TB Woes – Just did TB Job – Now has a Bad Moaning Noise
07-21-2004, 12:57 AM
#31
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Is it just me or does the new tensioner pulley (on the left) in your pic have a larger diameter than the old pulley (on the right)? Maybe the larger pulley is coming in contact with the tensioner arm when tightened?
07-21-2004, 01:17 AM
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Paul D - Is it just me or does the new tensioner pulley (on the left) in your pic have a larger diameter than the old pulley (on the right)? Maybe the larger pulley is coming in contact with the tensioner arm when tightened?
Must be an optical illusion. Cameras can do funny things.
07-21-2004, 10:57 AM
#35
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The facts given so far, do not point clearly to the reason the tensioner roller got hot enough to scorch the belt. However, based on what you have said so far, I would hazard a guess that the roller bearing is no good and at speed, under load, heats up tries to seize the roller.
This resistance MAY account for the belt traveling back and fourth across the cam gears, as well as the moaning noise you hear. So the "offset" scorch marks result from the position the belt took, just as you shut down the engine.
Replace the roller. I gotta admit, I would want to test the suspect roller. maybe clamp the arm in a vice and see if you can spin the roller with a drill or some other device and see how it deals with being spun at 1,000 rpm.......
This resistance MAY account for the belt traveling back and fourth across the cam gears, as well as the moaning noise you hear. So the "offset" scorch marks result from the position the belt took, just as you shut down the engine.
Replace the roller. I gotta admit, I would want to test the suspect roller. maybe clamp the arm in a vice and see if you can spin the roller with a drill or some other device and see how it deals with being spun at 1,000 rpm.......
07-21-2004, 12:44 PM
#37
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Originally Posted by Gretch
The facts given so far, do not point clearly to the reason the tensioner roller got hot enough to scorch the belt. However, based on what you have said so far, I would hazard a guess that the roller bearing is no good and at speed, under load, heats up tries to seize the roller.
This resistance MAY account for the belt traveling back and fourth across the cam gears, as well as the moaning noise you hear. So the "offset" scorch marks result from the position the belt took, just as you shut down the engine.
Replace the roller. I gotta admit, I would want to test the suspect roller. maybe clamp the arm in a vice and see if you can spin the roller with a drill or some other device and see how it deals with being spun at 1,000 rpm.......
This resistance MAY account for the belt traveling back and fourth across the cam gears, as well as the moaning noise you hear. So the "offset" scorch marks result from the position the belt took, just as you shut down the engine.
Replace the roller. I gotta admit, I would want to test the suspect roller. maybe clamp the arm in a vice and see if you can spin the roller with a drill or some other device and see how it deals with being spun at 1,000 rpm.......
So, spinning at 1000+ rpm is a great idea, but perhaps better under a load - how to do that is a problem. The other aspect of this testing is that it may be like testing wooden matches - as they usually only light once, the first test is valid - the second, not so good ...
- the bearing may now be burnished in to perfection!?
07-21-2004, 04:19 PM
#38
Three Wheelin'
a bad moaning sound...
Ok. I'll bite!
"After idling a couple of minutes, now there is a bad moaning sound...”
A few things come to mind:
1. One of the T-belt covers (right or left) did not seat correctly when being reinstalled (rubbing on the belt or one of the pulleys), which will produces a hollow reverb ('ed) sound.
2. Non-factory (looser QA standards) or defective factory belt (even a bad factory belt could have slipped by the QA dept).
3. T-belt tensioner improperly adjusted or related items improperly installed.
A grove in the belt is somewhat normal, but you should see the grooved "impression" all the way around the belt.
A little T-belt run out is also normal, though I don't know how much as far as measurement goes.
I would check the diameter of the new tension rollers against the old, look to see if the belt has some what equal thickness all the way around. Than when you reinstall the T-belt covers, make sure they seat correctly.
-----------------------------------------------------------------------
P.S.
One other thing you can try, once you put everything back together again. Start the engine up without any of the accessory belts installed. This will make it easer to isolate any strange sounds you hear.
"After idling a couple of minutes, now there is a bad moaning sound...”
A few things come to mind:
1. One of the T-belt covers (right or left) did not seat correctly when being reinstalled (rubbing on the belt or one of the pulleys), which will produces a hollow reverb ('ed) sound.
2. Non-factory (looser QA standards) or defective factory belt (even a bad factory belt could have slipped by the QA dept).
3. T-belt tensioner improperly adjusted or related items improperly installed.
A grove in the belt is somewhat normal, but you should see the grooved "impression" all the way around the belt.
A little T-belt run out is also normal, though I don't know how much as far as measurement goes.
I would check the diameter of the new tension rollers against the old, look to see if the belt has some what equal thickness all the way around. Than when you reinstall the T-belt covers, make sure they seat correctly.
-----------------------------------------------------------------------
P.S.
One other thing you can try, once you put everything back together again. Start the engine up without any of the accessory belts installed. This will make it easer to isolate any strange sounds you hear.
Last edited by T_MaX; 07-21-2004 at 04:35 PM.
07-21-2004, 04:52 PM
#39
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Gregg K said:
geekapalooza,
What Gregg K said! Me too! I must say that problems like the one you've encountered send shivers up my spine. Here's why: 1) my 928-specific wrenching experience is almost nil; 2) no known competent 928 techs in my area of N Central Florida; 3) the sheer terror of sudden 928 death (cam belt failure)
Nevertheless, I'm learning here...very good thread folks!
I'd rather do this job myself when the time comes...but need to go through some see-one-do-one training first...
Best wishes with your trouble-shooting...can't wait to learn what the source of the moaning was,
Tim
I've avoided looking at this post, just out of sheer fear. This is an area I only want to know about while doing preventative maintenance.
What Gregg K said! Me too! I must say that problems like the one you've encountered send shivers up my spine. Here's why: 1) my 928-specific wrenching experience is almost nil; 2) no known competent 928 techs in my area of N Central Florida; 3) the sheer terror of sudden 928 death (cam belt failure)
Nevertheless, I'm learning here...very good thread folks!
I'd rather do this job myself when the time comes...but need to go through some see-one-do-one training first...
Best wishes with your trouble-shooting...can't wait to learn what the source of the moaning was,
Tim
07-21-2004, 06:13 PM
#40
Three Wheelin'
Old bearings often spin easier than new ones. Unless it's actually hard to turn, it's normal.
T Max said it. I would recommend
1) Remounting the idler, and checking for parallel, or planar location. And tug on it to see if it has adverse play.
2) Check the belt for any nonhomogeneous structure. I highly doubt that that is the problem.
3) Run without the covers. That also gives you the ability to recheck tension as well.
Not much else, except doing a complete visual inspection to ensure that everything the belt touches is planar and or aligned. I"ve never done a belt before. I would expect overtension could cause this trouble. In fact, I wonder if you assembled the belleville washers correctly. Any thought is worth considering.
T Max said it. I would recommend
1) Remounting the idler, and checking for parallel, or planar location. And tug on it to see if it has adverse play.
2) Check the belt for any nonhomogeneous structure. I highly doubt that that is the problem.
3) Run without the covers. That also gives you the ability to recheck tension as well.
Not much else, except doing a complete visual inspection to ensure that everything the belt touches is planar and or aligned. I"ve never done a belt before. I would expect overtension could cause this trouble. In fact, I wonder if you assembled the belleville washers correctly. Any thought is worth considering.
07-21-2004, 06:38 PM
#41
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the washer configuration results in relief of tension as the block expands from heat, thus maintaining a static tension on the belt. Most other (than correct) configuations would cause greater than specified tension relief, the exception being if they were all stacked in the same orientation.......IE you could get the stacking wrong (there are two specified stacking arrangements, based on model year) and still not see a significant variation from specified tension throughout the temperature operating range.......FWIW.....
07-21-2004, 07:51 PM
#42
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Ok - Now I'm going to throw everything on it's ear, because I've found another clue, possibly...
I put the new / damaged belt back on, placing the heated up section back exactly over the tensioner roller, threaded the belt over the pass side cam gear and back around under the water pump pulley. Then I held the area of the T-Belt that directly touched the water pump pulley, removed the belt, walked outside and inspected under the sun. When I get the right reflection, you can clearly see another heated up section of the belt, where it rested on the water pump pulley. Pic attached.
I know what you're thinking, "well that belt just had to be too tight". That's what I would think, but there's no way that could be, unless Gremlins got to my belt tensioner tool.
Stymied once again...
I put the new / damaged belt back on, placing the heated up section back exactly over the tensioner roller, threaded the belt over the pass side cam gear and back around under the water pump pulley. Then I held the area of the T-Belt that directly touched the water pump pulley, removed the belt, walked outside and inspected under the sun. When I get the right reflection, you can clearly see another heated up section of the belt, where it rested on the water pump pulley. Pic attached.
I know what you're thinking, "well that belt just had to be too tight". That's what I would think, but there's no way that could be, unless Gremlins got to my belt tensioner tool.
Stymied once again...
07-21-2004, 08:04 PM
#43
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OK Rob, I'll bite again! You have my permission to ask me to touch my toes before you punt - but ...
How much coolant did you pour back into the block prior to starting? Sorry, but heat has to come from .....
How much coolant did you pour back into the block prior to starting? Sorry, but heat has to come from .....
07-21-2004, 10:12 PM
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Garth - I won't ask you to touch your toes, your post made me chuckle - something really needed right about now. Better to cover too much ground, than not enough!
Yup - I added 50/50 mix to the block via the top rad hose, topped it off. Then added to the rad via the lower hose. Filled overflow jug, burped and idled the engine til t-stat opened up, filled some more.
Just thinking out loud here - Could the tensioner be so hot as to have heated the belt that much, that wherever the smooth side of the belt parked (roller and water pump), it would create the imperfections?
Yup - I added 50/50 mix to the block via the top rad hose, topped it off. Then added to the rad via the lower hose. Filled overflow jug, burped and idled the engine til t-stat opened up, filled some more.
Just thinking out loud here - Could the tensioner be so hot as to have heated the belt that much, that wherever the smooth side of the belt parked (roller and water pump), it would create the imperfections?
07-21-2004, 10:59 PM
#45
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Phew, glad that one is not an issue ..
If the thinking is still that the two damaged areas on the belt are from heat-soak, then where was the heat generated? The belt was either sliding over the surface of the pump pulley or tensioner roller due to a (partial/temporary?)seizure - or the support bearing of the pump or tension roller were moving along at belt speed, but at a very high resistance - generating heat (and noise).
If the first case occured, the whole back of the belt would be scuffed up - is the printing on the back of the belt still crisp and legible? It looks as if the belt edges are undamaged, so tracking was unlikely an issue. Also, if the belt were seriously scuffed, there would likely be a dusting of rubber bits throught the covers.
Conversely, in the latter case, the belt would be as new with the exception of the two areas that made contact on shutdown: Was there any similar pattern on the tooth side contact with the 4 drive wheels?
BTW, I have absolutely no idea - but still fishing ....
If the thinking is still that the two damaged areas on the belt are from heat-soak, then where was the heat generated? The belt was either sliding over the surface of the pump pulley or tensioner roller due to a (partial/temporary?)seizure - or the support bearing of the pump or tension roller were moving along at belt speed, but at a very high resistance - generating heat (and noise).
If the first case occured, the whole back of the belt would be scuffed up - is the printing on the back of the belt still crisp and legible? It looks as if the belt edges are undamaged, so tracking was unlikely an issue. Also, if the belt were seriously scuffed, there would likely be a dusting of rubber bits throught the covers.
Conversely, in the latter case, the belt would be as new with the exception of the two areas that made contact on shutdown: Was there any similar pattern on the tooth side contact with the 4 drive wheels?
BTW, I have absolutely no idea - but still fishing ....