Comet Gearbox Problems

[melmerby]

Hi all

I have been building (for some time!) a Comet chassis for my mainline 43XX where the dreaded Mazak Rot got it whilst it was in storage from new.

I Included a Comet 2 stage 50:1 gearbox and a Mashima 1620 motor.

It has all come together (with much cussing and hair tearing) to the point that I had a nice free running chassis and all that needed fitting was the final gear on the middle axle.

 

Oh Dear! Once fitted it proceeded jerkily and with lots of gear noise, However the binding wasn't once per rev but a different but repeating rate.

Eventually I traced it to the idler gear which was eccentric (?) causing some binding on part of it's rotation.

 

Never mind I thought, I've got two more of these gearboxes, I'll swap the gear for one of the others. Unfortunately itwasn't that simple.

After several hours messing I eventually found just one combination of worm and idler gear that rotated completely smoothly.

 

Is it just my bad luck or have others found problems with Comet's gearboxes?

 

 

[hayfield]

I have had an issue or two with both Branchlines and Comet gearboxes, in the end they both work fine. Just needed a little fettling to get the meshing smooth and quiet.

 

High Level gearboxes I find easier to build (but equally I have built more of them) The only issue I had with a High Level box was of my own making during the build and was easily resolved

 

It is worth testing them first prior to fitting, advice I was given by Dave Ellis (SEF) when I encountered an issue with a motor mount. His advice was to test and ensure it meshed correctly prior to fitting, but I tend to have problems with motor mounts !!

[Barclay]

I'm not familiar with the Comet gearbox. If it has metal gears my advice would be to drench the gears in Brasso and run it each way for 5 mins. This is always worth doing with Romford style gears, or Branchlines which appear to mostly use them. Gears that have a slight hesitation or twitch can start running really nicely. Obviously afterwards clean thoroughly and lubricate. If the gears are plastic this can't be done, but then it shouldn't be necessary. High Level always seem to work first time.