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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Your bad info is stating Dow 55 is bad for Viton o-rings, and that Henry is omitting inportant info in his reccos. You post a chart from another manufacturer dealing w/tensile strength, when that is a non-issue in compression of an o-ring.

I'm done with this, and Henry certainly can speak for himself. Many, many here have benefited from Henry's advice, and I presume many more will in the future.

You, have NO credentials here to justify anyone heeding your warnings.

I used Dow 55 on Viton packings even aware of the loss of tensile strength because the packing in use of sealing through bolts is under a compressive stress.

You're a bit crossed up on your facts.

Facts:

1) The chart isn't from another manufacturer. It's from DOW... Who manufactures DC55. Go figure!
2) DC55 reduces tensile strength of viton by nearly 50%.
3) DuPont Krytox GPL-207 is inert and birthed the mil spec.
4) This information wasn't provided in this forum until I brought it up. This is then "new" information as of nearly 3yrs ago now.
5) The sharp edge of the thread on the bolt is present in the joint, even with chamfering of the case.
6) Henry, and this thread, recommend DC55 without mentioning the requirement of machining the case. (Opinion alert: I believe this fact is a problem).
7) Krytox GPL-207 which I suggest as alternative and doesn't reduce the strength of the o-ring.

If you don't find use in facts it doesn't mean others won't. Some people still voted for Clinton after all.



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Oh wow, you all of a sudden convinced me you're the person to listen to. :rolleyes: You're the new expert here. :rolleyes:

Lapkritis,
A small chamfer on the block keeps the o-ring from being forced/crushed into the threads by the chamfered washer. AND it can also help to prevent the o-ring from being crushed by the washer, causing it to come out the side as seen in the other thread "Your opinion wanted. Green bolt through viton o-rings with rtv. The o-ring has a tendency to walk itself out; this helps keep it in place.

I too have used Henry's sealant methods for rebuilding my own engine.
I really appreciate the fact that he shares, what I would consider, trade secrets.

The fact is, most of us folks on this forum, are newb's at this.
If Henry said, "Ya, just use some peanut butter instead". LOL!
A lot of us would probably say "Oh wow! So what brand should we use!"
No questions asked!

Henry has a lot of experience, and most of us look to that.
We can't afford to necessarily try new ways to do things.
We just want to get it done right the first time.
It might sound pathetic, but it's a fact.

i read this thread , and other threads. I thought about it. And used my experience to conclude the case chamfer is critical for success.

Easy to do with a chamfer bit and a hand drill. This should be done.

At this point in time, I'd think anyone looking here would get the idea that the chamfer on the case, combined with the factory washer with the chamfer is the right way to go.

I know the o-ring is in compression when the through bolt is torqued. Swelling to better fit a proper double chamfered joint is good. Especially because the swelling occurs in time, after the joint is torqued and the washer is in direct contact with the case, without o-ring material crushed in the joint.

Quick hits guys such as yourself are the ones who will benefit from using the list after it's updated. It's inadequate now because it lists a grease that weakens tensile strength but fails to list the requirement of machining the case. Imagine mixing the worst tensile strength grease/seal in the sharpest joint... Then imagine the strongest grease/seal in the smoothest joint. Only the first condition includes DC55.

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But now the list is complete:

1) you should chamfer your through bolt holes, if they were not installed previously

2) Dow 55 will work well with green viton o-rings when mated with chamfered holes.

3) green viton through bolt o-rings still seem to be the best.

So we have updated, and captured the knowledge! 🍻

4) Krytox GPL-207 offers roughly double the tensile strength over DC55.

Then you're done.

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I agree. Done!!

😀

As the father of this thread (OP) I would ask you to leave political references for off topic. This is about engine sealants that are empirically proven to work. To that end, I've put the advice Henry has provided here in practice on quite a few engines. They don't leak. Your histrionic, near nonsensical posts on "omitted" information are just cluttering up my thread. Stop.


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Hello,

I'm rebuilding my 964 engine, can anyone tell me if the DC55 can be used on the 'red' through bolt o-rings that are included in factory Porsche gasket sets? I'm not sure if they are Viton.
Also, I have purchased Henry's kit, are any of the products suitable for use on the factory Porsche 'black' cylinder base o-rings or are these only installed dry?

Thanks in advance.

I don't recommend installing any o-ring dry. Others will chime in on whether this lube or that lube is best, but the important thing a lube does is allowing the o-ring to settle in its place without pinching or distorting allowing unequal sealing between the surfaces it mates to. Also, not a lot of lube is necessary. Just enough to make the surfaces glassy in appearance will suffice.

On VW AC engines I've done dry with hit or miss results, same for oil.
Then switched to teflon pipe compound, worked, but I never liked it.
Once I switched to the Dow product I never looked back on both Porsche and VW.

Sealant on an O-ring is a big no-no, don't get me started on RTV....

The one big trick is to deburr all holes and surfaces, one nick and you will have a leaky O-ring.

With regard to the red o-rings, I would echo the warning by DOW itself against use of DOW corning 55 molykote.

From DOW:

Source is spec sheet on product site:
http://www.dowcorning.com/applications/search/default.aspx?R=392EN


No compatability concerns with Krytox... It's inert.

Strength of Materials........
 

Lapkritis,

Not sure if you are a technical guy or what, but you seem not to understand what is tensile stress or strength. The o-rings at the thru-bolts don't experience tensile stress. They are under compression. Yet, you keep telling us about tensile stress. Hope you have some accredited units in Strength of Materials Testing. Some of us here have. A guy read a technical article and suddenly becomes a guru! Research the technical definition of tensile stress in your Chemical or Mechanical Engineering Handbook.

Tony

I haven't until now typed the phrase "tensile stress", nor discussed it. The simple metric relation to tear resistance is the basis of the discussion. Put a sharp edge from the bolt in and that's the point. Pun intended.

We have used Dow 55 o-ring lubricant on every o-ring in the air-cooled 911 engine for over 15 years with zero failures do to deteriorating o-rings.
Every o-ring failure we've encountered all 3 of them (out of thousands) have been the result of errant installation. No one is perfect.
I endorse Dow 55 because it has proven to works flawlessly. No conjecture from an angry troll, just proven observation.

Complacency kills.

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^^^^
"If it ain't broke, don't fix it."