Gearbox rebuild....

FastFred · Jun 16, 2013

I am glad I got off my butt at last to sort it as it was spoiling the bike (the slack in drive chain). My old Commando was a beauty (when it was running..) but that's another story. This is going to be a £500-700 job with a shell and gears rebuild etc..I was going to sell the Commando the other week but I know it is the best British twin and it's failings were my laziness to sort them. If I have to go to Mallory on my RE then so be it..

kommando · Jun 16, 2013

Wonder whether a top hat flange could be attached to the shell in which the seal is held.

rwalker28 · Jun 16, 2013

I have a case with a crack in the webbing between the where the bearings sit...anyone can weld that successfully let me know. I 'd like to get it fixed. Sorry to hijack post, but seemed like germane to the discussion. I am not the only one.

FastFred · Jun 16, 2013

Thats what i am going to do Kommando. Medium press fit and epoxy or weld

Cheesy · Jun 16, 2013

Im not quite sure I follow everything but in this area of the shell there are 2 dias, there is the OD of the bearing then it steps down to the OD of the seal, the inside face of the seal locates against the bearing bearing outer race. I assume the lip you are talking about is the raised bit on the clutch side of the shell, if so I think it was 2.xx mm I gave the measurement in an earlier post. If it is infact missing before you get too carried away it is probably worth seeing if you can get a thinner seal to go in the hole you have

FastFred · Jun 17, 2013

Could someone measure the depth of the recess for the sleeve gear brg from the inner face please?

kommando · Jun 17, 2013

The bearing is in my shell, but the bearing is proud of the machined surface by a similar amount the layshaft being is proud of its housing.

FastFred · Jun 17, 2013

Could you measure the depth of brg protruding Kommando as they are tightly toleranced on width so I could work the depth out? is it up against a face in there (which you can't see..)?

kommando · Jun 17, 2013

Will try to measure tomorrow, did try but its difficult to see the reading inside the shell, the bearing does butt up to a face.

kommando · Jun 18, 2013

Got 40 thou with a depth micrometer, that is how far the mainshaft bearing face is proud of the machined area around the mainshaft and layshaft bearing holes.

FastFred · Jun 18, 2013

Thanks Kommando, 1mm in new money.

kommando · Jun 18, 2013

Funnily enough I had the same question for the B40WD today, had a crankcase with no bearing in the housing, housing depth 15mm, bearing width 16mm ie an installed bearing will stand 1mm proud to the layshaft machined flat. Too many design engineers moving between the big 3 no doubt

FastFred · Jun 18, 2013

Just come in from t'shed. Got stuck getting gbox shell out of engine cradle.Slackened rear three engine bolts but it looks like the cradle needs removing off the engine to get the box out? Do I ahve to remove rear wheel and chock the cradle as per Haynes?

Hobot · Jun 18, 2013

I don't remember you IDing the model Cdo but '72 with the low down breather must have engine lifted forward on front iso pivot to get shell out, which means rear engine cradle bolts out which means unless cradle supported the power unit falls down in half. Shell needs tipped and twisted forward for me to get mine out. You did knock the crappy thick trapping washer-spacer out the way on top DS didn't ya? For such simple things they sure can be maddening.

Cheesy · Jun 19, 2013

hobot said:
I don't remember you IDing the model Cdo but '72 with the low down breather must have engine lifted forward on front iso pivot to get shell out, which means rear engine cradle bolts out which means unless cradle supported the power unit falls down in half. Shell needs tipped and twisted forward for me to get mine out. You did knock the crappy thick trapping washer-spacer out the way on top DS didn't ya? For such simple things they sure can be maddening.

My 71 with cam breather needs the cradle tilted as well, well it did, a little touch up with a grinder to the cradle near the ISO tube and it will come out without dissasembly

Keith1069 · Jun 21, 2013

FastFred said:
Could someone measure the depth of the recess for the sleeve gear brg from the inner face please?

An old Dommie shell I have measures 0.594" from spot face between bearing housings and the wall thickness of the seal surface 0.221".

FastFred · Jun 25, 2013

Well I got the box out, bitch of a job, hardest bit was bottom rear eng/cradle bolt that reqd the crowbar to lever up engine so the bolt head could clear the frame (all eng mounts and iso were loose)
I am so glad I stripped this box but I will attempt a repair to recreate the seal housing. Will get the box on the bridgeport Saturday and centre up and clean up this mess back to the sleeve gear brg diameter first then make a top hat, press fit and epoxy or spot weld.
Note how the sleeve gear brg was about to self destruct as the layshaft gear ground into it!

Hobot · Jun 25, 2013

Hehe, hoho, boo hoo hoo. I've a shell with opening about exactly like that and I caused it myself so know what happened to yours. The main bore got so wallowed out the bearing would not stay in once cold against mere gravity so the mechanic thought he'd not seated it fully, so next time used a 3# sludge that drove home the bearing clear out the other side. It you can recover this one for reasonable effort-cost then there are literally 1000's of shells in piles in vendors all over the world you could restore back to life and times. I'd donate my shell, as has nicer cleaner more perfect hole and lay shaft bore ok, to use yours to trial error on first. They may have sold off most of em for scrap by now though. Do note that Atlas shells fit even better than Cdo specific yet cost about one half as dearly. Educational how thin the DS case wall is.

FastFred · Jun 26, 2013

Cheers Hobot. the main (sleeve) and layshaft bores are still both a press fit. I am going to have a go and will post the repair. A lick of paint and for sale on evilbay... Only joking!

FastFred · Jun 29, 2013

Went into work this morning and got on bridgeport and lathe. That's a top hat that I have made for the lip seal; will need a tweak before fitting but going order a gearbox brg and bush recon kit and work out the brg depths first. More later..

Gearbox rebuild....

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