Help please: difference between "idler bearing" & "tensioners" & "tensioner bearings"

I'm no expert, but from the diagram, I'd guess that'd be the "hydraulic tighteners".

http://www.ricambiamerica.com/parts_catalogs.php?M=FE&P=&V=diag&I=394

 

It's a good idea to make sure everyone is on the same page.

What we typically refer to here as "tensioners" are in fact usually an idler pulley that has an integral bearing that is known to be problematic on a few cars. On the CS it is part #15 on this drawing. The 360 also has a hydraulic gizmo that applies pressure on these pulleys that is known as a tensioner or "tightener" (part #24). I recall that on some early 360s there was a problem with these parts breaking that led to engine failures (Rifledriver posted a picture). I'm not sure that it's anything to worry about now but it would be a good conversation to have before the work gets done.
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See below in the diagram parts 18,22,26,27,25,21 make up the "tensioner"

parts 23 is the bearing

So you are really talking about two things here the tensioner device made up of 7 or 8 parts
and the bearing itself. So to replace the tensioner would be expensive for both sides. Usually unless a part is broken maybe just the spring part 25 is replaced. But the unit is usually cleaned up.
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In my own dictionary in my head if the pulley doesn't run any device it is "idle" and therefore serves another purpose to maybe redirect the belt or put tension on the belt. That is not official just my way of defining it. It can take the form of a bearing or a pulley. Depends on what is to be accomplished i guess. Others here may elaborate no doubt.

 

My version........

Belts - self explanatory.

Tensioners - this is the term used by most people to describe the idler pulley/bearing (which is the item many people replace with the Hill unit). The vast majority of people seem to feel that replacement of these is appropriate with each and every belt change. I understand that a number of belt failures are believed to have been caused by one of these bearings seizing or at least getting sufficiently stiff that they don't rotate at the correct speed and cause friction and heat which causes the belt to break. Some people simply check the bearings for smooth operation and lack of any play and will use them a second time. Personally I'd be inclined to replace each time the belts are done. The pulleys are mounted in a concentric (off centre) fashion and depending on where you set them they increase or decrease the tension applied to the belt. I guess in that respect they are in fact "tensioners"!

The other items (comprising of several separate components) are actually hydraulic dampers. They don't actually apply much by way of tension but what they do is prevent the belts from "flapping" at various frequencies by taking up and releasing any slap in the belts. As I understand it most people do not replace these each and every time they change the belts as it's considered over-kill. That said, I'm sure your mechanic will inspect them to ensure there is no obvious sign of wear or fatigue and recommend replacement if needed so I'd be inclined not to request replacement at this stage but ask them to to simply check them.

Hope this is of some assistance.

 

I am about to perform a belt change on my 2002 Ferrari 360 modena and I remember during the last belt change that my mechanic noticed that L.H. HYDRAULIC TIGHTENER was a little loose... He said that maybe on the next belt change we should replace it...

What do you guys think ?

I understand that it is a hydraulic damper (not a spring) so do these go bad over the years...

He noticed that the R.H. HYDRAULIC TIGHTENER was tighter... Could it be that our cars are prove to failure of the L.H. tightener...

My mechanic made a remark that on certain parts on-line retailer they charge more for the L.H. tightener than the R.H. tightener as they are more prone to failure...

Is this true ?

Thanks !