Recently Replaced then Retensioned TB Loses Tension in under 3k miles. Why?
09-24-2007, 03:32 PM
#16
Drifting
Well actually, you should hope that it's not a bad belt as that is the weak link in the system. It means that it can go at anytime if it's bad. I would venture to guess that if there's a problem it's related to the water pump as there have been plenty of discussions related to water pumps over the years in terms of rebuilt versus new, Chinese versus German, etc. I'm not sure why it's such an issue. The 928 isn't the only car that has a water pump incorporated into its timing belt.
09-24-2007, 04:05 PM
#17
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Well actually, you should hope that it's not a bad belt as that is the weak link in the system. It means that it can go at anytime if it's bad. I would venture to guess that if there's a problem it's related to the water pump as there have been plenty of discussions related to water pumps over the years in terms of rebuilt versus new, Chinese versus German, etc. I'm not sure why it's such an issue. The 928 isn't the only car that has a water pump incorporated into its timing belt.
09-24-2007, 05:02 PM
#18
Craic Head
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Personally, I would get a new belt to install since at this point you're going to have to remove a lot of stuff to check the condition of each pulley. I guess I've lucked out with mine. I've got about 2000 miles on my belt since I replaced it last year and haven't seen a warning light for the tensioner. That actually concerned me so yesterday I unplugged the wire and grounded it out while the engine was running to make sure it worked (it did.) So I haven't tightened mine yet. I'm kind of torn about doing it because I don't really want to mess with a good thing.
I would suggest checking the tension with a tensioner tool rather than just verifying continuity at the switch. I've got a technique for the '85 that can be done in about an hour. Let me know if you need a hand.
09-24-2007, 07:28 PM
#19
Drifting
I am actually planning to check it this week and I do have the proper tool. Thanks for the offer however. I am wondering though, what is the technique you speak of?
09-24-2007, 07:54 PM
#20
Under the Lift
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I read a post on here where someone (Bill Ball?) found that a belt he'd replaced needed adjusting more than one-time the initial wear-in period and he decided it was a bad belt and just replaced it. If everything else looks good and the belt is tracking true, I'd swap out the belt.
I think a contributing factor in my case was the tensioner would not hold oil for long. Consequently when the block heated up and expanded, the transfer of heat to the tensioner and its Belleville washers (which flatten in response to heat and reduce the belt tension) was compromised. The tensioner could not adjust to heat expansion of the block as well, and this over-tensioned and stretched the belt. At least that's my interpretation. The tensioner was serviced and holds oil better, and the replacement belt has been fine. In fact, I think it just hit 60K miles. Parts for my next TB/WP service were ordered today.
WHAT BRAND BELT IS THIS?
09-25-2007, 10:58 AM
#22
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Yep. In my case the belt lost tension at 25K miles after an adjustment 2K miles. Not a good sign. There is no rule on this, but the expectation is the belt can stretch initially, hence the check at 2K miles or so. After that it should be stable, although I check the tension every 15K miles and change the belt at 60K miles.
I think a contributing factor in my case was the tensioner would not hold oil for long. Consequently when the block heated up and expanded, the transfer of heat to the tensioner and its Belleville washers (which flatten in response to heat and reduce the belt tension) was compromised. The tensioner could not adjust to heat expansion of the block as well, and this over-tensioned and stretched the belt. At least that's my interpretation. The tensioner was serviced and holds oil better, and the replacement belt has been fine. In fact, I think it just hit 60K miles. Parts for my next TB/WP service were ordered today.
WHAT BRAND BELT IS THIS?
I think a contributing factor in my case was the tensioner would not hold oil for long. Consequently when the block heated up and expanded, the transfer of heat to the tensioner and its Belleville washers (which flatten in response to heat and reduce the belt tension) was compromised. The tensioner could not adjust to heat expansion of the block as well, and this over-tensioned and stretched the belt. At least that's my interpretation. The tensioner was serviced and holds oil better, and the replacement belt has been fine. In fact, I think it just hit 60K miles. Parts for my next TB/WP service were ordered today.
WHAT BRAND BELT IS THIS?
Mechanic checked the tensioner oil level (per my request) and it was normal. I had the same thought, BB. Never underestimate the power/effect of an oiling issue!!!
Picked it up last night and it ran like a champ; no light, for now. I'm headed to the Frenzy this weekend, so perhaps some local 928 experts can take a look at it to make sure it's ok.
09-25-2007, 12:12 PM
#23
Under the Lift
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My personal timing belt jobs tend not to be partiies, but if you want to participate, I'll let you know when it's going to happen. There are a couple of other locals out there who need it done soon. Those will probably become TB parties. If you need it done, let me know and we can schedule a party.
Last edited by Bill Ball; 09-25-2007 at 04:58 PM.
09-25-2007, 02:35 PM
#24
Burning Brakes
Bill yes I am, infact I have lead the 3 fun runs we did in Napa. I dont need a timing belt replacement any time soon, but would like to help out. I also just got the 85/86 timing belt manual from John Kelly which is an excellent write up! He did a really great job and it cost next to nothing to purchase.
Last edited by Mako 928; 09-25-2007 at 02:57 PM.
09-25-2007, 06:40 PM
#26
Just to add to the discussion - did you have your tensioner rebuilt when you had the belt work done? In my last TB/WP job, I pulled the tensioner and discovered it had actually corroded inside the sleeve. It still held oil fine, but the bi-metallic washers could not move completely freely, so belt tension was not maintained. If you have something similar, this could be part or all of the problem. By adjusting the belt and tensioning the tensioner you set everything up correctly, but over time the tensioner could slowly lose its ability to keep up with the tension requirements of the belt usage.
Just a thought - haven't seen anyone else with that issue, but it could help in the diagnosis. In my case, i had to get a rebuilt tensioner and I was good to go.
Just a thought - haven't seen anyone else with that issue, but it could help in the diagnosis. In my case, i had to get a rebuilt tensioner and I was good to go.
09-26-2007, 09:57 AM
#27
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Just to add to the discussion - did you have your tensioner rebuilt when you had the belt work done? In my last TB/WP job, I pulled the tensioner and discovered it had actually corroded inside the sleeve. It still held oil fine, but the bi-metallic washers could not move completely freely, so belt tension was not maintained. If you have something similar, this could be part or all of the problem. By adjusting the belt and tensioning the tensioner you set everything up correctly, but over time the tensioner could slowly lose its ability to keep up with the tension requirements of the belt usage.
Just a thought - haven't seen anyone else with that issue, but it could help in the diagnosis. In my case, i had to get a rebuilt tensioner and I was good to go.
Just a thought - haven't seen anyone else with that issue, but it could help in the diagnosis. In my case, i had to get a rebuilt tensioner and I was good to go.