Topic: 1978 cb750K8: Hole In Frame ** Advice Needed **

[liPPy]

I've just started work on my first ever bike, a non-running '78 cb750.

The bike is filthy and been left outside for a while. I started stripping it down tonight. After finding the foul smelling remains of a dead mouse in one of the exhaust headers I got to removing the kickstand when I noticed a slight bulge on the frame about 10cm from the kickstand mount.

Further inspection revealed a small hole. Pictures below.

How big of a problem is this and what do I need to do to take care of it??

As stated earlier, this is my first project and I really am learning as I go along, so any advice is hugely appreciated!

Thank you!


From directly below:

[Hasenkopf]

looks like water got inside and froze..... if the frame isn't too badly rusted with pinholes you could weld it back up, drill a small drain hole, or keep the bike inside from now on

[Toxic]

+1 on it looking like a frost split.

But you are going to thoroughly strip the whole frame and inspect all the welds anyway so welding it up won't be  a big deal.  I wouldn't just weld it up and assume the rest of the frame is good.  There looks to be allot of surface rust on it.

[liPPy]

+1 on it looking like a frost split.

But you are going to thoroughly strip the whole frame and inspect all the welds anyway so welding it up won't be  a big deal.  I wouldn't just weld it up and assume the rest of the frame is good.  There looks to be allot of surface rust on it.

Thanks for the quick response.

And you are correct, I'm stripping everything off and powdercoating the frame. Inspecting the rest of it will be no problem.

So once I confirm no other damage I can weld the gap and smooth it out before it goes to the powdercoaters.

The welded crack will not compromise the strength of the frame?

[Toxic]

[/quote]


The welded crack will not compromise the strength of the frame?



[/quote]

Not at all if it is done right..  I have seen much worse fixed up.  Stripe it bare and see what you have got.  Personnally I like to take the frame to a sand blaster.

[Roach Carver]

this is really REALLY common. I fixed mine by cutting another frame and placing a patch over it. A friend of mine tacked it over the area of the hole. looks ok. The way it was explained to me is that you dont weld it solid because there is a small amount of flex in the tubes and if yuo try to make it solid it will just crack.

[MoMo]

I had a similar problem with a CB400f, had a welder shape a plate and weld it to the frame. 

[liPPy]

I had a similar problem with a CB400f, had a welder shape a plate and weld it to the frame. 

Nice one. I'll add it to the ever growing list 

[Ouch]

not trying to thread jack...but what type of welding would due? Would Tiging somthing like that be the best way to go?

[754]

 Tap it back a bit if you can and mig weld it. If you dont grind weld all the way down, it might? be better.. thats the easy fix.

 I got a 77F here where the split is much longer and the frame swelled up to 1/8 INCH or MORE  in spots, the stretched area is about 3 inches long.. looks like a snake that swallowed a pig...