flahnd
Aurora Newbie
Posts: 12
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Post by flahnd on Apr 17, 2014 10:13:56 GMT -6
I had just finished replacing a head gasket in a 1997 Aurora 4.0L. Ran like a dream for about 3 days until it started sputtering some, and the RPMS would rise and fall. Thought it was the fuel injector.. threw in some cleaner (the fuel was 4 years old as the car had been sitting). Long story short it was the pistons hitting the spark plugs. Any input on what could cause this? I already took the engine back out, I just have no clue where to start. Timing belt slip maybe?
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RCA1186
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Rob
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Post by RCA1186 on Apr 17, 2014 11:21:23 GMT -6
No timing belt on the northstar, it has chains. Someone with better knowledge of the headgasket process might be better off chiming in on this one.
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randnon
Aurora Passenger
Posts: 248
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Post by randnon on Apr 17, 2014 11:47:14 GMT -6
Hi ,I am Rich from Buffalo and did my HG in Feb of this year. Did you have the heads surfaced or the Block machined? No change in timing chain position can cause the Pistons to hit the plugs. I would first check to see if the plugs you are using have a tip or threads that extend further in to the combustion chamber than the stock plugs. If you have disassembled the engine again their is a measurement to verify that too much material was not removed from the heads if they were machined. I am guessing that you may have a plug problem. Please let us know what you find so we can prevent this from happening to others. Rich
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Post by Kersh on Apr 17, 2014 12:33:36 GMT -6
I agree with randnon. The timing chains being off could cause the VALVES to hit the pistons, but the only way a spark plug could hit is if the head is physically closer to the piston at TDC (top-dead-center) or you've installed the wrong spark plug.
Based on the fact you said it ran fine for a few days, I'd say the timing chains are not off.
I don't know whether you have a 1G or 2G, but since the '95 to '03 4.0L and 3.5L(6) uses the same plug for all years (though the 3.5" uses a different gap) the following statement shouldn't be affected:
Looks like the stock plug should have a tapered seat, a .708" (17.5mm) reach with a .625" (16mm) projected tip.
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flahnd
Aurora Newbie
Posts: 12
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Post by flahnd on Apr 17, 2014 21:01:43 GMT -6
I installed studs without machining the head or block. I don't think it is the spark plugs, because we straightened them back out and turned the engine over manually twice, and they did not bend this time. This leads me to believe that the filthy fuel in the tank must've worked it's way to the injectors? Perhaps, causing the engine to misfire.
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Post by Toronado3800 on Apr 17, 2014 21:40:36 GMT -6
Pretty expensive engine.
Flahnd, do you have pictures of the plugs? I'd be going nuts trying to get some camera into them plug holes to see the piston tops if your plugs are broken.
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randnon
Aurora Passenger
Posts: 248
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Post by randnon on Apr 18, 2014 7:36:37 GMT -6
Did this happen to all the plugs or just one or two? I am wondering if you somehow injested some debris or if something broke off inside and was chewed up inside the combustion chamber ? Rich
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flahnd
Aurora Newbie
Posts: 12
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Post by flahnd on Apr 18, 2014 18:09:08 GMT -6
It happened to two plugs. I ordered a smaller bore scope to look down at the pistons. Here are the plugs: Attachments:
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plato442
Aurora Driver
Life, Liberty, and the pursuit of Oldsmobile...
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Post by plato442 on Apr 19, 2014 10:46:07 GMT -6
Misaligned timing chain maybe
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Post by guy48065 on Apr 19, 2014 11:58:47 GMT -6
Misaligned timing chain maybe Not a chance. Spark plug doesn't move... no way the piston is ever supposed to travel that far up the cylinder. There either has to be something bouncing around loose in that cylinder, loose bolts on the connecting rod, or broke piston or rod.
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Post by guy48065 on Apr 19, 2014 12:01:43 GMT -6
Thought of another unlikely possibility. Are Aurora pistons dished? If installed 180* rotated it could hit the plug -- but it would have done so on the very first rotation.
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bobsblue95
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Post by bobsblue95 on Apr 21, 2014 9:07:41 GMT -6
I see it's a Delco plug, but is it the exact one specified, and was it properly gapped?
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flahnd
Aurora Newbie
Posts: 12
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Post by flahnd on Apr 22, 2014 10:52:46 GMT -6
the pistons look fine. We did a compression test and got pretty inconsistent results, a lot of 0's from cylinder 1 and 3, and other times we'd get about 125-150. possibly the head gasket blew out by those cylinders?
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Post by sall on Apr 22, 2014 11:29:48 GMT -6
Well, how did you do the headgasket job?
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flahnd
Aurora Newbie
Posts: 12
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Post by flahnd on Apr 22, 2014 12:32:40 GMT -6
Re-studded and put in new gaskets. the repair kit from the Nordstar site.
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Post by Kersh on Apr 22, 2014 13:11:12 GMT -6
With the readings bouncing all over the place, my first thought is either a sticking valve or something pyhsically keeping the valve from seating each time it's closing.
Based on the condition of the spark plugs, I would guess whatever damaged the plugs is now stuck in the valve seat area.
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98redaurora
Aurora Driver
This is not your fathers Oldsmobile.
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Post by 98redaurora on Apr 24, 2014 8:44:31 GMT -6
Time to pull the heads back off, eh? Keep us posted!
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flahnd
Aurora Newbie
Posts: 12
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Post by flahnd on Apr 25, 2014 11:09:14 GMT -6
The head looked great and the seal was perfect. Replaced a leaking rear main seal while I had it all torn up.. I'm thinking that my problems were all from that old fuel. Oil was black after, and there was significant carbon build up on the pistons.
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flahnd
Aurora Newbie
Posts: 12
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Post by flahnd on Apr 26, 2014 10:47:10 GMT -6
Well we figured it all out.
Something I had never seen, nor had expected.
We only found it in reassembling the engine and lining up the camshaft pins for the initial timing chain setup. The right side intake camshaft was missing its pin!
Somehow it had fallen out and without it the sprocket had advanced several degrees. When the engine was initially torn down the sprockets were not removed, there is no need to.
If you turned the engine over slow enough by hand you can build compression, at normal speeds you are burning fuel without air. That's the best explanation I have for the bent plugs and carbon.
I'm guessing the pin is at the bottom of the oil pan. A new one was machined and pressfit into place.
Will give you an update when we hit the road again.
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plato442
Aurora Driver
Life, Liberty, and the pursuit of Oldsmobile...
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Post by plato442 on Apr 28, 2014 7:39:34 GMT -6
Wow, simple mistake yet almost very costly! Glad you got it taken care of and fixed!!
Hhmmm
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bobsblue95
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Post by bobsblue95 on Apr 28, 2014 8:34:05 GMT -6
Doesn't really add up. As previously pointed out, timing chain has zip/zero/nada to do with anything hitting a spark plug. If your missing index pin caused any interference, it would have been valve to piston.
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Post by guy48065 on Apr 28, 2014 9:42:08 GMT -6
...That's the best explanation I have for the bent plugs and carbon... What part of that is your explanation for how your headspace decreased til the piston hit the plug? ...and why didn't it hit on each and every cycle of the piston? If there was no damage found to the combustion chamber then I think the plug went in bent. Either it came out of the box that way and didn't get noticed, or it got dropped to the bottom of the deep recess in the head. With a long sparkplug socket, or adapters to make it reach, there's enough tool weight to bend the ground electrode on impact.
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flahnd
Aurora Newbie
Posts: 12
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Post by flahnd on Apr 28, 2014 20:19:55 GMT -6
...That's the best explanation I have for the bent plugs and carbon... What part of that is your explanation for how your headspace decreased til the piston hit the plug? ...and why didn't it hit on each and every cycle of the piston? If there was no damage found to the combustion chamber then I think the plug went in bent. Either it came out of the box that way and didn't get noticed, or it got dropped to the bottom of the deep recess in the head. With a long sparkplug socket, or adapters to make it reach, there's enough tool weight to bend the ground electrode on impact. In looking at the heads off the engine there is no way the pistons can actually hit the spark plugs. That they went in bent is certainly a possibility. The major problem with the engine was the camshaft pin falling out.
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