RTR (almost) P4 Deltic

Philip Hall
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Re: RTR (almost) P4 Deltic

Postby Philip Hall » Wed Nov 23, 2022 11:40 pm

Re6/6 wrote:As did Kernow with their Bulleid diesel.


John,

What wheels did you use - it looks like they might be Bulleid pattern. I have been tempted to try and turn the originals down. Did you drill some holes in your replacements to 'sort of' replicate the Bulleid centre?

Philip

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Re6/6
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Re: RTR (almost) P4 Deltic

Postby Re6/6 » Fri Nov 25, 2022 9:23 am

Hello Phil,

I'm afraid that the picture that I put up was somewhat misleading as it was one of the original '00' version.

I used Ultrascales which I think were from a Class 37 conversion kit. No, I didn't bother with the holes as it will be destined for Balcombe to be used occasionally (strictly speaking not a typical Central engine!) and the 'visual correctness thing' for an engine at speed on there is not an important issue!

The conversion was quite the simplest that I've ever done with the wheels just dropped in and the retaining plate clipped back on. It was made so easy by some clever forethought for us of the 'wider persuasion' after conversations the production manager in the planning stage.

The only issue that I had was the sprung plastic pony truck which was too light and was replaced by a heavier one in brass which now functions well.

20221124_170000.jpg
20221125_072717.jpg
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John

Tony Wilkins
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Re: RTR (almost) P4 Deltic

Postby Tony Wilkins » Fri Nov 25, 2022 5:34 pm

My experience with converting one of these locos to S4 was less than successful. I used Alan Gibson 3'6" and 3'0" Bullied Bogie / Tender wheels as these have the characteristic cast design. Try as I might, I could not get the loco to stay on the track. Even without the pony truck it still derails. I was not at all enamored with the design philosophy of allowing the inner part of the bogie carrying the driving wheels to pivot separately to the outer frames (as can be seen from the above picture) and pivot the pony truck from the outer frame, which is asking for trouble in my book. Currently this loco resides in its box pending resolution. Some years ago I converted a Lima class 40 to S4 and that runs very well with a much less complicated arrangement.
Regards
Tony.
Inspiration from the past. Dreams for the future.

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jim s-w
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Re: RTR (almost) P4 Deltic

Postby jim s-w » Fri Nov 25, 2022 5:49 pm

Seems a strange design decision to me. Can you fit spacers between the outer and inner bogies that make them act as a single unit?

For the pony trick would one of justins sprung peak pony trucks fit?
Jim Smith-Wright

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Re6/6
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Re: RTR (almost) P4 Deltic

Postby Re6/6 » Sat Nov 26, 2022 10:39 am

All very odd Tony. After the new heavier brass pony truck with the original springs were fitted mine stayed on track at all speeds.

The Ultrascales perform perfectly.

I would imagine the unusual 'double frame' design could've been to cope with tight trainset curves.
John

Philip Hall
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Re: RTR (almost) P4 Deltic

Postby Philip Hall » Sat Nov 26, 2022 12:10 pm

Thanks John,

Presumably you made new axles for the Ultrascales and the original gears? I might still have a go at reprofiling the existing wheels as there is always Plan B if that fails
.
Philip

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Re: RTR (almost) P4 Deltic

Postby Tony Wilkins » Sat Nov 26, 2022 3:54 pm

Re6/6 wrote:All very odd Tony. After the new heavier brass pony truck with the original springs were fitted mine stayed on track at all speeds.

The Ultrascales perform perfectly.

I would imagine the unusual 'double frame' design could've been to cope with tight trainset curves.


Hi John.
There is certainly something about Ultrascale wheels. I have had cases where vehicles fall off with AG wheels and don't when replaced with Ultrascales.
The side swing between the inner bogie and side frames is limited by the wheels touching the side frames as there is not much clearance. The problem would be worse with OO wheels were it not for the deep flanges. I was not able to test it before conversion. I think the reason this was done is so the outer frames only need to rotate whilst the inner power bogie can follow any undulations of the track, but this alters the geometry of the pony truck relative to the driving wheels.
The other thing I notice is that there is more play in the outer axles than the center one as it has 6 axle drive and that is a potential source of problems. As the inner axle is driven via the gear on the center axle, this can exert vertical forces on the center axle causing one or other outer axle to lift depending on the direction of travel although with the weight of this loco I would have thought it unlikely. I much prefer just the two outer axles driven with the center axle floating or sprung and have had reliable results converting locos designed this way.
Regards
Tony.
Inspiration from the past. Dreams for the future.

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Re6/6
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Re: RTR (almost) P4 Deltic

Postby Re6/6 » Wed Nov 30, 2022 10:36 am

Philip Hall wrote:Thanks John,

Presumably you made new axles for the Ultrascales and the original gears? I might still have a go at reprofiling the existing wheels as there is always Plan B if that fails
.
Philip

Hello Phil. To be honest I can't remember exactly what I did! The the wheels are on 2mm axles, 15mm in diameter and the gear has 12 teeth which all look to be from the U/S Bachmann class 37 wheelsets. You could ask Mr Rogers what conversion sets use a 12 tooth gear. Turning down the originals could of course be an option.


Tony, I gave it a good run on DRAG'S test track this week and it performed well with no derailments but a small persistent issue was the
pony truck derailing at one point which indicated either it needed further weight, a stiffer spring or maybe both. Another option might be to turn down two 'EM' wheelsets (herecy!) with the deeper flange being effective. The current test track can be problematical as it's rather elderly now and is being replaced by new Tim Horn boards. As you said there is something about Ultrascales particularly when compared with the likes of AGs
John

Tony Wilkins
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Re: RTR (almost) P4 Deltic

Postby Tony Wilkins » Wed Nov 30, 2022 1:15 pm

Hi Phil. As both set of driving axles are 2mm, I just reused the original gears, but there is a lot of side play to deal with as the gears are rather narrower than the inside width of the frames.

John. As a result of your postings I have been investigating my loco in a bit more depth and will report my findings shortly.
Regards
Tony.
Inspiration from the past. Dreams for the future.

Tony Wilkins
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Re: RTR (almost) P4 Deltic

Postby Tony Wilkins » Wed Nov 30, 2022 5:13 pm

As this conversion is one of those that does not require dismantling the loco, I had not needed to gain access to the interior. The first problem with the investigation was, as is so often the case these days, getting the thing apart. Each manufacturer seems to have their own design ideas.
The body was the easy bit, undo four screws and the body come off with a bit of gentle persuasion. The next job was to figure out how to get the bogies out. Consulting the diagrams helps. Unplug the pickup wires from the PCB (printed circuit board). There is a clip holding the top of the gear tower in, which needs to be sprung off.
DSCF2369.jpg

Then the drive shaft needs to be disconnected. At one end there is a speaker and this plus its support moulding will need to be removed. It should then be possible to remove the bogie assembly. This proved to be enlightening.
DSCF2361.jpg

The pony truck pivots on the beam to the right although the hole in the pony truck is a slot, which means the pony truck is effectively uncontrollable, so yes, making a new one is definitely the order of the day. The area under the center drive axle has a peg on which the inner unit pivots and four lugs.
DSCF2360.jpg

These are intended to limit the side play of the inner unit before the outer frames turn with it, which is quite a cunning design.
The top of the frames are flat apart from three small ridges to the left, top and bottom of the pivot to reduce friction. Sorry about the poor picture quality, but I don't fancy taking the loco apart again just to take another one.
DSCF2362.jpg

The frames on the real thing could only pivot relying on the springs to deal with any track variations.
The model attempts to deal with this by allowing the inner bogie to rock relative to the frames.
Above the center axle can be seen the pivot bar with the central pivot point and the outer crescent shaped bearers. These allow the inner bogie the rock for and aft, but there is no allowance for twist as both bogies are the same. This could be dealt with by removing the bearers on one bogie only and placing a washer the same thickness as the bearers on the pivot point.
DSCF2367.jpg

The two shiny patches either side of the screw head are where the lugs on the underside of the outer frames make contact.
Measurement over the the inner bogie at this point showed it was 6 thou or 0.15 mm less than the spacing between the lugs. This may not seem much, but is enough to allow the inner bogie to turn appreciably relative to the outer frame. My solution? I slackened the screw and inserted a 5 thou sheet of plasticard into the join before re-tightening it.
DSCF2368.jpg

This leads me to my final conclusion as to why I have been having problems.
DSCF2366.jpg

The axles are located in place by some quite large phosphor bronze bearings. These are visible in Johns original pictures.
Whilst I had the bogie out I tried a few tests. The center axle is quite rigid as it is securely held by the retaining plate. When the unit is placed on a flat surface, there is a distinct tendency for the majority of the load to be on the center axle meaning less weight is borne by the outer axles and any high spots in the track unload the outer axles increasing the chance of derailment.
Solving this is not going to be an easy fix. It has crossed my mind to use a one of the sprung chassis conversions intended for a class 40 or 45 loco, but don't know which would be most suitable, but then there is the fact that this is a low priority loco, totally unsuitable for my layout and I would rather spend my modelling time on higher priority projects at the moment.
Regards
Tony.
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Hardwicke
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Re: RTR (almost) P4 Deltic

Postby Hardwicke » Sun Mar 12, 2023 2:48 pm

Accurascale have the P4 and EM wheel sets at reduced price.
Ordsall Road (BR(E)), Forge Mill Sidings (BR(M)), Kirkcliffe Coking Plant (BR(E)), Swanage (BR (S)) and Heaby (LMS/MR). Acquired Thorneywood (GNR). Still trying to "Keep the Balance".

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Paul Willis
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Re: RTR (almost) P4 Deltic

Postby Paul Willis » Tue Mar 14, 2023 7:45 pm

Hardwicke wrote:Accurascale have the P4 and EM wheel sets at reduced price.


Thanks Michael! That's a message that has also gone out on the Society's Twitter and Facebook feeds.

Let's hope that a few more modellers are tempted to try finescale diesels.

best wishes,
Paul
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Horsetan
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Re: RTR (almost) P4 Deltic

Postby Horsetan » Sun Jul 02, 2023 9:19 pm

Hardwicke wrote:Accurascale have the P4 and EM wheel sets at reduced price.


Incidentally, the P4 profile pack are ideal for rewheeling the IRM CIE "A" class/001 diesel in 21mm gauge, being the correct 12.7mm diameter. All that's needed is to remove the IRM wheels from their axles, and the Accurascale wheels from theirs, then mount the P4 Deltic wheels on the IRM axles with the help of an Irish back-to-back gauge (19.67mm).
That would be an ecumenical matter.


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