7mm Fixing Split gears on a Heljan diesel

[richard carr]

Nearly all the early Heljan diesel models have been known to suffer from split gears. Those affected seem to be mainly the Hymek, and Class 47s, but the other week Scale 7 JB told me his class 26 was suffering this too, and last week we tried mine and yes it has got split gears as well.
Gaugemaster now handle Heljan spares, they list over 800 on their website, so it needed a quick phone call to them to identify the right spare part. For the class 26 (and 33) the part number is 19853582, you get 2 replacement gears for £9 you will need two packs to replace the gears in both bogies. For the original style class 35/47/37 and 55 the part number is 19854780.

Here I have removed the retaining plate for the bogie and you can see the gear that has split on the left, the gear on the right hasn't split yet, but it will in time as the push fit onto their axles is just too tight.



This is the other bogie you can see that the gear to the left of the worm has split on this side



As you don't really need 2 big motors in class 26, the solution for one bogie is simply removing the motor. The other bogie requires taking apart to replace the gears.

To remove the bogie you need to unscrew both the retaining plates located just inside the bogie side frames in the middle of the bogie side, you can see the lower one in the first photo above, once you have those removed the bogie will drop out of the loco body, be careful as you don't want to damage any of the wiring.
Then remove one of the side frames, these just pull off. The inner chassis is held together with 4 screws these need to be removed and the bogie then splits into two as in the photo below.



You can pull out the old gears and take the gears off their axles, I used a wheel puller. You can then easily push the replacement gears onto the axle. The black gear in the photo below is the replacement.
I have pushed a piece of brass into the split gear so that you can easily see the split.



You can then just push the replacement gears back into the gear train



Now it is just a case of reversing the process and putting the bogie back on the body.

Richard

 

[pricei]

It's good to know that replacement gears can now be purchased again. I repaired a Class 33 last year when spares weren't available (Heljan told me this was due to Covid) and I had to buy brass gears at £60 a loco. I've still got a class 26 and 47 to repair so your information will certainly save me some money.
Thanks, Ian

 

[Dog Star]

You can pull out the old gears and take the gears off their axles, I used a wheel puller. You can then easily push the replacement gears onto the axle. The black gear in the photo below is the replacement.

Richard (@richard carr),

Thank you for this description on how to replace the gears in a HJ bogie, gives me the confidence to do the same for one of our HJ fleet. The Gaugemaster web-site page for part 19853582 has an illustration of the replacement gears and shows that the packet contains gears and separate axles... so why did you retain the original axle (with the new gears)?

The text on the GM page comments that the gears are for the more/most recent models... has there been more than one batch of class 26 models?

regards, Graham

 

[richard carr]

Hi Graham

The pack does contain two axles but the diameter is too small to be of any use with the main drive gear, so you do need to reuse the original drive axle.
I have no idea why they supply those axles.

So far there has only been 1 version of the class 26 but another version is due next year.

Kind regards

Richard

 

[Pencarrow]

I've never quite understood how an obvious and widespread fault hasn't been accepted as a manufacturing problem by Heljan and owners are expected to buy replacement parts.

 

[simond]

The Guild, or perhaps more accurately, some members of the Guild tried to convince them, but I believe they were uninterested. And given that their sales didn’t seem to suffer, I guess that might be a commercially sensible decision.

I do remember that Jim Snowdon arranged some replacements in brass. I believe Arun Sharma may also have had an input, but I no longer have access to the Guild forum and I cannot recall the details.

 

[richard carr]

From a legal standpoint for most people this is problem that arose well after the warranty period had expired, so legally Heljan are not required to fix the problem. Both of my locos lasted 10 years before it happened, one had a fair bit of the use the other languished in its box for most of that time, then suddenly neither would work, nor would a friends.

At least they have provided the replacement parts and seem to have cured the problem for later models.

Richard

 

[Dog Star]

The pack does contain two axles but the diameter is too small to be of any use with the main drive gear, so you do need to reuse the original drive axle.

Richard @richard carr,

I have received replacement gears from Gaugemaster. The axles which are supplied are smooth, no splines, and seem to be of a diameter which is compatible with the new gears in the pack. How is the replacement axle / gear, as supplied, not compatible with the bogie?

thank you, Graham

 

[richard carr]

Graham

The axles supplied with mine are too thin, they go straight through the gear, you also need splines to get a good grip on the gear.

Richard

 

[simond]

Are the two gears moulded as a single piece? If so, there is no need for the shafts to turn with the gear, they can be free.

The splines will simply act as stress raisers on the bore of the gear. I would not use the splined shafts.

 

[paulc]

Having had to replace a few Heljan gears for other peoples locos the point that Simon raises about not needing the spline on the axle is well worth remembering. Well spotted Simon .

 

[class27]

So they have been modified to remove the stress raiser....

 

[Yorkshire Dave]

Looking at the earlier photos it should only be the final drive axle which should be knurled to prevent the gear slipping. The remainder of the gears, including the black replacement, should revolve around the plain shafts held in place by the side frames (Roco have been doing this in their HO electric and diesel loco drives for years).

The use of a knurled axle for the initial and use of two separate gears from the worm appears to me to be a fundamental design flaw.

 

[Dog Star]

Job done.

The (old) gear shaft which was removed carries two, separate, gears - drive is transferred between the two gears by the splines on the shaft.

The new gear shaft is smooth, the replacement gear is moulded as a single entity with two sets of teeth - hence there is no need for splines.

regards, Graham

 

[Dog Star]

Richard (@richard carr),

Please can this topic be extended to include the gears on the driven axles (the axles for the driving wheels)?

Job done.

So when I wrote the post above I had just replaced the four gearsets which connect to the worm gear. Testing the bogies separately showed that one of the bogies was continuing to make a clicking sound although at a lower frequency / noise level than before changing the gears adjacent to the worm gear. Investigation of the one bogie which is making the noise revealed that both driven axles had split gears. I have two questions:-

1/ The model is a 7mm Class 26, what is either the HJ part number or the Gaugemaster equivalent number for this gear?

2/ Given that the split gear is on a splined axle with driving wheels, what is the recommended method of replacing the gear without damage to the insulating bush in the driving wheel?

Anyone else had this problem (yet)?

thank you, Graham

[Richard, can you change the topic title to reflect the expanded scope of the subject?]

 

[Nigel Smith]

The Guild, or perhaps more accurately, some members of the Guild tried to convince them, but I believe they were uninterested. And given that their sales didn’t seem to suffer, I guess that might be a commercially sensible decision.

I do remember that Jim Snowdon arranged some replacements in brass. I believe Arun Sharma may also have had an input, but I no longer have access to the Guild forum and I cannot recall the details.

Hi Simon,

Your memory serves you correctly, some of us did try to get Heljan to accept there was a problem Despite lengthy correspondence between Heljan and me no satisfactory outcome for many owners of early Heljan locos was achieved. Jim did indeed produce replacement gears for a while. However, they are now available from Ultrascale gears who produce full sets of brass replacement gears.

Hope this helps,

Nigel

 

[richard carr]

Graham

You can just pull the wheel off the axle, it won't damage the insulating bush, change the split gear, then put the wheel back on.

Richard

 

[Dog Star]

You can just pull the wheel off the axle, it won't damage the insulating bush, change the split gear, then put the wheel back on.

Richard, thank you.

As yet I have not been able to find any of the gears on the driven axles... nor have I got a definite answer as to the necessary part number. I have worked through the parts diagram for most of the Heljan diesels (see Gaugemaster Download Instructions web site) and I think that the required part is described as "0.5 x 16T x 5L x 2.9mm" and that description appears in at least six of the loco parts diagrams... however, Gaugemaster say that there is no stock of that gear under any of the six stock item codes / associated barcodes in the HJ parts price list.

I am now considering the use of an Ultrascale gear for the driven axle, this part. What does the team think about mixing brass and nylon gears? And yes, I am aware that all HJ 7mm diesels have a brass gear on the motor shaft...

Although expensive, the possibility exists of replacing all of the HJ nylon gears with Ultrascale equivalents... is this an option worth considering?

regards, Graham

 

[simond]

Graham

I would not be concerned about mixing nylon and brass gears. They should run together without issues -IIRC TriAng/Hornby went to brass worms and plastic wormwheels in my childhood, and as you note, it is precisely what there is on the HJ worm and wormwheel in the photo above. The final drive will have lower tooth loads and lower sliding speeds than the worm, so should be less stressed overall.

The problem seems to stem from the nylon gears splitting between a tooth root, and the groove on the bore of the gear caused by a spline - that this is likely to be sharp, thus forming not only a narrow section, but a stress raiser too, is likely to accentuate the issue. I think I would tend to secure the gear to the axle with a drop of high strength loctite, eg 603. You might want to remove any excessively high splines with a file beforehand, and clean the metal well with Acetone, IPA or meths.

hth
Simon

 

[class27]

I have repaired all of the split gears I have had (about 5 now) by using gears from RS components and ebay. I have put the original splined axle in the mini drill and given the splines a lick of the needle file to remove the sharp points. This has so far been successful however it really does seem that the best plan would be to replace all, as I have twice now had to go back in to do the other one. The redesign should eliminate this, but not the final drive gear which is a problem I have not had yet!!!!!!!!!!