Which Head Gasket for me?
10-31-2003, 04:36 PM
#91
Burning Brakes
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Well it's interesting when you look at the parts list that the studs for the 944 and the 951 are the same part no for the 86 & 87 years. Then in later years, 89 the stud for the 944 shows two different part numbers and the 952 is shown with the same part number as the earlier, 86 & 87 951s and 944's. So after looking at this there may be a difference in the head studs used with the angle torque as the manual indicates Porsche changed the part number. However the Manual says to use the 90 degree method for all 944's after model year 82. Based on that I would assume all 944's including the turbo versions would use the angle torque method.
It would be good to hear from a knowledgeable factory rep on this. I did talk to PD and he said either way should work if done properly. The angle method does not necessarily mean a stud is a stretch design. It does insure that regardless of the amount of lubricant used the stud is subjected to a given tensile loading, whereas a torque only spec is subject to the use or non use of oil or lubricant on the threads, or surface friction between the nut and the washer it turns against.
It would be good to hear from a knowledgeable factory rep on this. I did talk to PD and he said either way should work if done properly. The angle method does not necessarily mean a stud is a stretch design. It does insure that regardless of the amount of lubricant used the stud is subjected to a given tensile loading, whereas a torque only spec is subject to the use or non use of oil or lubricant on the threads, or surface friction between the nut and the washer it turns against.
Last edited by dand86951; 10-31-2003 at 08:11 PM.
10-31-2003, 08:52 PM
#94
Instructor
What is the correct bore diameter to specify for the MLS gasket for a stock bore '86 951? I measured a new WFR gasket as 102mm. Cometic catalog lists a 100.5mm and a 103mm. The bore measures 100mm, so it would seem the 100.5 is the right piece.
10-31-2003, 08:57 PM
#95
Instructor
What is the correct bore diameter to specify for the MLS gasket for a stock bore '86 951? I measured a new WFR gasket as 102mm. Cometic catalog lists a 100.5mm and a 103mm. The bore measures 100mm, so it would seem the 100.5 is the right piece. Also, the catalog shows the thickness as .040. The WFR measures .045. Close enough? Cometic will make it to whatever is desired.
11-10-2003, 11:49 PM
#98
TRB0 GUY
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Originally posted by TonyG
pk951
Head gaskets almost never ever "blow" as in POP. Rather they [the failed head gaskets] start to leak out cylinder pressure into the cooling system, which slowly pushes coolant out causing the car to start to over heat.
In this case (if the head gasket didn't "blow"), you'd be left with a engine that is not over heating because of coolant being pressurized which results in it being pushed out of the cooling system and you would not be sucking in to the affected cylinder, coolant that will displace the lubricating oil, and provide you with a nice scorred cylinder wall/piston.
That's what would happen.
pk951
Head gaskets almost never ever "blow" as in POP. Rather they [the failed head gaskets] start to leak out cylinder pressure into the cooling system, which slowly pushes coolant out causing the car to start to over heat.
In this case (if the head gasket didn't "blow"), you'd be left with a engine that is not over heating because of coolant being pressurized which results in it being pushed out of the cooling system and you would not be sucking in to the affected cylinder, coolant that will displace the lubricating oil, and provide you with a nice scorred cylinder wall/piston.
That's what would happen.
11-11-2003, 12:46 AM
#99
Rennlist Junkie Forever
FSAEracer03
>>>well, head gaskets dont shoot out of their location, but they do create full separations between the cylinder and outside ( a nice bif crack) and thats whats ****s you up... so it kinda does "blow" hahaha<<<
Ha ha what? You think it's funny?
Obviously you don't have a lot of experience with these cars based on your comments.
It's not funny, and if you think it's funny then maybe you should get in with the rice burner crowd... it sounds like it's more your speed anyway.
TonyG
>>>well, head gaskets dont shoot out of their location, but they do create full separations between the cylinder and outside ( a nice bif crack) and thats whats ****s you up... so it kinda does "blow" hahaha<<<
Ha ha what? You think it's funny?
Obviously you don't have a lot of experience with these cars based on your comments.
It's not funny, and if you think it's funny then maybe you should get in with the rice burner crowd... it sounds like it's more your speed anyway.
TonyG
11-12-2003, 12:07 AM
#100
Any new data points on this?
11-12-2003, 11:35 AM
#102
Tony your saying that a bore should have a gasket that is approx 1.5mm wider all around?
Doyou have any specific info that points to why that is recomended?
Thanks!
Doyou have any specific info that points to why that is recomended?
Thanks!
11-12-2003, 11:44 AM
#103
Rennlist Junkie Forever
BrendanCampion
No, I'm saying that .5mm isn't enough (.25mm on each side).
If you have a 100mm bore and you use a101.5mm gasket (assuming that the actual ID is 101.5mm and you bore is actually 101mm), then you only have .25mm on each side of the gasket clearance to the bore.
The gasket will move a tiny bit. How much? I've not measured it, but it's located by the same dowels that the head is located by, and it will move a slight amount laterally. Will it move .25mm? Probably. This could probably be easily measured with a dial gauge with the head off, and the head gasket on the car just by pushing the head gasket back and forth, although the head in place would somewhat lock in the locating dowels further, it would still move around.
.25mm ain't much...
No, I'm saying that .5mm isn't enough (.25mm on each side).
If you have a 100mm bore and you use a101.5mm gasket (assuming that the actual ID is 101.5mm and you bore is actually 101mm), then you only have .25mm on each side of the gasket clearance to the bore.
The gasket will move a tiny bit. How much? I've not measured it, but it's located by the same dowels that the head is located by, and it will move a slight amount laterally. Will it move .25mm? Probably. This could probably be easily measured with a dial gauge with the head off, and the head gasket on the car just by pushing the head gasket back and forth, although the head in place would somewhat lock in the locating dowels further, it would still move around.
.25mm ain't much...
11-12-2003, 03:34 PM
#104
Instructor
I spoke to the tech at Cometic about this (gasket bore size relative to cylinder bore), and was told that .5mm clearance was sufficient to account for gasket movement. The 103 mm could be used too, but you'd be introducing a gap ring that isn't needed.
From examining my failed stock or WFR gaskets, the notable defect in the rings is the out-of-roundness. Its hard to determine if they also shifted. Hopefully the MLS design will be more resistant to distortion of any kind.
From examining my failed stock or WFR gaskets, the notable defect in the rings is the out-of-roundness. Its hard to determine if they also shifted. Hopefully the MLS design will be more resistant to distortion of any kind.
11-12-2003, 04:03 PM
#105
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Originally posted by BrendanCampion
Tony your saying that a bore should have a gasket that is approx 1.5mm wider all around?
Doyou have any specific info that points to why that is recomended?
Thanks!
Tony your saying that a bore should have a gasket that is approx 1.5mm wider all around?
Doyou have any specific info that points to why that is recomended?
Thanks!