Converting Hornby tender drive wheels

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I have recently completed a layout using Code 75 rails and turnouts, which all my locos negotiate without problem, with the exception of Hornby Britannia Class R2272 'Western Star', both loco and tender of which lurch very noticeably when passing over turnouts. It is a tender drive model (not liked by some I know, but it's one of my favourites) and has always run extremely smoothly on Code 100 rail, so I guess it's down to the flange depth of the wheels. Does anyone know if it is possible to replace the loco and tender wheels with those from other suppliers, please? I think the tender may be problematic.    

[34theletterbetweenB&D]

First step, push the tender through a point (ideally loose on a board so you can inspect closely from all angles at eye level to see what actually happens). Repeat with loco.

 

Hornby of this period is typically way to tight back to back, and will bind and thus lurch on code 75: bumping it out from the usual 14.1 - 14.2mm to 14.5mm is a very easy fix.

 

[DCB]

The back to back may well be way under 14mm.  The Hornby flange is pretty horrible and the unpowered stub axle mounted wheels on some tender drives are never going to run smoothly through code 75 turnouts.  We pensioned off our "Morning Star" years ago as it made the track filthy with its traction tyres, but the old 1960s "Britannia" is still going strong albeit with re profiled driving wheel tyres

As quoted above spacing the non drive wheels with washers keeps the drive gears in line but means you have to press off the wheels before adding washers.  You might have to elongate the powered chassis mounting holes in the tender base to get the tender to fit straight behind the loco

The Loco drive Brit which pre dated the Ring Field tender drive one is a lot easier to convert to code 75 as modern Hornby/Dapol County/ Castle tyres fit the old Brit driving wheels and there are lots of suitable  bogie and tender wheels which fit.

[knitpick]

As noted above, this is a back to back issue.  Confirmed by your description - lurches over points but (presumably) runs OK on plain track.

 

I've replaced wheels on some of my old Hornby locos with Romfords / Markits wheels.  This has the great advantage that the Hornby valve gear and coupling rod screws are a straight fit into the Romford (and thus Markit) wheels. Also the square axles ensure easy quartering.  The pony & bogie wheels are a press fit onto the Romford / Markit axles and fit well too.  As the Romford design has insulation at the wheel rim whereas Hornby's was at the wheel centre, you may need to tweak the pick-ups for some conversions.

 

The only issue is the tender drive.  As suggested above, the easy route is to use a washer on the non-cog side to increase back to back.  Otherwise, if I remember correctly, there was a company that did replacement tender drive wheels with better back to back - but that was last century and I don't recall the name (so not much help there - sorry).