'69 750 airbox cracked

[ndwind]

I'm working on a beautiful, museum quality '69 750 K0 (not sandcast) that has a cracked airbox. More specifically, on the top half, the surface that mates to the air filter gasket has numerous cracks across it. I believe it had some cracks that had been repaired previously, but were not repaired flat and level. And when it was reinstalled on the bike, the high spots caused more cracking.

If this were one or two cracks, I would repair it myself. But, with this level of complexity, and rarity of the part, I'm looking for knowledgeable recommendation(s). Can this be repaired to a level this bike deserves? If not, I appreciate recommendations to track down NOS or high quality replacement.

 

[brettp]

Look at plastic welding. If you don't want to try that, look into fixing it with fiberglass.

 

[hinksy]

You could plastiweld it with a similar colour or do fiberglass . As it is on the inside of the airbox and noone will see it , all you really need to do is make sure it all fits together once done

 

[Qaxe]

It really depends upon what you're going to do with the bike.

Not being an ass, but when you say "Museum" do you mean "Concourse" or do you mean bike-show quality? Proper museums are generally focused on preservation, and wouldn't patch something broken if it diminished the history (or value, especially in the case of art museums). Concourse on the other hand, is restoring something to brand new, and then parking it somewhere dry where the peasants can't breath on it. ;P

This is just my opinion, but if you want to ride it, AND you've already zeroed in on a replacement, then my personal preference would be to try to fix it so that it functions. And in that case, I'd watch some guys on Youtube repair plastic motorcycle side-covers and/or fairings and then give it a shot. At that point, if I messed it up, I'd buy a replica.

Replicas for the older K model airboxes are available sometimes on Ebay. Try here: https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=p2510209.m570.l1313&_nkw=cb750k0+airbox&_sacat=0

My preference would be Plastiweld, or the little plastic welding rods you use with a soldering iron (name?). The main thing about DIY in this case, is practicing first before you go for the gusto.