Topic: help... top and bottom case alignment after welding...pics

[Thunder]

Well i finally came across someone here in Capetown who is restoring a cb750 (1971).
I went there today feeling cocky after having restored one, but walked away humbled by a proper ground up restoration.
Really nice guy, nice workshop and lotsa  shiny new parts.

Problem is ... sometime in the past it had the chain smack the sprocket area and was welded up (badly.)
If you can see by my terrible photo's, the mating surfaces of the casing are bad.( I assume silicone was used to keep oil in)

I have told him about the tonnes of advice/help one gets from this site and will point him here where hopefully he will join and post some clearer photos.

In south Africa we have the problem that our paperwork has both the engine number and frame number, so getting another casing will be difficult and as its a '71 he would like to keep the number in that range.( i have a 74 casing which he can have but stuffs up the originality)


By thor7223 at 2011-10-15




So, what would you guys reccommend?

thanks
thor

[scottly]

Build up any low spots by welding, then carefully file until the surface is flat.

[Thunder]

What? Like a hand file?
Also, if there are any raised points would this not effect the crank and bearings? (all bearings seated in the 2 halves?).

Is there any way that you know of to weld (raised)  and machine it exactly flat like the head skimming process, but without taking anything off the mating surface?

Cheers

[MCRider]

What? Like a hand file?
Also, if there are any raised points would this not effect the crank and bearings? (all bearings seated in the 2 halves?).

Is there any way that you know of to weld (raised)  and machine it exactly flat like the head skimming process, but without taking anything off the mating surface?

Cheers

Curious situation. Keep in mind hundreds, maybe thousands of people have welded these up successfully.

Maybe use JBWeld to build it up. Then yes a flat, hand file to bring it back down. The oil in that area is not under pressure. Just slosh oil, and not much at that. So an external seal of silicone has often been used succesfully.

In my mind the crank bearing area is drawn down so forcefully that they should be fine and not affected by a few thousandths problem at the far end of the cases.  I would err on the side of taking too much off the repair with the idea that if it does leak, an external seal can be applied.

But, truthfully, I've never been in first hand on one of these repairs. Always swapped out the cases for good.

[scottly]

Any high spots will prevent the case halves from seating together properly. One could set the case on a mill, level it by indicating off the good surface, and then cut the repaired area until it is flush.

[Thunder]

@MC, thanks. Funny you mention JB weld. I actually found a shop here that has it and picked some up on friday. Fate. If he decides to go that route i will pass it on to him.

@Scottly, cheers. So a milling machine should do it, cool.

Well, I've given him this page's address, so will wait for him to come n see and post.

Cheers
thor

[MCRider]

The milling machine would certainly be the more elegant way of leveling the scar.

A file in the right hands should still work.

Good luck,