Building a London Road J69: Advice sought

[Jim de Griz]

I’m having a bit of a problem

I’m building a J69 from London Road and as the available motors wouldn’t fit between the frames i’ve used their Swing Link Motor Mount to connect the motor to the wheels.

My issue is I cannot reliably get the gears to mesh, even though that really shouldn’t be possible as I’m using the provided gear set. The only way I have found to get them to mesh is to put pressure on the motor, forcing it back towards the driven axle. Whatever my means this tends to be a temporary solution that only works for a few minutes before failing. (usually in reverse for some reason)

Does anyone have any experience using these motor mounts or getting this particular kit to work?

Jim de Griz

[nzpaul]

It looks like the two brass gears are not in contact. That would suggest one of those gears should be larger in diameter as no matter where you swing the extender portion of the gearbox to, the centre distance of the gears won't change. Is there a possibility that the gearbox was supplied with wrong gears? They look similar to the type supplied in Comet boxes and might have numbers stamped on them, perhaps a chat with London Road to ask what should be in there would be in order.

Paul

[Jim de Griz]

As recommended I've dropped London Road an email.

The gap is so small that I suppose it could be something as simple as a manufacturer's error on the gears.

jim de Griz

[John Palmer]

From what I can see in the London Road literature, the Swinglink motor mount's sole purpose is to alter the motor's location relative to the driven axle. For this purpose the illustrations in the LR literature suggest that the gear on the driven axle has the same characteristics as the wormwheel mounted in the layshaft. If these don't mesh correctly then the mount is unfit for its intended purpose, but I would be astonished to find that to be the case.

However, you refer to putting pressure on the motor to force it towards the driven axle. Judging by this comment and the posted pictures, I suspect the problem may lie in failure of the steel worm to mesh with the wormwheel on the layshaft, and that the reason for this is that the wormwheel is not centrally aligned so that it lies directly beneath the shaft carrying the worm. It appears instead to be offset towards one of the mainframes; if so then the application of pressure to the motor as you describe may distort the mountings so as to cause a temporary engagement of the worm with the nearest edges of the wormwheel teeth. The mountings may be returning to their undistorted shape as they may retain some 'memory' of their previous shape, and this would lead to worm and wormwheel dropping out of the minimal engagement attained by application of pressure to the motor.

As a solution, I would suggest investigation of whether the brass gearwheels can be repositioned so that their teeth are centrally positioned between the frames, and whether this brings the wormwheel directly beneath the worm and into correct engagement with it. This seems to be straightforward enough, as the brass gears are evidently secured on their respective shafts by grubscrews, and there appears to be plenty of room to move them sideways along those shafts to a more central position. If that's not the case because the bosses carrying the grubscrews are too thick then some judicious reduction of the bosses' thickness with a file may be necessary in order to get them centrally aligned beneath the worm.

A potential problem may be distortion of the motor/gear mount and/or the frames brought about by the pressure that's been applied to the motor in an attempt to mesh the gears. Hopefully any such distortion is not irretrievable.

A further thought is that the top hat bush connecting the swing mount to the motor/wormwheel mount (through which the layshaft carrying the wormwheel passes) is also of such a depth as to displace the wormwheel out of correct engagement with the worm. To correct that, possibly reversing the top hat bush so that its shoulder lies inside the motor and swing mount will do the trick. Otherwise it may be necessary to reduce the depth of the bush. Either way it looks as though sufficient room can be created to move the wormwheel up to 2mm inboard.

[Atlantic 3279]

I can't tell from those photographs.

Just to be clear, when the gears are not being forced into mesh by manual pressure on the motor, if you rotate the wheels by hand, does that intermediate gear rotate consistently too, or is it locked in mesh with motor worm?

If the two brass gears are not meshing, either they are too small, or consider the possibility that the holes for the axle and the layshaft in the frame of the gear box have been over-enlarged or have not had the correct/necessary bearings or bushes installed and centralised correctly. I did once see a J50 model that somebody was building, which the owner claimed he could not get to run properly, and the gearbox was a sloppy fit around the "driven" axle with holes in the gearbox frame very visibly larger than the axle diameter...

If the steel worm is not meshing with the intermediate brass gear, it may be that the brass gear isn't central enough as suggested above (the brass teeth look as if they've been eroded on the edges adjoining the boss). If the steel worm still doesn't dip down enough to mesh correctly when the brass gear is central, then the motor can always be made to tilt slightly by introducing a thin spacer between part of the end of the motor and the frame of the gearbox.

I assume you are familiar with the usual "strip of thin paper between the meshed teeth" starting point for setting / testing the clearances between the gears.

[john coffin]

I'm with John Palmer, you have not centered the cogs under the worm as your photo shows.
The mount, which I did NOT design has been successfully used by many modellers over
some years, and it would be safe to assume that no one else has had the problem you mention.
I get the impression that this is one of your early attempts at kit building and etched loco, and certainly
your first try at this kind of motor mount.
All the gear parts are supposed to align along their centre lines, what John and I see from your photos is
that the first gear is not under the centre of the worm, and also the second gear is not properly in
line with the first either.
As Graeme mentions using a thin piece of paper will give you the proper meshing gap, however, rarely these
days do people use cigarette papers, and post it notes are really to thick.

In the first instance you should try and adjust the gear so that it is visibly centered on the worm wheel.
There should be some small gap between the meshing surfaces, but it only needs to be a little.

It is possible the instructions are not clear enough to explain this, but overall too many have been sold
before to suggest that the mount is incorrectly produced.

Paul

[Jim de Griz]

Thank you for your advice

Paul is bang on, this is the first kit I’ve assembled that is supposed to move under its own power and my working assumption is I’ve messed something up during assembly.

As daft as it sounds, I assumed the gears were supposed to be offset. I’ll need to remove the entire unit from the frame to reposition them (there is a top hat bearing preventing me just moving the gear) That will give me an opportunity to check the rest of the assembly. Hopefully that will solve the problem of worm gear not reliably engaging.

The remaining problem is that the two brass gears do not mesh unless pressure is applied. I’m wondering if Atlantic might be on the money and I’ve got the bearings fitted incorrectly. ‘Conveniently’ removing the assembly should let me check this.

Jim de Griz

[Jim de Griz]

I assume you are familiar with the usual "strip of thin paper between the meshed teeth" starting point for setting / testing the clearances between the gears.

I was not, thank you for the heads up!

Jim de Griz

[john coffin]

We all have to start somewhere, and learn from the get go.

I might design these days, but I have built in the past.
Personally, I would have the flanges where the screws are opposite to each other, not directly over each other
as you have them.

I find it surprising that you should feel that the gears do not mesh properly, but it is possible that the bearings
are not properly opposite each other. That needs checking. You can adjust the side play using suitable washers.
They certainly should not need pressure being applied to make them work together. Sometimes it is possible
to make them mesh too hard, and thus need additional pressure.

Once the mount is off the loco, you can check to see if the gears mesh properly, and don't need additional pressure.

Paul

[Atlantic 3279]

Just in case there's any eccentricity or imperfection in the machining of the gears (there shouldn't be of course, but is this a perfect world?) make sure that the strip of paper "test" works no matter how the gears are rotated. On occasions in the past, I've set the clearance in one particular position, only to find that the gear train does not run evenly because the gears tighten up at some other point in their rotation.

[Jim de Griz]

London Road got back to me and like Atlantic suggested checking the bearings (along with a few other fixes) so I looked at that first.

The culprit turns out to be these.

In short, the taller top hat bearings come with the swing link, the short ones were supplied for use with the J69 kit. They look like they have the same diameter. But they do not, the taller ones have the same bore, but are a fraction of a mm wider!

For reasons that will hopefully be obvious below, I mixed and matched depending on the clearances and that introduced a tiny amount of movement that meant the brass gears only meshed if pushed together, the bearing moving a fraction of a mm in their mountings.

One problem identified, another appears.

As you can hopefully see from these photos, there is not a lot of clearance between the frames.

If I fit the larger top hat bearings to the swing link, there isn’t enough room to fit the smaller ones into the frame to support the axle. Unfortunately the hole in the frame is also a fraction too small to take the larger top hat bearings….

As I see it that leaves me with two unpalatable options

1. Fit the small hat bearings to the frame and the file them down flush to the inside of the frame

2. Ream out the hole in the frame to take the larger bearings and risk ruining the alignment of the axles/conrods

Any advice or observations would be most welcome

Jim de Griz

[jwealleans]

First of all.... "the bearing moving a fraction of a mm in their mountings."

Did you not solder them in? That's taking a risk, especially if (as seems to be the case) they're a slack fit. Use some sort of jig and secure them. I can't see hornblocks, so I'm assuming this is a rigid chassis.

You will have to file one set flush - in a High Level box it's the pair in the gearbox, but it cam be the case that taking some off the ones in the frames is helpful. Just be sure to ream them back out to a true 1/8" and clean them out when you finish.

Based on your last photo, one set on the outside of the frames and filed flush on the inside, one set on the inside of the gear mount filed flush on the outside. That seems to be the only way to make it work.

[John Palmer]

The outside diameter of the bearings supplied with the the Swinglink mount will have been designed to fit that mount and not for any other application. That is the likely reason for them being too big to fit the bores in the kit's frames intended to receive the driving axle bearings. Don't enlarge the frame bores to receive the Swinglink bearings, because you will then be left with the shorter bearings that already fit the frames (and were designed to do so). Those shorter bearings are too undersize in outside diameter for a close fit in the Swinglink mount, and their use in that mount may be accounting for your ability to bring the gears into temporary mesh with each other. Keep the Swinglink bearings in the motor mount and the shorter bearings that (presumably) came with the kit for their intended purpose as bearings fitted to the frames.

Your photograph shows a substantial gap between the cheeks of the swinglink and the cheeks of the motor mount. The frontal illustration of the Swinglink mounting in the LR documentation (at https://traders.scalefour.org/LondonRoa ... mounts.pdf) shows no such gap between those two components of the mounting. Yet it appears from your picture that both are etched one-piece items bent to a 'U' shaped configuration, and that the fold lines in the etches result in a swinglink considerably wider than the motor mount, leading to the gap that can be seen in your picture. Difficult to be sure whether that gap should be there, and it may make a big difference to the position taken up by the wormwheel. It's important that the toothed portion wormwheel is not offset so far from the centreline of the mount that the worm is only engaging the edge of those teeth and damaging them as it rotates, and I've attached an illustration showing how I think the wormwheel might best be positioned using the components supplied.

Judging by the fact that the boss carrying the grubscrew bore is almost as wide as the toothed portion of the wormwheel, the design of the Swinglink may be making that difficult to achieve.

[Jol Wilkinson]

I would recommend removing the driving wheels/axle to set up the drive train on the bench. It will be easier to identify the issues and also get more informative photos. It looks as though the crankpins aren't fitted to the wheels yet so you'll need to strip down all the axles if that is so. If you can post some photos of the unit out of the frames it may be easier to identify what the problem is.

The motor seems to be fitted rotated about the shaft centre line. The LRM etches have the motor mount screws "vertically". Does the motor have offset screws? it looks a Mashima but could be a Taff Vale 1227. The etches were designed around Mashima motors but the TV motor has the same boss diameter and 10.0mm screw holes according to their website, so should line up properly.

The worm should mesh fully with the brass gear but as thus is quite wide doesn't have to be completely centred under the worm, but enough to ensure full contact by the teeth. Likewise these brass gears can be slightly off centre to each other provided that there is at least two thirds overlap. LRM gears are supplied by Markits who stamp the gear ratio (38 or 50 in LRM's case in my experience). That may be the same as Comet supply and of course Markits supply them with their own gearboxes.

Bearings can be filed down to reduce the length if required. A ratio of 3:1 for bearing diameter to length is the minimum (according to my training as an engineer many years ago).

[RayS]

At risk of being drummed out of this discussion a CDC 3D printed J69 on a Dapol Terrier chassis is far quicker. OK the dimensions are not exact but I can have three J67/J69 running without all the hassle Jim is givimg himself and I am playing trains which to me is the point of the exercise. Good luck to him - I have a London Road J65 (built by someone far more skilled than me). It runs perfectly but so do the J67/J69s reminding me of 1951/2 holidays at Elsenham.
Chacun a son gout

Ray