Romford / markits back-to-back

[Michael CliffordParticipant]

I have just built a Comet Jinty chassis, fitted Romfford / Markits drivers with EM axles and a Branchlines motor and gearbox.

This runs perfectly on plain straight track but dislikes my 4′ radius curves.

Sideplay is more than adequate on all three axles.

Problem seems to be that the back-to-back is 16.9-17.0 mm instead of 16.5 mm.

Has anyone else had this problem and are there any easy solutions.  I don’t have access to a lathe.

 

Thanks,

 

Mike

 

[Paul TomlinsonParticipant]

Michael, my Markits axles are 16.00 millimetres across the “shoulder”. Markits also do “P4” axles, so it might be worth a check on yours? You could try removing the rods and running as a 2-2-2, to check if the rods are restricting sideplay of the centre axle, too – I don’t know if your rods are articulated or not (I think it wise). If you definitely need to reduce the back-to-back, you might like to think about running the backs of the wheels along a fine file, to remove a touch of the cast boss. I chose to resort to this as there was a discernible wobble on one or two of mine as bought. Obviously, care must be exercised if you try this, or you’ll end up with a wobbly set – maybe just on the centre axle at first? HTH.

 

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[Bob AllisonParticipant]

Or consider sending the axles back for replacements.  If the btb is 0.5mm out, any other remedial work is just skirting around the real issue.

[Michael CliffordParticipant]

Thank you both.

 

I have checked the axle measurement over shoulders and have 16.0-16.1 mm.

 

The coupling rods are jointed, and I have loosened the centre crankpin nut a fraction in case that was the problem, but no improvement.

 

The back-to-back seems to be the problem and the ‘boss’ on the rear of the driver appears to be the root cause.

 

Unfortunately I have had the wheels for some time and don’t recall from whom I bought them.  In any case it’s not their problem so will try again to contact Markits direct, but that’s not easy as there is rarely any answer to phone or email.

 

If there is any progress I will update this thread.

 

Best wishes for the New Year

 

Mike

[Michael CliffordParticipant]

I have solved the problem of the excessive back-to-back.

I used an old OO Romford axle, cut of the threaded portion from one end so that it would not protrude beyond a mounted wheel.

I mounted a troublesome wheel ‘inside-out’ on the shortened axle and set the axle in a Dremel vertical drill.  Checked the wheel was on squarely, placed a file under the wheel, ran the Dremel at its lowest speed setting and gently lowered the wheel onto the file.

After about 30 seconds I removed the wheel and checked the thickness measurement, and mounted the wheel on an EM axle and checked the back-to-back.

By trial and error, I have removed sufficient of the wheel boss on the inner face to obtain three sets with a back-to back of 16.5 mm rather than 17.0 mm.

Inspection of the wheels reveals that the tread width is slightly more than the width of the cast wheel centre, such that the tread slightly overhangs the centre.  Sometimes the overhang is greater on the inner side of the wheel, sometimes on the outer.  If the inner side of the tread aligns with the boss, the wheel is probably OK with regards to the back-to-back.  If it doesn’t align, i.e. the tread overhangs the outer edge of the cast wheel centre, then the back-to-back is excessive.

 

Mike

[Paul TomlinsonParticipant]

Result! Well done.

[Bob AllisonParticipant]

Neat. Very neat.

Bob

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