Cometic MLS Gaskets - Those in the Know
06-07-2007, 12:09 PM
#46
Rennlist Member
Thread Starter
Originally Posted by GregBBRD
I thought the original tread was to share information about Cometic gaskets, not to share just the good things about Cometic gaskets. Sorry to offend you, Brendan. I misunderstood.
My beef with you, if there ever was one, is that for many people here what you say goes. Flat out. The description for that is "Gospel" So therefore you may want to be a bit more diplomatic when describing your past experiences - because when you pan something, it becomes not "Greg Said he didn't like it," it becomes "You are NOT supposed to do that on a Porsche, and you go to hell if you do," See that Change? People may not understand that many things could work outside of Anahiem that didn't inside.
You probably stopped reading what I said Gospel, but take it for what its worth.
06-07-2007, 12:25 PM
#47
Rennlist Member
Thread Starter
I took the ARPs out last night and looked at them. The have the coarse threads at the bottom for the block, then the thread ends, and there is a larger ridge that increases the diameter, and then it necks back down quickly, to a smooth profile, and then stays that way until the much finer threads at the top for the head nuts.
http://video.arp-bolts.com/catalog/ARPCatalog.pdf
One page 21 is the three different types of material that ARP sells for headstuds, it seems, and I and a few others here bought the black kind, and it has that exact lip above the low-side threads. Is that goingt to at least be better than nothing at all?
http://video.arp-bolts.com/catalog/ARPCatalog.pdf
One page 21 is the three different types of material that ARP sells for headstuds, it seems, and I and a few others here bought the black kind, and it has that exact lip above the low-side threads. Is that goingt to at least be better than nothing at all?
Originally Posted by Mike Simard
More stud babble-
It's refreshing to hear about others that have experience with aftermarket studs and have gone back to OEM ones. I used to line up with the other sheep, buy the ARP studs from Summit or Jegs and wonder to myself during assembly why these studs are a fat stick with the smallest diameter being the thread root, doesn't that screw up pre-load stretching? Well you ask others including profesional builders and many never consider studs beyond just using the 'high end good stuff'. We're all like the cows in a Larson cartoon eating grass when one of them suddenly realizes "hey! we've been eating grass!". A stud needs to have a reasonable length dedicated to stretching, not just the remaining thread minor diameter that's not within the block or nut. I've built engines with speed shop ARP studs, after some street miles they still have the same torque level on the studs but then I go to the track and have detonation problems and notice that the studs have lost 'torque'. So what happened? Someting moved, either the stuff in between the nut and stud bottom(block, head, gasket) got shorter or the stud got longer. What I suspect happens in these cases is that the stud is a certain stretching amount away from deformation and this happens during detonation hammering. Also likely with aftermarket full body studs is that the block where the main and head studs anchor is being hammered by the full shock of detonation. I've seen other engines where a chunk of block is ripped out and suspect that a proper stud would have allowed the head to lift off of the block momentarily and returned to it's original condition and clamping force, same thing applies to main bearings IMHO.
If anyone wants custom studs, ARP can make custom studs and should be able to make them with undercut bodies per your (our) drawing. They quoted me something like 1000 bucks or so for a set of head and mains which is a good deal although it will presumebly be higher for reduced body designs. Well I'm ASSuming anyway, feel free to call them and ask, they do customs all the time. No non-production fastener companies should be making studs, mine included. I'm just being the machinist equivalant of the guy who has all the screw slots pointing in the same direction for a concours show, actually worse than that, I do all this work, nobody ever sees it and those that hear about it on a forum think I'm a hack working with a Shopsmith lathe in my garage. That's understandable because a typical machine shop would probably not even know where to buy the material necessary for studs as well as the heat treatment and importance of rolled threads after heat treating.
It's refreshing to hear about others that have experience with aftermarket studs and have gone back to OEM ones. I used to line up with the other sheep, buy the ARP studs from Summit or Jegs and wonder to myself during assembly why these studs are a fat stick with the smallest diameter being the thread root, doesn't that screw up pre-load stretching? Well you ask others including profesional builders and many never consider studs beyond just using the 'high end good stuff'. We're all like the cows in a Larson cartoon eating grass when one of them suddenly realizes "hey! we've been eating grass!". A stud needs to have a reasonable length dedicated to stretching, not just the remaining thread minor diameter that's not within the block or nut. I've built engines with speed shop ARP studs, after some street miles they still have the same torque level on the studs but then I go to the track and have detonation problems and notice that the studs have lost 'torque'. So what happened? Someting moved, either the stuff in between the nut and stud bottom(block, head, gasket) got shorter or the stud got longer. What I suspect happens in these cases is that the stud is a certain stretching amount away from deformation and this happens during detonation hammering. Also likely with aftermarket full body studs is that the block where the main and head studs anchor is being hammered by the full shock of detonation. I've seen other engines where a chunk of block is ripped out and suspect that a proper stud would have allowed the head to lift off of the block momentarily and returned to it's original condition and clamping force, same thing applies to main bearings IMHO.
If anyone wants custom studs, ARP can make custom studs and should be able to make them with undercut bodies per your (our) drawing. They quoted me something like 1000 bucks or so for a set of head and mains which is a good deal although it will presumebly be higher for reduced body designs. Well I'm ASSuming anyway, feel free to call them and ask, they do customs all the time. No non-production fastener companies should be making studs, mine included. I'm just being the machinist equivalant of the guy who has all the screw slots pointing in the same direction for a concours show, actually worse than that, I do all this work, nobody ever sees it and those that hear about it on a forum think I'm a hack working with a Shopsmith lathe in my garage. That's understandable because a typical machine shop would probably not even know where to buy the material necessary for studs as well as the heat treatment and importance of rolled threads after heat treating.
06-07-2007, 02:29 PM
#49
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Another muddying-the-waters chunk from Engine-builders.com...
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...
"Don’t go by what is in the ‘book’ (repair manuals) for clamping," Chris Brown, director of specialty products for ARP explains. "Who knows where those torque specs came from?" If you’re using specialty fasteners that have much higher strength than OE fasteners, then these torque specs will have no relevance. "These specs could have been lifted from an OEM bulletin somewhere," warns Brown. "And you’ll find out pretty quickly then, if you snap a bolt or stud, that it was wrong."
Most specialty bolt manufacturers provide detailed instructions with their kits explaining how to install, and torque their bolts, as well as what type of lubrication to use. Some even include charts showing how much clamping load to use.
Very few engine builders know how much clamping load they need, says Brown. In many cases, they’ll measure the clamp load by using torque values, and this, in turn, creates some confusion. “Say you torque a 3/16˝ bolt; you can torque it to 100 ft.lbs. if you don’t put any lubricant on it because it generates so much friction. But, if you put a dab of moly lube on the threads and under the head, you may only be able to torque it to 30 ft.lbs.," Brown explains.
Some of the confusion surrounding torque and preload comes from not knowing the difference between them. Torque is just the twisting force. It’s an index number and does not equal load. You also have to compensate for the friction coefficient of the oil. Therefore, torque values should be accompanied by the specified lubricant for the most consistent results.
Carroll Smith agrees that friction plays a vital role in achieving proper stretch and clamp load. And if you use a different lubricant than the one provided by the bolt manufacturer, Smith says, "good luck." It’s critical to use the correct lube because it was designed for the specific bolt and application in many cases, especially in high performance applications. Many high performance bolt manufacturers include the lube with the bolt kit when you buy them.
"Obviously, the more slippery the lube is, for the same amount of torque you’ll stretch the bolt further, and vice versa," says Smith. "Proper lubrication of head bolts doesn’t really matter as much in a vintage 289 Ford – but if you’re assembling a true high performance engine, you’ve got some real pressure inside of those cylinders.
"If you’re running a 13:1 compression engine at 9,000 rpms, you’re trying to lift those heads right out of there. If you’re running a 9:1 engine at 4,000 rpms, you can practically hold it on with nails! A little difference is huge; the devil is in the details," Smith quips.
"Thirty weight oil (a common bolt lubricant used in many rebuilding facilities) is a little more inconsistent because it goes away fairly quickly under extreme pressure applications, like high performance engines are,” says ARP’s Brown. A 7/16˝ head bolt can, for example, generate a clamping load around 14,000 lbs. – a significant amount of stress.
Ron Hukari, a racing engineer with SPS Technologies, says, "with sealing, a very important thing for guys who aren’t necessarily building engines for NASCAR or Formula One, is getting a good, consistent product and installing it correctly. Metallurgically the yield strength of the bolt needs to be consistent. If you have a problem with heat treating and don’t get enough yield strength, when you go to tighten to a certain torque, you’ll find the bolt doesn’t have the preload you think it does and you’ll have a leak."
There are several things that affect clamp load, according to George Lorimer, a former engineer with GM’s Powertrain Fastener Lab. In an article by Lorimer posted on www.boltscience.com, he states that one of the problems with clamp load is: "the second you take your wrench off the tightened head, it starts to decrease." Furthermore he claims that head bolt clamp loads can vary up to 40 percent when torque control is used. This "relaxation" effect can vary from bolt-to-bolt, thus the need for a proper tightening strategy.
Some of the factors that Lorimer says influences the relaxation effect are: Surface finish, Temperature - high and low, Type of joint: Gasketed (soft), Material of joint (hard or soft), Combination of metals (steel/iron vs. aluminum), Initial preload, Joint strength (spring rate), Bearing area under bolt head, Vibration, External loads to the joint.
Decreasing the variation of clamp load requires a good tightening strategy. One way that has proven effective is to "cycle" the fastener. Torque cycling bolts can reduce the relaxation effect by up to 50 percent or more.
DO THE TIGHTEN UP DANCE
Torque cycling – in essence, "breaking in" the stud or bolt – helps "ease" the threads. At the microscopic level, fasteners have peaks and valleys in the threads. Thus, when torquing, you have to overcome a certain amount of friction first.
According to the experts, new fasteners have a higher friction level because they have not been burnished. New bolts need to be seasoned with the threads it goes into. After this process, the grain will compress at the surface, which reduces friction. The proper torque cycling procedure is to tighten and loosen about five or six times, but only to 50 percent of the final torque value each time.
"You stabilize the friction coefficient after repeated tightenings," explains Brown. "This, correspondingly, increases the clamp load because the bolt or stud will stretch more. You’re overcoming less friction. More of your torque value is going into stretching the fastener, less into overcoming friction," ARP’s Brown explains.
legendary engine builder Joe Mondello of Mondello Technical School in Paso Robles, CA also points out a critical but often overlooked point: "Once you torque cycle a fastener, the nuts and washers must go back to the same stud because they will be married to that particular bolt or stud. When you go ahead and torque them down after following the recommended cycling procedures, you’ll be at about the fifth cycle, and you’ll be at the maximum clamp load and maximum distribution of the bolt or stud."
Torque-to-yield bolts in OE applications are usually only used in the most critical areas like heads, rods and mains, say these experts. For the manufacturers it comes down to a cost savings issue, but that’s not the case with racers because their cost is on a smaller scale. It is a way of wringing out every last bit of clamping load out of a relatively low strength bolt.
Torque-to-angle is a better method of tightening – it’s more accurate than straight torque. With straight torque, friction impedes consistent clamp load values. So you have to overcome a certain amount of friction in order to achieve load. "Friction is very hard to predict, too, even with special lubricants to try and control it," says Brown.
Brown believes that the inconsistency of straight torque is why torque-to-angle is a better method. "With torque-to-angle, you typically have very low torque values and then a rotation through a certain angle based on the helix or thread pitch to achieve a specific amount of load," he explains.
"With our fasteners, because the strength is much higher, the idea is that we select material that will generate the correct amount of clamping load at 75 percent of the yield strength of the fastener. With torque-to-yield you’re stretching it to the point just before it breaks." The advantage of very high strength specialty fasteners is that they reduce the chance of failure by not being as close to the limits of the material, say both Brown and Smith.
"With fasteners it’s a question of knowing just a little bit," says Carroll Smith. "You don’t have to know metallurgy, but you need to know the facts." Although it wouldn’t hurt to know the metallurgy, the important thing is to know how to get the best, most consistent clamp load.
...
...
"Don’t go by what is in the ‘book’ (repair manuals) for clamping," Chris Brown, director of specialty products for ARP explains. "Who knows where those torque specs came from?" If you’re using specialty fasteners that have much higher strength than OE fasteners, then these torque specs will have no relevance. "These specs could have been lifted from an OEM bulletin somewhere," warns Brown. "And you’ll find out pretty quickly then, if you snap a bolt or stud, that it was wrong."
Most specialty bolt manufacturers provide detailed instructions with their kits explaining how to install, and torque their bolts, as well as what type of lubrication to use. Some even include charts showing how much clamping load to use.
Very few engine builders know how much clamping load they need, says Brown. In many cases, they’ll measure the clamp load by using torque values, and this, in turn, creates some confusion. “Say you torque a 3/16˝ bolt; you can torque it to 100 ft.lbs. if you don’t put any lubricant on it because it generates so much friction. But, if you put a dab of moly lube on the threads and under the head, you may only be able to torque it to 30 ft.lbs.," Brown explains.
Some of the confusion surrounding torque and preload comes from not knowing the difference between them. Torque is just the twisting force. It’s an index number and does not equal load. You also have to compensate for the friction coefficient of the oil. Therefore, torque values should be accompanied by the specified lubricant for the most consistent results.
Carroll Smith agrees that friction plays a vital role in achieving proper stretch and clamp load. And if you use a different lubricant than the one provided by the bolt manufacturer, Smith says, "good luck." It’s critical to use the correct lube because it was designed for the specific bolt and application in many cases, especially in high performance applications. Many high performance bolt manufacturers include the lube with the bolt kit when you buy them.
"Obviously, the more slippery the lube is, for the same amount of torque you’ll stretch the bolt further, and vice versa," says Smith. "Proper lubrication of head bolts doesn’t really matter as much in a vintage 289 Ford – but if you’re assembling a true high performance engine, you’ve got some real pressure inside of those cylinders.
"If you’re running a 13:1 compression engine at 9,000 rpms, you’re trying to lift those heads right out of there. If you’re running a 9:1 engine at 4,000 rpms, you can practically hold it on with nails! A little difference is huge; the devil is in the details," Smith quips.
"Thirty weight oil (a common bolt lubricant used in many rebuilding facilities) is a little more inconsistent because it goes away fairly quickly under extreme pressure applications, like high performance engines are,” says ARP’s Brown. A 7/16˝ head bolt can, for example, generate a clamping load around 14,000 lbs. – a significant amount of stress.
Ron Hukari, a racing engineer with SPS Technologies, says, "with sealing, a very important thing for guys who aren’t necessarily building engines for NASCAR or Formula One, is getting a good, consistent product and installing it correctly. Metallurgically the yield strength of the bolt needs to be consistent. If you have a problem with heat treating and don’t get enough yield strength, when you go to tighten to a certain torque, you’ll find the bolt doesn’t have the preload you think it does and you’ll have a leak."
There are several things that affect clamp load, according to George Lorimer, a former engineer with GM’s Powertrain Fastener Lab. In an article by Lorimer posted on www.boltscience.com, he states that one of the problems with clamp load is: "the second you take your wrench off the tightened head, it starts to decrease." Furthermore he claims that head bolt clamp loads can vary up to 40 percent when torque control is used. This "relaxation" effect can vary from bolt-to-bolt, thus the need for a proper tightening strategy.
Some of the factors that Lorimer says influences the relaxation effect are: Surface finish, Temperature - high and low, Type of joint: Gasketed (soft), Material of joint (hard or soft), Combination of metals (steel/iron vs. aluminum), Initial preload, Joint strength (spring rate), Bearing area under bolt head, Vibration, External loads to the joint.
Decreasing the variation of clamp load requires a good tightening strategy. One way that has proven effective is to "cycle" the fastener. Torque cycling bolts can reduce the relaxation effect by up to 50 percent or more.
DO THE TIGHTEN UP DANCE
Torque cycling – in essence, "breaking in" the stud or bolt – helps "ease" the threads. At the microscopic level, fasteners have peaks and valleys in the threads. Thus, when torquing, you have to overcome a certain amount of friction first.
According to the experts, new fasteners have a higher friction level because they have not been burnished. New bolts need to be seasoned with the threads it goes into. After this process, the grain will compress at the surface, which reduces friction. The proper torque cycling procedure is to tighten and loosen about five or six times, but only to 50 percent of the final torque value each time.
"You stabilize the friction coefficient after repeated tightenings," explains Brown. "This, correspondingly, increases the clamp load because the bolt or stud will stretch more. You’re overcoming less friction. More of your torque value is going into stretching the fastener, less into overcoming friction," ARP’s Brown explains.
legendary engine builder Joe Mondello of Mondello Technical School in Paso Robles, CA also points out a critical but often overlooked point: "Once you torque cycle a fastener, the nuts and washers must go back to the same stud because they will be married to that particular bolt or stud. When you go ahead and torque them down after following the recommended cycling procedures, you’ll be at about the fifth cycle, and you’ll be at the maximum clamp load and maximum distribution of the bolt or stud."
Torque-to-yield bolts in OE applications are usually only used in the most critical areas like heads, rods and mains, say these experts. For the manufacturers it comes down to a cost savings issue, but that’s not the case with racers because their cost is on a smaller scale. It is a way of wringing out every last bit of clamping load out of a relatively low strength bolt.
Torque-to-angle is a better method of tightening – it’s more accurate than straight torque. With straight torque, friction impedes consistent clamp load values. So you have to overcome a certain amount of friction in order to achieve load. "Friction is very hard to predict, too, even with special lubricants to try and control it," says Brown.
Brown believes that the inconsistency of straight torque is why torque-to-angle is a better method. "With torque-to-angle, you typically have very low torque values and then a rotation through a certain angle based on the helix or thread pitch to achieve a specific amount of load," he explains.
"With our fasteners, because the strength is much higher, the idea is that we select material that will generate the correct amount of clamping load at 75 percent of the yield strength of the fastener. With torque-to-yield you’re stretching it to the point just before it breaks." The advantage of very high strength specialty fasteners is that they reduce the chance of failure by not being as close to the limits of the material, say both Brown and Smith.
"With fasteners it’s a question of knowing just a little bit," says Carroll Smith. "You don’t have to know metallurgy, but you need to know the facts." Although it wouldn’t hurt to know the metallurgy, the important thing is to know how to get the best, most consistent clamp load.
06-07-2007, 02:31 PM
#50
Former Vendor
Originally Posted by BrendanC
I don't get offended. I sell stuff for a living. This thread WAS and IS for the good or bad. The seaping is a bad. But my point in contention is that there are worked and working solutions out there for this issue, and I addressed them with the surface prep links and info. Whether or not it is feasible for create a (possibly) 20ra surface on heads and block - maybe you could tell us that. While a 50ra surface is much more attainable it seems, and the sealer like hylomar (Get it, Hi-Low, Mar) can indeed make a very dry engine - Its not a band-aid - its extra insurance.
My beef with you, if there ever was one, is that for many people here what you say goes. Flat out. The description for that is "Gospel" So therefore you may want to be a bit more diplomatic when describing your past experiences - because when you pan something, it becomes not "Greg Said he didn't like it," it becomes "You are NOT supposed to do that on a Porsche, and you go to hell if you do," See that Change? People may not understand that many things could work outside of Anahiem that didn't inside.
You probably stopped reading what I said Gospel, but take it for what its worth.
My beef with you, if there ever was one, is that for many people here what you say goes. Flat out. The description for that is "Gospel" So therefore you may want to be a bit more diplomatic when describing your past experiences - because when you pan something, it becomes not "Greg Said he didn't like it," it becomes "You are NOT supposed to do that on a Porsche, and you go to hell if you do," See that Change? People may not understand that many things could work outside of Anahiem that didn't inside.
You probably stopped reading what I said Gospel, but take it for what its worth.
Another observation....not Gospel, just truth. When one disassembles a Porsche water cooled race engine and looks at the head gaskets, the black coating on the gasket has transfered to both the head, the middle layer, and the cylinder water jacket.
When one removes a Cometic gasket, the black coating is still completely stuck to the layer it was originally attached to, without any transfer. If the layers that are supposed to have the sealing stuff on them, don't transfer the layer, it would seem that perhaps this layer is not quite right, in terms of sealing...at least ot me. Looking at Cometic gaskets, I believe they leak between the layers, as much as they leak between the gasket and the head or block.
Brendan:
I never pretend to know everything. As a matter of fact, the more I know, the less I think I know. I do have the benefit of working only on Porsches for 37 years....that's all I do. I have no idea how many engines I have built in that time, but it is certainly thousands! To give you an idea of how much I do, every 928 transmission gasket set comes with two cover gaskets and you only use one or the other. I have a box with over 100 gaskets in it and I've thrown many of them away over the years.
gb
06-07-2007, 05:39 PM
#51
Former Vendor
Sorry, I had to deal with work before I finished:
So, obviously, I have a bunch of experience with Porsches and 928s. Do I know everything? Nope. Am I wrong, sometimes? Absolutely. However, I do have a fairly huge amount of "hands on" experience to draw from. So when you, Brendan, say that you have a beef that people pay attention to what I say and that influences their decisions.....what am I supposed to say? I'm sorry that this is all I do and have done for almost 40 years? I'm not going to say that. Sorry, because I've probably built more engines than you've ever actually looked at? Not going to say that. Sorry, because I have credibility because of my experience? Not going to happen.
Look, some people have obviously had great results with Cometic gaskets. I have not. People I'm in direct contact with, have not. It indeed might be the "Anaheim" problem, but I doubt that location has much to do with sealing. I believe the clue to the problem is the fact that the "black" coating on the outer layers of the gaskets doesn't seem to transfer to other pieces....I've got samples of this many times over. Certainly, one could spray the outside of the gaskets with some trick sealant, but how do you spray between the layers?
Like I said....if you can seal up your engine with clay and drywall screws....I'm happy for you and will enjoy reading about it. However, I may reserve the right to be closed minded and not try it, here. I may reserve the right to not offer it to my customers. It's not that I'm closed minded or not on the leading edge of 928 development, it's just that I'm tired of looking at heads leaking all around the edges when I use a certain product, when I can use something else that has had NO downsides.
Peace. Out.
gb
So, obviously, I have a bunch of experience with Porsches and 928s. Do I know everything? Nope. Am I wrong, sometimes? Absolutely. However, I do have a fairly huge amount of "hands on" experience to draw from. So when you, Brendan, say that you have a beef that people pay attention to what I say and that influences their decisions.....what am I supposed to say? I'm sorry that this is all I do and have done for almost 40 years? I'm not going to say that. Sorry, because I've probably built more engines than you've ever actually looked at? Not going to say that. Sorry, because I have credibility because of my experience? Not going to happen.
Look, some people have obviously had great results with Cometic gaskets. I have not. People I'm in direct contact with, have not. It indeed might be the "Anaheim" problem, but I doubt that location has much to do with sealing. I believe the clue to the problem is the fact that the "black" coating on the outer layers of the gaskets doesn't seem to transfer to other pieces....I've got samples of this many times over. Certainly, one could spray the outside of the gaskets with some trick sealant, but how do you spray between the layers?
Like I said....if you can seal up your engine with clay and drywall screws....I'm happy for you and will enjoy reading about it. However, I may reserve the right to be closed minded and not try it, here. I may reserve the right to not offer it to my customers. It's not that I'm closed minded or not on the leading edge of 928 development, it's just that I'm tired of looking at heads leaking all around the edges when I use a certain product, when I can use something else that has had NO downsides.
Peace. Out.
gb
06-08-2007, 03:26 PM
#52
Rennlist Member
Thread Starter
My simple point is that MANY people, when the surfaces are prepared correctly (I am not saying exactly that you are not), have had great success with MLS-type gaskets. When they ARE installed correctly and don't have a leak issue, then they are far superior at what they are meant to do then the matrix gaskets that are OEM for us.
The "you need a fuse" issue can be debated wildly and for weeks on end. I'd rather do it right the first time and not have to use a very expensive fuse. This is why the engine will be run with a different EFI system.
The clamping of the block is supposed to be the thing that works with the gasket to seal what needs to stay in, in.
The MAJORITY of people who have had these installed have had great success. We may have an odd-man out engine, but since they work on the 951s when people surface both the block and the head, and even install them dry, and that engine is about the same in deck design, I don't think thats the case.
Real info question here - when was the last time you installed a set? More than a year ago or less? Because ToddTremel of Green Bay actually had Cometic FIX the bossing in certain areas that was causing some leaking issue.
The "you need a fuse" issue can be debated wildly and for weeks on end. I'd rather do it right the first time and not have to use a very expensive fuse. This is why the engine will be run with a different EFI system.
The clamping of the block is supposed to be the thing that works with the gasket to seal what needs to stay in, in.
The MAJORITY of people who have had these installed have had great success. We may have an odd-man out engine, but since they work on the 951s when people surface both the block and the head, and even install them dry, and that engine is about the same in deck design, I don't think thats the case.
Real info question here - when was the last time you installed a set? More than a year ago or less? Because ToddTremel of Green Bay actually had Cometic FIX the bossing in certain areas that was causing some leaking issue.
06-08-2007, 03:33 PM
#53
Administrator - "Tyson"
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Originally Posted by BrendanC
Real info question here - when was the last time you installed a set? More than a year ago or less? Because ToddTremel of Green Bay actually had Cometic FIX the bossing in certain areas that was causing some leaking issue.
I'm not sure Cometic changed the "off the shelf" gasket to Todd's specifications.
06-08-2007, 07:26 PM
#54
Former Vendor
All of the gaskets that I've used have been the "updated" style, with the improved "embossing"....according to Cometic. Perhaps we should see how many people are driving 928s around on Cometic gaskets, that don't leak.....not how many people have a 928 engine sitting on a stand that has Cometics, not how many people have a set of Cometics sitting on a shelf waiting for an engine to be installed on, not some "dream-mobile" that gets started up so everyone can go "wow", but never goes more than a block or two. In short, just how many sets are on engines that are used in anger? How many miles have the gaskets been used? How many days at the track?
I've personally installed 5 sets and they all leak/seap. Two sets are still on engines of those five. Both of those sets I added a "anti-leak additive" to see if they would quit leaking....and they definately got better. Mark Anderson has the two customers I mentioned that installed Cometics and they leak into the combustion chambers, so they are sitting waiting to be disassembled. That's 7 leakers out of 7 from here.....not a great start.
Again...I think the problem is not the gaskets themselves or the surface finish, but rather the fact that the black layer doesn't seem to do its intended job....which is to seal to the head, block, and the inner gasket piece. Again....the gaskets that Porsche uses in the water cooled race engines transfer this black layer all over the other parts.
gb
I've personally installed 5 sets and they all leak/seap. Two sets are still on engines of those five. Both of those sets I added a "anti-leak additive" to see if they would quit leaking....and they definately got better. Mark Anderson has the two customers I mentioned that installed Cometics and they leak into the combustion chambers, so they are sitting waiting to be disassembled. That's 7 leakers out of 7 from here.....not a great start.
Again...I think the problem is not the gaskets themselves or the surface finish, but rather the fact that the black layer doesn't seem to do its intended job....which is to seal to the head, block, and the inner gasket piece. Again....the gaskets that Porsche uses in the water cooled race engines transfer this black layer all over the other parts.
gb
06-08-2007, 09:23 PM
#55
Administrator - "Tyson"
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Originally Posted by GregBBRD
Perhaps we should see how many people are driving 928s around on Cometic gaskets, that don't leak
His previous motor with his self embosses Cometic was in there at least that long.
Tim Murphy's motor was assembled in 2004-2005. Was a daily driver until last fall (he started taking it apart for no good reason). Did one track weekend etc... no leaks.
We were all pretty sure Tim's would leak due to the simple fact he put it together (just kidding Tim).
So there are two for the database. I am NOT taking sides and trying to say "see Greg, they work". I'm simply supplying the data from cars I know about.
FWIW when I was putting the heads back on my 81 in preparation for a supercharger, I asked Tim about getting a set of Comecs for my motor. He told me not to bother, the stock units work just fine.
06-08-2007, 09:28 PM
#56
Rennlist Member
Thread Starter
Originally Posted by Hacker-Pschorr
IIRC Todd had some custom made for the 5.0 motors & he embosses his own for the larger bore engines.
I'm not sure Cometic changed the "off the shelf" gasket to Todd's specifications.
I'm not sure Cometic changed the "off the shelf" gasket to Todd's specifications.
06-08-2007, 09:30 PM
#57
Rennlist Member
Thread Starter
Originally Posted by GregBBRD
All of the gaskets that I've used have been the "updated" style, with the improved "embossing"....according to Cometic. Perhaps we should see how many people are driving 928s around on Cometic gaskets, that don't leak.....not how many people have a 928 engine sitting on a stand that has Cometics, not how many people have a set of Cometics sitting on a shelf waiting for an engine to be installed on, not some "dream-mobile" that gets started up so everyone can go "wow", but never goes more than a block or two. In short, just how many sets are on engines that are used in anger? How many miles have the gaskets been used? How many days at the track?
I've personally installed 5 sets and they all leak/seap. Two sets are still on engines of those five. Both of those sets I added a "anti-leak additive" to see if they would quit leaking....and they definately got better. Mark Anderson has the two customers I mentioned that installed Cometics and they leak into the combustion chambers, so they are sitting waiting to be disassembled. That's 7 leakers out of 7 from here.....not a great start.
Again...I think the problem is not the gaskets themselves or the surface finish, but rather the fact that the black layer doesn't seem to do its intended job....which is to seal to the head, block, and the inner gasket piece. Again....the gaskets that Porsche uses in the water cooled race engines transfer this black layer all over the other parts.
gb
I've personally installed 5 sets and they all leak/seap. Two sets are still on engines of those five. Both of those sets I added a "anti-leak additive" to see if they would quit leaking....and they definately got better. Mark Anderson has the two customers I mentioned that installed Cometics and they leak into the combustion chambers, so they are sitting waiting to be disassembled. That's 7 leakers out of 7 from here.....not a great start.
Again...I think the problem is not the gaskets themselves or the surface finish, but rather the fact that the black layer doesn't seem to do its intended job....which is to seal to the head, block, and the inner gasket piece. Again....the gaskets that Porsche uses in the water cooled race engines transfer this black layer all over the other parts.
gb
06-08-2007, 10:22 PM
#58
Rennlist Member
Stock headgaskets and stock studs or bolts....one of the keys to the success of the most powerful 928 NA engine design ever assembled.....tim, louis, don and others....
If you want to go break new ground, you need to "fully" understand the properties of the factory studs and bolts, and the gasket properties, materials, etc. And then go look for areas of improvement. Pull the studs/bolts on a tinius O and review the curves, understand the properties of the block as it heats and cools, etc. And work with a supplier to acheive what you consider the weakness of the stock parts, or what you have identified as the problem to solve.
BTW, what is the problem you are trying to solve???
Marc
If you want to go break new ground, you need to "fully" understand the properties of the factory studs and bolts, and the gasket properties, materials, etc. And then go look for areas of improvement. Pull the studs/bolts on a tinius O and review the curves, understand the properties of the block as it heats and cools, etc. And work with a supplier to acheive what you consider the weakness of the stock parts, or what you have identified as the problem to solve.
BTW, what is the problem you are trying to solve???
Marc
06-09-2007, 12:59 AM
#59
Former Vendor
Originally Posted by BrendanC
Do I have permission to word-for-word copy and paste this above info and send it to Cometic and see what they say? Hey, maybe MLS isn't the problem - maybe Cometic is.
gb
06-09-2007, 01:03 AM
#60
Former Vendor
Originally Posted by marc@DEVEK
BTW, what is the problem you are trying to solve???
Marc
gb