Con rods and slide bars

[Bernie333]

I'm on my second O gauge loco, and the same problem has arrived as on the first one.

 

This is a Severn Models Crosti 9F.   I just can't see how the slide bars can possibly clear the front wheels and the con rod. On the last model - a DJH 2P - I did a lot of fettling and got the thing to work, but this time I'm completely stumped. Please can someone who has built this save me from throwing a complete wobbly?

 

Bernie 

[N15class]

The best way on any loco of this type. Change front or all crank pins to 10BA, tap the crank pin 10BA. With the front one put the washer against the wheel and then use the crankpin the wrong way around. You can even countersink the coupling to get even more clearance.

[Simond]

Bernie,

 

This is a perennial problem, but less difficult in 0F than S7.

 

Fundamentally, it does fit on the real thing, so it must be possible in models, the problem is that our modelling is not terribly accurate to scale in some aspects, and coupling rod nuts are a particular issue.

 

I’d concur with Peter’s suggestion, fitting 10BA crankpins to the wheels, and tap the Slaters bush to suit. Whilst you may (I am sure “will”) need a washer or two between the back of the rod and front of the wheels to ensure the rods don’t catch on the wheelhub, this will remove the need for a 12BA nut sticking out from the front of the rod, which helps by about 1.5mm each side.

 

In one case, I had to bore the rods to recess the flange of the bush into it - this seems rare in 0F, but I believe a number of prototype locos had this feature, so I guess it’s common in S7. This will gain an extra 0.5mm, each side.

 

But perhaps first & foremost, no sideplay on the leading axle! You’re modelling a 9F. You'll need some side play somewhere, so I suggest axles 1 & 4 have none, axles 2 & 5 have whatever is needed, and don’t worry about axle 3 as it has no flanges anyway - you might need to limit the sideplay & any downward suspension movement to prevent it falling off the track.

 

Hope this helps, keep us informed, with pictures, and shout if you need help!

 

Best

Simon

[Michael Edge]

It would run better with zero sideplay on axles 1 and 5, maximum on axle 4 and a little on 2, 3 doesn't matter. Don't make comparisons with DJH kits, they all have the cylinders pushed outwards to a ridiculous extent. Photo is a 7mm scratchbuilt Crosti with scale width slidebars and correctly positioned cylinders in O gauge, you can see that it wasn't necessary to recess the leading crankpin fastener. The fastener on the second wheel is thicker, the sideplay as I suggested above and it ran easily round 6ft radius curves.

 

[Simond]

Very nice!

 

Best

Simon

[Bernie333]

Thanks gentlemen.

 

I've ordered up some 10BA screws and a tap.  Someone elsewhere (can't find it now) swapped the slidebar and motion brackets for Ragstone castings. I think I will do that too.

 

B