One of the US Alfa Club tech advisors suggested the following. Any thoughts?
Tensioner cylinder on a 164 24v engine will not cause this "problem". Tensioner pulley bearing or pulley mount bushing possible but my money is on either aux drive pulley shaft bushings worn in rear head or one of the two idler pulley's bearing worn and a pulley leaning.
It is possible to have a loose idler pulley mounting bolt, too.
I was following your thread on this over on AlfaBB..
...anyhoo, I'll probably only repeat what's been said, but most likely causes are badly worn aux shaft bush in rear head, loose aux shaft pulley (this one is actually easy to do if the engine has been worked on - there are two holes in the pulley, but only one actually fits the locating dowel properly...get it wrong, and it can go on slightly skewed, then go loose in time). Loose or worn out idler pulleys. Another potential issue with the aux shaft, and again, probably only likely if it's been worked on, the shaft passes through from the fornt of the head, then through the skew gear that drives the oil pump, then there is a locking washer and big nut. If the nut came loose for example, it would allow the shaft to walk in & out a bit. This one is easy enough to look at, get access to the top of the rear hear, front corner, remove the cover where the oil condensate return pipe connects to, to reveal the top of the oil pump drive and the aux shaft gear - have a nose in there. Any problem should be obvious. Again, another possibility is the central idler between the banks, the bolt holding this in can be VERY hard to remove....and knowing what some mechanics are like, they may not bother and just leave it partly loose, or leave the old idler in there. If you get a bad one, you have to remove the casting that carries the idler in order to get good access for more ....aggressive removal techniques.
Bad idlers, bad tensioner bearing, won't be a loose cam pulley or it wouldn't run! I guess you could possibly get a wandering pulley on a 12V as it is keyed, but not on a 24V.
I'd agree that it's not likely to be a simple tensioner problem - this would be far more likely to lead to the belt jumping a tooth than riding across the pulleys.
I forget now if you bought the car or not...if you did, my first step would be to get in there, cam-lock it up, remove the belt, all idlers and tensioner, replace waterpump, carefully check the aux shaft for play (axial and latteral) and a properly fitted pulley, then reassemble, carefully checking the idlers and tensioner as you go, and finally, put a new belt on.