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Author Topic: I found a hole in my frame  (Read 7538 times)

Offline Craizeehair

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I found a hole in my frame
« on: July 04, 2025, 03:56:25 PM »
I have finally stripped the frame and whilst I was giving it a once over I noticed a hole on the bottom of the frame. The only evidence of a problem with a on the underside, sides and top are fine.

I’m not sure if there is a seam or if it is split, I have no idea if this is major… Is it ok or am I looking at some extensive repair work?


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Offline Bryanj

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Re: I found a hole in my frame
« Reply #1 on: July 04, 2025, 04:07:05 PM »
What Bike?
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Offline Craizeehair

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Re: I found a hole in my frame
« Reply #2 on: July 04, 2025, 04:28:15 PM »
Sorry… CB350 K2
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Offline Athame57

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Re: I found a hole in my frame
« Reply #3 on: July 04, 2025, 04:35:22 PM »
What springs to mind here is a short section of the frame should be cut away removing any corroded metal around the hole, so a new section of narrower ( solid?) tube can be inserted within and welded up?
« Last Edit: July 04, 2025, 04:41:37 PM by Athame57 »
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I brake for animals!
1978 CB400F2 called Elen.

Offline Bryanj

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Re: I found a hole in my frame
« Reply #4 on: July 04, 2025, 06:00:54 PM »
As they aint easy to get that needs carefull welding/patching plus carefull checking of the rest.
Was not totaly unheard of on 400/4 by sidestand and caused by water getting in at the welds at top and just sitting there and/or the frame just sitting on the ground
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Offline Craizeehair

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Re: I found a hole in my frame
« Reply #5 on: July 04, 2025, 06:12:18 PM »
That’s a nuisance!!!

Anyone here undertake that kind of work
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Offline Bryanj

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Re: I found a hole in my frame
« Reply #6 on: July 04, 2025, 06:45:47 PM »
Where are you?
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Offline Craizeehair

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Re: I found a hole in my frame
« Reply #7 on: July 04, 2025, 07:09:37 PM »
Northamptonshire
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Offline Bryanj

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Re: I found a hole in my frame
« Reply #8 on: July 04, 2025, 07:34:49 PM »
Bit far from Gloucester, dont know if Trigger is still working, he is near Conningsby
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Offline Craizeehair

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Re: I found a hole in my frame
« Reply #9 on: July 04, 2025, 07:37:09 PM »
Gloucester is closer!
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Offline Craizeehair

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Re: I found a hole in my frame
« Reply #10 on: July 04, 2025, 07:37:26 PM »
Just over hour and a half on a good run
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Offline Bryanj

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Re: I found a hole in my frame
« Reply #11 on: July 04, 2025, 08:09:19 PM »
I will see if my mig still works, havent used it for a looong time
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Offline Toko_Jo

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Re: I found a hole in my frame
« Reply #12 on: July 04, 2025, 10:20:26 PM »
Very common on that model. The frame has pressed steel sections which act like a funnel if the seat is removed for any time and water somehow finds it's way and collects in the lower frame tubes.

Even seen ultra low mile USA imports with corrosion where mice have nested in that tunnel under the seat and their p*ss finds a path into  the bottom tubes and they rot badly.

It looks like a very poor repair has been done already ...The tube should be continuous .... Maybe someone had already tried to let in new section of metal...I would grind away until you get solid metal then take the decision of MIG welding a  replacement  section of tube or replacing the frame.

I have seen it argued that the lower section is mainly to support the footrest bar as there are bolts onto the engine either side of that section. In my humble view it needs to been done properly though.


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« Last Edit: July 05, 2025, 09:21:41 AM by Toko_Jo »
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Offline Laverda Dave

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Re: I found a hole in my frame
« Reply #13 on: July 04, 2025, 11:12:39 PM »
I've seen a couple of 400/4's with bad rot around the side stand pivot area. British bike frames weren't immune from frame rot either.
I hope you get it sorted considering the progress you've made in such a short time and your enthusiasm for it👍
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Offline Craizeehair

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Re: I found a hole in my frame
« Reply #14 on: July 04, 2025, 11:22:08 PM »
Thanks Gents,

Excellent info and appreciate the encouragement.  It will get it sorted one way or another.
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