Eduardo et al,
I've now been to a mechanic who seems to have given me a believable reason for all the problems my engine's given me.
Nito Vargas in Rio Gallegos, Santa Cruz, Argentina said that my asparragus are not strong enough! As far as I understand him an esparragos in Spanish is one of those double ended bolts (I don't know the word in English) that holds the head on tightly(?). It seems that the asparragus that I have from the Huerfanos rebuild in Santiago don't behave well when hot, i.e. they extend. So the heads become loose making the valves badly adjusted and resulting in a loss of compression.
Has anybody else had problems with loose heads because of these screws? Nito suggested they need replacing to fix the problem, for the moment he readjusted the valves and tightened the heads up to 3 (I think the units are m kg) (he said the ones that weren't loose were already at 2.4). He also said I wouldn't find replacement asparragus in Punta Arenas, but that I would in Comodoro Rivadavia.
I'm thinking of driving down to Ushuaia, Punta Arenas, Puerto Natales, El Chalten and then to Comodoro Rivadavia, a distance of a few thousand kilometers partially on dirt road before fixing the problem. At least I know what it is now and I can deal with a loss of power as long as I can start the bus.
It seems the problem with starting the bus was partially that I was using too much choke and that the 3000 km of dirt road had clogged up the carburetor. I will see tomorrow morning whether she will start cold. I still have the liquid starter fluid just in case.
Now all that remains is to replace one of the shocks, buy three new tyres, weld the back bumper on and fix the lights!
Thanks all, especially Eduardo, for all your help,
John.