Replaced intake gasket and messed something up!
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HT4100 4.1, 4.5, 4.9 Discussion, Replaced intake gasket and messed something up! in Cadillac Engine Technical Discussion; Hey guys, I just stumbled across this forum and wanted to see if anyone out there might be able to ...
  1. #1
    mikeyj350 is offline Cadillac Owners Member
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    Angry Replaced intake gasket and messed something up!

    Hey guys, I just stumbled across this forum and wanted to see if anyone out there might be able to help me out. I recently had a problem with the intake gasket in my 1988 Deville, 4.5 motor. I am pretty well versed with GM engines (rebuilt several Chevy 350s etc) and followed the instructions I researched online as best as I could. The repair seemed to go pretty well, but when it came time to start the engine we ran into a problem: The engine sounds very strange while cranking, almost like there is no real load on the starter, just a constant cranking speed. I took out the compression tester and found no compression on the first cylinder I tried (front drivers side cyl by cruise control, not sure what # cyl that is). Although the engine had a nasty coolant leak, it certainly ran on all 8 cylinders and smoothly, so I am positive that I messed something up.

    My guess is with that rocker arm assembly. I removed it as a whole unit as described in several posts I found online... I first removed the 4 10mm bolts and then backed off the 5 15mm nuts slowly and evenly. Re-assembly took place in the exact reverse order, and seemed to go off without a hitch. I have also confirmed that all 16 pushrods are properly seated into the lifters, and I have cranked the engine with the valve covers off and witnessed the rockers pushing the valves down. Everything seems fine, but like I said it cranks funny and there is no compression on, I would guess, at least half the cylinders.

    I'm pulling my hair out here guys, what the heck did I do wrong?

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  3. #2
    drewsdeville's Avatar
    drewsdeville is offline Cadillac Owners Master
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    Re: Replaced intake gasket and messed something up!

    um....I don't know.

    You didn't take the spark plugs out and forgot or something, did you?? Haha, I'm really at a loss if you have visually confirmed that the valvetrain is operating correctly after this no compression episode.

    Did you touch the timing chain at all?

    I'd go further and check compression on both sides of the engine to develop a process of elimination.

  4. #3
    mikeyj350 is offline Cadillac Owners Member
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    Re: Replaced intake gasket and messed something up!

    Haha you're the second person to ask me about the spark plugs being removed! First one was a smart-alec friend of mine :-) Anyway, yes the plugs were in and everything should have been ready to go. Tonight I got antsy and tried two things: (1) I tried checking compression for the next cylinder toward the front of the engine (#5 if you're following SB chevy convention... is this engine numbered the same way?) and got ~150lb compression, perfect. So at least _some_ cylinders are getting compression. I'll do a more thorough compression check when I get more time tomorrow. (2) The other thing I did, was I thought maybe I accidentally switched sides on the rocker assemblies. I was very confident that I had kept everything in order.... pushrods etc... but I thought maybe somehow in the mayhem I confused the two things. So I switched the assemblies over and now they are on the "wrong" sides, still have the exact same symptom. Does it matter which side they are on? My thoughts are "yes" but the cranking behavior seems the same.

    A little more information: When we originally tried starting the engine, we heard a muffled backfire once from the engine as we cranked. I thought, oh crap I messed up the timing... but after looking again that's damn near impossible, I've done this several times before on other cars, and I marked everything and it's all lined up perfect. So then I thought the only explanation for a backfire is an intake valve stuck open? Like, it sucks in fuel/air, comes up for compression and the spark ignites a backfire through the semi-open valve?

    One last thing.. on the cylinder I found with no compression.. I took the hose off the gauge and put my finger over it to see if I could feel any air while cranking. No suction, no pressure, nothing. It was like there was nothing happening in there at all.

  5. #4
    cadillac_al is offline Cadillac Owners Connoisseur
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    Re: Replaced intake gasket and messed something up!

    Does your compression tester allow you to hook an air hose on it? If so, put some air to that dead cylinder and see where it's going. You probably just have one bad cylinder and the car may have run good enough that you didn't notice it before.

  6. #5
    drewsdeville's Avatar
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    Re: Replaced intake gasket and messed something up!

    The rocker assemblies should really go back to their original positions to reduce any accelerated wear. If you switched the rocker assemblies, you now have the "wrong" pushrods and valves contacting the rockers and the wear patterns won't match.

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    Re: Replaced intake gasket and messed something up!

    I think your only choice is to pull that valve cover and see what's going on (or not going on) under there. Sure sounds like you have a valve stuck open.

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    carnut is offline Cadillac Owners Master
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    Re: Replaced intake gasket and messed something up!

    I agree. Even if the distributor was in wrong, you would still have compression. Pull that valve cover over number one, then inject air thru an adaptor to that cylinder. Air will escape either from the throttle body or out the exhaust.

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    mikeyj350 is offline Cadillac Owners Member
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    Thumbs up Re: Replaced intake gasket and messed something up!

    Alright guys, I finally fixed it! I stopped out to my local machine shop to pick up some parts for a different project I'm working on, and standing there talking to the guy, I thought what the hell, I'll see what he knows. So I kicked the ground a little and said "So, what do you know about Cadillac 4.5's?" I explained the problem to him, and he came straight back at me with the golden answer:

    "I bet your lifters are all pumped up."

    I had heard of lifters collapsing, sticking, etc. but I have never seen it, and I have never heard of them pumping up on their own. Apparently, since there was coolant in the oil (and the oil becomes very thick) the lifters can have a tendency to expand when pressure is released from them (like when I removed the rocker assemblies). So when I put it all back together, the lifters were stuck in their expanded state, and so were holding all/most of the valves open! The solution? Let it sit for a while with everything back together, and crank the hell out of the engine.

    Sure enough, after a bunch of cranking and a few nasty backfires later... the engine came sputtering to life, running like CRAP. Slowly, the remaining dead cylinders came back online, and within about 10-15 minutes of runtime, it was running smooth on all 8! Weirdest thing I have ever seen!

    Thanks a lot for all the advice on here guys, hopefully if anyone runs into this problem in the future they can learn from my puzzlement!

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    Re: Replaced intake gasket and messed something up!

    I'd give it another oil change to make sure all of the coolant is out of the oil!

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    steelybill is offline Cadillac Owners Enthusiast
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    Re: Replaced intake gasket and messed something up!

    For sure!!

  12. #11
    mikeyj350 is offline Cadillac Owners Member
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    Re: Replaced intake gasket and messed something up!

    For sure! I replaced the filter and drained the "syrup" out of there during the intake repair, and then refilled it with new oil and some GUNK engine flush stuff. Once I got it going, I ran it for about 30min and shut it down and changed the oil and filter again, this time adding Sea Foam to the mix. That's what's in there now. My plan is to hit 100mi (almost there by now, no problems to report yet!) and change oil yet again before calling it good.

    FYI if anyone is interested in diagnosing the intake gaskets on these (ran into a similar thread on here asking about this), mine had a very obvious corner of the gasket that had broken around the right-rear coolant passage of the engine (nearest to cyl #8). Upon lifting off the intake, the small piece that went around the corner of that passage stayed behind, stuck to the head, while the rest of the gasket stuck with the manifold. Also, the outer portion of the #8 water jacket exposed to the lifter valley appeared completely washed clean, directly beneath the failure point of the gasket, when compared with the other 7 cylinders.

  13. #12
    carnut is offline Cadillac Owners Master
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    Re: Replaced intake gasket and messed something up!

    And be aware this all comes from infrequent coolant replacement. The coolant/water mix becomes acidic much like fish tank water having a dangerous PH level. Once the PH is high, it eats away the gasket as described. Change the coolant every 24 months without fail!

  14. #13
    drewsdeville's Avatar
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    Re: Replaced intake gasket and messed something up!

    Quote Originally Posted by carnut View Post
    And be aware this all comes from infrequent coolant replacement. The coolant/water mix becomes acidic much like fish tank water having a dangerous PH level. Once the PH is high, it eats away the gasket as described. Change the coolant every 24 months without fail!


    The 4.x uses steel intake gaskets. Coolant does not "eat" steel gaskets. If it did, the iron head surfaces would be so pitted the heads would need replaced or at least resurfaced.

    The 4.X intake gasket problem is inherent with the design. Aluminum intake on iron heads, the thermal expansion and contraction properties are different on each side of the gasket, causing scrubbing and "walking" of the gasket.

    An intake gasket on my 4.5 leaked vacuum between two intake ports, never touched by coolant.

    Why, for the love of God, does this board believe in the magical caustic and corrosive coolant?!?!?!?

  15. #14
    steelybill is offline Cadillac Owners Enthusiast
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    Re: Replaced intake gasket and messed something up!

    The Chevy engines have the same type problem sometimes, I've changed intake gaskets frequently on aluminum intakes on Chevy trucks, due to coolant leaks.

  16. #15
    drewsdeville's Avatar
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    Re: Replaced intake gasket and messed something up!

    Quote Originally Posted by steelybill View Post
    The Chevy engines have the same type problem sometimes, I've changed intake gaskets frequently on aluminum intakes on Chevy trucks, due to coolant leaks.
    Exactly. Intake gaskets have been a problem for YEARS on MANY engines (with different manufacturer recommended maintenance cycles) that use dis-similar metals for gasket surfaces. There's not much the consumer can do about it. I'm sure the gasket problems would still exist if people were changing their coolant every month!

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