nose 8 bearing o-ring leak

[AndreasLanghoff]

Hi to all,

recently I got my freshly redone 2.4S ( is 2.7RS now) engine back. Unfortunately there is now a new oil leak coming from where the case halfes meet the o-ring for the nose 8 bearing.

It is quite clear that the oil drips from there and not from somewhere else as I have done a talkum powder test and you see after 10 seconds of running the engine without pulley where the leak starts. See the black arrow on the image (the picture is not my engine).

Now, before I would like to ask some questions, here some considerations beforehand.

1. The engine (4R mag case) was not leaking before. It was a much used engine though as P+C, valves + guides were complete out of spec. Oil pressure was always good though.

2. During the rebiuild the engine case was updated with time-serts, oil bypass modifcation and cylinder bore for 2.7 RS P+C. New P+C, new valves , etc. all to the best standards. MFI rebuild also to 2.7 specs.

3. The workshop is a reputable workshop here in Italy and is doing quite a few Porsche rebuilds, more on the 356 though.

4. The newly rebuild engine has no other leak and is totally dry except for the nose 8 0-ring.

5. The workshop explained me that he had recently problems with oil leaks in the nose 8 o-ring area as the last 3 rebuilds of 2.2 and 2.4 engines had problems only in this area.

6. Of these rebuilds the second last rebuild was done with the original 4 mm o-ring without silicon masic. It leaked. The last rebuild (on my engine) was done with the 4.5mm o-ring with silicon mastic also. It leaks also , but less according to the workshop.

7. The workshop is using a reddish Curil sealant for the case (not the T offcourse) . He claims that Loctite 574 is best on alumium cases, but prefers the curil sealant on mag cases.


Thank you for reading so far, hopefully someone of you can answer my questions. My goal is to resolve the problem of leaking , and for obvious reasons I have to continue with the very same workshop that I still trust.
It looks to me like the workshop is doing something systematically wrong as the latest engines all leak.

So

1 QUESTION:

Is it true that on older mag cases the depicted area around the nose 8 o-ring is a weak point and prone to leak?


2 QUESTION:
Has someone ever fixed such a leak for definetely by using epoxy glue?

3 QUESTION:
Has out of roundness been an issue on nose 8 bearing? Do you suggest buying a new nose 8 bearing block?

4 QUESTION:
Do you all agree that the mounting method described by Wayne is reliable? If I remember well he suggests 4.5mm o-ring, with some curil T sealant. Case with thin layer of Loctite 574.

5 QUESTIONS:

Before the workshop started the rebuild, I let him B. Andersons and Waynes book to look. He likes the books very much, but the leak is still there! What is going wrong? Is he simply too slow closing the case?


Thank you for your time
Andreas ,
Cremona, Italy


http://www.daedalussoft.com/classiccars/porsche2.4S_Targa.jpg

[AndreasLanghoff]

Here the image


Thank you for your time

Andreas

[Henry Schmidt]

As an engine builder with many years experience we have seen this problem over and over again. The truth is that the case can be out of round, we've measured .015 out. When the case is that far out, it's time to align bore the case. Oversized bearings are available. 901 101 138.63 You can try to glue it , lord knows I've tried but truthfully it hasn't worked for us. We gave up trying 15 years ago. Now when we build these early engine we first check for roundness. If not we align bore, period. If your machine shop can't align bore the #8 main, we can. If it is within .004 we go forth with the assembly. Clean, clean , and clean the area. We use the stock O-ring and Threebond 1211. We put a thin layer in both sides of the case (at the # 8 main only) and set the crank / bearing in. 1211 gives you 30 minutes to assemble but you should be ready when you drop the crank in. As of the last 5 years, no leaks.
PS; judging by your picture, more prep work may have been indicated.

[Fishcop]

This thread is giving be a bad feeling... I recently closed my case up with a new #8 bearing and standard (black) o-ring... but I didn't use a sealant.

Should I start pulling it back down now?

[Henry Schmidt]

How far along are you? One thing to remember, during the early 90s Porsche was having a 4% leak rate ( I'll guarantee you won't read that anywhere) on their band new 911 engines. They were leaking right on the dyno and being repaired before they ever got put in a chassis. They were leaking with brand new parts. We have to use every trick we can when building our engines from used parts or we're doomed.
Good luck

[Fishcop]

Timing cams and checking piston to valve clearance.... *****

[Wayne 962]

Yes, the early 3.6 engines were famous for their leaks. I have heard similar stories about oil leaks occurring under the 2.7 cars at the dealerships.

Anyways, there's not much good that I can say here. As Henry intimated, it sounds like the case was not properly prepared. You really need to align bore, or resize the case in order to get a good, leak-proof rebuild. A lot of people don't want to spend the money, or don't really believe that the cases warp and deform so much that they skip these vital steps. Or, they just don't know.

I hate to say it, but the only way to really fix this leak is to tear down the engine and reseal. I would inspect the case carefully before reassembly...

-Wayne

[AndreasLanghoff]

Thank you very much for the quick reply. Thank you very much Wayne for setting up this execellent forum, and thank you very much Henry Schmidt for the detailed answer!!!

I talked to the rebuilder, and we will drop the engine today and redo everything!

To Henry: The picture is not my engine, it is a picture I found on the web , its purpose was only to detail the leaking point!!

I translated all your answers to the italian rebuilder, and according to him the case is not wrapped. He has seen many cases, and he can well distinguish between a bent and not bent one. He points out that my case was in very good shape and that the crank was turning very smoothly. If the case was wrapped then the crank would never turn as well as it does on this block.

He did not do an out of round measurement; first because it is out of his workshop scope to rebore a case, and second because the crank was turning so smoothly.

Once the case is open again I will try to detail any problem encountered in that area, hopefully others will be able to learn from our mistake here!

Probably I will go for the Loctite 574 sealant as it is Porsche Original.

Have a nice day

Andreas

[ChrisBennet]

Wonderful info Henry!
thanks,
Chris

[Henry Schmidt]

The # 8 main bearing having too much clearance will not effect the way the crank turns. Because the bearing is loose in the case, it will align with the crank and cause no binding. As for the 574 as a sealant for this area. If you think carefully about the problem you might choose a different sealant. The bearing has an O-ring, an oversized O-ring grove and a slot that acts as a pressure relief port or channel. There is oil pressure that feeds the bearing and that pressure is why this leak is so hard to stop. If you use 574 to seal the O-ring it will harden around the O-ring. That's what 574 does. It is an anaerobic sealant that hardens in the absence of oxygen. As long as nothing moves the 574 will seal. If the bearing moves, the 574 cracks and you're back to square one. We use the Threebond 1211 because it to is anaerobic but non hardening. This allows the bearing to move if need be and the sealant still seals. If the bearing is not moving in the case the o-ring would be tight enough to seal without any sealant, new aircooled cases aren't glued from the factory at the # 8 main bearing.
574 is fine to seal metal to metal. Perhaps the best at that job, but is was not design to be flexible and this job requires flexibly. The Threebonb enhances the o-ring function, the 574 would replace that function.
Good luck.

[mtelliott]

Originally posted by Henry Schmidt
new cases aren't glued from the factory.

Are you saying that when Porsche first builds their engines, they use zero sealant between the case halves? I didn't know that? Are the tolerances so tight that they don't need to? If this is the case, I have even more respect for Porsche engineering.

Michael

[Henry Schmidt]

No, I didn't say that "the factory doesn't glue the case halves". Of coarse they glue the case halves. I don't build late model engines ( no water for us) but it's my understanding the Porsche uses 574 Loctite on there case halves. What I said was that " Porsche does not glue the # 8 main bearing into the case." The factory relies on the oil control channel and the o-ring to seal that portion of the case.
I hope this clears up that misunderstanding.

[Superman]

John Walker uses a sealant that does not harden. I used it, and my nose bearing does not leak. If you're going to try to seal this without align boring the case, you'd better use a non-hardening sealant.

[mtelliott]

Henry,
OK. I wasn't trying to "bust your chops". I truly misunderstood what you said. Thanks for enlightening me.

[AndreasLanghoff]

Hello again,

please, could you enlight me some details that I couldn'grasp properly:

1. Do you put the Threebond 1204 in the o-ring groove?

2. Do you also apply Threebond 1204 to the case halfes sealing surfaces?

My idea was to use Loctite 574 only for the case halfe surfaces and to mount the 4mm o-ring (not the 4.5 any more) dry in its groove.

Now I have the understanding that you put some soft sealer in the groove also. What type of sealant is Threebond? Is it as soft as Hylomar blue or is it black silicon stuff?

Engine is out already and dismantled tomorrow morning.
Thanks to your info I will probably be able to reassemble over the weekend.

Please confirm if you have time.
(In the meantime I am busy answering MFI questions in another thread)

[Porsche_monkey]

Originally posted by Henry Schmidt
The truth is that the case can be out of round, we've measured .015 out.

What would be acceptable on the main rear? On my re-assembled engine case (7R) the output shaft is central but the case measures .004" ovality. Will this leak?

[Wayne 962]

Originally posted by AndreasLanghoff
He has seen many cases, and he can well distinguish between a bent and not bent one. He points out that my case was in very good shape and that the crank was turning very smoothly. If the case was wrapped then the crank would never turn as well as it does on this block.

100% false information! These magnesium cases almost always are deformed in some way. Just because the crankshaft turns (is that really his test?) doesn't mean that the case isn't warped. Wow, the fact that he would even suggest that as a test tells me that he's somewhat clueless.

Read pages 48 thru 53 again. This details all of the things that need to be done to the case in order to achieve a leak-free engine. If you don't follow these guidelines, the cases have a high probability of leaking.

Back to the crankshaft again. Spinning it in its bore is a horrible and misleading test. The engine heats up and expands heavily when running - the clearances when the engine is cold are not applicable to when the engine is warm. You have to spec out the case and machine it back to spec. You can't just look at it and tell. Did they machine the spigots? Did they measure the center bores?

I'm not sure what to tell you, but it doesn't sound like they have a whole lot of experience. At least they are standing behind their work, which is sometimes rare, here in the states...

-Wayne

[Wayne 962]

Originally posted by Superman
John Walker uses a sealant that does not harden. I used it, and my nose bearing does not leak. If you're going to try to seal this without align boring the case, you'd better use a non-hardening sealant.

I think the point is being lost here. The sealant is a fix for another problem - these should not leak if the case is properly machined...

I agree with Henry on the sealant - 574 is a poor choice. Its designed as a gasket sealer. I would go with Curil-T, as I have had good luck with that.

-Wayne

[Wayne 962]

Originally posted by PBH
What would be acceptable on the main rear? On my re-assembled engine case (7R) the output shaft is central but the case measures .004" ovality. Will this leak?

What's the spec? (They are in the back of my Engine Rebuild Book).

Simply put, if the case is within spec and assembled properly and cleanly, it should work perfect! If it's not in spec, you are increasing your chances that it will leak and/or wear out prematurely.

There's no such thing as a free lunch with these engines - as many will confirm, they are very unforgiving when it comes to leaks. You've got to follow along carefully and do it by the book, otherwise the engine will leak. Some engines will run fine even if you slap a bunch of junk together. But, they will leak like a sieve...

-Wayne

[Henry Schmidt]

Loctite 574 is a Form-in-Place Anaerobic » Flange Sealant . Fast curing, medium strength compound specially formulated to cure through large gaps. It is not a gasket sealant.

Curil T on the other hand is a non drying, non hardening, non curing, sealant. It has limited use in large gap, high pressure applications. We only use it where smooth surfaces meet or on assemblies with gaskets that come apart often ( race gear boxes, etc.)

For this unusual application ( high gap, high pressure) we use Threebond 1211 Silicone based anaerobic sealant that is both heat and chemical resistant.

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