front pulley torque
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HT4100 4.1, 4.5, 4.9 Discussion, front pulley torque in Cadillac Engine Technical Discussion; My '91 4.9 had a recent water pump replacement (dealer completed) and one of the bolts behind the front pulley ...
  1. #1
    go4it is offline Cadillac Owners Member
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    front pulley torque

    My '91 4.9 had a recent water pump replacement (dealer completed) and one of the bolts behind the front pulley came loose and was dragging on the main pulley. A mechanic friend offered to pull off the pulley and replace it (I had a road trip the next day). He did so with a puller and air gun. He replaced the loose bolt and remounted the pulley with a high torque air gun.
    I since read a thread that said the dampener pulley needs to be torqued close to 300 ft/lbs.
    Within 500 miles the engine developed a low end knock when warm and accelerating...could the oil pump be slipping? Is there any way to check oil pressure through the on board diagnostics?
    I want save this engine...
    Thanks
    Go4it.
    91 fleetwood. 85000 miles and mint

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  3. #2
    BeelzeBob's Avatar
    BeelzeBob is offline I'm a Cadillac Fanatic!
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    Re: front pulley torque

    Quote Originally Posted by go4it
    My '91 4.9 had a recent water pump replacement (dealer completed) and one of the bolts behind the front pulley came loose and was dragging on the main pulley. A mechanic friend offered to pull off the pulley and replace it (I had a road trip the next day). He did so with a puller and air gun. He replaced the loose bolt and remounted the pulley with a high torque air gun.
    I since read a thread that said the dampener pulley needs to be torqued close to 300 ft/lbs.
    Within 500 miles the engine developed a low end knock when warm and accelerating...could the oil pump be slipping? Is there any way to check oil pressure through the on board diagnostics?
    I want save this engine...
    Thanks
    Go4it.
    91 fleetwood. 85000 miles and mint
    I think you are confusing posts about the 4.9 and the Northstar engine.

    The 4.9 has the oil pump mounted in the oil pan and driven off the distributor gear at the rear of the engine. Nothing to do with the damper bolts or tightening it. I don't recall off hand what the torque was on the bolt for the 4.9 but it wasn't close to 300 I don't think....that was the number quoted for the Northstar engine.

    If the damper was pulled on with the original bolt then the bolt could be damaged and not seating the damper fully. This could cause the timing chain sprocket to fret and move and fail eventually. A mechanic should NEVER pull the damper on with the bolt and should absolutely NEVER pull the damper on with an impact wrench like you describe. A damper puller should be used to install the damper and then the bolt should be installed and tightened.

    At this point it is hard to say what to do. I would try removing the bolt that holds the damper on to make sure that it is not damaged/crossthreaded from the impact. Sometimes, as the impact hits the bolt when it is just starting into the crank it will deform the first threads and cause th ebolt to jam as ti goes on into the crank. If it comes out freely then it is probably OK. You would want to inspect/replace the bolt and then reinstall it correctly with a torque wrench.

    Possibly the engine knock you hear is the main bearing thump that shows up on some 4.9 engines at high miles when hot...??? If that is the case then it is harmless but annoying. It can be fixed by replacing the front main bearing shells with the undersized service shells to reduce the clearance at the front main bearing. If a new belt was installed or the tensioner changed or something then possibly the belt load changed which caused the noise to be more evident.

  4. #3
    go4it is offline Cadillac Owners Member
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    Re: front pulley torque

    Thanks for the reply- Iwill check the tensioner and do some further analysis.
    Go4it
    91 Fleetwood 4.9

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