Topic: CB750 k0 Crankcase Damage

[Steph550]

Hi all,

My partner is looking to buy a CB750 k0, he's found one he likes and took it out for a test ride the other day. However, when he got back there was a significant oil leak from the crankcase area. On further inspection it turns out that at some point the drive chain has let go and damaged the crankcase, which was then welded. The weld has now failed - there is a fracture running along one side of the repair and hole of around 1-2mm diameter.

The question is, should this put him off the purchase of the bike? It's not so much a question of the cost of repairing it, as the seller is a dealer and will have to get it repaired before he can sell the bike for the price he's asking. But if it is welded again, is it likely to cause trouble in a couple of years' time? Is it a specialist job to do a really good repair or would it be a fairly easy thing for a decent welder to do?

Any advice would be appreciated!

Thanks,

Steph.

[70CB750]

They were welded succesfully before.  There is not much going on there in that area when it's not hit by a chain.  I would get it, especially when the dealer will do the repair too.

Oh, result of a quick search:

http://forums.sohc4.net/index.php?topic=36600.0

[ekpent]

Guess it all depends on the asking price also. A major repair in that area certainly does not increase its value and will turn some people off. Do you have a pic of the bike by chance ?

[Muckinfuss]

First off, that's an excellent price for aluminum braze rod.  Durafix and others are twice that price and more at welding supply houses.  Don't forget to FLUX!

As to the "do it" or "don't" aspect.  If you're buying an investment bike, you wouldn't be asking the question, so here's my experience.....back in the day, 'we' used to build race frames for flat track as well as brit bikes for hare scrambles using braze instead of welding.  The characteristics of braze gave a solid, yet flexible frame.  If that makes sense.  Rickman, and I think Martin frames were brazed as well.   I've picked up a rock or two at speed creating a crack in the primary side cases of my Heritage (Wyoming at 110mpg, the road ended...long story) and limped it to a small town auto shop in Montana where the guy there used aluminum braze rod to patch the leak.  That was in 1991 and I still have the bike....and it doesn't leak.  I'm a fan of brazing.