Timing belt tension question.

[frankenbeemer]

New timing belt and tensioner. Using spring pressure only results in the timing belt riding on the forward edge of the cam gear, with about 1/32" actually hanging off the front edge. Adding a little tension with a pry bar results in the belt centering itself on the cam gear in two revolutions.

Worried about setting it too tight or too loose. Any insight?

[Cabriolet]

you might be a hair too tight. you can buy a new spring for like $2 at BMW.
if you are using a pry bar to tighten it you get a lot more than the ~10lbs of pressure given by the spring. this will cause the tension and belt to wear prematurely.
i took apart an engine that had ~7k miles on it and the belt was at half life bc it was installed too tight.

[frankenbeemer]

if you are using a pry bar to tighten it you get a lot more than the ~10lbs of pressure given by the spring. this will cause the tension and belt to wear prematurely.
i took apart an engine that had ~7k miles on it and the belt was at half life bc it was installed too tight.

Appreciate your reply Cabriolet. Using a pry bar could get (a lot) more than 10 pounds or maybe exactly ten pounds or maybe less than 10 pounds depending on how gently you pry on it and how tired the spring was (not to mention other factors). It's all in the wrist.

Is the belt location (i.e. centered on the gear after a few rotations) not a good indication of proper tension? If not, why not? If it was too tight would it still be centered or would it not be closer to the motor side edge of the cam gear as opposed to the timing cover side of the cam gear? Tightening the tension moved it to the center within two revolutions of the crank for me, and I repeated the experiment with the same results. I didn't try to overtension it to see if it would move all the way to the motor side though, for fear of damaging the belt.

I decided to change the belt before the recommended interval because it was rubbing the timing cover. Before I removed the timing cover, I compared the tension to my 88's m20b27 by thumb pressure, the difference was enough to make me thank the e30 gods for not letting it break or skip. I'm convinced the lack of tension caused the belt to move forward enough to rub, so why wouldn't a centered belt indicate correct tension? It seems less susceptible to error than relying on spring pressure. I could be wrong, especially today....

I think I'll order a new spring as I managed to wring the head of one of the vibration dampener bolts off, and now am replacing the crankshaft gear wheel because it cracked when I tried to extract the remains of the bolt. By the way, I didn't hamfist that bolt either. I suspect the (very expensive yet incompetent) shop which did the timing belt job for the PO some years ago overtorqued the bolts enough to weaken them, so now they are suspect and I will be ordering new bolts too.

Cabrio weather is here FML.