How easy to replace them ? thanks

easy once u have taken

 

Heads off

cams off

valves/springs off

 

then u can remove them and replace

easy once u have taken

 

Heads off

cams off

valves/springs off

 

then u can remove them and replace

 

Can it be done without taking heads off ? if i take spark plug out and use compressed air to keep them valves from falling down ? :)

Some people replace with heads in place but if you do end up dropping anything into a cylinder it's heads off anyway, would be ideal time to change some worn gaskets if you whip the heads off

there are tools expensive ones you can use to change steam seals/springs with the heads in place...

 

but like Mattin just said ..

 

take heads off is fare better and makes it loads easer to work on