An interesting issue today

[Adrian Harris]

Getting towards the end of the day and the left hand track on the Elefant wouldn't go backwards. Forwards was no problem, but it made driving quite tricky as any attempt at reversing just resulted in a right track turn.

Having removed the motor and proven that it was a mechanical problem, I isolated it to the left hand sprocket.

Removed the sprocket and found that the drive gear shaft was really stiff forwards and blocked backwards.

Removed the gear casing and found that:

1) The drive gear wasn't glued into the bearings, so it could rub on the hull side. This meant there was at least 5mm of play in the sprocket.

2) The drive gear had worn a lip around the edge of the teeth

3) This lip had just caught the top of one of the countersunk hull bolts, and unscrewed it

4) Once it had unscrewed a little way, it had started to catch on the drive gear, and was acting as a pawl, hence the lack of motion backwards. See the witness marks in the drive gear where the bolt head had dug in.


Quick and dirty fix was for Denny to file the gear smooth again:

I then discarded the damaged screw and rebuilt the drive casing and sprocket so it could be driven back into the van.

Also had one of the axles unscrew from the bogie arm, which forced the wheel out of alignment, which in turn forced the track off the idler.

This week, I will be mostly... removing the bogies and drilling and pinning the axles in place.

Adrian

[Jerry Carducci]

...and they tell us "....that's easy! anyone can drive a tank model! "

[Paul Sparkes]

Adrian,

I think I may have a similar issue on the Jagdtiger, I sometimes get a slowing down of the track causing the tank to steer.
I’m yet to investigate but what you have found supports my suspicions.
Thanks

[Gerhard Michel]

An interesting issue, indeed. I wonder if a big well spring and some grease could be a suitable solution, because I'm not a friend of glueing gear parts. Such a spring would also cover the screws.

[Jerry Carducci]

How practical would it be, of course while the model is being built or dismantled in a restoration, to center punch the hull side plate
where the driven gear is? With this center punch as an index one could place some sort of thrust bearing or series of washers that could absorb lateral
forces preventing this sort of wear. It seems to me based of what you've shown is that there is a need to counter any lateral force that is induced
by play in the clearance. As the design seems to be common among the models this sort of wear could happen to any of them including my M3 Lee.

I think I will incorporate some modification to counter this in my next builds. I'm thinking perhaps a small bore on that large gear where in contacts
the side plate in order to employ a flanged bearing and appropriate shim washers to keep it from touching the side plate.

Jerry

[Chang]

Not running my Elefant much, yet the left track came out once. I thought it came from the tension loss of Idler wheel. Now I may need to find out another possibility.

[Phil Woollard]

To late now but during the build maybe try packing the final drive with grease and use thread lock on all venerable fixings.

[Adrian Harris]

The Elefant instructions do show that Loctite should be applied to the inside and outside of the inner bearing. I must admit it's not particularly clear on the Elefant instructions but it is clearly stated in the Easy8 and Churchill Instructions for example.

I find a little Loctite applied around the inner end of the shaft is sufficient to hold the gear in place. To remove, just heat the centre of the drive gear until the Loctite hold is compromised. Then tap the gear out from the outside with a plastic mallet. The worst that can happen is the bearing comes out of the casing rather than the shaft coming out of the bearing.

When stripping down a model which has been run for a while I would probably invest in a new set of branded bearings anyway, so wouldn't be concerned about any heat passing into the bearing.

Adrian.

[Shayne Sutton]

What about machining a spacer to go between the bearings, then another spacer between the taper lock and the outer bearing and an other one between the gear and the inner bearing, you can then set a small amount of end float using the taper lock, locktite is a waste of time when the shaft has no way of staying in position mechanically, please post some more photo's of the reduction disassembled. I am currently building my Churchill turret and I modified the gun elevation bearing assembly by machining the blocks on the inside face and fitting a 17mm long spacer so you can lock the bearing, bolt and spacer together making a friction free assembly that is bolted together solidly.

[Uwe Gerstenmayer]

Hello folks,

driving my KT since years without any issue. Just thought to show what has been my approach to fix any axial freeplay.
The taperlocks have far enough power to hold the sprocket in place so I lined up the tracks and wheels and evaluated the spacer size.
Important to shorten the " Nutenstein " to the lenght of the taperlock bush. Any Grease should be of course the standard.
In one go I made the centrefix for the hubcaps
Maybe something of interest for other builds ?

cheers from Cologne,

Uwe

[Robert E Morey]

I make Spacer as described by Uwe for all my models. Although not a "sanctioned" part- it does prevent the drive gear from hitting the hull side.
Bob

[John Clarke]

I make Spacer as described by Uwe for all my models. Although not a "sanctioned" part- it does prevent the drive gear from hitting the hull side.
Bob

Same trick can be achieved using shims brought off ebay if you don't have a lathe, Measure the gap and buy the shims to suit.