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CX-GL Honda MCC

I Used To Have One Of Those

Andrew B

Rusty frames - causes and cures

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As part of my resto I’d appreciate some thoughts on what I’m planning to do with the frame. I don’t know how many on here have stripped their bikes to this level

 

2w5575v.jpg

 

but when you do you start to notice all sorts of odd things that could – and should - have been done differently. (Excuse the primer - just threw it on in case I don't get back to this soon). Actually I haven’t stripped my 650 at all because my starting point is a randomly collected pile of bits which have yet to be joined up. And in the process of collecting I acquired (nearly) 4 Euro frames but only ended up with 2 good ones - and quite a lot of rusty scrap.

 

Obviously rotten bottom brackets like mine

143icd5.jpg

 

are a major problem with all CXs and I attribute this mostly to some poor design details and possibly some variability at the build/assembly stage.

 

Similarly afflicted are the pillion footrest mounting bosses on the side diagonals and it is the design of the diagonals and associated bracketry which are at fault.

 

358xi54.jpg

(Don't know why that pic comes out upside down - and I'm still kicking myself for spraying the rubber bung in the side panel mount)

Note the 'daylight' visible through the bracket around the lower boss - also visible in the pic below.

 

In the centre of this picture you can see what I believe is the cause of the problem.

 

37x4n.jpg

 

Note where the two halves of the sub assembly close around the tube leaving a small triangular hole. When ridden in wet weather water would be streaming down the underside of the diagonal and straight down that hole where it will sit until it rots its way out via the lower boss. It wouldn’t have taken much to close that hole with a bit of weld or better fitting piece parts would it ? What’s really worrying is that there are half a dozen places on a CX frame with exactly the same condition and several more with gaps or openings just waiting to fill with water. Doesn’t it ever rain in Japan ?

 

Having started behind the boss the rust then carries on eating away the diagonal until it gets inside the tube - like this

 

vqpirp.jpg

 

and then runs downhill to start work on the inside of the bottom bracket.

 

Here's a shot of where the engine hangers bolt to the frame.

 

ri5b9d.jpg

 

Note the gap at the left hand side of the pic. How much water could sit inside there ?

 

As I don’t intend to restore this bike twice I plan to close up all of these voids – either with just weld for the small gaps or if they’re a bit bigger I’ll be welding in a small piece of steel. I did consider just bodging it with Sikaflex but I’m happier with weld. I’d be interested to know of people’s thoughts on better ways of doing this or any potential disadvantages?

 

Incidentally, and on the subject of keeping the water out, the last frame I acquired had plastic bungs fitted in the ends of the top tubes which go to the tail. They look ‘factory’ but I’ve not seen them on my other frames.

 

21ce51v.jpg

 

Anyone else got these ?

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Youre right Andy, the CX GL frames almost went back ti the old C50 days of pressed steel fabrication with poorly fitting plates instead of "proper" tubular frames. I guess price must have played a big part in this decision because the rest of the bike must have been expensive to produce ie shaft drive, completely new engine design etc.

M

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