Dear Paul,
I got your messages. It may be best to put your questions up on the forum so others might benefit from the answers at a later date.
The tensioner is just a spring loaded bit of plastic, pushing the chain towards the centreline of the engine by default.
When the chain is worn down too much or the cam sprockets not fitted onto the camshafts, the tensioner is very much an inverted “U” shape and the chain contacts metal on the engine.
When the chain is still good, i.e.unworn (and within its operating length) and the B cam sprocket is on its camshaft and the A sprocket is very close to being mounted onto the camshaft or on the camshaft, then the tensioner is “U” shape is flatter than before and the chain is not contacting any engine parts.
The latch mentioned is a clip which, if the tensioner is pulled so its “U” shape is nearly pulled flat, allows the fully extended length to hang and sit on a ledge, leaving the chain untensioned so you can easily mount and dismount cam sprockets. The tensioner is massively tensioned when pulled flat like this.
My suggestion, is simply that the tensioner never needs to be pulled fully flat to get the sprockets off in the first place and that you can also get the A sprocket back on its camshaft by simply pulling the A sprocket up, together with chain anyway. You’ll get 90% of the way there very easily and the last bit can be aided if you push down on the tensioner to make it a bit flatter. This you do by pushing a finger, or a ruler, or something like a long screwdriver on the chain (which sits on the tensioner) whilst simultaneously pulling the A sprocket up.
Typically this is done when you have finished doing valve timing and if the engine has not been turned over in between when you dismounted and remounted a cam sprocket - and the sprocket has stayed with the chain - then the relationship between the camshaft and crank is unchanged.
If you have turned the crank inn the meantime, then the most sensible thing to do is put cylinder 1A at TDC and then mount the camshafts with the notches facing upwards. You’d then verify cam timing.
The reason Kirby and others put the fear of God into you is that if the tensioner is pulled almost flat and temporarily sat on its holding clip, then it sits under more tension than it usually does in the engine and the release of this clip makes it snap back to its normal position all at once. What you have to get your brain around is that in normal operation, the chain tensioner is not under a lot of tension but is pushing the chain tight, whilst when it is retracted, the chain is loose but the tensioner is stressed like a fully pulled out coiled spring sitting on a flimsy latch, ready to spring back and bite you.
All I am suggesting is that we never pull it back fully and leave it sitting under tension on its latch, because we don’t really need to.
http://www.jag-lovers.org/snaps/snap_view.php3?id=1381505777
Other pictures are available if you search.
kind regards
Marek