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Discussion Starter #1
I have recently changed belts and pulleys on my wife's 147. I had someone starting the engine before putting back the covers to visually check if all was well. I was shocked to see the amount of movement on the automatic cam belt tensioner during start-up, shut-down and low rpm. There is no lubrication on the spindle of the tensioner - I can imagine that it can easily get stuck in the maximum position with some slack in the opposite side of the belt, causing damage to the belt.
Half of the time during shut-down, the engine comes to standstill with one of the cylinders compressed more than 50%. This pushes the crankshaft back in reverse direction. Due to the shape of the cam lobes, and the tension of the valve springs, the camshafts are reluctant to turn in reverse direction. The tensioner spring is weaker, causing the tensioner pulley to snap to the maximum tension stop on the frame of the tensioner. On the other side of the belt I could visually see slack of about 1 cm in the belt. Upon restarting the belt is jerked, causing point load on the belt - the first tooth on the belt on the pulley has to take all the punch. This is not good for the belt, causing long-term damage that will accumulate and cause premature belt failure.
The benefit of an automatic tensioner is that it takes up slack resulting from belt stretch, and do not need to be retensioned every 30 000 or 40 000 km, as is the case with a fixed tensioner. However I am convinced that the automatic tensioner does more harm than good, and is seriously considering modifying and old tensioner into a fixed one, fitting a new bearing, and to use that in the next cam belt change.
I have three other vehicles, all with fixed tensioners. One of them has a non-interference engine. On this car the water pump is eccentric and serves as the fixed tensioner. However retensioning the belt is a major issue, since the water pump seal usually leaks if installed for more than a year and then disturbed by turning the pump. I thus decided not to retension the belt at all. When I eventually replaced the belt at 120 000 km, it was still in good condition, except for a bit of excessive slack while installed.
I would rather go for change intervals of 80 000 km, with just a retension at 40 000 km. This would also be better in line with the expected life of the variator and other pulley bearings. I am sure that with a fixed tensioner I can safely achieve that. Cam belt related costs will also decrease by 33%.
Any other opinions on this?
 

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I have second thoughts on installing a fixed tensioner. The waterpump pulley is toothless and sits on the wrong side of the belt for a fixed tensioner to work properly. When the belt stretches and becomes somewhat undertension or loose, the waterpump pulley will start slipping on the belt, chafing the back of the belt.

Well I guess I am stuck with changing belts and pulleys every 2 or 3 years... :cry:

I still hate the automatic tensioner for what it does to the belt though... :mad:
 

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Interesting reading, with some very comprehensive views. I never had belt or tensioner problems with my 16v Turbo'd Lancia Thema, other than one contra rotating balancer shaft belt tensioner bearing that I thought was 'roughish' so I replaced that. Sold her at 72k, one of my all time favourite machines.:thumbs:
 

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when you set the tensioner was the pointer of it aligned with the hole in its frame.

its MEANT to fluctuate, as you describe BUT it has to be properly aligned in order to work correctly
 

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I had the Beta, with it's massive spring auto tensioner, which never gave problems. The Thema's was pre-set, using the appropriate balance weight method, no problems with that either, and that old girl got some 'wellie' on occasions for sure.:):
 

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To SEARs

Yes, the pointer is set to the hole. I do not have a problem with the fluctuations, except the movement around a NON-LUBRICATED spindle. This may cause the tensioner to become 'stickey' at some point in time. :rolleyes:

What I do have a problem with is the tensioner sometimes allowing such a large amount of slack on the other end of the belt when switched off (I guess about 1 in every 3 shutdowns, depending purely on coincidence when the ignition key is turned and the position of the crankshaft). :rant:
 
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