recalls a failure when the loco was running on the FR, ‘the bell crank that operated the first gear fractured. The Glaslyn Foundry forged a replacement and a beautiful job they made of it’. To engage that gear, there must be a need to use quite a bit of force!

This is the bell crank for the high/ low gear selector. It is the component replaced by Glaslyn Foundry. Is this ‘the beautiful job’ or did it need replacing on a regular basis throughout its career?

The rather harsh gear change also accounts for the damage to the saddles which mount the gearbox on the lay shaft; when you engage gear, the forces on the pinion drive to the layshaft will place the saddles in tension. As these are part of a casting and cast iron does not behave well under tension, these forces have resulted in failure. The photo below shows the saddle in situ on the lay shaft, with the missing chunk being all too evident.

The gear box has been temporarily placed back in the frames to enable the team to measure up clearances and devise a solution. The previous repair option, brazing the saddle back on has been discounted, and we have reservations about a cast iron welding repair as the shock loadings which have caused the damage will reoccur once the loco is running again.
When we took the loco to pieces, the function of a couple of short little stays between the gearbox and the loco frames where not apparent. Their role became all too apparent in the trial run; these stays are an attempt to increase the degree of security between the gearbox and the frames. One of the stays can be seen on the gear box to the right side of the pinion.

Current thoughts on a repair are to form two large brackets which pick up from the annular row of bolts on the gear box end cover and to bolt these brackets to the frame stretchers.  

Saturday, 24 June 2017

Flats and Knobs

Photos by Rob Bishop

Just as nature abhors a vacuum, so the Ffestiniog Railway abhors an empty waggon. With the frames on their wheels there was an urgent need to re-load the WD flat before someone else took a shine to it. This is waggon 72, the ‘in’ tray, with (from left to right) the gearbox, the 1945 MR4 engine and parts of the cab.

The next item on the agenda is the gearbox, another load for waggon 71.

Something that needs some thinking about are the two saddles which locate the gearbox on the lay shaft. The gearbox casing is a casting and both saddles have been damaged and repaired in the past. 

KS4415 has very clean lines. The gear box oil filler which projects through the running plate on the right hand side harks back to an earlier time.


 Its restoration is not on the critical path, but Rick couldn’t help himself!