Determining the failure mechanism, multiple blown headgaskets.
11-07-2010, 07:46 PM
#1
Determining the failure mechanism, multiple blown headgaskets.
Ok, so here is my situation. My accord was overheated very badly about a year ago. The head gasket blew as a result, and was repaired at a professional mechanic. It subsequently failed again. Was repaired at the same shop, the heads were milled flat as they were warped.
The gasket sealed, then after a small coolant leak resulting in low coolant running conditions for about a week, (repaired) the gasket failed once again. It started slow, bubbles into the coolant, and has been accelerating for quite some time. Now misfiring upon cold start, lurching during warmup etc.
Now being an engineer, and the fact that the car has toasted three head gaskets makes me desire to figure out why it failed of course.
Now I have several theories on the matter, and was hoping that someone might have seen something like this before.
Theory number one:
Cracked cylinder heads.
It occurs to me that a small crack in the surface of the cylinder heads, and if deep enough would cause rapid gasket failure. Now, the subsequent milling of the heads, would have wiped out most of the crack, while leaving a small portion of the crack. Slowly eating away at the gasket until bam, leak.
Theory number two:
Warped heads. When cylinder heads containing an overhead camshaft deform enough, the camshaft journals become misaligned. Resulting in misaligned cam(s). my thoughts are that the forces acting on the camshaft journals are significant enough it may possible that the heads warped as a result of these forces. Also, low coolant, may have resulted in re-warping of the heads.
Theory number 3:
Cracked block. There is a crack in the surface of the engine block. The surface of the engine block is warped, cracked, or eroded from the previous gasket failure.
Any inputs, similar experiences etc?
The gasket sealed, then after a small coolant leak resulting in low coolant running conditions for about a week, (repaired) the gasket failed once again. It started slow, bubbles into the coolant, and has been accelerating for quite some time. Now misfiring upon cold start, lurching during warmup etc.
Now being an engineer, and the fact that the car has toasted three head gaskets makes me desire to figure out why it failed of course.
Now I have several theories on the matter, and was hoping that someone might have seen something like this before.
Theory number one:
Cracked cylinder heads.
It occurs to me that a small crack in the surface of the cylinder heads, and if deep enough would cause rapid gasket failure. Now, the subsequent milling of the heads, would have wiped out most of the crack, while leaving a small portion of the crack. Slowly eating away at the gasket until bam, leak.
Theory number two:
Warped heads. When cylinder heads containing an overhead camshaft deform enough, the camshaft journals become misaligned. Resulting in misaligned cam(s). my thoughts are that the forces acting on the camshaft journals are significant enough it may possible that the heads warped as a result of these forces. Also, low coolant, may have resulted in re-warping of the heads.
Theory number 3:
Cracked block. There is a crack in the surface of the engine block. The surface of the engine block is warped, cracked, or eroded from the previous gasket failure.
Any inputs, similar experiences etc?
11-07-2010, 08:05 PM
#2
Re: Determining the failure mechanism, multiple blown headgaskets.
11-07-2010, 08:31 PM
#3
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Re: Determining the failure mechanism, multiple blown headgaskets.
Hi there...
Any who...I would definetly go with you theory #3...
As the engine over heats, not only the head gets warped, but also the short block itself. Let's remember that the long block is made of aluminum (4 and 6 cyl) so any good wrench monky would perform the milling of the whole engine.
Here's a interesting link: http://www.youtube.com/watch?v=6wria2XqBzs
Let's not forget, that some times, when the engine REALLY over-heats, a cylinder wall can crack do to the extreme condition... (seen it myself)
I don't think the problem comes from the head or heads being cracked, specialy since they're very malleble, at least I've never seen it yet.
I hope this info comes in handy
Any who...I would definetly go with you theory #3...
As the engine over heats, not only the head gets warped, but also the short block itself. Let's remember that the long block is made of aluminum (4 and 6 cyl) so any good wrench monky would perform the milling of the whole engine.
Here's a interesting link: http://www.youtube.com/watch?v=6wria2XqBzs
Let's not forget, that some times, when the engine REALLY over-heats, a cylinder wall can crack do to the extreme condition... (seen it myself)
I don't think the problem comes from the head or heads being cracked, specialy since they're very malleble, at least I've never seen it yet.
I hope this info comes in handy
Last edited by JDM4mee; 11-07-2010 at 08:58 PM. Reason: type o
11-07-2010, 08:57 PM
#4
Re: Determining the failure mechanism, multiple blown headgaskets.
After seeing these videos, I am thinking that theory #3 is more than likely the correct answer.
The symptoms are consistent with that of a warped gasket surface. Initial gasket sealing, followed by failure. The cylinders cannot be cracked, as the gasket was sealed for two months. This rules that out, by the fact that if the cylinder walls were cracked, there would never have been initial seal.
I was skeptical that an engine block could warp, but after seeing it I am in agreement, as the car was badly overheated XD due to my lack of car knowledge at the time.
I think that the final solution is that the motor needs to get pulled and machined. I suspect, that as the leakage pattern has been the same, the block has been eroded due to the combustion leak, in addition to potential warpage.
And either way, new heads (Vtec F22B1) are going on. Worst case, I have a set to sell.
The symptoms are consistent with that of a warped gasket surface. Initial gasket sealing, followed by failure. The cylinders cannot be cracked, as the gasket was sealed for two months. This rules that out, by the fact that if the cylinder walls were cracked, there would never have been initial seal.
I was skeptical that an engine block could warp, but after seeing it I am in agreement, as the car was badly overheated XD due to my lack of car knowledge at the time.
I think that the final solution is that the motor needs to get pulled and machined. I suspect, that as the leakage pattern has been the same, the block has been eroded due to the combustion leak, in addition to potential warpage.
And either way, new heads (Vtec F22B1) are going on. Worst case, I have a set to sell.
11-07-2010, 11:24 PM
#5
Re: Determining the failure mechanism, multiple blown headgaskets.
A lot of the major shops actually use some kind of straight edge piece of metal plate pressed against the the head and put into a 500 degree oven to straighten out the head. Not sure if this can be done to the block as well.
11-08-2010, 12:03 AM
#6
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Re: Determining the failure mechanism, multiple blown headgaskets.
The straightening of a cylinder head by pressing against a flat surface while heating for certain amount fo time is mainly use due a bolt or bolts failing on a working engine.
Imagine a B Series engines head that's only working with the 6 of the 10 head bolts, the heat will bend that thing like butter, living it with too much warpage do fix using just a simple milling machine, it would literally cut the life out of it, by trying to level it using only that method. That's why the machine shops (some) will try to straightening first using the heating process.
As for the same process applying to a cylinder block, I have never hear of it.
Imagine a B Series engines head that's only working with the 6 of the 10 head bolts, the heat will bend that thing like butter, living it with too much warpage do fix using just a simple milling machine, it would literally cut the life out of it, by trying to level it using only that method. That's why the machine shops (some) will try to straightening first using the heating process.
As for the same process applying to a cylinder block, I have never hear of it.
11-08-2010, 08:57 AM
#7
Re: Determining the failure mechanism, multiple blown headgaskets.
Warpage is usually caused to to overheating. The metal expands more in the middle, where the heat is more concentrated, and then pulls up when it cools off. And this isn't a B series anyways, it's an F22. And the bolts are intact.
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11-08-2010, 12:23 PM
#8
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Re: Determining the failure mechanism, multiple blown headgaskets.
Thanks for the reply, but I already knew that... and I also use de B series as an example of what I seen in the past.
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