Modelling

5" gauge NZ logging loco

Modelling

Introduction

This 5" gauge model was built by Bob Short in Sydney but was never steamed or run on a track. Apparently some air testing was done. Bob has spent many years making model ships, cars, and trains and the detail in this model highlights his expertise.

The real loco was made by A&G Price Ltd in Thames, Auckland, New Zealand for the Marlborough Timber Company. Only one such loco was ever made. There are a few grainy photos but no other details of its life. The loco is a Meyer locomotive with both bogies powered. The pistons drive jackshafts with gears to the axles. The steam from the rear bogie exhausts via a small chimney at the back of the cab. How well the real loco steamed is unknown but many Meyers were reported to be poor steamers.

The goal now is to get the model to run on a track. Although it is an excellent model it will require some work to make it an operational model. There are some design issues to contend with and other shortcomings ro overcome.

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Initial Test

Here is the loco up on blocks for a test using compressed air. Prior to this I'd put oil down both chimneys but unfortunately most just leaked out. The leaks here will have to be fixed.

The boiler has a number (NK09202) which indicates to me it has had a squeeze (hydro pressure test) at least. So it should be safe to pressurise the boiler with air for this test. At first I supplied air via the clack valve for the injector. Then I found an adaptor Bob had made so I could pump air (or water) into the boiler via the auxiliary feed pipe from the hand pump in the bunker.

The testing didn't go very well. Both bogies were binding. To check where the problem lay I disconnected the connecting rods. Luckily the big-ends are just like a real loco with split brasses, a wedge, and a keeper. The second photo below shows the assembled big-end and all the amazing detail on the fabricated cylinder and valve caps. The binding appears to be due to the gears which are meshing a little tightly.

The gear ratio from the jackshaft to the axles is 2:1 and the wheels are 90mm diameter. This means the jackshaft must rotate just over seven times for the loco to travel one metre. For a speed of 1km/h the jackshaft needs to rotate twice per second or 118 times per minute. I'd say that 2km/h will be the top speed for this loco. Definitely too slow for running with other locos on a club track. Of course it could be thrashed and run faster but this would look silly and wear it out prematurely.

The back bogie stopped working in reverse as one of the eccentrics came loose. Accessing most of the bogie is very difficult even over a pit so I decided they have to be removed for servicing. Removing the bunker provides access to the pipes and reversing control arm for the back bogie and also the strap that holds the sprung bolster in position. It really would be good to have a stretcher bar and jacks to support the loco here so the bogie can be wheeled out. Looks like I'll have to make such an implement.

Notice the piping for the bogie. The steam exhaust is a flexible corrugated pipe with a flange mounting at the bogie and a screwed connection at the cross member. The steam feed pipe is rigid with a ball joint at the cross member and a sliding connection next on the pipe. Both these connections handle the bogie movement when cornering. What doesn't work is the reversing control rod which is near the right and the expansion link position is affected badly by bogie movement.

I made some rollers using 6200 sealed bearings. This is important here as the axleboxes only have a bearing surface in the top half and running the loco with the wheelsets suspended is not a good idea. The bottom halves are removable and have an oil pad. The rollers will be used when this loco will be run on a demonstration stand. Such a demonstration is one of the planned goals in this modifications project.

The picture of the inverted bogie shows the Stephensons valve gear and the brake rigging. The drain cocks are little safety valves from coffee percolators. Replacing these with manual cocks is on the cards. The brake rigging is true to life but not compensated nor adjustable. This was recognised as a problem in the real bogies and corrected in the later version of the bogies. The later version had inclined cylinders rather than horizontal possibly to provide more ground clearance.

Testing here showed a problem with the left cylinder (remember that the cylinders are at the back of the bogie). There was a serious blow in one quadrant of revolutions of the jackshaft and it was when air went to the back of this cylinder. Removing the covers didn't reveal the leak so the cylinder was removed and disassebled. Rather than being made from a casting these cylinders are fabricated using bronze bushes and brass plates.

Eventually I discovered a leak between the cylinder back port and the exhaust port. This was a brazing pinhole and I could poke a piece of 8A fuse wire through the hole. My fix was to poke a piece of copper wire into this hole and seal it with Loctite 620. Both cylinders still have a slight blow past the valve bobbins. Getting piston valves to seal any better seems very difficult to me.

These fabricated cylinders are a work of art. The steam enters via the mounting plate and travels to the valve via the little pipe on the outside. The exhaust is via the manifold above the mounting plate. The only issue is that there should be a groove from the drain cock hole to the end of the cylinder to allow for drainage when the piston is at the ends of its stroke. A facility to squirt oil into the cylinder at the end of a run would be a nice extra.

After re-assembly I refitted the cylinder and tried to set the valves. For setting the valves I measured when the steam ports just open and averaging these gives me the midpoint. Then I measure the full travel of the valve in full gear and then adjust the linkage so the travel midpoint matches the opening midpoint. Finally I adjust the eccentric sheave position on the jackshaft so the steam ports open just after the ends of the piston stroke.

The bogie is running better than before but still binding slightly on the gears. The next step is to remove the wheelsets and make sure it will run smoothly with just the jackshaft. Also, access to the eccentrics will be much better so this is definitely the time to make sure the valve settings are optimal.

I removed the wheelsets to do an air test with just the jackshaft. Unfortunately the rotations still weren't smooth and it became apparent there was a blow from the front of the left-hand cylinder to the exhaust port. This was much less than the previous leak. To verify the leak I plugged the cylinder port in the valve liner and put acetone in the exhaust port. Sure enough some slowly leaked through to the cylinder. As before I poured Loctite 620 in the port at the valve liner and spread it around to hopefully find and block the leak.

While the cylinder was here I machined little channels from the drain cock holes to the end of the bore. This ensures there is a leak path when the piston is at the end of its stroke and covering the drain cock hole. I wonder why people don't put the holes in the end caps rather than the bore. This would avoid the risk of packing or rings catching on the hole and it would be impossible for the piston to block the hole.

The old flexible joint for steam to the back bogie was a swivelling joint (only) that didn't allow for bogie movement due to grade changes. The real loco had two ball joints with a sliding joint in between. The replacement joint near the bogie pivot is a ball joint using a 1/2" SS ball and a Viton O-ring to hopefully seal it.

Here is the steam pipe joint assembly and a picture of the trial fit after the last pipe was bent and trimmed to fit. The original Y-connection to both cylinders is hidden behind the frame members between the cylinders. The ball joint is directly over the bogie king pin and the bent pipe slides in the straight pipe from the ball joint.

The reverser control link to the back bogie was about 50mm off centre meaning it was severely affected by bogie rotation when on a track curve. The replacement linkage has cranks pointing up rather than down and a carefully bent rod with M3 Heim (ball) joints at the cranks. The Heim joint pivot points are diametrically opposed around the bogie king pin to reduce the error movement due to bogie rotation to a minimum.

The flexible pipe for the steam exhaust is metal spiral sheathing for electrical cable (I suspect). It bends easily but leaks like a sieve so not really suitable here. Now I've encased this in clear heat shrink tube and the new front fitting is secured to the front of the crossmember. The fitting on top of the crossmember pushes into the new fitting and is held in place by the six screws. This picture shows the steam supply with the ball joint in the crossmember and the sliding connection after. Also, just visible is the new reverser link with the bent rod that sneaks through between the crossmember and the bolster. Lagging for the steam pipes will come later.

The connections (steam, exhaust, reverser) for the back bogie are now all accessible for disconnection by removing the cab floor.

Removing the bogies for maintenance required serious disassembly to access the pivot bolt that connects the bolster to the crossmember. So I've made new king pins that are permanently fixed to the crossmembers and have a groove for the new quick release plates that live in the bolsters. The bolsters are above the springs and now have spacers to stop tilt which will strain the kingpin. The spacers will limit the tilt to 0.5mm. Pulling both little loops near the spring recesses will release the bogie.

Oiling the locomotive is difficult. To facilitate oiling the jackshafts and axles we now have holes in the axle ends and cross holes to a groove in the axles/shafts. The end holes are 2mm dia and 30mm deep and drilled carefully so the cross holes meet them. Luckily all holes so far have worked. If a cross hole didn't meet the deep hole I guess I'd just have to make a second cross hole. I still haven't found an easy way to oil the eccentrics and expansion links.

Notice that the wheels have been pulled off the axles slightly. This is because the loco is being regauged to run on my 134mm gauge track. The wheels end up being very close to the jackshaft crank wheels and require new thrust washers to keep the wheelsets centred. Normally I wouldn't change a standard 5" gauge loco but in this case the loco will be too slow for club tracks and much more suitable for the Banool 134mm track.

Here is the start of the replacement piping for the front bogie. The difficult job here was bending the 9/32" thin-wall brass steam pipe. This required a homemade pipe bender. There are two exhaust pipes in the left. The leftmost one is a provision for steam from the rear bogie. Currently the rear bogie exhaust from a small chimney in the cab. Sending this exhaust to the blast pipe in the smokebox to improve the draught so the boiler will steam better.

Well, I've decided the rear exhaust should go to the smokebox so here is the rather complicated and wiggly pipe from the rear crossmember to the front one. Now I have to make a Y-connector to go from the front crossmember to the smokebox. This has been designed but how to cut the tubes is yet to be decided. These pieces must be cut accurately enough so they can be brazed together and fit correctly.

The cylinders are 1" bore and the piston stroke is 37mm. The issue with the bores is that the cylinder ports start at 4mm from the end and extend to 7mm. This means the piston packing will encounter these ports at each end of the stroke. My solution is to fit liners and drill diagonally from the ends to the existing ports. For liners I use bronze bushes that are 1" OD and 7/8" ID. The first picture shows a bush on a mandrel so I can file/sand the outside so it will fit in the existing bore. The bushes are about .004" oversize and the bores are very close to 1". The second photo shows the setup I made to push the bush into the cylinder. This setup turned out to be redundant as pressing the bushes in seemed risky so I made them a slide fit and secured them with Loctite.

Here is a cylinder with the bush fitted and the port oprning at the top. The opening was made using a tiny burr in the milling machine. The final operation was to ream the bushes. I bought a 7/8" hand reamer and had this held in the vice. I then rotated the cylinders by hand and they slowly slid down the reamer as any excess metal was removed. I'm not sure this was a good idea as the finish wasn't great. I subsequently polished the bores using very fine sandpaper which did improve the finish.

For the replacement pistons I used some 7/8" stainless steel bar. I decided to use a 7/8" Viton O-ring as the seal. As recommended the groove is .055" deep and .092" wide. The first picture shows the new piston and the cone used to push it into the cylinder. Although the O-ring slides once moving it does stick when the piston stops. So I dropped the O-ring idea and made a piston ring from stainless steel. The bore is 22.2mm and the ring was made to 22.5mm before cutting the gap. Although the groove depth is .055" I found a ring depth of .050" made the ring too rigid and it distorted when stretched over the piston. So a replacement with a depth of .040" was made and this can just be stretched over the piston. Notice the scratches in the bore. I thought the reamer had done these but the reamer didn't rotate this much when cleaning the bore. So, who knows what happened here.

Last modified 2022-06-25