The Complete Engine Sealant Thread...

[Lapkritis]

Missing the critical requirement of machining the case while using the DC55 (that weakens the seal) is "broken" guidance in my opinion. Taking it a step further and recommending an inert alternative is fair... This is a discussion forum not a static, private, copywrited publication after all.

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[WERK I]

Geez, one would think from the content of this thread, we're dealing with the construction of a Solid Fuel Booster rocket. Instead, we're dealing with a low pressure seal (up to 60lb/in2) preventing oil from seeping out an orifice containing a chamfered thru-bolt. If the block didn't weep before the rebuild AND you're methodical and meticulous in your assembly, there is no reason to fear failure.

[Henry Schmidt]

Originally Posted by Lapkritis

Missing the critical requirement of machining the case while using the DC55 (that weakens the seal) is "broken" guidance in my opinion. Taking it a step further and recommending an inert alternative is fair... This is a discussion forum not a static, private, copywrited publication after all.

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There is no "critical machining" required to use Dow 55. There are machine processes that should be performed on a case by case basis and suggesting a better way to prep an old case does not negate the usefulness of Dow 55.


Andrew, the truth is, after I was critical of some of your engine building techniques, you've made it your three year (Ninja like) mission to discredit/question my expertise.
You pounded away until your own rebuild thread as well as a few others were locked. At this point, a pretty informative thread is being trolled for your personal gratification and what you've offered is nothing new.
You talk about "complacency" to a guy who has devoted 35 years to improving the 911 air-cooled engine.
At this point your obsession to the "Dow conspiracy" makes you look a little kookie.

[Lapkritis]

Summary on case through-bolt o-rings:


1) You should chamfer your through bolt holes, if they were not machined previously.

2) With regard to installation grease, it is fact that although more expensive, Krytox GPL-207 retains approximately double the tensile strength of the o-ring relative to Dow 55 when used on the green viton o-rings measured after 70hrs of operating use. DC 55 trades strength for swelling of the ring intentionally.

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

4) It is fact that DuPont Krytox GPL 207 is non-reactive. It is also fact that DOW publishes warnings for thoroughly testing DC 55 on certain elastomers including silicone rubber, which are found in off the shelf 911 seal kits, due to chemical reaction. It is further fact that although Viton loses half of strength after 70hrs, other elastomers experience even more profound losses of strength when exposed to DC 55. End user confirming compatability with materials is advised.

5) It is fact that the chemical reaction with DC 55 that reduces tensile strength advances over time and operating temperature. Engines that are frequently rebuilt or used less frequently (race car, garage queen, collector storage etc) will therefore experience slower advancement of seal weakening and than would daily driver or heavy use vehicles when using DC 55.

End of summary.

[John McM]

I have a leak at the Intermediate Shaft cover on my 964. I checked the engine building DVD and saw they fitted the o ring and cover with no sealant. However this thread talks about Threebond 1211. I want to use that. Where do I apply the sealant? Just around the exterior cover?

[Henry Schmidt]

Originally Posted by John McM

I have a leak at the Intermediate Shaft cover on my 964. I checked the engine building DVD and saw they fitted the o ring and cover with no sealant. However this thread talks about Threebond 1121. I want to use that. Where do I apply the sealant? Just around the exterior cover?

You really don't need to glue that cover. The cover that you might glue is the early cover with a gasket. 65-82 or so.
For all o-rings in an air-cooled 911/930 we've found that Dow 55 out performs everything on the market. Not only is it an exceptional lubricate but the chemical properties of the Dow 55 converts the o-ring slightly to improve crush resistance and swells the seal slightly to enhance sealing.

[John McM]

Originally Posted by Henry Schmidt

You really don't need to glue that cover. The cover that you might glue is the early cover with a gasket. 65-82 or so.
For all o-rings in an air-cooled 911/930 we've found that Dow 55 out performs everything on the market. Not only is it an exceptional lubricate but the chemical properties of the Dow 55 converts the o-ring slightly to improve crush resistance and swell the seal slight to enhance sealing.

Thanks for the quick reply. I'm at a loss to know why this cover is leaking so badly. I suppose I will find out when I take the cover off to fix it. If you look closely at the pic you will see ball peen hammer marks as if someone has tried to flatten it in the centre. I may seal around the outside lip, just because I can and also because I don't want to come back to this seal anytime soon.

[WERK I]

^^^^
"If you look closely at the pic you will see ball peen hammer marks as if someone has tried to flatten it in the centre."

That'll do it. I suspect the cover is now concave slightly.

[Henry Schmidt]

It's also possible that the leak is actually the #8 main bearing (directly above the intermediate shaft cover plate). If that is the issue, you'll have a big decision to make.

If it turns out to be a cover plate issue, I have a good used one I can give you if you pay the shipping.

[KTL]

I too was thinking it may be a #8 bearing insert/o-ring leak. Many people mistake a leak in that area as being from either the crankshaft snout seal or the intermediate shaft cover.

[Henry Schmidt]

Originally Posted by KTL

I too was thinking it may be a #8 bearing insert/o-ring leak. Many people mistake a leak in that area as being from either the crankshaft snout seal or the intermediate shaft cover.

If it turns out be the #8 main bearing you have three choices.
Live with the leak (horrible)
Disassemble the engine and reseal the case (best)
Try the Supertec #8 main bearing sealing kit. (compromise but could give you a chance to budget the proper repair).

[WERK I]

How serious is the leak? Is it possible to clean the area above the cover with alcohol and run the engine to check if the area is oily?

Henry, are you suggesting the pressurized oil on #8 is going down in an area behind the intermediate shaft cover and then forced out indicating a bad case sealing?

[John McM]

On a 1,200 mile road trip I used 4 litres of oil, it was that bad! The back of my car was covered in oil and I left palm sized patches of oil on the ground whenever I stopped. It became intolerable in a engine otherwise dry after a full OPC engine rebuild.

I first found a leak when I dropped the engine in late 2015. At that time it was definitely the nose bearing area as the OPC had covered the area in RTV which had ballooned with escaping oil (a separate discussion I'm having with them as to why I had RTV there on my engine after a full rebuild)

I took the RTV off and installed a Tom Amon collar. I didn't think to check the Intermediate shaft seal as it was hidden under the AC support piece.

My assumption with the continuing leak was that the Tom Amon collar wasn't working. Now that I have full access I suspect that the Intermediate shaft cover is a bigger leaker, but likely not the only thing.

My plan is to replace the O ring and seal the outside of the IS cover. I will also add a layer of sealant around the Tom Amon collar as I don't want to mess with the JB Weld to get the collar off. I will then refit enough items to allow the engine to run and see what comes out.

I can tolerate a small leak there, if faced with having to split the case as an alternative. I've just ordered equipment to allow a rebuild of my other 964 with 147,000 miles and that's the bigger priority.

[John McM]

Nose Bearing RTV ex OPC rebuild as discovered in 2015

[John McM]

Nose bearing with Tom Amon collar. Not light oil smear on lower front of the collar

[John McM]

I cleaned the nose bearing and Intermediate shaft area with degreaser, then dried it. In the intervening 11 hours the cover leaked enough oil to run down the case join area and drip. The engine has not been run for 4 days and the nose bearing area is dry.

[John McM]

I cleaned the nose bearing and Intermediate shaft area with degreaser, then dried it. In the intervening 11 hours the cover leaked enough oil to run down the case join area and drip. The engine has not been run for 4 days and the nose bearing area is dry.

[Henry Schmidt]

Originally Posted by WERK I

How serious is the leak? Is it possible to clean the area above the cover with alcohol and run the engine to check if the area is oily?

Henry, are you suggesting the pressurized oil on #8 is going down in an area behind the intermediate shaft cover and then forced out indicating a bad case sealing?

When the #8 main bearing leaks it can be caused by one or both of two issues.
When the leak occurs on a fresh engine quite often the case journal that holds the bearing is out of round. I've measured ovality over .015". The bearing seals by compressing an o-ring and because this area is under pressure, a standard o-ring (unassisted) is incapable of sealing with this kind of tolerance. This ovality is the reason why (after years of resisting) we started using ThreeBond 1211 in the #8 journal.
The second issue, the most common on an engine with higher mileage is a compressed and hardened o-ring. After the engine has heat cycled and sat year in and year out the o-ring under compression takes a set, hardens and fails.

[John McM]

Originally Posted by Henry Schmidt

It's also possible that the leak is actually the #8 main bearing (directly above the intermediate shaft cover plate). If that is the issue, you'll have a big decision to make.

If it turns out to be a cover plate issue, I have a good used one I can give you if you pay the shipping.

Thanks, I appreciate that. A generous offer given the new cost. First I will see if my existing one is faulty.

[Henry Schmidt]

Originally Posted by John McM

Nose bearing with Tom Amon collar. Not light oil smear on lower front of the collar

The key to making a good seal on the (nightmare) # 8 bearing project is cleanliness.
You really have to get a clean surface for the glue to bond to.
What glue did you use?
It a nice product but one problem we found with the Amon solution was a gap that can form when you tighten the set screws. The set screws in effect push the collar away from the bearing creating a passageway for the oil to leak.
Our solution was to fit each collar to the individual bearing perimeter and press/sweat it on.
This in combination with the Hysol 9340 seems to create a rigid /pressure resistant seal.