Found the first real problem I've had with the car today. When doing oil changes I always reach behind the belt covers to feel the belts and today when doing that noticed the passenger side belt had almost no tension. Last major was done 6 years ago. I planned on doing it over the winter but never happened as I spent all my time on another project car. No mention of tensioners replaced at the last major so assuming they are original or at least very old. I removed the alternator and belt cover and rotated the tensioner pulley clockwise to get tension on the belt for now. I'm not going to drive it, just did that so I could move it around it until it comes apart. No big surprise, or disappointment. Just glad I found it before the valves and pistons became intimate
That came from the right bank of my 550 along with 23 others bent at similar angles. It happened years ago to the previous owner of my car as a result of a failed tensioner. I keep the valve on my desk as a reminder to service my cars regularly.
While you’re in there, check that the pivot point of the tensioner pulley arm/bracket is not seized or sticky. Ours was this past winter and was stuck pretty good. It can be disassembled, cleaned, and reinstalled good as new.
Even when done correctly, the belt can feel loose if the engine is stopped at certain point. If you feel the belt on the long side at that point, it would feel like there is no tension. The proper way to check is to rotate the engine over a couple times, bring it to 1 TDC, and then feel the tension to see if it is tight and if the gap is 2.5mm.
The 355 is self tensioning. The belt should never feel loose. The only adjustment is to the gap to assure the tensioner can move in and out of the housing without bottoming. A failed tensioner typically fails in one of two modes; either the spring breaks or the piston seizes in the housing. In either case there is no way to correctly set the tension because, again, it is self tensioning and depends on the spring being intact and the ability of the tensions to move in and out freely. I think you are thinking of a 3x where the tensioners are locked. But even then, setting the tension is not done by bringing the engine to TDC. You are suppose to rotate the engine and monitor the movement of the tensioner. When the tensioner move towards the belt the most you stop rotating the engine and tighten the tensioner bolt while maintaining tension on the belt, per factory tech bulletin.
You know now that you mention it, that is probably the most likely scenario here. Before loosening anything I tried to pivot the tensioner pulley towards the belt and it was on lockdown. Would not budge at all. So yes, probably more a stuck pivot but I will replace the hyd tensioners anyway. I can put up a video later. I could see at shutdown a slight kickback putting tension on the tensioner side of the belt slightly collapsing it and reducing tension temporarily but the belt was literally just flopping around. Had there been nothing else in the way I could have slid it off.
Well, the arm is NLA (I think) so fixing it was our option. I think its a bronze bushing on an aluminum pivot. Interestingly enough, the RH side was stuck tight, the LH side was fine. We also swapped the tensioners as well, along with Hill bearings. Left nothing to chance...
