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I f**ked up and need help.


My '99 C4 needed the Variocam guides replaced so I dropped the motor to replace them along with the 4 long chain guides and IMS bearing (among other things). Following the procedure from the Bentley manual I pinned the crank at TDC and removed the 3 chain tensioners. I had to remove the oil pump/coolant manifold to get at the bolts holding the long chain guides (not realizing that it supported the other end of the IMS shaft). I completed the chain guide job without much issue and put the valve covers back on then started with the IMS bearing replacement. Since I went with the EPS bearing id have to replace the oil pump hex drive so I decided to leave the oil/coolant manifold off during this process (probably where I made my mistake). Process of removing the old bearing went smoothly till I noticed the IMS shaft was way out of center before installing the new bearing. The shaft can move a small amount, but not nearly enough to get it centered for the manifold or bearing plate to be reinstalled.


Please help me understand whats going on here and how I may be able to remedy this issue. I THINK since the motor is pinned at TDC for bank 1, then bank 2 cams are under tension from the lifters which is putting tension on the chain from the IMS shaft to the cams (pulling the IMS shaft to the right). That tension is also making the IMS shaft want to climb the chain from the IMS shaft to the crank.


My current idea of how to fix this is as follows:

  1. Carefully spin the motor over to TDC for bank 2 which should allow me to reinstall the oil/coolant manifold (since that bank wont have tension anymore).
  2. Spin the motor back over to TDC for bank 1 relieaving the tension on the bearing side, then installing the bearing
  3. Re-time the cams on both banks
  4. Spin the motor over by hand a few dozen times and recheck the cam timing


What do you think? Terrible plan, or it might work?



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Welcome to RennTech :welcomeani:


The problem happened because I don't see any mention of locking the cams, a critical step, to keep them from turning while releasing the hydraulic chain tensioners when doing the IMS, which will cause this exact problem.  If the cams are not held in a locked position, valve spring pressure will cause them to try and rotate, and with the chain tensioners release, it usually caused the engine to jump time and pull the IMS shaft to one side.  Once this happens, you are not going to get it back to center without a lot of effort.


Most likely, you are in for a complete retiming of the valve train system.  In its current state, you cannot rotate the engine as some of the valves can hit the pistons once the timing goes off, and even hand rotation can result in damage.  And, in any case, you cannot rotate the engine backwards because even fully assembled you can get into bending valves, much less if it is already jumped time.


If this were in my shop, I would stop right where you are, obtain the cam holding tools required to remove the cam covers (again, a critical step as the holding tools prevents the remaining spring pressure from breaking the cams when the cover is removed), pull the cam covers, remove the cams, finish the IMS and chain pad replacement, and them start the cam allocation procedure to get it all back together and ready to pop back into the car.


Good luck.

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Thanks for the help JFP. I forgot to mention the exhaust cam on bank 1 is locked, the install kit only came with one lock and I must have misunderstood the instructions so I placed it on bank 1. Bank 2 is currently unlocked.


With the cam holders installed will I run into any issue removing the cams on bank 2 when the engine is at TDC for bank 1? I have the cam holder tools that hold the cams by their main bearings, I guess ill install those to hold the cams after the cover is off and slowly unbolt them evenly to release the pressure without damaging anything.

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Update: The fix for this was much easier than anticipated. I didn't have to remove the cams after all, just had to loosen the cam sprocket allowing the cams to move a little bit to release the tension. Reinstallation of the oil/coolant manifold and IMS bearing went easily and re-timed the cams again per the book. Now im ready to put it all back together and reinstall the engine back into the car.


Thanks for all the help

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