97 855 after timing belt job: tat-tatatata noise RESOLVED

S373N · Post by **S373N** » 11 Mar 2014, 17:52

Just buttoned everything up from my alternator and TB change and went to start it up and heard a tat-tat-tat-tatatata-tat-tat noise coming from the engine????? It ran fine except for the noise? Timing marks were all lined up and things seemed fine.... Had the wife start it while I was looking in the engine bay to double check and the noise is the accessory belt tensioner popping back and forth. Noticed a couple small marks on the edge of the new belt, nothing else irregular...

Post by **rspi** » 11 Mar 2014, 19:48

Congrats on the successful timing belt change.

S373N · Post by **S373N** » 11 Mar 2014, 19:51

Would compression cause the accessory belt to tense up and flip its tensioner? I'm wondering if the little bit of slack between the exhaust and intake cams may have been taken up and created just enough of a difference in their timing to cause that kind of tension on every revolution? I'm at a loss.. Any ideas?

S373N · Post by **S373N** » 11 Mar 2014, 19:52

rspi wrote:Congrats on the successful timing belt change.

LOLZ.. Successful? You a funny man RSPI!

S373N · Post by **S373N** » 11 Mar 2014, 19:58

Something is causing the accessory belt to tense up and flip the tensioner up and make the knocking noise I initially thought was something more severe... There were two small nicks on the outside edge of the belt and it seemed to not be tracking true but I chalked that up the slipping during the moments the belt tenses up?

Post by **scot850** » 11 Mar 2014, 20:08

It may be no worse than the tensioner spring for the serpentine belt has failed. This happened to me on replacing that belt for the first time. When you stretch the tensioner spring to remove/fit the belt it puts a fair load on the tensioner, and can cause an old spring to fail. Remove the tensioner and check the tensioner isn't just flopping around.

when you replaced the timing belt, did you lock the cams when fitting the belt? Check all 3 of the timing marks on the 2 cams wheels and the crank and make sure they are still aligned.

Do you have the spring tensioner for the timing belt on your car? Can't remember what is on the 97 850. If you did not tension the tensioner correctly you can damage it so it will allow the timing to fluctuate.

Neil.

S373N · Post by **S373N** » 11 Mar 2014, 20:17

scot850 wrote:It may be no worse than the tensioner spring for the serpentine belt has failed. This happened to me on replacing that belt for the first time. When you stretch the tensioner spring to remove/fit the belt it puts a fair load on the tensioner, and can cause an old spring to fail. Remove the tensioner and check the tensioner isn't just flopping around.

when you replaced the timing belt, did you lock the cams when fitting the belt? Check all 3 of the timing marks on the 2 cams wheels and the crank and make sure they are still aligned.

Do you have the spring tensioner for the timing belt on your car? Can't remember what is on the 97 850. If you did not tension the tensioner correctly you can damage it so it will allow the timing to fluctuate.

Neil.

I'm thinking it may be the acc belt tensioner. It was locked at full compression for almost two weeks so very well might be toast...

Timing marks at all three spots (IN cam/EX cam/Crank) were all within a millimeter or so of dead-nuts on. Tensioner for TB is hydraulic.

I've been reading about the same issue on other types of cars and it seems tensioner or pulleys is the most common cause. My alternator is brand new so it would either be tensioner, AC comp or PS pump. Scared the living shit out of me when I first started the car and heard that noise....

S373N · Post by **S373N** » 12 Mar 2014, 18:22

So.... Pulled accessory belt and tensioner, checked that all of the accessory pulleys were spinning freely and made sure the tensioner was tight and all was good. So I yanked the timing cover and re-checked the timing. All lined up fine so I started the car without the accessory belt and no problems. So reinstalled everything and turned the engine by hand at the crank a revolution or two just to ensure the accessory belt was tracking fine and found that it was tracking over the outer lip on the alternator pulley. I first wondered if the place that rebuilt the alternator failed to properly space the pulley so started checking that all of the pulleys and rollers were aligned and everything looked good except the idler roller, which looks as though it has been bent up after years of abuse - like a wheel with negative camber. I am certain this roller not being true is what is causing the belt to pull off of the alternator pulley, causing the belt and tensioner slap that I initially thought were my valves bending when I started the car yesterday. So.... New roller? Or can I get away with replacing the bolt that mounts it? I'm still somewhat shocked the same thing didn't happen prior to this work I am carrying out.... Perhaps there was enough slack in the old belt?

Post by **scot850** » 12 Mar 2014, 20:10

If you are convinced it is the idler pulley, then remove it and check the bolt. If it is bent the question is how did that happen. Did you use the pulley as a levering point at any time during your repairs? Can't say I've ever heard of the bolt bending by itself.

When the pulley is off, spin it by hand. If it sounds noisy, replace it. I tend to only use OE parts, but someone else may have experience of aftermarket parts. If the bolt is bent, suggest getting a new one from the dealer or if you have a breaker nearby, see if you can get a used bolt and pulley and try again.

I remember having a pulley alignment issue with one of my V70's but can't recall what caused it. Once you have everything back together, when you fire it up, watch the tensioner pulley is giving steady pressure to the belt on a steady throttle/rpm. If it is jumping back and forward, it is likely failing.

Again, if you find a car to pull the idler from, pull the tensioner too if it looks ok.

Neil.

Post by **rspi** » 12 Mar 2014, 20:19

I said congrats because I knew that you had done the timing belt correctly. If you start the car and it runs, there is no problem with the timing belt. 1 Bent valve means at least 6 are bent, and the car would not run.

After reading your post is seemed as if you were making a statement, not looking for help. It seem that you have found your problem.