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cam tensioner - A8

  #1  
Old 12-02-2010, 02:59 PM
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Default cam tensioner - A8

I figured I'd create a separate post since I'm starting to do the replacement. Have any of you guys done this on an A8 (2000 AKB engine) w/o removing the TB?

Fortunately I have two spare heads from my old part out car with the same engine. This allowed me to do a dry run on the bench and practice removing the tensioner. Just the head, no timing belt attached.

(doing the driver side so TB tension is right there, it's probably easier doing the rear/pass side tensioner)

I was able to get the old one out but I had to pick up the cams/cam sprocket really high and then pull the tensioner assembly out towards the back of the engine. I'm trying to visualize whether I can get the same amount of room with the TB clamped to the cam sprocket. It doesn't seem possible.....any thoughts?

The cam cover adds to the problem. One of the 10mm cam covers bolts threads into the 1st cam cap so you have to remove that one, and the I removed the other two as well. You also have to remove the cam position sensor cap in order to get the back cam cap off.


Bob
 

Last edited by A8CT; 12-02-2010 at 03:11 PM.
  #2  
Old 12-02-2010, 05:53 PM
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I can NOT imagine doing the job without removing the T-belt. You're going by a Bentley or Elsa, aren't you? I personally also wouldn't attempt the job without a manual.
 
  #3  
Old 12-02-2010, 07:31 PM
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Default yes, I have the Bentley

I know that some people have done this job by clamping the belt to the cam sprocket and lifting everything up. I think auditech even wrote a procedure for it and I've seen it a couple of places.

I just don't know if it's been done on the AKB engine. I have all of the TB tools for the 40v, I really didn't feel like doing a full TB job now which I would probably do if I took the belt off.

I did it on the bench, the rear cam cover seems to be the potential snag. With the motor at TDC, two of the 10mm bolts are right behind the sprocket. If I rotate the cam, I can loosen them, do the work but then I would have to rotate the cam again to get them back on...

Bob
 
  #4  
Old 12-02-2010, 08:07 PM
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You're changing the adjuster on bank 2...driver's side, right? I've never done the cam adjuster job, so don't know about clearances, etc. But I think I see what you're getting at: Removing the cam belt gear with belt strapped on to it? Because, as I understand it, the cam belt pulley is directly attached to the outside cam, right? If so, you might need to untension the T-belt eccentric pulley to let off tension on that side...I really don't know...have never seen a short cut for this posted(?)
 
  #5  
Old 12-02-2010, 10:33 PM
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Found a thread where Auditech79 was talking about adjuster change without removing belt or cams. He's helped me with another shortcut that worked out great. So, I'd love to hear how this can be done, for future reference and fascination with alternate simplified methods.

https://www.audiforums.com/forum/sho...light=adjuster
 
  #6  
Old 12-03-2010, 08:42 AM
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Default correct,bank 2 drivers side

and that's the thread I was referring to.

I just don't know if I'm comfortable untensioning and then re-tensioning the belt.

I don't think clamping the belt to the sprocket is going to work. The backside of the cam cover bolts into the 1st cam cap (going front to back) so the three bolts have to come out. I don't see a way to do that w/o moving the cam. The "spokes" on the sprocket are right in the way. An inch to either side and it would be ok.

I'll have to decide what I'm doing today...

Bob
 
  #7  
Old 12-03-2010, 09:08 PM
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That DIY thread was more or less for a 1.8T engine, because you can take the pulley off the cam with the belt clamped to the sprocket. The V motors are still possible, but its very difficult to do, especially the driver's side tensioner. You will have a hell of a time getting the cam sprocket back onto the cam with the belt pulling on it, it CAN be done though. If it doesn't work you would have to move the front end forward and loosen the tensioner, and put the grenade pin in the hydraulic tensioner. That of course is almost like doing the timing belt job though.

I would get your white out, mark the cams (just in case) then try to do it by pulling off the cam pulley first. YOU WILL NEED THE CAM LOCK BAR TO DO THIS, the cam lock bar locks both camshafts together keeping the engine from turning over, it also sets the engine at TDC when you do the belt.
 
  #8  
Old 12-04-2010, 12:23 PM
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Default question on the cam reinstallation

I bit the bullet and doing the whole job. I have about 75k miles so I figured I'd do it now.

I have the old tensioner out, it looks ok has some slight grooves worn into the guides. Is that normal?

I have the new tensioner and cams sitting in place. My question is about the way the cams are in position now. It doesn't seem like the just "drop" down into place, it feels like I'm fighting the spring tensioner on the rocker arms.

When I install the bearing caps, does that "draw" down the cams? They're both sitting up a little too high now. I have the cam sprocket and chain marked at 15 links (drivers side), that's still good. Crank is locked the cams were locked until I removed the cam pulley.

The cams "sprung" once I took the cam sprocket off which has happened to me when I've done TB's on the 4.2's before.
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Update - I had to rock the cams back and forth a little and got everything together. I have 15 links between the tensioner sprockets and the arrows on the sprockets line up with the marks on the bearing caps. I'm able to reinstall the cam locking bar. That's all good except I made one bonehead move....

I saw the Bentley note saying to "rotate 2 revolutions". I did that, it stopped... and I immediately realized what I did (the TB was already off). Do you think I could bend the valves rotating by hand?

I removed all the plugs and looks down at the tops of the pistons with my scope and didn't see any marks. It looks like only one piston could be high enough to hit, I think the other 3 are too low. Is there any other way to check short of putting everything back together?




Bob
 

Last edited by A8CT; 12-04-2010 at 03:17 PM.
  #9  
Old 12-04-2010, 05:50 PM
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Update - I had to rock the cams back and forth a little and got everything together. I have 15 links between the tensioner sprockets and the arrows on the sprockets line up with the marks on the bearing caps. I'm able to reinstall the cam locking bar. That's all good except I made one bonehead move....

I saw the Bentley note saying to "rotate 2 revolutions". I did that, it stopped... and I immediately realized what I did (the TB was already off). Do you think I could bend the valves rotating by hand?

I removed all the plugs and looks down at the tops of the pistons with my scope and didn't see any marks. It looks like only one piston could be high enough to hit, I think the other 3 are too low. Is there any other way to check short of putting everything back together?




Bob[/QUOTE]

Ouch, Bob!
I assume you mean you turned the crank over 2 revs?
I would be a "little" scared about bent valves, BUT if you didn't feel unusual resistance when turning the motor, I would hope that the extreme low speed and possible absorption of some of the contact by the hydraulic lifters (not sure if they'd actually back off a little?) would not bend anything(?)...PLUS the fact that don't see marks on the pistons, which I would think WOULD show if there was sufficient strength of contact to bend a valve.

Note: My theory about the hydraulic lifters absorbing some movement is based on the fact that Bentley recommends time to let the valve train reseat before starting the engine. And when you think about it, when a belt breaks in operation, imagine how many revs the motor turns at high speed and full oil pressure before shutting off...resulting in bent valves.

There is NO question that pistons contacted valves, at least a little...you should have heard some clicking at points when hand turning, when normally it's a pretty smooth operation with occasional quiet click-sliding sounds as cams contact lifters. In 2 revolutions, every piston reached TDC, BUT only a few valves were fully extended.

ANYWAY, Myself? I would complete the job and start the car...much easier test than the only other alternative...and should not damage anything further, if valves are already bent. My guess is that they are OK (as I explained above)...just theory though

Please let us know how it goes.

P.S. I'm sure you already answered your own question about having to compress some of the valves to reseat the cams...yes.

Sam
 

Last edited by silverd2; 12-04-2010 at 06:31 PM.
  #10  
Old 12-04-2010, 07:38 PM
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Im confused, you said you rotated the engine over by hand with the timing belt off? You won't do any damage to the valves that way, the lifter buckets would absorb the hit from the piston, i've done it before LOL! Never had a problem rotating it over with the belt removed, the clearances are large enough that it won't cause damage unless it was hit with great force. Put it back together and it should be fine.
 

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