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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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.

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.

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.

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?

http://forums.pelicanparts.com/uploa...1487267945.JPG

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.

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.

^^^^
"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.

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.

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).

http://forums.pelicanparts.com/uploa...1487282758.jpg

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?

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.

Nose Bearing RTV ex OPC rebuild as discovered in 2015

http://forums.pelicanparts.com/uploa...1487288244.jpg

Nose bearing with Tom Amon collar. Not light oil smear on lower front of the collarhttp://forums.pelicanparts.com/uploa...1487288405.jpg

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.http://forums.pelicanparts.com/uploa...1487288691.jpg

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.

http://forums.pelicanparts.com/uploa...1487288691.jpg

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.

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

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.

Looking at this again, it appears your right case is proud vs left side.

If so, it'll be really hard to seal that.

Glad I am seeing this.

Almost ready to assemble the engine, I did notice there is allot of movement to place the case together, I know #8 will help align it but the for and aft can also be an issue of the two mating surfaces.

I put the jack under the engine right next to the drain plug so I had to take the cover off and let the oil drain from there. More than 4 litres of oil came out. That's a lesson for next time if there is one!

The cover, o ring and case bore had traces of some type of sealant. I used a plastic trim spatula and finger nails to remove it all. I was careful not to drop any in the opening at the base of the bore.

The case halves are not perfectly level at the case join but not that bad. Equally the cover appears straight.http://forums.pelicanparts.com/uploa...1487375757.jpg
http://forums.pelicanparts.com/uploa...1487375795.jpg

I then put a smear of oil on the o ring, the cover channel and slipped the cover back in place. It went very smoothly. I torqued the bolts to 10 Nm (less than I think the previous installer used), degreased the area and put 1.5 litres of oil in. Now I'm watching for any leaks before I go any further.http://forums.pelicanparts.com/uploa...1487376110.jpg

John, I notice some extra info on here from the rennlist thread. The hammer marks on the cover would worry me. I would hope that a new cap from Porsche wouldn't be too expensive. Though maybe the incorrect use of a sealant on the o-ring is the real problem.

I don't remember anymore from when I replaced this o-ring, and I wasn't sure from the descriptions above- can you feel any kind of lip inside the o-ring bore where the case halves meet?

For another data point on sealants, I followed Henry's recommendations on my 964 rebuild and it's 100% leak free (except the nose bearing/ims area) after a few years, around 10k miles, and hundreds of autocross runs. I didn't split the case but I did replace the through bolt o-rings one at a time. Many of them came out mangled. The motor had about 70k miles and had never been opened before, so the factory must have destroyed a few o-rings during the original assembly. It had a number of leaks from the through bolts. I would put dc55 on my pancakes if I could. Love that stuff. Good luck John.

Yesterday, I put everything back together, ran the car for 5 km and it still leaks :(

Tonight I pulled it all apart and while oil is notorious for spreading to obscure its source there appears to be an obvious gap in the RTV on the top side of the Intermediate shaft cover. I've cleaned the area up and will check in the morning. Then I will put the engine back on the mounts and run it. Would taking out the DME and turning it over with the starter motor generate enough oil pressure to test this? I really would prefer not to start the motor.http://forums.pelicanparts.com/uploa...1487585469.jpg

Well, if your cases aren't flush as they appeared in the photo above, here will be my ghetto fix.

RTV is a huge no-no on aluminum, but I think you're forced to use it in this case. All the non-hardening sealants are just too weak IMO.

So, with that said, I'd remove the cover, clean up everything again with brake cleaner, and try a light amount of RTV.

In the US, we have Permatex Ultra Grey. Not sure what's in NZ?

The key is to apply it and carefully put the cover back on ensuring the RTV doesn't get mashed unevenly.

Torque the bolts to 50-75% of final torque.

Let it sit 2 hours.

This allows a "gasket" with high durometer to be formed.

Then torque to final.

Some will balk at this, but I have lots of experience fixing leaking old Chevy V8's! ;)

Don't know if it is a good idea but i would oil stone the 2 halves and create a flat surface

The intermediate shaft cover for the 964 3.6 is the same as the 993 3.6 and also the same as the Carrera 3.2 from '84 to '89. Part number 930.105.165.00 So the search for a good used one could come up pretty easily.

Henry's offer of the good used one for the cost of shipping is probably the best deal you're going to find. Put a new o-ring on it with silicone grease and you should be all set.

Thanks all for the comments, all of which have good thoughts.

The new cover is $28 from Pelican and I have a big order in anyway so will add to that. Thanks for the offer Henry in any case.

I will have a very close look at the mating surfaces. I like the oil stone idea to ensure a completely flat surface. I will use a new cover, o ring and silicon. Is threebond 1211 ok for the RTV idea? Right now all of the red RTV is external. I gather I'm working on sealing full oil pressure here.

No worries, we have a huge inventory on these kinds of ancillary parts.

If the cover really require a sealant I would use Dow 55 and LocTite 574 on the perimeter making certain not the get it on the o-ring. In the alternative, 1211 can be used to seal the o-ring.
In this application it's important not to use a lubricant that will cause wicking.

Just ordered the Dow 55, more O-rings and a cover. I have 574 but don't like the chances of keeping it off the o ring. I used Wurth's orange flange sealant on the valve covers, but decided not to try it on the oil pressure sender due to the risk of getting it in the oil. Is 1211 a safer alternative?

As soon as I can get this engine (relatively) leak free I'll pull the engine out my other 964 and prepare for a Southern Hemisphere Winter of rebuilding that. It's great to know there's a group of people out there so willing to share.

Plans have changed. A closer look indicates that the JB weld has seperated from the case and the area is leaking. Unfortunately, the collar has to come off but the JB weld is holding strong on the bond to the other parts of the bearing area. I don't want to use heat near the bearing and use of tools without marking the case are problematic. That combined with a call to the OPC where it's clear I won't be getting a pickup and redelivered engine has me starting the reseal process myself.

Thanks for all your help here. I will be back with reseal questions. Luckily I have two cars.

Gratuitous pic of cars. The White car on the lift is the one prepped for surgery http://forums.pelicanparts.com/uploa...1487972036.jpg

You must be in Austraila

LOL, Actually New Zealand. Still its down under...

JAFFA land I'm guessing?
Alan

Yes, Auckland aka Just Another F.....g Aucklander land to those not in Auckland :rolleyes:

Way down under, a fact we are reminded of each time we see the shipping cost. Despite that, the final costs shopping at Pelican and others overseas are far less than local ones, if we could find the items.

Have you tried discussing the fix with Steve Rassmo - he is usually quite helpful and knowledgeable.
Yes, the shipping costs ex US often double the price of the item, but the supply of bits is unbeateable.
Alan