bent #1 con-rod 4.6 N* no signs!!?
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Northstar Engines and System Technical Discussion Discussion, bent #1 con-rod 4.6 N* no signs!!? in Cadillac Engine Technical Discussion; Whats up all? Im a new member. I have worked a chevy/caddy dealer for almost 2 years now. No reseals ...
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    DMC783 is offline Cadillac Owners Member
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    Question bent #1 con-rod 4.6 N* no signs!!?

    Whats up all? Im a new member. I have worked a chevy/caddy dealer for almost 2 years now. No reseals or rings in a N* yet, but maybe soon.Anyway I have ? regarding a bent connecting rod being found while a tech I work with (you know him well,but I wont say who)was doing rings. The caddy had no noticeable symptoms of a bent rod. There was a de-carbon peformed on the vehicle by an expeirenced tech,so it's unlikely it was hydro-locked with top-eng. clean. There was no internal eng. damage either.

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    Re: bent #1 con-rod 4.6 N* no signs!!?

    You can bet your first born child that it was hydrauliced at some point in it's life. I have seen engines that ran hundreds of hours before something broke that had suffered a hydraulic lock and others that failed in a very short time. Be sure to check the crank for straightness and have it carefully MagnaFlux inspected by an expert. Sometime accessory drive gears will also be damaged. It depends if it was turning up pretty good when it swallowed that slug of liquid. Sometimes you can get a clue of how long the engine has been running with a bent rod by seeing if one cheek on the crank throw shows wear distress from side
    pressure. Also sometimes the wear pattern on the thrust sides of the piston will be strangely diagonal.

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    Re: bent #1 con-rod 4.6 N* no signs!!?

    There is a story about a Las Vegas hit man that tried to kill a gangster by filling the cylinders of the engine in his personal plane with nitro-glycerine. Amazingly enough it didn't explode but it sure created problems for the bomb squad.

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    Re: bent #1 con-rod 4.6 N* no signs!!?

    Quote Originally Posted by DMC783
    Whats up all? Im a new member. I have worked a chevy/caddy dealer for almost 2 years now. No reseals or rings in a N* yet, but maybe soon.Anyway I have ? regarding a bent connecting rod being found while a tech I work with (you know him well,but I wont say who)was doing rings. The caddy had no noticeable symptoms of a bent rod. There was a de-carbon peformed on the vehicle by an expeirenced tech,so it's unlikely it was hydro-locked with top-eng. clean. There was no internal eng. damage either.

    If the engine had the "deep carbon clean" procedure done AND it has a bent rod there is little doubt that the engine was hydorstatically locked when the deep carbon cleaning was done. Experienced tech or not.....everyone makes mistakes. If it wasn't the deep carbon cleaning it has to be the greatest coincidence known....LOL.

    However it occurred the bent rod was the result of a hydrostatic lock. Rods don't get bent otherwise. I suppose that it is possible that the owner previously drove thru a deep puddle and hydrostatically locked it that way but usually when that happens the engine blows up completely. When a rod in a Northstar bends it pulls the piston out of the bore at the bottom of the stroke (due to the shorter rod now that it is bent) and the crank counterweights hit the piston and break it up and the engine comes apart. For a rod to bend such that it wasn't short enough for the piston to hit the crank it had to be a pretty minor hydrostatic lock...such as with the limited fluid from a carbon cleaning. Also, bent rods from the carbon cleaning happen on startup when the first few cylinders fire and the engine isn't at higher RPM like when people drive thru puddles or flooded streets....so....the rod bends slightly, the engine starts and then it makes a pretty constant clicking.


    Let me set the stage.....LOL.....car comes in for cold carbon rap/excessive oil usage. Tech does deep carbon cleaning. Now engine REALLY makes noise on cold starts. Engine torn down for re-rining. Bent rod found. NO WAY tech did this....... LOL LOL


    GM has seen quite a few bent rods from the deep carbon cleaning procedure...some techs just do not get all the solvent out of the chambers. It has happened a bunch of times. It even happens on the top engine fluid cleaning when an impatient tech pours the top engine cleaner thru the throttle body too fast creating a puddle in the manifold plenum... Then the next cylinder in the firing order sucks the puddle thru the tuning tube in the intake and locks that cylinder. Way too common.

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    Re: bent #1 con-rod 4.6 N* no signs!!?

    When I first started my car after the flood I pulled all the plugs to make sure there was no standing water in the cylinders. I peeked into the intake, but didn't remove it. In retrospect, there had to be water in there. After further disassembly of the car I got water out of places I'd never expect it even after being in a heated garage for a month and a half now. When I started it, the throttle was propped open (I wasn't aware of this) because the cruise cable was not seated in the bracket properly. It started and ran at like 3,000 RPM. I immediately shut it down, fixed the cable and started it again. Runs fine - no bent rods as far as I can tell. You'd have to dump a bunch of top engine cleaner in there to bend a rod.

    Anyhow, when I did have the plugs out I noticed a fair amount of carbon on the tops of the pistons. I was going to have it cleaned w/ top engine cleaner but after reading the above maybe I'll pass. It would be the perfect scenario. I bring the flood car in (running fine), tech f's it up, they say "well it was a flood car - must've hydro' locked before you brought it in".

    You think the stealership in the original poster's scenario will step up to the plate and admit the fault? Done laughing?

    Jim

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    Re: bent #1 con-rod 4.6 N* no signs!!?

    I'm thinking "stealership" was not a slip of the finger....LOL....Never heard that one.Well we would be stealing from GM since it's a warrantee job. If GM investigates the bent connecting rod they would most likely come to the conclusion that the de-carbon previously performed was the culprit and the dealer would be charged back for the rod and the labor to replace it.Now, there are two ways to introduce solvent to the combustion camber.One is quick and easy and the other is more time consuming but much more effective.Which process was used on this car,I have no idea.

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    Re: bent #1 con-rod 4.6 N* no signs!!?

    It is actually not that hard at all to cause a bent rod on some of todays engines (including the Northstar). Much easier than you think. First, in case you missed it, compression ratios are creeping back up...so, with the smaller chambers at TDC to make compression it leaves less "room" for any sort of liquid. Second, with a highly tuned intake like the Northstar has, the common plenum chamber can accumulate enough water to hydrostatically lock one cylinder and then "send it" all to the next cylinder that happens to draw from the plenum thru the tuning tube for that cylinder. Previous engines with more conventional intake manifolds (like on the 4.9 style of engine) would tend to disperse liquid water coming thru to several or more cylinders thus more volume would be needed to hydrostatically lock one. This occurs because the plenum is small and the runners are all "downhill" from the plenum. With the large plenums and individual runners the runners travel "uphill" so any water or solvent introduced into the intake can accumulate and lay in the bottom of the plenum until enough accumulates to get sucked into a cylinder and then the cylinder tends to take a "gulp" so that all the liquid goes to one cylinder...instant hydrostatic lock.


    A dealership or garage owning up to hydrostatically locking an engine due to a mistake....!!!!!....?????.....get real. It would never happen in a million years. It will be blamed on the "stupid engine" or some other scapegoat. No one would own up to doing something like that..!!!

    I have mentioned the issue of hyrostatic locks many times in the past when cautioning people about changing the induction system, opening the induction system up to the fender area or underhood area or changing to a cold air intake style of aftermarket system. A great deal of work goes into making sure the engine cannot injest water because of its propensity to hydrostatic lock. Given a deep enough "puddle" you can still lock one but it takes pretty deep water and/or high speeds.

    I have also mentioned the possibility of a hydrostatic lock with the decarboning procedure in the past.....only because I have seen it happen. The decarb or deep carbon cleaning process is likened to a transmission flush in my opinion. It will work and can do some good under rare, isolated conditions and it certainly can be done without harming the engine....but....there is always the chance of a mistake or screwup and when it happens the engine/trans is toast. The only way to totally avoid the risk is to avoid the process.

    Besides, there is no better deep carbon cleaning process than a frequent dose of WOT. Do frequent WOT accels thru the redline upshift points and oil consumption, ring sealing and carbon buildup will be a non-event with a Northstar engine.

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    Re: bent #1 con-rod 4.6 N* no signs!!?

    I completely agree with you bbob on the de-carbon being risky.Unfortunatly GM and my boss both think it is a "quick-fix". I dont see service advisors at my dealer telling a 70 year old man to floor his caddy that he has probobly waited his whole life for.I personally have no problems with WOT in a n*.It is quite a rewarding expereance!So where do you think GM is going with this issue?

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    Re: bent #1 con-rod 4.6 N* no signs!!?

    Quote Originally Posted by DMC783
    I completely agree with you bbob on the de-carbon being risky.Unfortunatly GM and my boss both think it is a "quick-fix". I dont see service advisors at my dealer telling a 70 year old man to floor his caddy that he has probobly waited his whole life for.I personally have no problems with WOT in a n*.It is quite a rewarding expereance!So where do you think GM is going with this issue?

    As I said there are some cases where the deep carbon cleaning can help the situation. If the rings are frozen in the ring lands due to carbon build up and lack of exercise then the solvent penetration can help free them. It is not a sure fix for all situations but it is less risky than ripping the engine apart....so it is considered the first step.

    The service ring set does allow the dealer to further address a high oil consumption engine that they had no recourse for before.

    I think the real issue was the variability in engines for oil consumption and the lack of heavy duty break in on some engines. With the service "fixes" the dealer has some means of addressing the worst case oil consumption engines as outlined in the service bulletins.

    In most all cases, simply whipping the engine for better breakin and to exercise the rings and free them up will solve the problem...but...as stated you are not likely to see that in the service or owners manuals.

    The ring package in the production engines was revised for higher ring tension several years ago which should prevent any further episodes of high oil consumption even on babied engines with carbon buildup. Similarily, piston compression height was also modified to eliminate the possibility of the cold carbon rap even with severe carbon build up.

    The main issue was dealing with engines in the field that had complaints registered. Now there is a means of doing this.

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    Re: bent #1 con-rod 4.6 N* no signs!!?

    Bbob, I can remember when I was a kid, a process being adverised over the radio that involved a machine that you stuck in the sparkplug holes that would blast the combustion chamber with walnut shells. Since that time I have seen a lot of walnut shells used as blast cleaning media and even heard of them being tossed in the intakes of jet engines to clean off combustion deposits. It sounds like the best process is still WOT.

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    Re: bent #1 con-rod 4.6 N* no signs!!?

    Older engines from the pre-70's had inherent problems with "carbon" buildup due to the leaded fuels. Leaded fuels caused pretty nasty deposits along with fouling spark plugs every 20K and poisoning catalysts when they came along. Lots of the old school nut blasting, water injection, top engine cleaning, etc. came about due to leaded fuels in pre-historic times...LOL LOL

    Engines run reasonably hard always have good ring seal and are relatively clean of carbon. The best looking engines (internally) that I every see at teardown inspection are the ones that are run the hardest.

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    Re: bent #1 con-rod 4.6 N* no signs!!?

    Of the two cleanest engines I've ever seen; one was a 300HP IO-520F Continental that had been operated on aviation gasoline contaminated with jet fuel to where it was undergoing light detonation for about an hour and a half. It looked like it had been blasted clean inside with a very fine abrasive. The other was a Japanese forklift operated for years on propane.

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    Re: bent #1 con-rod 4.6 N* no signs!!?

    Quote Originally Posted by DMC783
    I'm thinking "stealership" was not a slip of the finger....LOL....Never heard that one.Well we would be stealing from GM since it's a warrantee job. If GM investigates the bent connecting rod they would most likely come to the conclusion that the de-carbon previously performed was the culprit and the dealer would be charged back for the rod and the labor to replace it.Now, there are two ways to introduce solvent to the combustion camber.One is quick and easy and the other is more time consuming but much more effective.Which process was used on this car,I have no idea.
    That's cool. I've had some bad experiences with dealers in the past. If it's a warranty job then it shouldn't matter. I'm out of warranty so it's a risky procedure for me.

    I wasn't questioning your explanation, bbob, I was just sort of thinking out loud about how much liquid it would actually take to lock the engine up (and considering the risk I unknowingly took when I fired my car up for the first time after the flood). I guess the answer is not much liquid at all.

    As far as carbon build-up goes, I was pretty surprised to see the carbon atop the pistons on my Northstar. It has 46k on it, but I'm not sure under what conditions it was driven. It was a corporate limo, I believe, based on its title history and some interior cues. You can bet I'll be pretty hard on it but that doesn't sound like a bad thing.

    I was amazed at how clean the combustion chambers on my GN were when I had it apart for the first time. At 100k miles, it looked pretty good. I guess running at the edge of detonation all the time makes for an efficient burn. Ultimately, though, I crossed the line and hammered the rod bearings out of it with detonation. Live and learn.

    Jim

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    Re: bent #1 con-rod 4.6 N* no signs!!?

    Yep...any engine running near detonation all the time will be pretty clean in the combustion chambers. A little carbon on the pistons and in the chamber will not hurt anything. I just leave it alone. I raises the compression...LOL.

    Engines leaking coolant past the fire ring into the combustion chamber will also have a clean cylinder. The water does an excellent job of blasting the carbon off .

    You'll find that Northstar engines run hard all the time will be pretty clean, too.

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    Re: bent #1 con-rod 4.6 N* no signs!!?

    Hydraulic lock was a real and constant problem with the big old round aircraft engines. It was customary to pull the prop through by hand at least two complete revolutions to make sure there were no cylinders with liquid in them. The Koffman combustion starter which was the only starter available for quite a while that would crank the biggest engines developed upwards of 25 horsepower and could do some real damage. If resistance was found during the pull through the correct procedure was to remove some lower spark plugs and drain out the oil before proceding with the start. There were some dummies that instead turned the prop backwards. This pumped the liquid up into the intake system to where the starter could really get the engine rolling and maybe even firing before the liquid hit the cylinder. If the crew was lucky the cylinder head would split open and the whole operation came to a halt. If the crew was unlucky, the engine would start and continue to run and they would take off for a flight over enemy territory with an engine full of bent parts. Whoopey!! The Napier SabreII 24 cylinder engine had a unique problem because it had sleeve valves rather than poppet valves. Oil could get trapped between the end of the sleeve and the recess around the cylinder head. The early fix was to start and run the engine every two hours or so 24/7. Later on, some mechanic who wanted some sleep found he could drill a small hole in a strategic place on every cylinder and let the trapped oil drain. it made a mess but compared to all the other places that leaked oil it was pretty minor. The Sabre II engine was 2200 cu.in, turned 5500RPM, and on the test stand developed 4500HP for 275hr without shutting it down. How's that for 1hp/cu.in? The run was made on a special 165 octane brew and BMEP was in the 500PSI range. How would you like you pay that fuel bill? The Sabre II was used in the Hawker Tempest and Typhoon. The Tempest was the only Allied aircraft that could catch a V-1 Buzz Bomb without diving on it. Try this link http://tempest.nerdnet.nl/tempest.wav This is the only known recording in existance of the highest powered and most complicated reciprocating engine ever put into sevice.

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