Gotta love a semi..

[DaveyT]

So when I couldn't get a consistent ferequency reading on the new cambelt, i decided to strip and check the semi-automatic tensioner, and found that the plastic piston had swelled and become jammed in the tensioner barrrel. (Pic stolen from Steve below).

A little fettling on a drill mandrel with fine emery and then fastcut polish brought things back within tolerance so that, when on the bench, the spring will push the bearing out to its fullest extent.

re-installed, and set belt tension to 110 Hz at 30 deg BTDC....However...

if I then pull the belt on the Ex to crank run, the tensioner gets pulled bak but the spring pressure wont overcome it while static. As soon a I rotate the crank, even by 1-2degrees, it takes up the slack and settles back to the correct frequency measurements.

Is this normal operation (spotted a Molemot post saying this might be expected- something to do with valve spring pressures at different points), or should the tensioner take up that slack without being moved?

thanks Gurus

[Tony K]

Probably ok.  Never pulled on that span specifically, but I do recall the tensioner being touchy like that when static.  I am always careful when taking the tension reading that the engine's last movement was completely clockwise (that it didn't get bumped backwards even the slightest as to reduce the tension).  

What I would make sure of:   As long as the tensioner has two springs inside the piston and the piston moves freely in any and all instances, I think you are fine.    With the tensioner looking like that, I would disassemble the whole thing, clean it, new grease, and replace the neoprene washers, and maybe the bearing depending on age and condition.  If the pivot does not move smoothly or if there is excessive play (rare), consider replacing the bushes.   When the tensioner is apart, rotate the piston within the cylinder, and rotate it while moving it in and out, to see if it binds at any point.   

I don't see anything in the Workshop Manual about a ground strap on the tensioner, but many of the early cars I had and worked on had one or some remnant of one.  So I always make a new one when I service the tensioner.   A simple curved wire from the 10mm bolt to any bolt on the body of the tensioner, using eyelet connectors.

Hope this helps!

[DaveyT]

Thanks @Tony K,

all stripped, cleaned and greased ( mine was in a similar state to the one shown above) and new brg installed. Earth strap also in situ. Tested under fwd motion only...

it was just that stuttering in static testing that was of slight concern

[ramjet]

I had a semi once,

but I passed out.

 

Braggin', braggin', braggin'.