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Northstar Engines and System Technical Discussion Discussion, Engine parts cleaning during overhaul in Cadillac Engine Technical Discussion; Originally Posted by Submariner409 Studs DO NOT "yield". GM Northstar head bolts do. Studs can be reused many times, GM ...
  1. #31
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    Quote Originally Posted by Submariner409

    Studs DO NOT "yield". GM Northstar head bolts do. Studs can be reused many times, GM Northstar head bolts cannot.

    Studs are seated finger tight in the block and the head bolt hardened washers and nuts are torqued to a specific lb/ft specification. GM Northstar head bolts are torqued to a small initial figure to establish a starting base, then twisted an additional XXX degrees to pull the shank of the bolt to its yield - "rubber band stretch" - point.

    You install studs, you torque the nuts to a specific torque in 3 passes. Install BigSerts or NS300L Inserts and ARP studs, you torque the stud nuts to a specific figure in 3 passes. You install BigSerts or NS300L inserts and use GM Northstar head bolts, you torque to initial spec + the extra XXX degrees for bolt stretch.

    Why do I specify "GM Northstar head bolts" as such ? Because they are torque to yield pieces and are useless after removal. GM Oldsmobile 455 head bolts are huge affairs and can be reused forever.

    Grab a pretty good-sized rubber band. Hold it so as to remove all droop, no tension ........ now pull it to some length. Notice how the rubber band itself becomes smaller in width ??? THAT'S what happens to a GM Northstar head bolt - except the head bolt will never return to it's original shape - it's like a rubber band that has been left wrapped around the box too long. Useless.

    As an aside, the entire "twist to yield" procedure may be partially responsible for head gasket failures - the very statement "Torque to yield" or "Twist to yield" implies that there is no "spring" left in the bolt(s). A tiny something goes wrong and the bolts cannot maintain clamping pressure. Tim Carroll's studs, Jake's studs, and Norm's Inserts with ARP studs will NEVER lose clamping pressure.
    Very good and illustrative post. Thank you. I suppose the stretch could be measured. Is it millimetric? Begs the question: why on Earth would the engineering team choose these type of bolts? I don't think they're cheap are they?

    Also are Tim Carrol's and Jake's studs the same? Norm's use non TTY bolts like the Olds you mention?

    ----------

    Quote Originally Posted by maeng9981
    Weird, after reading that I looked at the pictures of my first head gasket repair again - and found that it was indeed the #1 cylinder that had the most amount of coolant in it with the carbon buildup looking pretty different than others.
    Do you have a link to the 1st repair pics? Also how much do you know about the coolant change on either cars? I think in our discussions you mentioned the Seville had a decent coolant service history.

    It does look like there's some rust and flaking around the passage holes in that gasket. Is it surprising? Otherwise the gasket looks pretty solid. No bunching up, it seems.

    What's up with the # 1cylinder coincidence? Bizarre or onto something?

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    Re: Engine parts cleaning during overhaul

    Head stud stretch can be accurately measured with a dial indicator. When Norm's Inserts are used with head bolts they are the OEM GM bolts, tightened according to the correct year service manual. When Norm's Inserts are used with ARP studs, the studs are inserted finger tight and the nuts/hardened washers are torqued to a specific value in 3 passes.

    I don't know if ARP or anyone else makes Northstar head bolts in a good ol' straight shank torque-only monster like the Olds bolts.

    Studs are torqued to a specific lb/ft value which stretches them several thousandths of an inch = clamping pressure. Read the theory in the ARP site. "Torque (or tighten) to yield" bolts are, by definition, tightened very close to the limit of their metallurgy strength - much more and they break, which is why you DO NOT re-use the Northstar head bolts during top overhaul.

    Regardless of supplier/manufacturer I would imagine that Northstar stud packages are designed and machined from stock that is more than adequate in tensile strength specs. (ARP studs are treated to tensile strengths approaching 180,000 pounds. Sufficient.)

    ........... In the head gasket pictures - the #1 cylinder with the cylinder leak past the fire ring. The gasket material itself looks shiny and well compressed. How much "meat" is there in the cylinder head area just over that water passage/gas leak area ??? ......... Where I am going: Did the cylinder head "bow up" at that end, between the head bolts, and allow gas to blow by ?

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    Re: Engine parts cleaning during overhaul

    Quote Originally Posted by mtflight View Post
    Begs the question: why on Earth would the engineering team choose these type of bolts? I don't think they're cheap are they??
    I'm not sure Sub really touched on WHY they work as much as HOW they work.

    They use these bolts now because todays engines demand more precision. Everything is aluminum now, and expansion and contraction rates are much higher than with old iron engines. With everything moving around so much, it all needs to "slide" on the gaskets to retain the seal without interrupting the integrity. This is where torque to yield bolts come in. They provide a much more accurate and even torque across the entire head, allowing the greater expansion/contraction rates to occur without tearing up, pinching, or otherwise destroying the gasket.

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    Re: Engine parts cleaning during overhaul

    Nice try.......... but there may be other factors here.........

    In that scenario, the aluminum engine parts slide around ??? If the block and heads expand (swell) with heat and the steel bolts don't (or to a lesser degree) then why doesn't clamping pressure increase with heat vs. decrease ?? (and why don't the cast-in iron cylinders pop away from the block ?) If the block and heads changed geometry to any degree, what would then happen to crank, rod, and cam bearing alignment ?

    Do ANY of the posted gasket/head/block pictures show evidence of parts sliding around ?

    Something else is going on here and it's not the aluminum engine - there are too many examples of aluminum and aluminum/iron engines working perfectly satisfactorily. (It's all mechanical - it ain't forever)

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    Re: Engine parts cleaning during overhaul

    I think you misunderstood - my post wasn't aimed directly at the N* and it's problems - it's just a summary of changes made in modern engines (most of todays engines use TTY bolts - not just the N*). He asked why a manufacturer would choose to use TTY bolts

    Modern headgaskets are coated with teflon, silcon, and other anti-friction materials for a reason, and it's not because everything stays perfectly in-place. If everything was clamped down rock solid with no movement, all we would need for a head gasket is a simple piece of stainless steel. No layers, no coatings, no nothing. Hell, with todays manufacturing processes, we wouldn't even need head gaskets - just machine the surfaces perfectly flat and bolt them down with 500 ft-lbs.

    This is exactly the reason why you can see the scrubbed gaskets in "normal" head gasket failures.

    If the block and heads expand (swell) with heat and the steel bolts don't (or to a lesser degree) then why doesn't clamping pressure increase with heat vs. decrease ??

    It does, to a degree.

    (and why don't the cast-in iron cylinders pop away from the block ?).


    They have, in some engines. On a related note, what usually happens first is the valve seats drop out of the head. This is a very common failure on engines that have been overheated. Since the seats are generally a press fit from the factory, and failure occurs mainly at high temps, this is good supporting evidence that thermal expansion/contraction is a major player in close-tolerance engine parts.

    If the block and heads changed geometry to any degree, what would then happen to crank, rod, and cam bearing alignment ?


    This has also been an acknowledged problem in some engines. GM's 4.X series is one of them.

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    Re: Engine parts cleaning during overhaul

    I'll buy some of that ^^^ but throw a hook in there.......... I have used steel sandwich (MLS) head gaskets in Olds 455 engines and not had a problem for years - in a salt water environment (the engines are fresh water cooled - sealed coolant system with heat exchanger).

    It would be interesting to find out if a member had ever coughed up the $125 (apiece ?) for the Cometic Northstar MLS gaskets.

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    Re: Engine parts cleaning during overhaul

    I'm a big proponent of the mls experiment if only for the fact they're one piece (many layers) and the blow rings aren't floating in the composite material. If I have to get a hg replaced it will be mls. The Viton coating is resistant to OAT but I'd be using conventional green anyway.

    Edit: IXSLR8 has used Cometic http://www.cadillacforums.com/forums...earchid=801211

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    Re: Engine parts cleaning during overhaul

    http://www.ebay.com/itm/COMETIC-HEAD...10427795970%26

    I find this conversation about the headgasket for the Northstar very interesting, especially pertaining to the MLS headgasket.

    Yes, I can say you're going to pay a bit more for them, but in reality the factory headgasket has proven itself for a life expectancy for a range of 80k or better depending on a number of factors, maintainence of vehicle etc.

    I can only say from the headgaskets that I've removed from the Northstars that I've disassembled that used Dexcool for coolant that were well maintained to a range or poorly maintained. We're dealing with a multi faceted problem.

    The thread pitch on the bolts are too fine, the bolts "stretch' to some degree. The "open" deck block design, could be contributing to the headgasket issues. The expansion rates of the metals coupled with the combustion ratio could be a factor also. The Dexcool issue, well that can go on forever, but my personal experience with it it's poison to intake and headgaskets.

    I've only had one expereince so for with a MLS headgasket and it wasn't on a Northstar.

    I had to work on a 00 Dodge Intrepid R/T 3.5. It unfortunately jumped time and wiped out the intake valves. Therefore the heads had to be removed. Upon removing the heads I never knew this motor used a MLS headgasket, but it was a pleasant surprise.

    After the heads were off, there was almost no cleaning of the heads or deck surface of the engine block. The gasket is basically a flexible shim, that if I didn't know any better you probably could have reused it. Yet, I'm not that crazy to go that deep into a motor and chance something like that, but it came off the motor that clean.

    The price of the gasket kit, well that was another story. It was a bit pricey, but what you saved in clean up time and the gasket looks virtually indestructible was priceless.

    I'm on the fence about using the MLS gasket on my Northstar, but from what I've seen from personal experience, I'm leaning that way.

    I just think during the Northstars design to production, some corners were unfortunately cut to save the usual, $$$$$$.

    The motor is too nice of a motor to suffer some of the ills that it has. If you ever get one to really run nice, you'll be extremely happy. That too I can say from experience. I look forward to rebuilding my eldorado motor.

    Good luck gents

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    Re: Engine parts cleaning during overhaul

    I read somewhere that GM was one of the last manufacturers to go MLS route--they took their time to get there. As far as Dex, why do the 93-96 have significantly lower failure rates (the fewer ones may indeed be neglect to change the green silicated coolant every couple of years). We can agree that corrosion is a factor, and some well-maintained systems on DEX have it too. MLS would be much more resistant to corrosion, and the shim design prevents discrepancies of the composite gasket between the cylinder bore rings and the remaining gasket material (floating).

    The only argument for using the factory style gasket is that it works as well as it does, sometimes corroding, sometimes flaking, sometimes failing.

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    Re: Engine parts cleaning during overhaul

    The only true argument for GM NOT using the MLS gasket on their hi-tech Northstar was to save $$$. You take a nickel or a dime here and there multiply it by a million or so engines, add that up. Don't say save a dollar......

    The factory gasket performs well under the circumstances, at least to get the car out of the factory warranty period. After that, throw the car basically away or prepare to fix it at your own cost.

    It's a shame because the engines and the cars themselves are nice.

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    Re: Engine parts cleaning during overhaul

    Quote Originally Posted by 98eldo32v View Post
    The factory gasket performs well under the circumstances, at least to get the car out of the factory warranty period.
    That argument doesn't hold water because there are millions of 40 year old engines, worldwide, that are still running around with their original felt/graphite/steel mesh/coated original head gaskets.

    Every year, for the past 22 years, I have taken apart (for rebuild) Olds 455 and GM454 engines from the 70's to use as marine workhorses. I can safely say that I have NEVER seen a failed head gasket in a stock GM built big block - even in engines with broken off head bolts ! Worn rings, pistons, cams, lifters, valves, chains - yes. Head gaskets - NO.

    The Northstar cylinder leak bugaboo is something other than the head gasket itself - and even then the failure percentage is, in the order of things, insignificant. (No, it's not insignificant to the owner of a leaking engine - but just how many million Northstar engines are out there ?)

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    Re: Engine parts cleaning during overhaul

    "That argument doesn't hold water because there are millions of 40 year old engines, worldwide, that are still running around with their original felt/graphite/steel mesh/coated original head gaskets."

    I can argee to that statement, but the Northstar isn't one of them.

    You have "supposedly" a technical advanced engine that refuses to retain a headgasket over some "poorly" designed bolts, and/or some coolant that was never "tested" throughly for it's corrosive properties with other materials.

    No motor is perfect, but if you can make a statement of 40 year old motors and technology has advanced since then, are you saying the engineers 40 years ago were smarter than the ones now? I truly hope not.

    This is more bean counting measures that the consumer in some shape or form turns into the guinea pig.

    Let's not go back to the TRUE darker days of GM. 2.3 quad 4's loosing headgaskets, 4100's/ V8/6/4, that weren't nothing but boat anchors, paint peeling off of cars because the primer that was used was never tested with the paint for proper adhesion. The list goes on.

    I worked for GM during those ugly times. I truly loved their cars, great idea's, but poor execution of the idea's. I used to scratch my head and wonder what was going on, only years later when I talked to some engineers, it all made sense.

    The engineers idea's started out one way with certain specifications and materials, the final product ended up ANOTHER way thanks to bean counters. That's just nature of the beast.

    You keep pinching too many pennies, now you're pinching into your reliability of your car. Who wants to drive a car that's unreliable?

    If I shell out the money for GM's top of the line vehicle, I EXPECT top of the line performance and reliability. If I shell out money for a chevette, then I get what I pay for. That USED to be the saying, "You get what you pay for". There is no way someone should shell out Cadillac money and get Chevette reliability.

    That's bad business. Period.

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    Re: Engine parts cleaning during overhaul

    Quote Originally Posted by Submariner409 View Post
    I'll buy some of that ^^^ but throw a hook in there.......... I have used steel sandwich (MLS) head gaskets in Olds 455 engines and not had a problem for years - in a salt water environment (the engines are fresh water cooled - sealed coolant system with heat exchanger).
    Thats not a hook, that's support. Those are iron engines, not aluminum. The coefficient of thermal expansion on an iron engine is SIGNIFICANTLY lower than an aluminum.
    Like you said, 40 years ago, head gasket leaks were virtually unheard of, even when overheated. Today, as we pump out aluminum products almost exclusively, gasket failures are relatively common, across all manufacturers (some worse than others, of course).

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    Re: Engine parts cleaning during overhaul

    Quote Originally Posted by 98eldo32v View Post
    "That argument doesn't hold water because there are millions of 40 year old engines, worldwide, that are still running around with their original felt/graphite/steel mesh/coated original head gaskets."

    You have "supposedly" a technical advanced engine that refuses to retain a headgasket over some "poorly" designed bolts, and/or some coolant that was never "tested" throughly for it's corrosive properties with other materials.

    This is more bean counting measures that the consumer in some shape or form turns into the guinea pig.

    Let's not go back to the TRUE darker days of GM. 2.3 quad 4's loosing headgaskets, 4100's/ V8/6/4, that weren't nothing but boat anchors, paint peeling off of cars because the primer that was used was never tested with the paint for proper adhesion. The list goes on.

    I worked for GM during those ugly times. I truly loved their cars, great idea's, but poor execution of the idea's. I used to scratch my head and wonder what was going on, only years later when I talked to some engineers, it all made sense.

    The engineers idea's started out one way with certain specifications and materials, the final product ended up ANOTHER way thanks to bean counters. That's just nature of the beast.


    That's bad business. Period.
    With the Northstar being so reliable as far as ring and piston and overall engine wear, the missing piece is a reliable head gasket.

    While the failure rate of the headgasket some claim is "insignificant" as far as percentage, it is enough to give the engine line a reputation of having cooling system issues. People that haven't owned them have heard stories or know someone who has had issues with headgasket or "bad heads" as I've heard some say. It's an issue to the used car lots as well. It's enough of an issue that anyone who is aware and is in their right mind does some research prior to purchasing one.

    If the issue is clamping force, the studs should take care of that, but do bad bolts rust a head gasket? With the thermal properties of aluminum being what they are, there is a lot more demand on the head gasket, so the old school gasket does not work too well, does it?

    As far as the errors that GM made in the past, such as not testing primer with paint or the V8/6/4 etc, the undeliberate OAT coolant experiment sounds like it is not far fetched at all. But, in light of the clamping issues and the piss-poor headbolt assignment and overall head gasket failure issue--why do the 93-96 have significantly fewer headgasket issues? Sure there are many ways to ruin a headgasket (overheating, no cooling system maintenance, a porosity mishap/manufacturer defect, etc).

    But back to 93-96, the issue could be that simple, and a neglected failed gasket could make it look to be much more complicated than it really is (waiting for all hell to break loose causing collateral damage to the bolts. etc.).
    98eldo32v and 98eldo32v like this.

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    Re: Engine parts cleaning during overhaul

    Quote Originally Posted by mtflight View Post
    If the issue is clamping force, the studs should take care of that, but do bad bolts rust a head gasket? With the thermal properties of aluminum being what they are, there is a lot more demand on the head gasket, so the old school gasket does not work too well, does it?
    No, "bad bolts" do not rust a head gasket.

    If the issue truly was different expansion rates of parts, then the idea of using a Cometic MLS head gasket is doomed from the start: they are essentially solid steel/copper and once torqued to spec they are solid metal - while a good ol' FelPro head gasket flexes a few millionths of an inch, a MLS gasket will not............. So where does that leave the "uneven expansion" theory ?

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