This morning the swap was completed and I had a quick shufty round under the bonnet to see where we stand... It appears it's going to be more involved than just a new cam/caps and belt kit, on initial inspection the inlet valve on the far right appears to be bent as it's sat about 1 maybe 2mm lower than the rest (and the inlet manifold makes a different resonant noise to the other three when I tap the lifters with a screwdriver handle!)
Also, as mentioned by the seller, the engine wasn't turning on the starter & now I've removed the camshaft it's still locked up solid. How solid? well, I managed to remove the crank pulley nut in my effort to wind the piston back down away from the valve head!
So I'm definitely going to have to decapitate the engine, and possibly even then the bottom end is going to be damaged.
All this is no great surprise to me, albeit a little disappointing to find, what does shock me though is the order of events I believe led to the failure.
Basically, what was originally thought to have happened was that the cambelt/tensioner failed resulting in piston/s meeting valve/s and snapping the camshaft & one cap. What I believe though is that this was a delayed camshaft failure from a previous belt snapping.
In other words, I think the cambelt has failed some time previously and the owner "got lucky" and it appeared that all was fine with the camshaft etc & it had a new belt fitted/re-timed and away it went seemingly in rude health. However I believe that during that failure, the camshaft was indeed damaged although only cracked & not picked up during a visual inspection.
I say that the engine then ran for "X" amount of time with this crack gradually growing across the full diameter of the shaft until finally the reduced area sheared and caused the cam to go tight in the head (damage/scoring on the centre and right bearing surfaces but left side is perfect) and then at some point the right cam cap fractured allowing enough play for the broken off end to drift enough out of time, allowing the inlet valve on the far right cylinder to make contact with the piston (possibly repeatedly, while the engine continued to fire on the remaining 3 cylinders, hence the bent/broken valve).
Sounds pretty strange, but my "old car forensics" tells me it's possible (even likely) because of the nasty scoring to the centre and right bearings with the left (drive end) being good as new. Also the break in the camshaft tells of an old "injury" with only a small area of clean, shiny metal where the 2 parts rubbed. The rest of the break area is dark and granular, this is very reminiscent of crack/fatigue failures on other things I've messed with & suggests that the engine continued to run with the broken shaft for at least some minutes if not more.
Sorry for the long post, maybe it's interesting or maybe not. if anyone's still reading at this point, I welcome your opinions on this theory as well as your encouragement to get the thing stripped and sorted! How likely is it to have damaged a rod or big end given that it's locked up so tight I wonder? I just hope the valve head hasn't fallen off and jammed down the side of the piston...
