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.
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
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.
'Taw' AKA 'Mr Slippy' gets
a pushy friend |
After several successful exhibitions, I began
to notice that 'Taw' was beginning to slip when climbing up from the
station to the viaduct. At first, the problem was resolved by removing a
coach from the consist but in the end, no reasonable length of train could
be drawn up the grade. Close examination showed that the wheels had become
highly polished. It has been suggested that the wheels are nickel silver
plated which has much less adhesion than solid nickel silver wheels that
have been turned.
There seemed to other way to get up the hills
except fitting a power chassis in the companion wagon! I purchased a Tomytec
Scale 16m Chassis from Wellington Models. This has a wheelbase that fits
perfectly. The chassis is a very quick runner and needed some
programming to bring it down to the same speed as 'Taw'. A Digitrax 125
chip is fitted and additional ballast added to the car.
powered companion wagon prior to painting
The rear Greenwich coupling was removed from
'Taw' and the ensemble is now fitted with a link and pin coupling. This is
more suitable when the rear wagon will be pushing against the loco. The
two chassis are connected still to make track power common.
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