K-series water rail repair and re-paint (EDIT: Engineering question..)

[Smithy77]

When replacing my coolant and upgrading to mikalor hose clips last Autumn, I must have put some excessive stress on the water rail / cylinder head flange joint as I now have coolant weeping ever so slightly. I'm pretty certain it is coming from the joint between the flange and water tube itself (as opposed to between the flange and head). I'm told / have read this is a notorious weak point so it looks as though the welded joint is failing.

I plan on removing the water rail and taking it to a local fabricator for repair. I'm told a brazed repair is best. Can anyone confirm the what metal is used for the water rail and flange? Also, should I get it brazed around the outside of the joint (visible once fitted) or around the inside over the existing welded joint?

I will likely have to re-paint the water rail after the repair and I assume some sort of high temp paint would be required. I've seen Halfords do 3 types:

Here

Here

Here

Which is likely to be best for the job? Or is there something better elsewhere?

Cheers

[CharlesElliott]

Hammerite Satin is probably the best paint. Arch use it when the need to touch up powder coat. I was going to ask why you don't by a new one, but then I saw the price of them!

I'm pretty sure they are steel; if Arch made them originally, which is highly likely, then I suspect it is actually brazed and not welded already.

If you put a post on Wanted, you might find someone that has a spare one?

Another problem is that they are attached in two places. The best thing to do is to determine whether the mounting halfway along the head puts any stress on the elbow when being tightened.

[Smithy77]

Hi Charles, thanks for the quick response.

I briefly considered sourcing one second hand, but due to their notorious weaknesses I thought there would be a good chance of it failing again. I'm hoping with a decent repair it will be fixed forever.

I'm ahead of you on fitting, as I've read that half the problems occur due to poor fitting. When I come to fit I'll clean/flatten the head/flange surfaces before dry fitting and tighten up the head/flange bolts. I'll then assess the front monting point and file down or pack out the mounting point as necessary to keep the flange joint nice and square to the head. I'll then re-fit it with a new gasket and a smear of RTV silicone.

I was leaning towards Hammerite so I'll go with that. Is the Hammerite High Heat paint (matt black) overkill then, or will the standard Hammerite satin black do the job? The pipe must get quite hot where bolted to the head...

[CharlesElliott]

I use Hammerite Satin for everything! I did just check and it says up to 150 deg.

[Smithy77]

I'll go with the high heat stuff then - up to 600degC! Hopefully the finish will be just as good.....

Thanks Charles

[Smithy77]

So I've just dropped the water rail off at a local metal fabricators for repair. I'm aware that the general concensus on here for the same repair is to braze the joint around the outside of the flange. When I put this to the engineer, he suggested the he'd probably just weld the joint as it will give a stronger joint. I went with his advise and asked him to do what he thought was best, i.e. weld it.

I don't know too much about the technical differences and merits of welding vs brazing to really decide what is best. What are the merits of brazing for this particular repair, and should I call them to change to brazing?

Edit: I've done a little research on brazing vs welding, essentially:

Welding - Uses much more heat, joins the two metals by melting and fusing them together, forms much stronger joint (I think this will mean it is also more brittle?), puts base metals under higher stresses and can alter physical properties (more so in thinner metals).

Brazing - Use less heat (enough to meld the solder but not the base metals), joins the two metals by flowing solder into the joint via cappilary action, weaker joint (but does this give it more flexibility?), distortion/warping/stresses to the area is minimized.

I would still like a second opinion from someone with more experience to advise which would be best for this particular repair. If I have interpreted things right regarding brazing being more flexible, perhaps this is the reason why this might be the favoured method?

Cheers

[Ian Mackenzie]

Six and two threes for this one I think......the only concern I'd have that with more heat the flange may distort a little....

I've welded over a brazed joint before and the brazing will spit and fall out the joint with the heat (I used a biggger weld pool to help this, but again this means more heat....), The best weld would be to remove the brazing first to ensure there is no contamination. However it's not load critial so I would not be too concerned, it will be stong enough for its purpose.

Hope this helps

Ian

 

[Smithy77]

Ian, thanks for the advise. Just to clarify, are you saying it would be best to get it brazed because the existing joint is brazed around the inside? All the other joints on the pipe look welded, where as the flange joint on the inside did look more like a soldered/brazed joint - I could be wrong!

[Smithy77]

Just called the fabricators at lunch to discuss welding vs brazing and they had already completed the welding. I guess that put this debate to bed!!

[Jonathan Kay]

Did it refit OK?

Jonathan

[CharlesElliott]

Brazing is like soldering - only melts the braze material and 'glues' the joint together.

Welding melts the target item(s) itself.

As long as it fits, it doesn't matter. More chance of distorting things with welding though.