Well, thought I'd quickly post this up before I head off to bed, hopefully I'll have inspired dreams and sort out the problem in the morning in time for a burn out into the country for lunch...
So I'm changing the coolant this afternoon, plastics off, exhaust dropped down (don't have a slim universal joint socket to get to the cylinder drain plugs), old coolant drained, recovery tank emptied, flushed out with the garden hose until clear. Plugged everything back up and filled with water and a good dose of Tectaloy Mukowt, then fired her up and let the engine run for a bit over 10 minutes, temp gauge was reading just above the first marker when I shut it off.
As I'm reading the manual, waiting for the engine to cool enough to drain the flush out, she gives a little hiss, then another, then an almighty "POP" and a gush of water...
dang...
So, whatever went 'pop' was somewhere above the back of the engine, if I fill the radiator up it'll eventually start gushing down the sides at the back, but everything's crammed in so tight back there I can't see what's going on. I took a breather to have a cuppa and Onesie called to see how it was all going, we had a bit of a chat speculating what it might be, he had a look over an engine on his bench for inspiration. Definitely something right up in the back... So, back to the shed, air cleaner off, fuel tank out, I'm still not far enough in to find what blew (did discover that the overflow tube & T-section for the two right carbies is missing though...), but it's time to call it a day...
I'm guessing (and here's where I'd love some input) my next move will have to be to remove the carbs to get a better look further along the top of the engine, it looks very wet under there, so I'm sure the damage is further back still somewhere.
Even when I do find either a dislodged hose (best case), a split hose (about what I'm imagining) or the engine blown in half (my paranoia won't let me rule that one out just yet...), there still remains the question of WHY did enough pressure build up to cause that? The radiator cap looks to be in good condition, however there was a little gunk under it when I first opened it up (gelatinous gloop, my guess is from the suspected mix of red & green coolants). Any and all suggestions would be warmly welcomed! But for now, I'm off to dream about riding through the hills...
...on a purple unicorn...