Why are you worried about tensile strength on a situated and seated o-ring in an assembled engine, after 70 hours of "curing" in 55?

Compression strength, yes.

From the Dow chart I originally posted, every o-ring is effected not just Viton.
The design feature of Dow 55 is to transform the material (every o-ring material) to reduce compression set and swell the seal (at operating temperature) to increase sealing.

Zero o-rings in a 911 air-cooled engine are under tension.....

Stop beating a dead horse.....
It only makes you look like a troll.

Because of the sharp edge from the thread of the thru-bolt.

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Precisely the reason we should list the inert alternative that birthed the mil-spec, krytox. Let people be educated fully and choose. Denying facts once they're released is Clinton-esque.

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I'm wondering what "new" facts you've offered?
The chart you've posted a half dozen times and on which you so heavily base your singular concern over, is not new. It is a chart of the research preformed by Dow before offering the product for sale.
Every engineer contemplating the use of Dow 55 has access to this research and many of the world's finest engineers evaluated the enhanced properties of the product as being beneficial.

Why do you insist on denying this "fact"?

Good stuff guys. Technical stuff is always great.

Would have never known about this without Lapkritis bringing up.

I don't deny it's beneficial in many circumstances, however, I do present that in this application where a sharp edge in the joint exists, perhaps retaining tensile strength is desirable. Reducing strength by nearly half would be detrimental.



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Your argument on tensile strength and relation to threads on the through bolts and is quite a stretch. Pun intended.

My opinion is different I suppose.

http://i458.photobucket.com/albums/q...ps15641f63.jpg

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Here we go again....................... Ugh

Great picture.
The problem is that you assume that any lubricant would have prevented damage to an an o-ring on an improperly prepared case.
The damage to the o-ring was caused (IMHO) by the fact that the through bolt washer mounting surface was apparently ignored by the "mechanic" that assembled the engine.
The mag case moves during excessive heat cycles and the movement can create an uneven sealing surface.
A proper overhaul includes the surfacing of these bosses.

http://forums.pelicanparts.com/uploa...1484335041.jpg

Lapkritis, you are absolutely correct.
We should all consider the use of new or different products such as krytox.
It may be well worth investigating the use of this product in our air-cooled engines!

But... At the same time, I also understand what Henry is saying.
The study you present from the use of Dow 55 on various materials is, no doubt important.
But, the effective loss of tensile strength, does not necessarily apply or affect our intended use of these products.

Also, there is something else that perhaps was not mentioned, or forgotten, in these recent posts.
As shown in your last picture of the red o-ring, it appears that there is little, if any, chamfer in the engine block. This, I believe is important. Assuming the same size o-ring in a block with and without chamfer, the effects will be quite different. You will likely have more force placed on the o-rings by the treads. A similar effect would occur on the other end, effectively over compressing the o-rings between the block and washers, likely resulting in premature failure as well.

Improper setup can also be the root-cause for a lot of these issues.

The purpose of DOW 55 is to swell the o-ring into a properly chamfered section.
I believe, if you don't have that chamfer setup, then you will have premature failure regardless of o-ring types and lubricants used.

Paul Icinkoff

Before this thread on sealants (one of the "sealants" in the suggested list, is a lubricant for the case thru-bolt o-rings) gets going on a hard tangent, some folks may be interested as to what's the background on this Dow 55 vs. Krytox debate

http://forums.pelicanparts.com/911-engine-rebuilding-forum/452985-your-opinion-wanted-green-bolt-through-viton-o-rings-rtv.html

And since we're rehashing stuff again, i'd like to rehash a point I made before. Krytox is a line of lubricants. When touting what's best to use, one should name the specific lubricant. In this case I believe it's GPL-207 (general purpose lubricant) that's being touted.

Yes, would be best to continue gyrations there as this is all a repeat of past discussions. GPL-207 is correct.

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A pic of a mangled o-ring is your argument?

Ed, please join us in the other thread. Let's keep this one clean. Thanks!

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The topic is sealing a Porsche engine case and what works. Not what might work....

To that end I'll state unequivocally that for over 35 years I have produce high quality Porsche engines.
Over the years, when appropriate we update our process. We even develop new products when a suitable product is not available.
15 or so years ago we were introduced to Mil Spec Dow 55 o-ring lubricant.
We began using it (Dow55) on low hour race engines to test it's suitability.
After a few hundred race hours on multiple engines, tearing down when hours dictated, we became satisfied that the product preserved the o-ring fit and flexibility better than dry, plain oil, synthetic oil and silicone grease.
After that we started assembling every engine (200+) using Dow55.
No leaks attributed to o-ring deterioration were ever observed.
No leaks attributed to o-ring deterioration was ever reported.

As soon as someone comes up with the same or similar data, I'll change our process.

There are a plethora of proven techniques and even more theories in this thread.
My goal has always been "to help the novice with advise to aid in a successful rebuild". I don't own Dow stock, I don't sell Dow 55 separately (I include it for free in our kit). If you're unsure of this or any other technique I share, you are certainly welcome to ignore it and go with the advise of a "one timer".

Henry, You need to disclaimer the use of DOW grease with the requirement of machining the case. That is not clear in this thread where hobbyists are coming for quick hit information. Given the weakening of the seal with your chosen grease, it's a HUGE omission with very real potential consequences. These readers may find information I present as valuable as well as your expertise machining cases and using a weakening grease.

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I'd take Henry's word-oh yeah, I did...through two engine builds- rather than somebody who has no visibility or credibility on his background or even his name on this forum.

I've been to Henry's shop to pick up assorted parts (gaskets, seals, head studs, sealant pack, etc) I purchased for my builds many moons ago. He was plenty busy, multiple engines in various states of process-some basic, some WOW, meaning he has a proven commodity, and isn't a flash in the pan that builds one engine every few years.

There is no OMISSION in his statements. Please stop spreading bad info, Lapkritis. Your the only one polluting this thread.

Henry's suggestions, unequivocally, result in a tight dry motor.

Unless one cannot get O-rings on without mangling them, that is.

Where is the bad info that I'm spreading exactly? Insult me all you want, I'm dealing in facts. :)

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