I have been following this thread with considerable interest as my engine rebuilding is still ahead of me. Thanks to all, especially Henry for sharing their knowledge.

So I have a brand new 1988 Carrera engine case, no serial number, never used that will be the basis for my build. I checked it for the chamfer that is referred to and was surprised that only one side (passenger side) had the chamfers and the other did not. I guess I figured since there are O rings on both sides, both ought to have the chamfer.

I can't believe that the factory was that forgetful since they are pretty precise about most things....so, what gives? Is the intent to use beveled washers on one side and the chamfer on the case on the other side?

Seems odd...

Dennis

Dir sir (mr self proclaimed expert on everything o-ring and lubricant related),

Please explain to the masses, that you have now effectively stirred up, exactly how tensile strength comes into play on an o-ring that has been trapped inside a confined space once everything is sealed/tightened up.

Please provide some proof that tensile strength is the mode of failure once the o-rings are installed in an engine.

I'm sure that you have detailed reports showing that tensile strength is the only property that people should consider with these o-rings. Please "share" with us "lesser folks" than yourself.

Sure. Let's use the example of a stick of butter. At room temp you have soft, weak butter. Place a stick right from the fridge next to it and note how relatively strong it is. Now apply pressure to each equally in your hand and notice how the soft butter fails to hold shape and squeezes between your fingers and the cold butter holds shape with only indentation (same pressure for both sticks). This same example can be applied to Viton seals in this example when one is weaker than the other such as is the case when you use a grease that weakens the seal such as the Dow 55. The space is not confined in a perfectly sealed space where you could argue hydraulics. There is a gap between the bolt and the case where the seal is unsupported and sharp threads on the threaded end. When the seal fails to hold shape like a weak stick of butter it will tear and fall into this space partially. You see this all the time when you take these apart... my engine had a bunch in this condition where the ring split into two donuts. When they fail like this with a weak ring you'll develop oil leaks.

I don't get your attitude with this last statement. We're all equal here and I claim no high ground over others. Detailed reports on the importance of seal strength? Get real. Why are people using Viton in the first place over the weak blue seals? The answer is obvious. Strength is important as is longevity of the material service life.

The Viton rings are far stronger than they need to be to do the job in my opinion. A loss of some strength seems negligible, especially in a compressed state. As far as attitude Andy, your condescending nature has a way. And instead of private messages, which you seem to be fond of, lets keep the communication out in the open for all to see.

It may seem condescending if you try to tell me off and it doesn't work out for you. I understand - maybe the first shot fired when you decided to show me a properly cleaned engine in response to my photos showing you are wrong about the chamfer was in jest and I missed it. Otherwise it looks like you attack when you're proven wrong. That's all you between the ears and has nothing to do with me.

Please enlighten us on how "TENSILE STRENGTH" plays into this. If your o-rings are not constrained by the bolt/washer/case, perhaps you need to "do your homework" on tightening torques.

I understand that upon dis-assembly, many of these o-rings appear torn (even on never-before-rebuilt engines). More than likely, the tearing occurs when dis-assembling (after the o-ring has stuck to the bolt/washer/case and then is disturbed after service.

Most of us REPLACE these o-rings when they are disturbed. If they are installed properly without cutting/pinching them, they will last for a very long time. Tensile strength does not come into play unless you try to stretch them.


The o-rings are compressed when installed (under compressive loads not tensile loads).


I still have not seen where you "Prove" that one lubricant is better than another. This is a silly thread and you can believe (wrongly) what you want.



To the original poster, it's not right to have o-ring squeeze out on these. They can be replaced on one bolt at a time. Try not to turn the bolt or washer, but turn the nut only when tightening. A small chamfer on the case hole can help more easily seat the o-ring. Use a light coat of lubricant of your choice. Good luck!

The gap exists by design under the washer where the ring creates the seal. Technique will not change this and make the gap disappear.

Tensile strength is measured in the same way as resistance to tearing which we can agree is the reason for the stronger seals. This makes the value important; we all want strong seals so why knowingly weaken them? That's the question I ask for those of you who fight the information presented here. There's no good reason to knowingly weaken your seals other than because Henry does it. Think about how absolutely silly and cute that looks to an outsider. Free education:

http://en.m.wikipedia.org/wiki/Tear_resistance

You're missing some knowledge here on what these seals do. The engine case when heated will grow in width at a different rate than the case fastener due to good old fashioned thermal expansion. The oring is used to maintain the seal between the case and the fastener due to those different thermal expansion rates. This is not a static joint. It will be constantly loading and unloading with heat cycles. This loading and unloading would have the effect of squeezing the butter and releasing the butter, squeezing the butter and releasing the butter (imagine the butter had elastic deformation properties for a moment). This continuous action is the reason you need a strong seal resistant to tearing which is the same test as tensile strength.

Wrongly? I've presented spec sheets from the manufacturer on negative effects of DC 55 on seal strength. That supports discontinuing the use for reasonable folks when inert alternatives exist.

For the sake of the original intent of this thread, I abstain from further comment involving Andy. Fact is, unless you're really lucky, Viton O-rings need a chamfer in the case as well as the washer. You can use all the lube you like but if there isn't room for the O-ring it will squeeze out. Consider that if the O-ring doesn't seat with the magic lube mentioned and does squeeze out, the engine must be FULLY disassembled to address the screw-up. The bolts will not come out of the case without removing the cylinders so why in hell would anyone take that chance?

Andrew, making friends again I see. You are abrasive but not unique.
You're very much like the sports fan, sitting in the third row yelling at a star player claiming to anyone who will listen that "I can do better than that".
Of course no one is listening and in your arrogance you miss the fact that you're not even in the game.
The sad part is that while you're jumping up and down trying to be noticed, you're ruining the game for everyone else.

Attacking the messenger doesn't change that the grease in the discussion is a poor choice. I'll save my clowning on your guys for another time.

The folks who are spending this thread arguing about who is smarter than the other, will you please take it offline, if possible off planet. It is not helpful.

I remain interested as to the manner in which Porsche intended to do the O rings.....I checked my "scrap" engine case which is a 930/03 (3 litre Euro) and it is chamfered the same way as my new Carrera case. Drivers side is square cut, passenger side is chamfered.

Just trying to learn why Porsche would do that.

Thanks

Dennis

Oh no another wwest type of character.

It's an ongoing question that I don't think anyone has had an answer to so far, this thread and many more. I think the non-chamfered side would be the bolt head end, using the old softer O-rings. The chamfered side would be for the nut end of the bolt so the O-ring has somewhere to go when compressed with a moving nut and washer.

When I did my SC, the nut end is what failed not the bolt head end but I put the nut end on the non-chamfered case. I can see how some people might get away with the O-ring mashing up into the threads of the nut end and finding some success but it seems risky to me knowing that a simple case chamfer solves the problem all together.

It is quite often difficult if not impossible to ascertain "why" a company might do one thing and ignore it in the same situation elsewhere.

In these situations I tend to minimize the value of "why" given it's impossible to know for sure and deal with the "what" instead.
What we know is that they chamfered one side to promote proper o-ring seating and the same issues should apply to the other side as well.
Chamfering a case that has no chamfer has no down side.


As for the Dow55 compatibility question:
Some experts in the field of Viton feel it is compatible giving it combination their highest rating.

Elastomers compatibility with chemicals starting with D

http://forums.pelicanparts.com/uploa...1376321947.jpg

Thanks Henry, and yes, the mysterious workings of corporations are often lost in legend and what have you. I will chamfer the holes, does not look too hard with the tool as was shown.

When I get that far I'll get all the materials and follow the best practice I can find.

Thanks again

Dennis

Another page for the three ring binder. Thanks!

I don't think Dow would even recommend against the combination but they do publish (the manufacturer, not some retailer) data showing a huge loss of strength. Can you get away with that loss? Apparently so for awhile. Some may find that acceptable, and that's their right to choose. That doesn't mean they should attempt to suppress the info and be belligerent when someone suggests alternatives.

A company (PSP Global) who's specialty is solving sealing problems for original equipment manufacturers interpreted the same data as Andrew and more, with a different conclusion and Andrew would have you believe that his conclusion carries more weight.

Third row heckling at it's best.......once again, why the confrontation?
BTW: Jim was not attacking you, he was making a rather astute observation.
Noise quite often obscures the value of a specific discussion.

You don't need my conclusion when the fact of measurement from the manufacturer is indisputable. Do you question that this company Dow which is a behemoth with a legacy of invention and their specially trained and experienced engineers that thoroughly test and rate their own product made a mistake and PSP rinky dink corrected them? Keep dreaming. You can spin it anyway you want but that grease you use weakens the seal and that's not an opinion or conclusion. It's a fact sheet from the manufacturer.
Inert alternative:
"Introduction to Krytox® Lubricants
Discovered in 1959, the polymer that would become known worldwide as DuPont™ Krytox® showed remarkable thermal and oxidative stability.Potential uses envisioned then included lubricant for the MACH 3+ turbine engine, hydraulic oil, rocket gear box lubricant, and even gyroscope oil.
In 1963, Krytox® oil was used in a GE engine test for the supersonic transport aircraft.In 1964, new Krytox® PFPE-based grease formulations were developed jointly with the US Navy and the Air Force, resulting in military specification MIL-G-27617, which was developed specifically to cover Krytox®.The first commercial sales of Krytox® were for non-flammable lubricants for the Apollo space program in 1965.
Prior to 1981, the only commercially available Krytox® lubricants were aerospace oil and greases.Since then, PFPE-based oils and greases have been adopted across a very wide range of industries and applications.There are PFPE oils and greases for industrial operations, vacuum pump fluids, incidental food contact, automotive uses, reactive gas, and of course, military applications — to name just a few.
Today, of course, it’s our well-known trademark for high performance synthetic lubricants used for a variety of applications.Krytox® oils are made from only fluorine, carbon, and oxygen — a mixture of compounds collectively known by many names — including perfluoropolyether (PFPE), perfluoroalkylether (PFAE), and perfluoropolyalkylether (PFPAE).Krytox® perfluorinated oils and greases deliver high performance, perform at wide temperature ranges, and provide superior quality lubrication under extreme conditions in comparison to hydrocarbon alternatives.And, with a global distribution network and world-class technical service, Krytox® is the lubricant of choice for extreme conditions and extreme performance.
The use of PTFE as a thickener provides superior chemical and thermal stability to all Krytox® grease product lines.Many greases are also available with additional anti-wear and anti-corrosion additives to further boost performance in critical operations.
Krytox® performance lubricants provide superior performance and extended life as lubricants, sealants and dielectrics...
Key Benefits
The key benefits of Krytox® lubricants include:
<DIR>• Extreme temperature stability, with operating ranges from –75 °C up to 350 °C (–103 °F up to 662 °F) and as high as 400 °C (752 °F) with appropriate metallurgy
• Longer lasting lubricant life
• Decreased equipment failure and maintenance: warranty claims and replacement costs may be reduced
• Increased profits: reduced downtime and maintenance costs
• Odorless and colorless
• Inert, nontoxic, and non-flammable
• Stable in 100% liquid or gaseous oxygen environment
• Global distribution
• World-class technical service
• Chemical, biological, and environmental inertness
• Non-toxic and silicone-free formulation
• No hazardous VOC materials or chlorine content
• Non-hazardous to the atmosphere or ozone layer
• Smaller environmental footprint"

Accessed 8/12/2013; Source:
</DIR>http://www2.dupont.com/Lubricants/en_US/assets/downloads/Krytox_Overview_LowRes_H-58505-5.pdf

??