how to modify a Backwoods L&B Manning Wardle using Grafar class 8 chassis

'Taw' has the only chassis that was not built by Peter Wallace and has never run as well as her sisters and had a slight wobble. Peter has been unable to rectify the problem.  'Taw', therefore was rebuilt with a Grafar chassis. The plan is to develop a system where the minimum work is needed to replace the working Grafar chassis should this ever be required.

from this

a completed Backwoods chassis

to this in 12 minutes!

the attack of the Dremel cutoff disc!

The paint was stripped off most of the chassis and the axle holes slotted with the cutoff disc. The front and rear slots were opened .5mm towards the centre wheel to accommodate the slightly different wheel base of the new chassis. It was difficult to do a very clean job of the slotting on this retrofit due to access. This will fortunately not be visible when the new chassis is fitted

14BA screws were soldered in to the return cranks and the connecting rod bushed to fit 14BA.

The bracket to support the front pony truck also has to be removed and also the brake rods.

ready for the new chassis installation - click on image to enlarge

the chassis with body and footplate removed

part of the metal work has been sawn off and the rods and cranks removed - click on image to enlarge

The chassis has to be stripped down now. The cranks stick out too far and have to be shortened. This is easier as it seems although the result will need quartering. Firstly, when removing the cranks, take out the wheel sets  and then firmly pull off the crank while holding the wheel. The extended axles are easily bent. The coupling blocks are also carefully cut off from the keeper plate.

this is as depressing as it gets! - click on image to enlarge

The L&B Manning Wardles are steam operated sausage dogs and the boiler height is too low to fit the motor in its normal position. The mounting bracket has to be cut down and the motor will be mounted on the footplate connected to the gearbox by a drive shaft. For this reason, the chassis is reversed and the motor was mounted from the left hand side when looking at the photo above.

The only modification to the body is removal of part of the bottom of the smoke box to accept the new chassis.  I do not fit a firebox in the cab as it is quite invisible once the cab crew are installed.

Now we can start putting it all together.

New cross members are soldered to the Backwoods chassis with central  12 BA back nuts. Great care is needed to ensure the Grafar chassis is central and that the chassis is level and at the right height. I held the cross members in place with modelling clay and adjusted the alignments prior to soldering. Check all is well with alignments by fitting the body.

the front cross member fitted

The Grafar chassis now fitted.

There is side play in the Grafar chassis and the next step is to line the inside of the Backwoods chassis with very thin Plasticard to prevent any possible shorting. In addition, the slots in the plastic can be cut to the new required dimensions and the enlarged slots in the Backwoods side frames filled.

The remains of the Backwoods wheel bearings need to be filed or ground flat with the chassis frames prior to fitting the plastic sheet.

the chassis with plastic inner frames fitted - click on image to enlarge

one can see the wheel slots where they have been filled - click on image to enlarge


the crank on the left is Roco and that on the right, Grafar - click on image to enlarge

the chassis with one set of cranks added - click on image to enlarge

The forward and rear cranks were shortened using a craft knife and once set, fitted and set onto the axle extensions using Loctite 603. The axle extensions need to be shortened by about .75mm so they are flush with the cranks. Replace the coupling rod including refitting the pin into the centre driver. We have since found that it is possible to reduce the thickness of the crank itself, thus obviating the need to cut the cranks. The centre crank pin was tapped to take a 14BA bolt. This showed to be better practice

Add the cranks on the other side, fitted with Loctite 603 and again refit the coupling rod. Offer to the chassis once happy with the quartering. The chassis must be very free running (or your quartering is slightly out). I set the cranks to not allow for side play on the front and rear wheels but with a small amount permissible on the centre driver. Now leave the whole lot for at least 12 hours to let the Loctite set. I check every hour for the first two hours that everything is still moving just in case the Loctite went for walkabouts.

the cranks are quartered and the rods fitted - click on image to enlarge

We now have enough space for the Backwoods valve gear to be fitted.

The valve gear fitted one side - click on image to enlarge

The centre crank pin hole has to be opened out to provide a push fit for the 14 BA bolt which is attached to the return crank. This is fixed in position with Loctite 603. Make sure that the gear works and then leave for some hours to harden.

The Joy valve gear on this chassis had caused some problems in the past. We therefore returned the chassis to Peter Wallace at this juncture for him to take a look at it.

Backwoods Joy valve gear

Peter Wallace found a basic flaw in the Backwoods design and construction sequence that results in 'self destructive valve gear'. This was very clear with the chassis of Taw, which had been built by another builder.

The fitting of the valve gear covers causes displacement of the slide bars and the eccentric is wrong placed and subsequently bottoms out. Equally, there is contact between the crosshead and the cover. It is better to build the whole thing up as a unit prior to assembly on the chassis.

"locate the cover to the motion support bar with no overhang. With the model, I have riveted a new row and ground back the cover by 1.5mm. The cover now fits the motion bracket flush and allows for a neat seam weld of solder to join it all together. The slidebars are now parallel with the cover and the oscillating cam is no longer masked "

The lower is modified while the upper is after following Backwoods instructions

As you can see, it is now a neat package for fitting to the loco and everything is parallel. I now think that fitting the valve gear the Backwoods way (with the cover already in place), pushes the slide bars upwards because the motion bracket profile is deeper than the cover at the rear. This in turn raises the connecting rod and the point of lift of the motion rod causing it to belt out the cam, and, as we have experienced, the little radius link attached top rear also fails. With everything parallel this should not happen.

left after, right, before

interior of rebuild

completing the chassis

The chassis should then be complete and ready for the installation of the electric motor. The first thing to do is to carefully remove the worm gear on the motor shaft. This is quite well fastened and I had to make a jig to tap it off using a fine punch. The motor shaft is 1mm diameter. As the gear pillar is too high to attach the motor alongside, the worm gear was mounted on a 1mm drill shaft and fitted into a gearbox.

The gearbox was made from bits of a failed motor which had 1mm bearings.

A Kato universal joint is connected to the motor which is mounted in the cab on a block of hardwood. It is not visible as it is hidden by the locomotive crew. Also note that the loco has been fitted with a plug to allow attachment to the adjacent coach.

The chassis with motor mounted, connected to gearbox with a Kato universal joint - click on image to enlarge

click on image to enlarge

the underside of the completed project - click on image to enlarge

the completed loco - click on image to enlarge

Despite perfect bench testing, the loco initially ran perfectly forwards but bounced all over the place going backwards. No amount of examinations found why this was the case. In the end, I modified the loco to run forwards (lights and connecting plug moved) During more running, suddenly it began to run perfectly backwards too! A real mystery and the answer is probably 42!

I am now extremely happy with the conversion. It is powerful and slow running characteristics are excellent. It is a challenging job but only time will now tell me whether it was worth it. The Joy valve gear is extremely hard to get working properly. Unless perfect, bottoming out will occur on the eccentric and the assembly will eventually all fall apart.

Taw is now back on the roster and no longer waddles! I tried a number of drive shafts and I have to say that the very best by far is the Kato unit. It is designed for 1mm shafts and is a perfect piece of engineering and completely smooth.

For a period of time, I found the loco suffered from wheel slip. This was probably due to the plated wheel treads. It has now run 7.5 miles and the wheel slip has long gone. The loco is a reliable smooth running unit.