Cylinder Liner Fitting –Good News & Bad

 

With the engine block back at Boston Lodge, job No 1 (or more precisely job No 2, after the painting epic) has been to fit the new liners. The manner in which the liners are fitted is a little unusual, as they are secured into the bottom of the block with an arrangement which is akin to a gland. The photo below shows the arrangement before dismantling. The liner clamp is secured by the four studs with the natty, shaped washers and there is a coil spring (in compression) between the washer and the clamp. Looking at the second picture, which shows the clamp being removed, may help understand the arrangement.

With the locked nuts, natty washers and springs removed the liner clamp can be lifted out.

The clamp both holds the liner in place and also compresses an ‘O’ ring, fitted around the liner to form a seal between the liner and the cylinder block water jacket.
The cylinders are off-set slightly from the line of the crankshaft (to ensure that the full force of the cylinder firing it put to good use) and to accommodate this each liner is slotted at the lower end to accommodate the movement of the piston rod. It goes without saying that ensuring the alignment of the liner is correct is critical. Rob Bishop fabricated this simple jig, which locates on the studs and then ensures that the slot in the liner is in the correct location.

With the liner in, the ‘O’ ring can be fitted, some sealant applied and the liner clamp re-fitted. Simples! The need for the jig can clearly be seen in the photo below where liner number 2 is clearly out of line.

One of the liner clamps had a crack;

So Rob fabricated a replacement. The old, cracked liner clamp on the left, new, fabricated replacement on the right.

The photo below, showing the new liner clamp being bored out on the lathe makes the welded construction more apparent.

Back on the engine, this view below shows the fitted liner and ‘O’ ring.

Things don’t always go to plan, the liner clamps are in compression, but the lugs are in shear and cast iron is the best material in shear. When the liner clamps were being fitted the lugs started breaking off. It looks like this one may have been cracked too.

The solution? We are going to get some new ones cast in ‘SG’ cast iron, which is more ductile than the normal stuff. Why didn’t McLaren use SG iron, you may ask? It was not invented until 1943, 15 years after the engine was built. In addition to the change in material the clamp has also had a modest size increase, to beef it up a bit. Thanks to Andy Williams for making a pattern for the replacement component so quickly.

As I expect the majority of people reading this will know, The Ravenglass & Eskdale Railway also had a Kerr Stuart Diesel (Standard Gauge, MDB6 powered) which if you didn’t know, takes a bit of taking in. Thanks, or possibly no thanks, to Neil Glover who forwarded an extract from a contemporary record (reproduced in the R&ER Magazine). It starts…

'we returned to Ravenglass a few days later after a pleasant holiday and discovered that the MacBenz engine had been in trouble.The water joints on the cylinder head and the liner joints had been leaking water into the sump’. After a vivid description of the rather unpleasant task of sorting the mess out it goes on to say ‘the job of renewing the joints was always with us, probably caused by vibration of the engine and also to some extent by a shortage of oil, causing the pistons to get hot. We always had a good stock of rubber joints to replace the faulty ones and as oil often stood on the cylinder heads from the tappets, the rings to seal the water often became impregnated with oil and were made useless’.

Maybe we are about to find out why liners were not often fitted like that. Let’s hope that improvements in rubber & sealants may give us a little bit of latitude.

Governor Body

 Lack of blog entries are a measure of personal lethargy, rather than lack of progress, as followers of the Facebook page will know there’s lots of riveting stuff going on, but let’s get some of the blog backlog out of the way first. 

The previous blog entry described the high-tech CNC work undertaken to produce the fuel pumps. These sit on top of the governor casing, the reproduction of which has to date been a painstaking exercise of draughtsmanship, pattern making and founding (blog entries 16th February 2020, 17th October 2021, 19th January 2023). At every stage in the manufacture of this component the words ‘it’s a bit tricky’ seem to crop up. The most recent star of mastering something that is ‘a bit tricky’ is John Dunn of John Dunn Engineering who has patiently machined the casting.

Mounted on a horizontal borer, the first operation was to mill the top face, which will ultimately carry the fuel pumps.     John Dunn Engineering

Another view, showing how the casting was mounted and clamped to the table   John Dunn Engineering

With the casting rotated through 90 degrees the end of the casing, which mounts onto the engine is shown here being faced off. John Dunn Engineering

Now it starts to get tricky! The shaft carrying the governor runs along the whole length of the casting. To ensure that it aligns perfectly the bores on both the left and right hand side of the box area need to be bored without re-setting the machine. Consequently the right hand bore have been machined with a boring bar projecting into the casting. John Dunn Engineering

An ingenious boring bar set up to allow the internal faces of the casting to be machined. John Dunn Engineering

The rather long reamer in the photo above is required to finish the bearings for the spindle of the governor operator bell crank lever. This is the sub-assembly 619 – 622 in the spare parts diagram included in the blog entry of the 10th February 2020. The photo below shows the same area on the MBD2 engine and tries to illustrate and explain how this part of the mechanism works. The lever is on the end of the shaft and is part 620, the fuel reducing claw lever (the kill switch for the engine).

The arm of part 621, the governor operating bell crank lever (which is carried on the same shaft) can be seen (with the low ball joint) inside the casting. The crank arm passes from one cavity of the body to the other via the hole in the top RH corner of the photo with the boring bar. The casting is upside down in the boring bar photo.

This view shows the machined top face of the casting, ready to receive the fuel pump assemblies. John Dunn Engineering

The interior of the machined casting. This end of the body receives the drive from the engine and contains the governor weights.

Even machining up the face of end cover was not a straightforward task, seen here on a vertical milling machine fitted with a rotary table.

Job done! John Dunn stands here with the finished item and the deserved look of pride that is usually associated with big game hunters. It seems rather underwhelming to record just another component has been finished.