Cylinder rings blown on 18 thousand miles??? (cylinder nr 8 totally w/o compression)
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Northstar Engines and System Technical Discussion Discussion, Cylinder rings blown on 18 thousand miles??? (cylinder nr 8 totally w/o compression) in Cadillac Engine Technical Discussion; Cylinder rings blown on 18 thousand miles??? (cylinder nr 8 totally w/o compression) I'm confused!! Can it really be so ...
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    Mustalintu is offline Cadillac Owners Member
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    Cylinder rings blown on 18 thousand miles??? (cylinder nr 8 totally w/o compression)

    Cylinder rings blown on 18 thousand miles??? (cylinder nr 8 totally w/o compression)


    I'm confused!! Can it really be so that my STS yearmod. 2000 with only about 18 tousand miles has blown the cylinder rings on cylinder nr 8??

    There is full compression on all other cylinders, expect for nr 8 that shows no compression value at all.

    So my question to you Northstar engine experts:

    Is it most likely cylinder rings, hole in piston or bended / stuck valves that causes the lost of compression??

    The spark plug was OK, only very dirty because of unburned gasoline + oil rests the gasoline had already been dissolving from the cylinder walls?

    Could someone also give instructions where to start from with the sisassembly of the engine?

    I'm a brand new member of your society and also a brand new Cadillac owner....unfortunately this relationship started in a odd way.....

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    dkozloski's Avatar
    dkozloski is offline Cadillac Owners 10000+ Posts
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    Re: Cylinder rings blown on 18 thousand miles??? (cylinder nr 8 totally w/o compression)

    Tell us your story. When and how did the trouble start? What did you do to troubleshoot? How do you know there is no compression on the one cylinder? Have you drained the oil to check for metal? Are there any clicking or clacking noises like excessive clearance in the valve train somewhere?

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    zonie77 is offline Cadillac Owners Connoisseur
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    Re: Cylinder rings blown on 18 thousand miles??? (cylinder nr 8 totally w/o compressi

    Beside giving us more background, did you do the compression test or a mechanic?

    You can try adding oil to #8 and see if there is any increase. That would indicate rings. You should do a cylinder leakdown test. Put pressurized air into the cylinder and listen to where it escapes. This is the more definitive test.

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    zonie77 is offline Cadillac Owners Connoisseur
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    Re: Cylinder rings blown on 18 thousand miles??? (cylinder nr 8 totally w/o compressi

    You posted this twice...91TexasSeville added trying some WOT runs on the other post. The oil in the cyl will tell you if it's stuck rings, then you could try the solvent procedure Caddy has, some WOT, or frequent oil changes.

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    Mustalintu is offline Cadillac Owners Member
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    Re: Cylinder rings blown on 18 thousand miles??? (cylinder nr 8 totally w/o compression)

    Quote Originally Posted by dkozloski
    Tell us your story. When and how did the trouble start? What did you do to troubleshoot? How do you know there is no compression on the one cylinder? Have you drained the oil to check for metal? Are there any clicking or clacking noises like excessive clearance in the valve train somewhere?
    Hello!

    Some further backround info:

    The engine doesn't actually make any odd noises expect those caused of misfiring one cylinder and excessive engine shaking already in idle speed. The noises are not getting any worse by higher revs....the uneven and misfiring running just continues in higher tempo.

    The compression check was done by me and my father with a professional compression measurement gauge....all other cylinders showed actually full scale, but this nr 8 nothing at all.

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    Mustalintu is offline Cadillac Owners Member
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    Re: Cylinder rings blown on 18 thousand miles??? (cylinder nr 8 totally w/o compressi

    Quote Originally Posted by zonie77
    Beside giving us more background, did you do the compression test or a mechanic?

    You can try adding oil to #8 and see if there is any increase. That would indicate rings. You should do a cylinder leakdown test. Put pressurized air into the cylinder and listen to where it escapes. This is the more definitive test.
    Hey guys....you have really good ideas! The one with oil I actually knew....and i will do that as soon I have time!

    The second one with compressed air is a clever one as well....I will make an adaptor that fits to the spark plug threads ....and try that as well!!

    I will come back with results as soon I have some!

    Could some multipurpose penetrating oil (WD 40 for example) do the same work as this specific Cadillac oil with loosening the cylinder rings?

  8. #7
    Anthony Cipriano is offline Cadillac Owners Fanatic
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    Re: Cylinder rings blown on 18 thousand miles??? (cylinder nr 8 totally w/o compressi

    I hate to break this to you but even the most stuck, worn out, used up rings will always show some compression. Even a piston without any rings on it at all will show some compression. If you truely have zero compression in the cylinder then it is either a valve stuck open/bent valve/debris under the valve/etc. or a large hole in the piston. I would bet on a valve being the problem. It's not the rings.

    Applying compressed air to the cylinder will tell you where the compression leak is. If it is an intake valve I would pull the intake off and simply look into the intake port for starters. Perhaps the valve injested some debris from somewhere that is hanging the valve open. It might be as simple as retrieving the debris from the port.

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    eldorado1 is offline Cadillac Owners Connoisseur
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    Re: Cylinder rings blown on 18 thousand miles??? (cylinder nr 8 totally w/o compressi

    I'll place my money on broken valve spring and/or burnt/bent valve.

  10. #9
    Mustalintu is offline Cadillac Owners Member
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    Re: Cylinder rings blown on 18 thousand miles??? (cylinder nr 8 totally w/o compressi

    Quote Originally Posted by Anthony Cipriano
    I hate to break this to you but even the most stuck, worn out, used up rings will always show some compression. Even a piston without any rings on it at all will show some compression. If you truely have zero compression in the cylinder then it is either a valve stuck open/bent valve/debris under the valve/etc. or a large hole in the piston. I would bet on a valve being the problem. It aint' the rings......

    Applying compressed air to the cylinder will tell you where the compression leak is. If it is an intake valve I would pull the intake off and simply look into the intake port for starters. Perhaps the valve injested some debris from somewhere that is hanging the valve open. It might be as simple as retrieving the debris from the port.

    Thanks for hints Anthony!

    I was figuring out something like this with my father as well! Nice to be around such helpfull specialists! Unfortunately we will not have any time to make further investigation to the engine this week anymore as the car is by my fathers garage and I live some 1300 miles away from him!

    He will anyhow prepare a tool from a old spark plug to conduct pressurized air to the cylinder and we will take a look when I'm around next time.

    Are valve springs / hydraulic tappet clearance parts or valves themselves somewhat sensible in these engines?

    Secondly should at least bent valves make some tapping sound as well hole in piston??? This engine is quite silent, only shaking a lot.....

    What we will do is that we pour some engine oil + WD 40 into the cylinder and let it "make out" with the piston rings for few days. Then we will measure the compression again if still no indication ... next we dismantle the valve cover and intake manifold and try out with the compressed air. I will inform you guys what our findings will be!!

    If the reason would be bent valves is there a possibility for bent piston rod as well? (also how big clearance there is between the piston and valves?) As it seems the engine is so tight package that I have to dismantle the whole engine to be able to dismantle the cylinder head....Oh boy! This means new gaskets, possibly Time-Serts....new Timer Belt?....also a lot of $$$$!!! I really wih for broken valve spring or similar easy repair in valve gear....

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    Re: Cylinder rings blown on 18 thousand miles??? (cylinder nr 8 totally w/o compressi

    It uses two timing chains, that are run off of the intermediate shaft, and sprockets. They should be fine, as long as you don't damage them. It sounds like you've got your work cut out for you, let us know how it turns out.

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    Mustalintu is offline Cadillac Owners Member
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    Re: Cylinder rings blown on 18 thousand miles??? (cylinder nr 8 totally w/o compression)

    Thank God for that at least! I really hate timing belts!!

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    eldorado1 is offline Cadillac Owners Connoisseur
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    Re: Cylinder rings blown on 18 thousand miles??? (cylinder nr 8 totally w/o compressi

    I'm kind of curious as to what transpired leading up to you finding out that the cylinder had no compression...... Did it make any noise? Or did the engine just start shaking?

    It might even be worthwhile to borrow a mechanic's boroscope, and peer in the cylinder. Wouldn't be worth all the hassle if you find a piston missing... If the valve spring did break, it probably dropped the valve into the cylinder, piercing the piston (and making a hell of a racket while it does this).

    Another possibility I see is if that cylinder's fuel injector suddenly decided to flow less than it should (debris), causing that cylinder to lean out, and melting a valve (probably exhaust), keeping it in a constant open condition. This would happen silently, except if it were going up a hill or something, then you'd hear it pinging.

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    haymaker is offline Cadillac Owners Fanatic
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    Re: Cylinder rings blown on 18 thousand miles??? (cylinder nr 8 totally w/o compression)

    I would agree with eldorado1 as to the problem being an exhaust valve. If it were an intake valve I would listen for some popping in the intake manifold. If it were a holed piston I would expect, higher than normal oil consumption, maybe exhaust smoke and oily residue on the exhaust tips at the back of the car plus the sparkplug’s tip should be covered with liquid oil. Even a weak or broken valve spring some times will allow some measurable cranking compression. Given the amount of combustion byproducts that build-up in the combustion chambers of these engines for some of this material to break free and become crushed then trapped between the exhaust valve head and its seat is possible. One of the two exhaust valves in that cylinder may have been held open by a small piece of this debris. I think the N* is an interference engine so the piston may have kissed the valve head from being held partly open by this debris then bent from contact with the piston head but it is also possible the valve head may not have hit the piston an been bent. Under the right conditions an exhaust valve could burn. Either from the cylinder going very lean and thus much hotter than normal or if the exhaust valve were held off its seat a very small distance by the debris and couldn’t transfer the combustion heat from the exhaust valve’s head to the valve seat. In either case (like eldorado1) I think the exhaust valve is the more likely cause of the low compression.
    I would be interested to know the outcome. I don’t think I have read any post describing this problem on a low mileage N*.

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    Anthony Cipriano is offline Cadillac Owners Fanatic
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    Re: Cylinder rings blown on 18 thousand miles??? (cylinder nr 8 totally w/o compressi

    It isn't the rings. Putting solvents in the cylinder and waiting is a waste of time.

    Pull the intake and check the intake ports/valves from the backside thru the intake port and pressurize the chamber to ascertain in which direction the leak is going. This isn't likely to cure itself so you may as well dig into it.

    If you find an intake valve sealing issue I would pop that cam cover off to check the valve lineup on that cylinder. Possibly there is an issue with a roller rocker on that valve that has been present for some time?

    I'm assuming that you bought the car this way. So, you have no way of knowing how long it has been this way or what circumstances were surrounding the engine when this happened. As in, could it have been hydrostatically locked due to water intrusion, breaking a piston, then sold at auction for cheap? What is the situation behind this. Doesn't sound like it just happened to you idling at the drivethru window...

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    Re: Cylinder rings blown on 18 thousand miles??? (cylinder nr 8 totally w/o compression)

    How about a broken camshaft between cyls. #6 and #8? Does the water pump pulley still turn? Pull the front valve cover and have a look at everything. That's where I would start.

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