Re: 2A Gearbox crack

I can see no evidence of the layshaft roller bearing having moved since I fitted it 20 years ago. Having said that I have not removed the bearings this time - so far. It strikes me that the heating/cooling effect related to bearing changes here is as likely to cause a crack in such a thin web as anything else?

I am encouraged by your comments related to the service notes. If a crack in this area was considered safety critical - then I doubt they would even mention the loctite fix!

Previously david_watkins wrote:

Previously Dave Broadbent wrote:

I have stripped my Commando 2A gearbox this winter to examine it after installing the layshaft roller bearing mod a few (like 20) years ago. All is well. But there is a small crack in the gearbox shell. It is on the inside of the shell, in the tiny web between the sleeve gear bearing and the layshaft bearing. Pic attached.

I saw the crack when I had the box in bits the last time, but decided to do nothing about it (!) on the basis that (a) it wasn't visible outside the box - so probably just the thin web that was actually cracked and (b) to repair would have been a major weld and remachine operation. (c) I was younger and probably much more gung ho than today! Now I'm looking at it again and really at the same decision point - plus the fact that it's done 20k miles since last I saw it and it hasn't got any worse!

My question is to the gearbox experts out there - notwithstanding the mileage aleady covered. I have heard of cracks in the inner case between the bearings, but not about cracks in the shell. Is this crack something I have been lucky to get away with, and should get fixed without delay, or is it in an area commonly cracked without dire consequences?

All advice much appreciated.

Hi Dave,

Mine was so badly cracked the bearing just fell out when I stripped the box. They all do that I am told by the experts. You can get a stronger new on from Andover and RGM. Use a brass cage bearing in the small hole.

Good luck mate.

Oh dear, it sounds from this like the crack in mine is likely to keep getting bigger. I think I'll pop the bearings out today and see if I can get a price for repair to compare to the purchase price of a new replacement.

Gentlemen,

thank you all very much for your responses. I have the bearings out now - and they were both reassuringly tight!

I have cleaned up the area locally and you can make out the crack in the web - almost full depth of the web. (pics attached)

I dont think the case is not bad enough to require a weld repair, and that Dave's suggestion of cleaning and loctiting etc is the way to go. I'll look at it again in another 20 years...

The aerospace engineer in me however is inclined to dress out the crack, leaving a decent radius in the bottom of the resultant slot to prevent the crack spreading any further. The metal has already parted so it will lose nothing in strength, but cracks will spread if not "stopped."

This is the other pic of the web from the other side. For some reason it woyuldn't let me attach two pics to the same post!

Previously ian_soady wrote:

I wonder whether you could drill a small hole at the inner end of the crack to stop it propagating.

Those pictures do illustrate how thin the web is, although all the force is away from the web as the shafts try to separate, so the main issue is preventing the bearing outers from rotating.

I must confess I may well have missed that crack if it had been my bike!

A bit of work with the drill this morning and the job looks good to me! I can feel quite relaxed running round now. I will use abit of loctite on the rebuild, but the problem there is the temp you need to get the shell up to in order to accept the deep frozen bearings rather burns off the loctite in my experience?

Thanks again for your help.

Dave