Timing Belt Tensioner: "Over" or "Under"?

[jeffhambone]

So here I am, doing my first CB timing belt in several years, and I'm looking at the pictures of how everything goes back together. Looking at how the tensioner can apply pressure to the belt, it appears there are two options: turn it clockwise ("Over"), so that the distance between the crank sprocket and the tensioner is maximized while the distance between the tensioner and the cam sprocket is minimized (although still not small); or turn it counterclockwise("Under"), which minimizes the distance between the tensioner and the crank sprocket and maximizes the distance between the tensioner and the cam sprocket. The latter method is the one specified by the FSM as the picture of the Miller tool clearly shows it applying torque in the counterclockwise direction.

The main reason this question came to mind was the replacement tensioner I have looks like it'll come close to rubbing on the shroud near the crank sprocket if I use the FSM method. I also recall, however, a discussion several years ago over on "that other site" about a theory some folks had that part of the reason T-III belts had a short life expectancy was the small/sharp radius changes caused by the close proximity of the tensioner and the crank sprocket. Going from the "Under" to the "Over" position was thought to be one way to extend the life of T-III timing belts, and if the theory held for those belts, it should hold for these as well.

Bottom line: Is there any reason not to turn the tensioner the other way, i.e., clockwise (or "Over")? I don't see anything else in the way....

[mock_glh]

As I see it, tension is tension, whether you go over or under. The tension tool is of course made for the "under" method, using the weight to apply the proper amount of tension when the crank is turned. You could turn the engine (or the car) upside down and use the tool the proper way to do the "over" method .

[glhs875]

I've been using the over (clockwise) method on all my engines for many many years. Just be careful when tightening the lock down bolt that the tesioner doesn't move and tighten up against the timing belt as well.

[tryingbe]

Over always worked for me.

[jeffhambone]

Thanks for the input, gents. "Over" it is, then...

glhs875 -- good point about not adding extra tension when tightening the bolt. I suppose the same idea is true for the "under" method, you don't want to relieve any tension while tightening the bolt.

[Turbodave]

I've got the little factory weight thing and I've always done the under method, never had any trouble. I usually let the weight tension it, then hold the weight in place while tightening the lock bolt. Then I rotate the engine 2 revolutions, recheck my marks and make sure that the front stretch of belt will twist approx 90deg.

[MiniMopar]

+1. I have the factory tool also and therefore it goes under. On a new belt, I add a bit more tension to compensate for stretch and hold it while tightening.

[cordes]

Wow, I never even thought about doing it "under". I think that will be a little easier, so I will give that a go next time.

[jeffhambone]

Got it all buttoned up today, well, at least the timing belt and enough other stuff so the engine would start. Belt is headed toward the pass side of the cam pulley, so I guess I got it a little tight. I think I'll let it run like that while I'm flushing the cooling system (apparently the first time in 115k, ugh) and recheck afterwards.

Unrelated rant: good grief, the vacuum lines on this thing ('91 Lebaron GTC 2.5TI) are a mess! They look factory, but I swear there are a couple of loops and at least two were disconnected. Probably explains why I couldn't get more than 4psi of boost the few times I've driven it

[ShadowFromHell]

I use to run mine over, and had problems with the cam skipping a tooth if I tagged overboost. Never happend after switching to under.

[WVRampage]

I use under so the the pressure fomr the tensioner will hold the bolt in the tightening position.I feel the over could cause the bolt to loosen.