Gearbox removal on Goldflash

[farmboyuk]

Hi,
Well it looks like I've got a crack delevoping on my 1952 Goldflash pre-unit gearbox, where it bolts to the frame.





My question is can I remove just the gearbox, it to have it welded, or do I have to remove the engine and gearbox complete. Is it possible to just to take out the gearbox. Different service manuals seem to tell me different things.

Many Thanks.

[a10 gf]

Hello, and welcome to the forum. I removed engine together with gearbox when I had my plunger box out, to get access to the 4 bolts between engine and gearbox. Think there was something else in the way too, but do not remember. If anybody has any tricks that makes it possible to keep the engine in place, please tell us!

Regards
E.

[fido]

You can take just the gearbox out on the later models but I think with the semi-unit lump it will be easier to take out the whole assembly. In either case you will need to strip off the primary case, so you will see better what's involved at that stage.

[dpaddock]

Semi-unit GF's cannot be separated in the frame.

[unclemeat]

I'm pretty sure dpaddock is right - you can't remove just the box. I think you'd have problems with the g/box mount flange hitting the rh crankcase and the main shaft would hinder things too.

I have to admit though, unless dpaddock has actually tried this...

How about you remove all g/box internals including the main shaft, remove the magneto and oil tank too, then try.

You will probably end up with a couple of scraped knuckles and a 'told you so'  !! from dpaddock but would be great to know !!!!

Good luck

[farmboyuk]

Well, I removed the engine+gearbox - got the gearbox welded up, but after putting it all back together again it cracked again in the same place after a ride out . I've managed to get hold of a replacement housing (no cracks) but was wondering is there anything I can do make this stress joint as strong as possible, the aluminum casting seems very thin at this lug. Any suggestions would be apreciated.
Thanks

[a10 gf]

Sorry for all the extra work you had to do, but (like all of us here, I suppose  one becomes an A expert by owing and riding one, redoing things a few times is what gives expertise.

Have never heard, read, or seen the gearbox problem you have, may have originally started due to a crash or shock, then the tension of the bolt + vibrations\movement  made it worse 'til it cracked. Welding aluminium is a skill, did they weld the part back on? If so, better to forget the cracked piece, and rebuild the whole with aluminium welding. Needs a good man to get the rebuilding right. Then drill out, file and polish etc until it gets the original shape. Then chech that the frame is completely flat against the gearbox surface, eventually straighten, file\polish or whatever till it is, use a correct diameter bolt then use a selflocking nut and do not tighten more than neccessary.

Your new gearbox housing may be 100% fine, but still do a check for 100% parralellness (is that the word) to the frame at the contact point and use a selflocking (or loctite it) with just enough tightening, then check all other engine\gearbox mounting bolts, if something is moving the stress may end up at the point where you got the cracks. Just some toughts that emerged, hope some of it may be of help, good luck.