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Noise Behind Timing Chain Cover

Discussion in 'GM Powertrain' started by captluigi, Dec 26, 2008.

  1. captluigi

    captluigi New Member

    Hello everyone, thanks for the welcome Steve,
    This is my first post so I hope I do it right. I have a problem with a 7.4 lt., appx. an 1984 or 1985. I have two of these fine engines and they have both served me well. They are in a 38' Chris Craft. Yes I know this is a Chevy truck forum. It's just that I grew up with trucks and truckers so I thought I would post where there will be the most coverage. A lot more 454's in trucks than boats.

    The engine in question has appx. 1000 HRS. run time. Most consider that to equate to about 100K miles.
    It is the starboard engine and is counter rotating. I doubt that is relavant but wanted to be clear as possible. I have a noise (yeah I know) that at first I thought it was rocker arm/push rod related. But after applying a stethascope all over I have determined (Ithink) that the noise is coming from the timing chain area. I have never experienced this on any engine GM or otherwise. Before I tear into it I thought I would reach out to this truck communityfirst.I am not as agile as I once was so I would like to get it right the first time.

    Any feedback would be greatly appreaciated and thanks again to all.

    Capt. Lewis
  2. vncj96

    vncj96 Epic Member 5+ Years 1000 Posts

    What kind of noise? Grinding, a tick? Is it a rythmatic tick or random every once in a while?
  3. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Early model 7.4 engines had issues with timing chain tensioners and timing chains. Marine engine internals are about the same as truck/car engines.
    Counter rotation for the props should all be handled in your stuffing box and outdrive sections so this shouldnt change the mechanicals of the engine.
    I had to rebuild the 7.4's in my 1979 Wellcraft Nova a few years ago, at the time I had about the same hours as yours. This is when I found out about the timing chain tensioner issue on the 7.4.
  4. captluigi

    captluigi New Member

    Thanks for the response. It is a rythmic click, tap directly proportionate to throttle advance. More noticible on right side of timing cover as viewed from from of engine. This moto turns counter clockwise as I mentioned. I have had these (not this) motors down to nuts and bolts in a parts cleaner and can not figure what would cause this type of racket. This is a double row chain drive just for clarification. It's not a major job to replace timing gears and chain as there is no rad, fan etc. in the way. It's just not my usual approach to a problem to throw parts at something.
  5. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    I rebuilt mine because I had a loud clicking noise coming from the timing chain cover. It ended up being a piece of the teflon coating on the timing gear had delaminated and was hitting the inside of the cover with every rotation.
  6. captluigi

    captluigi New Member

    Well that is some food for thought. But just to be certain we are all on the same page or at least in the same chapter. This moto DEFINETLY turns counter clockwise as viewed from front. It is not controlled via Velvet Drive trans. A stuffing box is just a packing gland to reduce drippage . Has absolutly nothing to do with rotational direction. They don't care which way they spin. Same gear reduction either way. I stopped by the local NAPA to view a chain & gear set. There is no teflon coating on the Cloyes set nor are there any tensioners involved., There is a simple stretch measurement by simply loading the cam end of chain and measuring deflection. But who would get that far into it and not replace a $30.00 part? Perhaps we are talking about different motos.

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