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  #1  
Old 10-13-2008, 02:42 PM
 
Join Date: Oct 2008
Posts: 4
Default Timing Belt Auto-Tensioner concerns

I seem to have discovered a potential issue with the auto tensioner used on many Mitsubishi vehicles, and I am wondering if anybody else hasnoticed this, or if I am doing something wrong. I apologize for how long this post is, but I wanted to fully explain the situation so it is (hopefully) clear exactly what I am asking.

I am replacing the timing belt on a 2000 Mitsubishi Montero Sport 3.0 V-6 SOHC I replaced the timing belt, the idler pulley, the tensioner pulley, the hydraulic tensioner unit, and the water pump, all with new parts from the Mitsubishi dealer. I am an experienced mechanic, but I have never encountered this particular issue before.

The manual for this car says that to set the timing belt tension leave the retainer pin in the hydraulic auto tensioner to keep the push rod in the base position, and you apply 39 inch-pounds of torque, counterclockwise, on the offset tensioner pulley and then tighten the nut to 35 foot-pounds. Then remove the retainer pin from the hydraulic tensioner and rotate the crankshaft a few turns, stop at TDC and recheck the timing mark alignment. Once the marks are confirmed to be correct, it says to wait at least 5 minutesand then measure the distance that the push rod of the hydraulic tensioner is extended out of the housing, and that it should be between 3.8 mm and 5.0 mm. I was able to measure this pretty accurately using drill bits of those diameters as a gauge between the end of the tensioner housing and the contact pad on the tensioner pulley bracket where the hydraulic tensioner rod pushes on the tensioner pulley bracket. It was just under 5 mm, which leaves the hydraulic tensioner push rod in just about the right position so you can slide the retaining pin right back in because the holes are still lined up. So it looked to me that everything was spot-on perfect. I put the lower timing belt cover back on, and installed the crankshaft pulley. I was putting the upper timing belt covers on, and noticed that the timing belt wasloose around the water pump pulley - the part of the timing belt that goes between the two camshaft sprockets and under the water pump pulley had slack in it - I can move the belt in and out over an inch between the right camshaft sprocket and the water pump pulley; it is completely loose.

So I took the crankshaft pulley and lower cover back off, and I could see that the contact pad (that theauto tensionerpush rod pushes against)on the tensoner pulley bracket was touching the auto tensioner housing. I rotated the engine in the normal direction back to where all the timing marks line up. As I turned the engine I could see that the push rod of the auto tensioner extended back out and took the slack out of the belt. With the engine at TDC with the cam timing marks lined up, I verified that the distance between the hydraulic tensioner housing and the tensioner bracket was still just under 5 mm, and I can slide the retaining pin back in the tensioner easily. At this point, the timing belt is nice and tight all the way around, and it will stay tight as long as I leave the engine in this position. Here is the deal - if I rotate the crankshaft, in the direction that then engine normally turns, about 20 to 30 degrees past TDC, and leave it there for about 15 minutes, the belt will loosen across the top where it goes under the water pump pulley, pushing the auto tensioner push rod back in. At this rotational position the right cam wants to turn in the direction it normally rotates due to valve spring pressure - a valve is closing and it is pushing on a cam lobe trying to turn the camshaft. The hydraulic tensioner slowly bleeds down from this pressure,the tensioner push rod is pushed in, and allows the camshaft to have its way and rotate forward a little more, putting the slack in the top section of the timing belt. As far as I can see, there is nothing to stop this from happening if the engine happens to stop in such a position when it is shut off. Frankly, it scares the crap out of me to think about hittingstarting the engine when the timing belt is this loose. I can see that it would probably just pull the slack out of the top section of the belt when the crankshaft started to turn, transferring that slack to the part of the belt that goes around the tensioner pulley, and that the hydraulic tensioner plunger would extend and tighten the belt back up. But I can also imagine that the belt could jump a tooth on one of the sprockets when the starter starts to turn the crankshaft - the belt is loose enough that I think I could work it over a tooth on the cam sprocket if I tried. It just seems like a really bad idea to start the engine with the belt so loose, but as far as I can see everything is working as designed, assembled and adjusted correctly, and that the belt could be this loose if the engine happens to stop turning in such a position when shut off.

So my questionsare: Has anyone ever noticed that the timing belt will loosen in this way if the engine if left in a certain rotational position? Do you think this is normal? Does it concern you like it does me? Is there anything I should do to address this, or should I just assume that the Mitsubishi gods will watch over this engine and not let the timing belt jump a tooth or otherwise get screwed up because of this? Looks like I can use the tensioner pulley adjustment (turn the offset pulley farther counterclockwise) to force the auto tensioner push rod to extend less than the specified 3.8 to 5 mm, and that would keep the belt from loosening as much because the tensioner pulley bracket would hit the auto tensioner housing sooner if the push rod was forced back in by the rotational force of the camshaft, but I hesitate to deviate from the setting the manual prescribes. The result would be that the auto tensioner push rod would always be in farther than it is with the retaining pin in place, since the specified 3.8 to 5 mm setting puts the push rod in the postion where the retaining pin holes line up. The belt could still loosen a little, but not so much.

Any help will be greatly appreciated!
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  #2  
Old 10-13-2008, 04:18 PM
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Default RE: Timing Belt Auto-Tensioner concerns

can you post a picture of the t/belt replacemant?
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  #3  
Old 10-13-2008, 04:23 PM
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Default RE: Timing Belt Auto-Tensioner concerns

My 90 tsi is very similar when the car is off, the belt will seem loose but once you rotate it the belt gets tighter. Its normal b/c once the car runs it will apply tension to the belt. Hope this makes sense to ya.
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  #4  
Old 10-14-2008, 02:06 PM
 
Join Date: Oct 2008
Posts: 4
Default RE: Timing Belt Auto-Tensioner concerns

What is is you would like a picture of exactly, mitsupartsman? I am getting ready to put the covers on, but I took some pics and hopefully I will have what you want and can post it for you.

I need to get this thing back together and on the road, so I decided to set the tensioner up so that the gap between the auto tensioner and the pulley bracket contact pad is just a bit less than the 3.8 mm minimum specified in the manual when the belt is tight all the way around. It seems to be a reasonable compromise between providing the auto tensioner push rod with enough travel, but not letting the timing belt get so loose that I am afraid it might jump time upon startup. If I rotate the crankshaftabout 30 degrees past where all the marks are lined up and leave it there for about 15 minutes, the top section of the belt gets pretty loose, to where I can move it in and out about 3/4 of an inch. At that amount of slack it does not seem that I could get the belt to jump a tooth if I tried, which it seems I could with the original setting as described in my original post. I would still like any more feedback that anybody might have on this topic. Thanks!
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  #5  
Old 10-14-2008, 03:17 PM
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Default RE: Timing Belt Auto-Tensioner concerns

Athough it sounds to me like you did everything by the book, if you were to post a picture of how you have the tensioner pulley and hydraulic setup anyone browsing this thread who
may perfrom a t/belt job daily on a Sport will know right away if it was setup correctly. There's only two reasonsI can thinkof that would be a problem; imroper parts or improper install.
Either of them would be obvious by seeing the picture.



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  #6  
Old 10-14-2008, 05:07 PM
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Default RE: Timing Belt Auto-Tensioner concerns

yes, its totally normal for the hydraulic tensioner to collapse if the load on the timing belt pushes against it.

you're really overthinking this whole thing.
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Old 10-14-2008, 05:07 PM
 
 
 
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1990, 2000, align, auto, autotensioner, belt, eclipse, hydraulic, marks, mitsubishi, montero, problem, sport, tensioner, tensionner, timing


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