DJH Crosti 9F - Conversion to P4

[barrowroad]

A while ago I purchased DJH Crosti 9F on Ebay. The model was OO and has a rigid chassis. On test it ran really smoothly and I put it to one side for future conversion to P4.
My intention was to replace the chassis with a sprung Bradwell kit at some point. However now that I have a number of RTR locos successfully converted to P4 which are not compensated - other than the usual 'slop' in the chassis - I decided to have a go with a P4 conversion keeping the rigid chassis. Ooooh heresy some might say. I had a set of Gibson wheels so decided to try my tried and tested method of conversion using Markits 10BA crankpins.

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Photo: Chassis after fitting Gibson wheels with Markits deluxe crankpins to axles #1,2,4 and 5 but with the standard Markits version on #3.

I had clearance issues on the front axle and decided to reposition the cylinders by inserting a 0.5mm spacer between the frame and cylinder casting on each side.
A test on the straight with DC proved promising so I hard wired a DCC Concepts Zen Black decoder and refitted the body.
The critical test on the layout was then carried out with a run from the storage sidings to the left hand curve of 4ft 6in radius on a gradient.
Here is the result.



In this case the weight of the model at 601g obviously helps keeping the wheels in contact with the track but I am pleased with the result I am now going to fit an AJ to the tender.

[Philip Hall]

Very impressive Robin. Shows what is possibly with decent track and wheels.

I have a 00 chassis I built for a friend to go under an old K’s 44xx which came to me when he passed away. As it’s a bit ‘more rigid’ than a RTR chassis I had thoughts of adding compensation, but your work here has confirmed to me that I just don’t need to bother. I have another Mitchell 44xx built rigid in 00 which I have been asked to convert to EM, and I am going to do the same.

Philip

[Julian Roberts]

Hi Robin - Looks great. Can I clarify, do you mean the centre flangeless wheelset is a 00 Markits one? Is it a bit wider than the usual P4 width?

[barrowroad]

Julian, Sorry if I didn't make it clear, all the wheelsets are Gibson including the flangeless centre wheels, it's the crankpins that are Markits. I've used their deluxe version - threaded - with a standard non threaded set on the centre axle. The reason for this being the original OO wheels used this version and it enabled me to fit the motion without opening out the holes which the deluxe version required.

Robin

[triumph3]

Robin, looking good and further evidence that rigid chassis work well as long as the track work is good.
On the Crosti, how is the pony truck engineered to keep it on the track? As we both know some RTR models the pony trucks are sometime problematic. I still have to fix the Stanier Mogul you converted for me, the loco runs fine but the pony truck has a mind of its own.

David

[barrowroad]

David, the front bogie is the original DJH casting that I have rescheduled. It is heavy which helps the track holding.
If possible try and add some weight to the mogul bogie. If it doesn't work let me have the loco and I'll try and sort it for you.

Robin

[Julian Roberts]

Thank you Robin for that clarification. You can guess I have a monster of similar wheel arrangement in the to-do cupboard, though in my case it's the DJH WD. I wonder if you allow the flangeless drivers side-play or not - my thought is whether they can fall off the rails on a 4 foot curve and how to minimize that likelihood! - obviously not happening on Barrow Road.

Just one more - how do you fix the return crank to the crankpin?

610g - serious stuff!

[barrowroad]

Julian,

From the front, axle 1 - no side play; axle 2 - 0.1mm per side; axle 3 [ the flangeless wheel] no side play; axles 4 and 5 - 0.1mm each side.
The centre flangeless wheels, like the others on this model are all rigid on this model so there is no problem with the centre axle wheels dropping of the track. However another 9f with sprung wheels did have this issue the flangeless wheels dropped off the track and caused a derailment. A solution would be to keep this axle rigid.
The crank is soldered to the standard Markits crankpin. I used the Markits 'washers', one between the coupling rods and the connecting rod, the other between the connecting rod and crank the latter used as a support for the crank.

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Robin

[davebradwell]

I'll keep well clear of the re-wheeling but would comment on a couple of matters arising: mixing wheels from different manufacturers, or even from the same one is likely to end unhappily as the crank throws will be different. Look at Dave Holt's Royal Scot thread where he used 2 different patterns of Gibson wheel. The other is the suggestion to use a rigid axle on a sprung loco to prevent the flangeless wheel falling in the track. This would be a sin as the main point of springing is to achieve that light touch on the track. I suspect problem is due to excessive sideplay but why not widen the b-b of the flangeless wheels a little - they don't have to go through any flangeways. Prototype, I believe, has wider tyre.

Have a good Christmas, however. you spend it.

DaveB

[Dave Holt]

Gosh. Two mentions in successive posts, one direct, the other inferred, so I should probably respond.
Yes, it was my 9F that Robin was referring to as derailing because the flange-less centre wheels came off the rail head and dropped down under the springing. In the past, it had run faultlessly round Dewsbury but suffered the same derailment on Slattocks so the problem must be marginal, depending on local track geometry and radius of curvature. I need to check if the centre axle has any (unnecessary) side play and am, despite Dave's concerns, considering packing under the sprung centre axle to prevent the wheels dropping below rail level but still accommodating track humps/peaks. Any resulting loss of traction will not be of major concern with this loco. The loco suspension is a bit odd in as much that the front truck is sprung, the front two driving axles compensated using a central rocking beam, the centre axle sprung and the two rear driving axles are compensated on twin beams. The drive is to the 4th axle.
Regarding the mixed wheel types on my Scot, as Dave says they are both by the same maker and have the same specified crank throw. Any variation in crank throw would be down to the accuracy of the die tooling which, i imagine, is done to quite tight tolerances. In practice, having adjusted the quatering (or thirding in this case), the loco runs as smoothly as one having all wheel sets of the same type.
Dave.

[Julian Roberts]

Thanks Robin - really useful picture, which reminds me (just for interest) of a couple I took of the real thing at the NRM

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I suppose the rounded edges are to assist it ride over the edge of check rails in those days before raised check rails. A very heathen thought is that perhaps that would assist re-railing on the move on model non-rigid locos! I suppose given the right kind of brain it would be possible to work out what curve would be in theory the minimum, if one had no sideplay on this wheel and the front and rear drivers - and then work out how much widening the BB as per your suggestion Dave (B) would ameliorate the issue. But I think I'll follow your idea Dave (Holt) of allowing upward but not downward movement. If I ever get to making this behemoth...

Interested to know the soldering technique on the return crank - the often expressed fear being of melting the plastic where the crankpin attaches to the wheel.

[barrowroad]

Thanks for the interesting 9f photos Julian.
One point I forgot to mention is I drilled a 0.45mm hole through the Markits crankpins on the centre axle into the plastic boss of the Gibson wheel and inserted a piece of 0.45mm N/S wire to secure the crankpin.
As for soldering I used 145 to secure the crank to the crankpin - clean everything, apply a dab of powerflux and quickly apply solder.

Robin