Hi, today I cleaned all the oily sludge from the bottom of my k100rt (couple of bad gaskets, leaking coolant bottle, split clutch pushrod gaitor, oil from peek hole in water oil/pump) to get a better look at what is underneath and foud that there is a fracture in the front most exhaust outlet manifold jus above the header and sweeping up then laterally to the left... My question is (I think I already know the answer in my heart)... How much of a problem is this for bike + mot testing? Are there any repairs/remidies?

Did the bike run okay before you found the crack?  If so, I would let it be until it was leaking enough to mess up the running of the engine.  Then I would replace the head with a used one.

I may be wrong but I think you will find that is a surface mark and not a crack.

I'm with Rick. Looks more like a casting mark.

looks like  the head gasket to me

the orientation of the picture is quite ...um deceptive

Has the bike been rear ended? That could result in a crack like that. I can't zoom in and keep a sharp enough picture to say whether it is a crack or casting pattern mark...but I would say crack! Wonderful place this forum  - you ask for an opinion and get opposing ones!

In terms of MOT, I've never know a tester get their head down that low to inspect the underside of the bike and a healthy dose of road dirt in that vicinity will hide such sins...unless it is so bad that it is blowing when the bike is running, in which case the sooty tell tale and escaping exhaust gases give the game away. 

If it is a crack and not blowing, I would simply put a smear of exhaust repair gum over it and smooth it out so it is not obvious.

Yeah it's a crack, I might have a go at welding it, don't like the idea of drilling a bell stop in though 🤪

I don't think she's been rear ended, but the I've got a feeling it may have happened when the guy I bought it from removed the muffler, I was given that separate and the header bolts look undisturbed! The mating faces of the engine components don't seem to sit together great (could be due to the amount of Dow corning "gaskets") and some of them seem mismatched in shape. Runs OK though and can't see any oil in coolant or visa Versa, jus oil on the corner of rocker cover, half way up along the bottom of the timing cover and through the 🕳 in the water pump casing + oil from split gator. Coolant leak is from the perished viewing tube on the expansion tank. It over heated and cut out when waiting to get to temp during oil change... Broken fan! Need to check the thermostat too make sure it's not stuck closed!

There is a few tests around to check for cracks, the one I have used was called Dye Mark or Dye Check. There are also a magnetic crack tester which is not applicable to Bricks. An automotive machine shop should be able to do a check which is a very simple process.
Regards Martin.

Its a mark on the metal due to probably a bit of dirt/muck/shit and the mark is at the edge as you can see it continues onto the steel and where the arrow points is a break in the "crack".

It's a crack guys...

OK

Thanks for taking the time tolook at it in detail though Rick G, think my photos of it are a bit poo... wish it was just a casting blemish though 👎🏼

So I guess short of welding it I should just suck it and see?
Give me time to find a save for new one anyways... 🙄

Blackthumb wrote:.. wish it was just a casting blemish though 👎🏼

So I guess short of welding it I should just suck it and see?

Properly prepare the surface then cover the crack with the appropriate Devcon or JB Weld product. After that, you'll probably be less obsessed by it.

There are the makings of a side- or top-case sticker in your post.
I sucked then I saw.
  K100-forum.com

Weld it in situ, if the crack is only as far as it is visible then you could just gouge it and fill with weld TIG. You wouldn't put enough heat into it to cause any warping especially as the head is bolted to the block. Use a tungsten burr to clean it up.
The alloy is nothing special and easy to weld.

Yea I think I'll give it a go, I imagen it's made from A356 so should hold fairly srrong if I weld