Author Topic: The "Plastic Bugger" .... aka GRS kit for GWR 8750 Pannier.  (Read 7099 times)

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Offline John Candy

A popular member of the G3S (and this forum) has long referred to his 8750 class loco as the "plastic bugger", as I understand it, that is a reference to its "easy build" characteristics!

I have five unfinished GRS loco kits on hand, two of these being of the 8750 class loco.

I decided that being "Easy Build" (a quote from GRS's own advertising) it would be a simple/quick task to "knock out" these two before reverting to other urgent tasks.

As is normal practice, I started with one of the chassis.

As a starting point, to the list of tools given in the instructions, you can add 8BA and 10BA taps (and a tap wrench) plus No.49 & No.54 drills (or metric equivalents).

Unexpected obstacles so far encountered (and overcome but with "time" penalties) are:-

1) Axle keep screw holes in steel mainframes enlarged with No.49 drill and tapped 8BA, the instructions make no mention of this (also beware, the instructions erroneously refer to 6BA being the size of screw required but 8BA screws are supplied.....drilling for 6BA clearance would seriously weaken the brass axle keep castings).

2) Brake hanger screw holes in steel mainframes enlarged with No.54 drill and tapped 10BA (again no mention of this in the instructions).

3) Hornblock guides/Axle keeps : Holes need opening to 8BA clearance and then elongating to match the spacing of the holes in the steel frames.

4) Coupling Rods : These are not completely machined, it being necessary to reduce the rods to half-thickness where the overlap occurs at the centre crankpins.
(the rods are not strictly the correct shape; they are parallel whereas should be "fish-belly" pattern but not much you can do to correct, other than scrap and make new rods).
The dummy "knuckle joint" (indicated by a small hole in the longer of the rods) needs to be drilled out and a representation of the pivot fitted... I drilled to 8BA clearance, inserted a cheesehead 8BA steel screw, soldered it in, then filed the head down to remove the slot.

5) Gearbox axle holes required enlarging slightly to accept axle.

6) The arrangement intended to retain the motor/gearbox (described as "Motor Torque Bar" in the instructions) is 8mm too short and will not reach the gearbox mounting holes when anchored to the locating point on the frame spacer!

Well, I haven't yet got to touching the "plastic" parts but can already appreciate how this kit acquired its nickname!

My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline John Candy

Re: The "Plastic Bugger" ........ "KISS" and make better!
« Reply #1 on: May 05 2015 13:39 »
Don't forget "KISS", an acronym introduced by the U.S. Navy for "keep it simple, stupid", as a principle for reliable design !

Now GRS supply the contraption in the first two photos for securing the motor gearbox (in fact it wouldn't work because the parts don't fit!) but all you have to do is rotate both the gearbox attachment block and the adjacent frame spacer (the anchor point) through 90 degrees (so the already threaded holes are horizontal instead of vertical) and all you then need is the long 6BA bolt (see 3rd and 4th photos) and none of the other paraphernalia!

A classic case of "KISS" and make better!

My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline hornbeam

I have one of these in the cupboard waiting to be started so will find how you get on your build most interesting.

Offline blagdon

The genuine 'Plastic Bugger' was at Reading yesterday!

The 'Pirate'

Offline John Candy


Was it still trying to backwards and forwards at the same time or have the gremlins been exorcised from the electronics?!

My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline blagdon

8793 ran for 20 minutes in forward mode on a rolling road; Sod's Law, it did not perform it's reverse trick. However some other G3S members on the stand commented they had heard of others having similar problems. Mark, if you are reading this, has a loco driven forwards ever gone into uncontrollable reverse with you?

Ian the Gauge '3' Pirate

PS - following the rolling road test, 'she' shunted round the 'test tract' with no problems for the rest of the day.

Offline AllWight

In my experiience that is a Mac5 fault. When the engine flies into full reverse it means the Mac5 is faulty and this is to be sent back to Brian Jones for resetting as it is beyond my abilities to rectify. It may have taken a thump of power and overloaded something within the circuitry.

I have never had any of my locos do this, but i have seen others such as Rogers Prairie wheer it used to eat Mac5's due to the fact he was using 2 flat lithium batteies. He now has AA rechargeables. It was just over the maximum capacity of the Mac5 and it cooked it every time. It always happens at low speeds when the resistance is at its highest.


Offline John Candy

GRS kit : GWR 8750 Pannier.....OLD shoes for NEW!
« Reply #7 on: May 14 2015 21:34 »
OLD shoes for NEW!

The two panniers I am building are Nos. 4667 (built Dec. 1943) and 5786 (built Jan. 1930).

The GRS kit is supplied with the later type of (single piece, cast steel) brake hangers which are appropriate for 4667 but not for 5786 as built.
The "old style" cab batches and some of the early "enlarged cab" (8750 class) batches were fitted, when new, with fabricated hangers of a different profile.
While many (but by no means all) of the earlier locos ended their lives fitted with replacement cast type hangers, my model requires the early type.

I made patterns from which to cast replacements in resin (see comparison photo below).
It may seem a trivial modification but helps to highlight the differences between the two versions of this, the most numerous class of British locomotive.

If you are building a 57XX (or an early 8750) in original condition and require the original type of brakes, these are available for the cost of the postage (address as in the G3S membership list).

My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline John Candy

The "Plastic Bugger" earns its stripes!

I am now beginning to understand how it became known as the "Plastic Bugger".

I knew from an early trial fit that the motor sits too high for the main body casting to fit over it ..... I had already lopped 2.5mm off the top end of shaft to bring it down to the top of the flywheel (which itself only just clears the electric terminals).
Now the chassis has been completed and the running plate fitted, it was time to see whether the body would fit over the didn't....there was a 1.5mm gap between lower and upper sections of the body.

First inclination was to remove the flywheel and lop more off the shaft (general view is that in G3 a flywheel of that size performs no useful function). The flywheel is so firmly jammed onto the shaft that I dare not risk damaging the motor bearings trying to remove it.

Only alternative was to remove material from the inside of the firebox to clear the motor.

If you are building one of these kits, you will, by now, know that the list of tools for this "easy build" loco does not include a set of Forstner drill bits....but you are going to need one....35mm diameter, to be precise.

The firebox roof is 6mm thick in the area to be "reduced", so aim to remove around 2mm depth and no more than 3mm.
Drill a pilot hole first (to engage the point of the Forstner bit) and this will go right through the roof of the firebox (fortunately there is no external detail in this area and the hole can later be filled with Isopon P38).
Drill at the slowest speed possible (about 60 to 100 rpm is a good speed) since you will risk splitting (or going straight through) the casting (also you will generate a lot of heat if too fast).

Photos show the tank "before" and "after"; the motor; the Forstner drill (in case you are not familiar with that type .... one use is for cutting hinge recesses in kitchen cabinets); the inside of the tank with the recess and, finally, the hole to be filled!


My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline AllWight

You missed your calling John. You should have done key hole surgery


Offline John Candy

Well, if you thought you now had the motor problem sorted....think again!
With the tank/boiler unit in position, the cab overhangs the rear of the running plate by about 0.75mm.
The problem is insufficient clearance between the motor and the rear inside face of the tank (the tank unit is forced rearwards by about 2mm and consequently the cab unit is displaced from its correct position).

A recess needs to be cut in the tank unit rear (both top and bottom sections). Fortunately, it has been possible to retain the cab locating lug (on this loco at least...the other has a larger diameter motor, so it may not be possible to retain it) by contouring the inner surface to match the curvature of the motor.

Photos show result of a couple of hours, sawing, carving, filing and sanding.

You may recall a popular pair of TV comedians from the 1960's/1980's, one of their catch phrases being, "What do you think of it so far?!"
Their response sums up my feelings about this "easy build" kit.

My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline John Candy

Last night turned my attention to the tank/boiler castings.

In general, they are quite well detailed (including some extraneous banding which was not on the real thing!) although the "finish" of the castings is a little coarse/rough in places (due to file and other marks, etc. on the patterns from which the parts were cast).

The two locos. I am building have different features on the tank tops, so I will list the mods. in three sections.

1) Applicable to both 57XX and 8750 sub-class :

a) Remove the "banding" from the tank tops/sides .... these locos had either riveted tanks or welded ... in the latter case the weld was barely visible (just a very slightly raised thin line). DO NOT remove the "band" nearest the cab if you are modelling a loco with the prominent top-feed fitment.
b) Remove the "band" on top of the firebox (the one centred on the valve casing).
c) Reduce (chamfer) the rather too prominent long "edges" of the curved central portion of the boiler top casing (the edge is barely visible in photos.).

2) Applicable to 57XX and early 8750 class without top-feed and with original (circular) tank fillers.

a) Remove top-feed casing.
b) Remove oval tank fillers and bases.
c) Check photos. but 57XX (and possibly some early 8750 class) locos did not have the inverted "T" iron transverse stays (just behind smokebox and across firebox) they were fitted with plain "flat" remove the vertical leg of the "T".
d) Remove the tank "band" in front of the cab (this band is only required on locos with top-feed).

3) 8750 class with oval tank fillers .... early examples had circular fillers...check photos.
a) Remove the filler HINGED COVER ONLY (this is mentioned in the instructions....a metal casting is supplied to replace the resin cover).


There are a few items missing from the tank top which are visible in most photos.

1) A wedge-shaped cover of triangular cross-section, on the RH side of smokebox, just below chimney (the locos were not superheated, so I can only assume it covers pipework associated with the regulator lubricator....does anyone know?). It does not appear on the 1929 Swindon GA drawing but is visible on photos taken both in late GWR and BR periods. Unfortunately, all the 1930's GWR photos I have found have either been of the LH side, or, if of RH side, taken from ground level making it impossible to know whether the cover is present or not. At moment I don't know whether this cover was present on the early locos when built or is a later addition but am making enquiries.

2) Photos show protrusion on the front of the cab, just to right of the whistles (looking forward from cab) , which covers pipework (don't know whether this is original fitting since not shown on GA and older photos taken from wrong angles to judge).

3) There are a couple of small cover plates missing, which I shall add.

By the way.....if you have reached the point in construction where you are about to apply the transfers, you will need to know this.
The route classification under the GWR was BLUE .... the restriction was eased to YELLOW in BR days.....the GRS transfer sheet for GWR provides a YELLOW transfer, which is incorrect.
Another snippet of info.; the route classification was moved from high up on the cabsides, to just above the number plates during the war, to aid with identification during the "blackout".

More soon!

My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline John Candy

The pannier duo have been side-lined for a couple of months, while pointwork construction and tracklaying took precedence.

Raining all day today, so decided to tackle some "butchery" on the tank of 5786, to provide clearance for the motor.
The motor supplied with this kit is a Mabuchi RS-545, which is of a slightly larger diameter when compared with the motor (no indication of origin) which came with the (otherwise identical) kit for 4667.

This necessitated a larger recess being cut into the rear of the tank castings, as shown in photo. (shown during test fitting .... aperture still needs tidying).


P.S. If you have one of these 8750 (57XX) pannier kits, what type of motors does it have..... the RS-545 or the "anonymous" type as shown further up this page?
My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline John Candy

The mystery of the wedge-shaped casing on the smokebox at the base of the chimney has been solved ... thanks to Bill Bedford.

The 1929 Swindon GA does not show the casing but Bill's pipework drawing dated 1928 (an NBL works drawing) does show it, covering pipework unions and providing access to a steam cock, etc.
Since that NBL drawing covers the first-built batch (including No. 5700), I think one can safely assume that all subsequent builds would have carried the cover from new (I am told that, like the LMS 3F tank, the 57XX were known as "Jockos" by enginemen ... presumably a reference to the fact that the initial orders for both classes came from the Glasgow works of NBL).

My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline John Candy

Hoping for a GWR 57XX for Christmas?... Read this before you start.

If you receive a GRS kit for the GWR 57XX 0-6-0PT, then you will need to know the faults and foibles to watch out for (and there are quite a few)!

The chassis problems have been catalogued earlier in this thread (I shelved my pair of locos after assembling the chassis and have only recently begun to sort out the bodywork).

So far I have worked on the cab and tank/boiler castings for No. 4667, which was built in 1943 and has the Collett cab, tall whistle shield and top feed casing (basically the format of the kit as supplied).

First act is to put the chimney in the spares box and substitute the tapered cast iron type from GRS (the type supplied as a whitemetal casting with the Dean Goods kit). The 57XX/8750 class were all built with the tapered chimney and never carried the type supplied with the kit.

The Cab Unit anomalies

1) The roof sliding ventilator is too wide.
2) Remove the bunker top beading (there is a brass etch which replaces it..don't plant it over the resin will then be too thick)
3) The rain strips are not very convincing : Replaced mine with 1mm x 1.5mm brass angle.
4) Check the holes for the cabside vertical handrails.... one required moving almost a millimetre to make handrail vertical.
5) The circular recess in the cab backplate (to accommodate the handbrake movement) is missing.

Tank/Boiler anomalies

1) There are raised bands around the tanks (and one above the firebox, centred on the SV bonnet) which should not be there! Remove all except the one adjacent to the cab front which is part of the pipe arrangement for the top feed (remove only if you are modelling a boiler without top feed).
2) The "hinged" cylinder cover (below the smokebox door) is set too far back : The frames need extending forward by about 1.5mm and a new cover is required.
3) The profile of the cladding on the smokebox front is wrong (and the prominent rivets are missing).
4) The washout plug covers on the firebox shoulders are puny little "pimples", whereas they should be bulbous affairs.
5) The hinged washout covers on the rear of the boiler (where it meets the firebox) are missing.
6) The most glaring omission is the large pressed steel cover which sits below the chimney on the right hand side and runs the length of the smokebox (it covers lubrication pipes and steam cocks).
7) The insert representing the safety valves (it sits inside the brass bonnet) is not supplied.
8 ) The small pipe/manifold pressed steel cover is missing from the firebox top abutting to cab front.

Also spotted : I have not yet soldered up the running plate but inspection of the etchings reveals a serious fault with the cab steps.
The steps are asymmetrical, so there should be one pattern for the RHS and another for the LHS. Both on the etch are to the same LHS pattern.
This mean you will have to fill holes, drill new ones and then fold up the etch the opposite way intended by the design (which will inevitably result in a weakened unit unless additional strengthening is added). Cunningly, since obviously being aware of the fault from assembly of the the model featured in the instructions, there is no mention of the fault AND all the photos accompanying the instructions have been taken of the LHS, presumably to conceal the problem.

They still have the cheek to call this an "Easy-build" kit .... their interpretation of that phrase differs considerably from what most people would understand it to mean!

I have listed faults discovered so far and, when I have a bit more time, will describe in more detail the remedies and provide some sketches and photos.

Merry Christmas!


My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.