Hornby Crosti 9F

J Gleeson

Hornby Crosti 9F

Postby J Gleeson » Fri Jan 22, 2021 1:39 am

I have a Hornby Crosti 9F model that I would like to convert to P4.
Are there S4 modellers who have completed this conversion, and if so, how was this achieved?
Can this conversion work if just the wheels are changed out, with no suspension?

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Julian Roberts
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Re: Hornby Crosti 9F

Postby Julian Roberts » Sat Jan 23, 2021 11:27 am

https://traders.scalefour.org/DaveBradw ... s-tenders/

Don't know if this is helpful in that no one else has replied! Maybe anyone who can get a 9F going in P4 doesn't spend time keeping up with the Forum!? Actually I'd be interested in any replies as I'd like to know what the issues are with the flangeless centre wheelset - if they are wider, by how much, and if not, do they derail, what if any sideplay do they need...etc.

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Mike Garwood
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Re: Hornby Crosti 9F

Postby Mike Garwood » Sat Jan 23, 2021 11:41 am

You might want to read John Darch's account of building a proper 9f chassis. It's a class project, with no holds barred. A beautiful model. It's on RM web:

https://www.rmweb.co.uk/community/index ... e/page/20/

Starts entry dated 30 Jan 2016. Well worth a read.

Mike

Philip Hall
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Re: Hornby Crosti 9F

Postby Philip Hall » Sat Jan 23, 2021 12:24 pm

Hello John,

I haven't converted one of these (nor a Bachmann 9F for that matter) but I have a feeling that the Hornby model is based on their Railroad model which I believe is more basic than the conventional range. This might make some of the chassis components a bit different from the standard Hornby methods. If it were to be the same, I would expect there to be sufficient play in the bearings etc. to allow for a P4 conversion. The blind centre driver should not cause any problems, but on this size of engine with all those wheels it would be paramount to ensure that the replacement driving wheels are perfectly concentric. Any eccentricity at all will cause all sorts of problems.

However, my caveat is that this is a very big engine with lots of wheels which is interesting to keep on the rails in P4 with suspension, never mind just a bit of slop in the bearings. So I guess my unhelpful response to your original question is that I probably would feel happier avoiding it. But then, I have never fancied building a suspended 9F either!

Good luck with it and keep us posted with your progress.

Philip

davebradwell
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Re: Hornby Crosti 9F

Postby davebradwell » Sat Jan 23, 2021 1:53 pm

With no play in the axleboxes you'll only need a 6 thou' bump in the track over the length of the wheelbase for one end to be in danger of coming off. I hope you don't want it to go round 2ft curves as well. It would be much less of a problem in EM.

DaveB

Dave Holt
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Re: Hornby Crosti 9F

Postby Dave Holt » Sat Jan 23, 2021 6:38 pm

I too am a bit sceptical whether a straight re-wheel of a rigid chassis would be a success in P4. I've seen 2-8-0s like this run satisfactorily, presumable helped by the slight play in the narrow axle slots/holes in the frames. But a 2-10-0 might be a step too far.
If it were me, I'd build a replacement chassis with some suspension movement.
For a Rolls Royce job, Dave Bradwell's chassis kit is beyond compare but would need some cosmetic modifications to suit the Crosti configuration.
A simpler alternative would be the Comet chassis kit but that has a stretched coupled wheelbase to allow clearance for over-scale flanges. I made a chassis using Gibson milled frames and coupling rods, which do have the correct wheel base.
Either way, with the benefit of 20/20 hindsight, I'd only allow the flange-less centre wheels to move upwards and no downwards travel at all. These wheels should have no side play.
How do I know? Well, my model has a sprung front truck, single compensating beam between the front two drivers, twin beams for the rear two and a coil sprung centre axle (other forms of suspension are available, as they say). On straight and gently curved track, track holding is brilliant. However, on tighter curves (as found at the ends of oval layouts), the flange-less wheels sometimes come off the rail head and drop down alongside the rail. Something of a problem as the curve opens out!
I do intend to modify the chassis to prevent such downwards movement, some day.
Good luck with it.
Dave.

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Julian Roberts
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Re: Hornby Crosti 9F

Postby Julian Roberts » Sat Jan 30, 2021 3:03 pm

Just to acknowledge your very helpful reply Dave for my one-fine-day project, tho a WD in my case. I hope the original author of this thread found everyone's advice useful.

On the flangeless wheel subject, I happened to have taken a photo of it at the NRM when last there 3 years ago. Though I doubt the rounded edges are for quite such a catastrophic derailment scenario! Interestingly Dave B informs me these wheels are wider than normal ones and for that reason are banned from any modern track where there are raised checkrails. As I have raised checkrails on a diamond crossing I've made I won't follow this aspect of the prototype.
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Terry Bendall
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Re: Hornby Crosti 9F

Postby Terry Bendall » Sun Jan 31, 2021 9:22 am

Eddie Ford had 9Fs running on Blackgill but they nay not have been RTR conversions. The layout was also fairly straight.

Terry Bendall

davebradwell
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Re: Hornby Crosti 9F

Postby davebradwell » Sun Jan 31, 2021 9:24 am

Eddie Ford's 9Fs use my chassis.

DaveB

J Gleeson

Re: Hornby Crosti 9F

Postby J Gleeson » Sun Jan 31, 2021 11:28 am

Many thanks for all the replies to my query.
I will probably utilise the Dave Bradwell chassis, as I think five coupled wheels in in rigid P4 chassis is asking for trouble-certainly from what Eddie Ford observed in his email to me.


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