Slow running Hornby Class 67s

[panzerjaeger]

I have three different types of Class 67 locos, the original Lima model, two 'updated' Hornby/Lima models and the current Hornby offering R3039. My layout is approximately 12' x 7' and at maximum speed, it takes the Lima loco 21 seconds to complete a circuit pulling the EWS Management Train. My 'updated' Hornby/Lima locos take 28 and 30 seconds respectively to complete the same circuit despite having both bogies stripped , clean and lubricated. The current Hornby loco (R3039) takes 21 seconds per circuit, the same time as my old Lima model! These models are supposed to represent a 125 mph capable model diesel locomotive. Is it possible to replace the motors in these locos with something more powerful and if so, what would be a suitable replacement?

[Sir TophamHatt]

DC or DCC?

[The Johnster]

We need to know the linear distance of a full circuit and to work this out we need to know the radii of the end curves, but I'll make some assumptions for the sake of rough figures.  Assuming 2' radius end curves connected by straight track, you have 8' straights on the long sides, 16', and 3' straights at the ends, 6', i.e. 24'. If we assume the curves are = to 3' each if they were straightened out, that's another 12 feet, 36 feet for a circuit.  At full size we have to multiply this be 76; 76x36'= 2,736', just over half a mile.  A train travelling at 125mph, over 2 miles a minute, will do this in about 20 seconds.  

 

So, a loco that does it in 21 seconds is about on the mark. 28/30 seconds is a little slow and might do with some working up, but the old LIma and recent Hornby are running very close to scale top speed.  Speed is a function of gearing, not power, and the motors are powerful enough if they can manage a scale length train at full speed in the same way as the prototype, but it is very difficult to assess this objectively on a model where coaches are not scale weight, and oversharp curves increase rolling resistance way beyond any scale effect, and that's before the drag of lighting pickups is taken into account.  I'm a steam age Luddite so the EWS management train means nothing to me, and I don't know if it's a full load for a 67, say 8 mk3s or 4s and a DVT.

 

if the EWS train is not a full load, I'd strongly recommend removing any traction tyres, which will increase friction and hence drag, and do some trial running; noting the circuit times with light engines.  If the slow locos are up to speed running light, then you need to check out the train; wheel back to backs, freeness of running, coupling compatibility, buffer interface on curves, and remove any plastic wheelsets for replacement with all metal Hornby or Bachmann 14mm coach wheels. 

 

If the light engine timings don't improve, at least you've exonerated the train!  But we need to do a bit of thinking, as there are no real replacement upgrades for these sorts of RTR power bogies with pancake motors.  Everything has you say already been stripped and cleaned, and lubricated, and if you haven't overdone the lubrication, my initial suspicion would be on something mechanical such as poorly meshed gears or drag from the keeper plate beneath the wheels.  This would be accompanied by jerky starting and stopping and perhaps mechanical noise.  Check the spur gears for splits.  If these locos have been acquired off 'Bay, they may have been subjected to rough use that you don't know about in their past.  My next suspicion would be a motor related issue such as worn brushes, weak magnets, or even shot bearings, though we are scraping the barrel for causes now.  Worn gears from high mileage could be a cause as well, but I'd expect meshing problems rather than slow running form this.

 

Beyond that it's replacement with new power bogies, if they'll fit the older body toolings.  

 

[newbryford]

ISTR that only a few 67s were actually cleared for 125mph running - the norm being 100.

And there haven't been any regular scheduled services at 125 with the 67s.

They struggle to reach those speeds in thunderbird duty hauling a 91 set.

[Il Grifone]

They wouldn't be doing 125mph around those sort of curves anyway, so I wouldn't worry too much.

 

I thought modern high speed coaches had 3foot diameter wheels, but I'm rooted in the steam age. My most modern stock is from the eighties. I have a project to do a Europhoenix 37, but I won't have anything for her to haul.

[panzerjaeger]

My circuit of track is approximately 40feet in length and the curves are 2nd radius. The layout is DC and the EWS management train consists of a loco, three Mk 3 coaches and a DVT. I have checked all the back to backs, there is no buffer interlocking, all the wheels are steel and track is clean.

 

The Lima Class 67 may have been the first Lima loco to feature a can motor with drive shafts delivering power to a pair of tower bogies. These locos were purchased new and have all run smoothly from first use. However, from the start it was obvious that they were a lot slower than the majority of my locos, both steam and diesel.

 

Unfortunately, it is not possible to replace the power bogies as the newer Hornby model has a completely redesigned chassis. It would seem that, as suggested, the gearing of these locos is the problem and one that cannot be solved easily.

 

My thanks to the members who replied to my post and especially The Johnster for his detailed assessment.