Repeated Blown Head Gasket
10-05-2007, 01:37 AM
#16
Join the club, I had the same problem. Never had a problem with blown head gaskets, then had the head off a couple times to deal with other issues. I think taking the head off and putting it back on so many times may have led me to yield the head studs upon retorquing them. I'm now in the process of swapping all my parts onto another bottom end.
You may want to look into aftermarket head studs, but I understand it's a pain in the butt to remove the original ones.
You may want to look into aftermarket head studs, but I understand it's a pain in the butt to remove the original ones.
10-05-2007, 07:43 AM
#19
HMMMMMMM.
Let's move away from mechanical cause now.
Always #4?
The car has stock management?
Any work to the intake manifold?
What fuel do you use?
How much alcohol is in the fuel out there in hippierado currently?
How old is the fuel regulator?
Have you tested static fuel pressure???
You didn't do something suicidal like remove the vac signal from the fuel reg., did you?
Let's move away from mechanical cause now.
Always #4?
The car has stock management?
Any work to the intake manifold?
What fuel do you use?
How much alcohol is in the fuel out there in hippierado currently?
How old is the fuel regulator?
Have you tested static fuel pressure???
You didn't do something suicidal like remove the vac signal from the fuel reg., did you?
10-05-2007, 08:41 PM
#20
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Okay. Let's re-hash information contained in earlier posts in this thread shall we...
NO. Not always #4. Inconsistencies with this issue are bleeding me. First #4. Then #1.
Car is BONE STOCK. NO mods besides a MSD coil.
Last tank was 91 octane (premium) no ethanol until next month or so.
FPR is fine. I have tested it static, with the car running, I have pulled a vac on it and it is fine. Hg of vac are questionable (only about 5 hg at idle last time it was running). Fuel pressure is subsequently a little high at ~2.7 bar. The car was failing emissions by running rich last month, but that is neither here not there, becasue a rich mixture did not cause this.
Everything is connected properly - I work on these cars for a living. I've also R&R'd the head a few times before so I know howit all goes back together.
Non-mechanical issues do not seem to be causing this.
I am leaning more and more toward replacing the studs. Took some very exacting measurements of the studs today and they are all between 74.5mm and 75mm. This may indicate that they have stretched slightly. I wouldn't do raceware, I'd retain the stock hardware, but this will probably be the next step.
Not even other *extremely experienced* Porsche mechanics can wrap their heads around what is going on here.
NO. Not always #4. Inconsistencies with this issue are bleeding me. First #4. Then #1.
Car is BONE STOCK. NO mods besides a MSD coil.
Last tank was 91 octane (premium) no ethanol until next month or so.
FPR is fine. I have tested it static, with the car running, I have pulled a vac on it and it is fine. Hg of vac are questionable (only about 5 hg at idle last time it was running). Fuel pressure is subsequently a little high at ~2.7 bar. The car was failing emissions by running rich last month, but that is neither here not there, becasue a rich mixture did not cause this.
Everything is connected properly - I work on these cars for a living. I've also R&R'd the head a few times before so I know howit all goes back together.
Non-mechanical issues do not seem to be causing this.
I am leaning more and more toward replacing the studs. Took some very exacting measurements of the studs today and they are all between 74.5mm and 75mm. This may indicate that they have stretched slightly. I wouldn't do raceware, I'd retain the stock hardware, but this will probably be the next step.
Not even other *extremely experienced* Porsche mechanics can wrap their heads around what is going on here.
10-05-2007, 10:23 PM
#21
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I would not overlook this. It could be a clue. A bad sensor (e.g. AFM) or mechanics part (FPR, injector) could make it rich (or appear rich) off boost, and lean on boost. When you get it back together, I'd start by finding and addressing the tuning issue before getting on the boost. Also, is the combustion chamber of the n/a head the same as the turbo -- i.e., are you sure you're compression ratio is ok?
10-06-2007, 08:18 AM
#22
Burning Brakes
Are you sure the head and block are flat? Are you doing the 90degree and then 90 degree tightening sequence?
Its unlikely the studs are a problem, as you wouldn't be able to build much torque. If the threads in the block have stripped, you wouldn't be able to build much torque either. When you torqued did it feel right? the last 90 tightening is a very high torque.
Don't think about Raceware, you don't need them, they are a pain and won't solve a problem.
Its unlikely the studs are a problem, as you wouldn't be able to build much torque. If the threads in the block have stripped, you wouldn't be able to build much torque either. When you torqued did it feel right? the last 90 tightening is a very high torque.
Don't think about Raceware, you don't need them, they are a pain and won't solve a problem.
10-06-2007, 08:36 AM
#23
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- may want to find a turbo head
- must replace 02 sensor if you have not- antifreeze will kill them every time
-i would replace the head studs after being stretched four times w/ gasket replacements
- must replace 02 sensor if you have not- antifreeze will kill them every time
-i would replace the head studs after being stretched four times w/ gasket replacements
10-06-2007, 11:10 AM
#24
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I can count the times I have got on the boost on this car on one hand. The car never revved above 3K this last time it blew. Litearally drove it ~6 miles on surface streets after the last gasket replacement. If this was happening on boost, I'd have a lot more options, but idling, coming up to temp at an intersection...
AFM may be an issue (rich running condition) because it has been f****d with by a PO. I don't know how but they broke the cover off of it - I assume to try and do something stupid...
I have taken a GENUINE SE to this block and head in multiple places - across each cylinder, across all cylinders, at this angle and that angle. Never could I get the thinnest (.003") feeler gauge under the SE. Same holds true for the head.
15 ft/lbs torque for first stage, 90 degree turn, then another 90 degree turn for final stage. Stud threads lightly oiled with engine oil. Final torque was tight, starts to get tough to crank that bar when you get close to the final position. So in other words, it seemed as though it had enough clamping force. Only thing I didn't do was wait between stages.
The NA 8-valve head and turbo head are IDENTICAL aside from the ceramic coating in the exhaust ports. The coating may make a difference on the limit when the boost is on, but at this point, the NA head is just fine. I will not be puddle-welding the original or sourcing another at this point in time. The C/R is determined by the piston design on these engines - turbo's are dished, NAs are not. Heads are the same.
O2 sensor has been replaced since the #4 cyl. failure and I have only been using water in it lately until I could assure myself it was okay. Coolant gets pricey and so does oil wehn the two keep mixing...
Next step is the head studs. Nobody takes issue with the 75mm measurement? I am considering it a distinct possibilty that the studs may be fatigued and stretching MORE as the temp comes up. Cold may be only an addt'l mm, but warm may be 1.5 or 2mm?
AFM may be an issue (rich running condition) because it has been f****d with by a PO. I don't know how but they broke the cover off of it - I assume to try and do something stupid...
I have taken a GENUINE SE to this block and head in multiple places - across each cylinder, across all cylinders, at this angle and that angle. Never could I get the thinnest (.003") feeler gauge under the SE. Same holds true for the head.
15 ft/lbs torque for first stage, 90 degree turn, then another 90 degree turn for final stage. Stud threads lightly oiled with engine oil. Final torque was tight, starts to get tough to crank that bar when you get close to the final position. So in other words, it seemed as though it had enough clamping force. Only thing I didn't do was wait between stages.
The NA 8-valve head and turbo head are IDENTICAL aside from the ceramic coating in the exhaust ports. The coating may make a difference on the limit when the boost is on, but at this point, the NA head is just fine. I will not be puddle-welding the original or sourcing another at this point in time. The C/R is determined by the piston design on these engines - turbo's are dished, NAs are not. Heads are the same.
O2 sensor has been replaced since the #4 cyl. failure and I have only been using water in it lately until I could assure myself it was okay. Coolant gets pricey and so does oil wehn the two keep mixing...
Next step is the head studs. Nobody takes issue with the 75mm measurement? I am considering it a distinct possibilty that the studs may be fatigued and stretching MORE as the temp comes up. Cold may be only an addt'l mm, but warm may be 1.5 or 2mm?
10-06-2007, 12:02 PM
#25
I have two headstuds in my toolbox with permanently elongated threads. I bet you've got the same issue. The studs are a serious PIA to get out, but I'd switch to Racewares or ARPs if I were you.
The spec you're using doesn't measure torque. The old spec used to...I'd bet you've got a couple of studs not holding their designed clamping force.
The spec you're using doesn't measure torque. The old spec used to...I'd bet you've got a couple of studs not holding their designed clamping force.
10-06-2007, 12:54 PM
#26
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I have always heard only re use head studs 2-3 times MAX.
BUT, I see Ben's point that with no or very few boost runs, physical head lift/shift is probably not the issue. This sounds like a fuel/lean issue especially since the po might have messed with the AFM and could have turned the dial in there the wrong way and leaned it out on idle???
Not on the boost much would also eliminate the FPR being the culprit also, right?
BUT, I see Ben's point that with no or very few boost runs, physical head lift/shift is probably not the issue. This sounds like a fuel/lean issue especially since the po might have messed with the AFM and could have turned the dial in there the wrong way and leaned it out on idle???
Not on the boost much would also eliminate the FPR being the culprit also, right?
10-06-2007, 01:08 PM
#27
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Oh.... I seeeeee. Are you absolutely sure its the head gasket, and not another mechanical failure -- cracks/leaks in bores, head or turbo?
10-06-2007, 01:16 PM
#28
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First, thanks for all of the replies.
Absolutley the HG. I have THOROUGHLY inspected the cylinders for cracks and everything looks just fine. Again, head was basically an "off-the-shelf" head from my boss which had been removed, inspected, deemed good (was also taken off of a running engine w/ a rod knock), cleaned, new valve guides installed and put on the shelf. No signs point to the head as being suspect at this point.
And not the turbo because I had water on top of #1 (this time) and #4 (last time) pistons. The car also ran at what seemed like 25% power after the smoke came on.
Absolutley the HG. I have THOROUGHLY inspected the cylinders for cracks and everything looks just fine. Again, head was basically an "off-the-shelf" head from my boss which had been removed, inspected, deemed good (was also taken off of a running engine w/ a rod knock), cleaned, new valve guides installed and put on the shelf. No signs point to the head as being suspect at this point.
And not the turbo because I had water on top of #1 (this time) and #4 (last time) pistons. The car also ran at what seemed like 25% power after the smoke came on.
10-06-2007, 01:21 PM
#29
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I have always heard only re use head studs 2-3 times MAX.
BUT, I see Ben's point that with no or very few boost runs, physical head lift/shift is probably not the issue. This sounds like a fuel/lean issue especially since the po might have messed with the AFM and could have turned the dial in there the wrong way and leaned it out on idle???
Not on the boost much would also eliminate the FPR being the culprit also, right?
BUT, I see Ben's point that with no or very few boost runs, physical head lift/shift is probably not the issue. This sounds like a fuel/lean issue especially since the po might have messed with the AFM and could have turned the dial in there the wrong way and leaned it out on idle???
Not on the boost much would also eliminate the FPR being the culprit also, right?
10-06-2007, 02:00 PM
#30
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I wish it had been running lean at ldle. Failed HCs and CO the past two times, only HCs the very first test. I would lean more toward the DAPO turned the dial to richen the fuel mixture. I don't know how to do that on these AFMs, but know how to do it with a Nissan Z AFM which uses the same principle.