Heljan O2/3


Another loco aimed mainly at our extended "Little Histon" layout, to add to our LNER period rolling stock operating through coal trains.



Hattons photos of 3965


As it arrived:

This is the first Heljan product I've experienced.  Sorry to say its not looking great so far! 

As received, the metal hand rail on the smoke box door had broken off, with one of the tiny end plastic fixings missing. (I'm sure this is fixable.... just annoying!)

Of more concern is the DC slow running characteristic:  Moving forward, its not too bad, but moving slowly backwards, there is a distinct hesitation occurring at one driving wheel rotational position, coincident with the cab being displaced briefly upwards. Clearly there is something amiss with the wheel coupling or valve driving mechanism. Possibly a quartering error of obstructed valve movement.  To identify and fix this problem, the locomotive will have to be dismantled and there remains a risk that the problem may not be fixable. Nothing ventured, nothing gained and I will endeavour to fix the problem as a learning exercise.

Heljan do not include a service sheet. The only dismantling information I have found so far is some English text on the Heljan website that outlines the dismantling process without any graphical assistance.


The Heljan information:



A few adjustments needed to Heljan's instructions: Step 1..... No spacers found on either side of the drawer bar fixing screw. Step 3..... Also undo the screw at the rear of the lower motor housing. Otherwise, no difficulties encountered.

Removing the motor allows the chassis to be manually propelled along a section of rail. There are a few tight spots and it is possible to completely lock the mechanism if the chassis is allowed to take up the entire lateral wheel movement at the front. But..... no sign of any problems with the valve gear linkage and although the quartering maybe (only maybe!) a shade out on the driven axle, its barely noticeable. I suspect that if the coupling rod attachment holes were fractionally larger, then the linkage would be able to absorb any issues associated with imperfections in quartering. The bottom line is that, as there is no obvious way to separate the rods from the wheels, I'm not able to make any adjustments....... So I've lubricated all the pivots and exercised the motorless chassis assembly to and fro along a short section of rail and that's about all I can do!

It remains to be seen how well the loco goes back together again!

Nightmare! No wonder the boiler/cab assembly was a bit fiddly to extract! ..............Plastic location lugs are easier to separate than join!  I ended up having to surgically remove or streamline the lugs near the cab and below the steam pipes (Oh yes and the protruding edge of the lower motor housing!)

I also managed to detach one of the rocking leavers on the valve gear...... and had to completely dismantle everything again to repair that........ Also broke a side hand rail lug. Now also fixed.    I don't plan to get that apart again if I can possibly avoid it!!!!!!

But surprise surprise, I find it difficult to believe its anything I've done, but the loco is running much more smoothly on DC having just checked it again....... ????

I'm not complaining....... just relieved!

Just need to touch in a couple of scratched rivet heads with matt black paint.


Fixing the broken hand rail:

The remaining fitting lug was glued back into the vacated hole. A simplified new lug was constructed from plastic rod and glued into position. After filing a fraction of a mm off the rail length, it was glued to both original and newly fabricated lugs. (Super glue was used throughout.)

Finally a little matt black paint hides the grey plastic of the new lug.



Decoder choice:

The O2 is a 3 cylinder Gresley design.  The Digitrains Zimo A1/A3 on an MX644D would be a possible solution. Not sure yet about an alternative LokSound solution, but this decoder might deal better with any remaining slow running hesitation.

If a 40x20mm ESU 50344 speaker can be made to fit, that would be a first choice.

An over-voltage protected SC68 super cap would provide good stay alive performance.



No room behind the cab front bulkhead for the usual LED fit, so the O2 will just be equipped with a white disc on the right hand side of the buffer beam (reflecting its through coal train status) but a sound system will still be part of the programme.




Tender Modifications:

The tender incorporates a massive ballast weight with provision to mount a tiny speaker. The original weight has to go, in order to accommodate a more appropriate speaker. I can add some replacement ballast, but the tender weight will inevitably reduce. Hopefully the 6800uF supercap will help reduce any consequent brown out issues. I will have to trim the existing circuit board to fit the remaining space, so that I can still make use of the on board 21 pin connector.

New speaker, decoder, stay alive capacitor and plate ballast weight, placed in the tender body to confirm the fit.


The massive original ballast weight, now removed.


Completing the saga:

The tender mods went well. (Although I substituted an ESU 21 pin adapter for the Heljan PCB.) Speaker, decoder and stay alive capacitor all fitted successfully and additional ballast weight added to partially compensate for the loss of Heljan's metalwork. Crew were glued in place and a mineral train head code disc was mounted.

However, during early operations it became apparent that the rods were occasionally locking up. Some careful bending largely cured this, but next one of the brackets supporting the valve rods separated from the upper body shell. This was glued back in place, but probably not quite in the correct way as reliability continues to be a problem.  Its a pity because the model looks good............... I didn't dare run the machine at our recent first public display of the updated village layout and instead, obtained a Bachmann O4 to haul our long coal train........  so I think I'm going to have bite the bullet, salvage the useful parts and dispose of the remains.

I might consider getting a replacement first and swopping in the modified tender...... but its obviously a fragile machine and that might not be a prudent move, as straight out of the box, before I disturbed the model, its DC running performance was flawed (As described above) !   Its quite likely that a replacement would be no better and after this experience there is no way that I would dismantle another machine.



Supplier website links:
Hattons    The O2 was sourced from here.
Digitrains    Source for decoder, stay alive supercap and speaker.


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