Case Through O-Ring trouble??
 

I was working on my engine assembly today after being away from the project for a month and I noticed some little bits of the Viton O-Rings showing around the edges of the washers on the case through bolts. These bolt heads never turned while I was torquing the nuts, the rings were lubricated with the 3M goop from Henry's kit, and I have nothing showing on the nut side, only on the bolt head side.

You guys think I need to pull these bolts and install new seals?
Or is a little squeeze out on these things normal?


http://forums.pelicanparts.com/uploa...1375635060.jpg

I had a few like that on my rebuild and I redid them one at a time.

That happens on the case half that does not have a relief/chamfer cut in the bolt bore. Mike Bruns gave us a nice tip to buy a countersink for aluminum and cut the bores yourself with a hand drill on slow speed.

http://forums.pelicanparts.com/911-engine-rebuilding-forum/646102-chamfered-case-through-bolt-holes.html

I bought a c-sink from McMaster and it was very effective at cutting the case material w/out any chatter or mess. I chose the middle of the selection and got a 90 deg cutting angle McMaster-Carr

Needs more lube. If you see any bits of o-ring at all come out then the ring has failed during assembly and should be replaced.

http://i458.photobucket.com/albums/qq302/aagvt/P911/IMG_3361_zps2958f588.jpg

KTL is absolutely correct. No chamfer equals no seal due to failed o-ring. The Viton O-rings are not the same as the original stock O-rings and don't squeeze down around the bolt. They are too hard to do that. You can either chamfer the hole or find the original O-rings (impossible). No amount of lube will cure this problem.

I disagree and have no such failure with proper lube.

Hey Andrew, good for you. On what year engine are you having no failures? Probably not a '78 or '79 as those are the only years with the chamfer problem. A thin coat of lube is all that is needed if there is a chamfer which is likely in your case.

'74

There you have it. You have a chamfered through bolt hole which explains your success. A case without a chamfer through bolt hole, like the one posted above, has little chance of sealing without a chamfer or an OEM O-ring.

Thanks guys.
I plan on pulling them one by one and resealing next weekend.
I will definitely look to see if my case has chamfered holes.

That's strange... my case holes are not beveled but the washers are.

http://i458.photobucket.com/albums/qq302/aagvt/P911/IMG_3354_zps1eae5b24.jpg

Is that what you mean?

Maybe on Andrew's '74, with the coarse threads on the thru-bolt nut side, the coarse threads allow more squish of the o-ring?

Incidentally I chamfered the one side of my case that was not. Cut it to a chamfer depth similar to the already chamfered case halve. Measured it by the precision of my sharp eye of course....

Had no leaks but still found the nice Viton o-rings mangled upon disassembly. All washers were watched to avoid spinning during tightening and plenty of Dow 112 paste was used to install them. Engine was disassembled shortly after rebuild due to oiling problem. So more chamfering (or thinner/softer o-ring) is in order to avoid wrecking the o-rings. Yep, my washers are beveled underneath too.

Speaking of case thru-bolts, i'd be interested to see what the washers in the spendy ARP thru-bolt kit look like. I wonder if they made sure to bevel their washers?

Speaking of o-rings, I think I found an alternative to the DPH Viton o-rings. Sourced a bag of 25 from McMaster but haven't put them to the test yet on the engine rebuild.

McMaster-Carr 2.4mm-8.3mm Viton Rings

Size of these is apparently better to be a bit on the small side to avoid excess squish, as well as plenty of o-ring paste to facilitate damage avoidance. I'll check the dimensions of my McMaster o-rings to the typical Vitons and see how they compare.

Whatever the case, I just can't bring myself to use RTV as a belt & suspenders solution in this location. That stuff is such a PITA to clean up both during assembly and down the road at disassembly.

Not all lubes are equal either. I use Krytox by Dupont exclusively. Pricey but by far is the best in my opinion.

Andrew,

I can't tell for sure from your picture but it does look like a small chamfer on the edge of that hole. Did you have the O-rings squeeze out like the original poster? The SC case I have had chamfers only on one side.

-Andy

My dilemma is that the portion of the thru bolt that comes out thru the case hole in question is threaded. How can any o-ring seal against a threaded surface?

With the Krytox and Viton seals I do not have any squeezed seals. The previous owner/mechanic had used red seals (original?) but had left powdercoat on the case surface where the ring was to contact. I would approximate greater than 80% failure rate of those red seals when disassembling. Chamfer/bevel/lube/technique all contribute for sure. Case is not beveled but I did remove the powdercoat with sandpaper by hand. I would suggest to use a papertowel plug technique which is a ramrod from behind with the bolt and hold your thumb over the hole to make a nice seal with a small chunk of towel. This would also work well for when beveling the case holes to keep debris from entering the case/oil galleys.

Some better pictures:


http://i458.photobucket.com/albums/qq302/aagvt/P911/IMG_3344_zps1a560e24.jpg

http://i458.photobucket.com/albums/qq302/aagvt/P911/IMG_3348_zps15641f63.jpg

http://i458.photobucket.com/albums/qq302/aagvt/P911/IMG_3347_zps96435e8d.jpg

http://i458.photobucket.com/albums/qq302/aagvt/P911/IMG_3363_zpsc476ef34.jpg

Papertowel plug in place:
http://i458.photobucket.com/albums/qq302/aagvt/P911/IMG_3357_zps2ae3bc99.jpg

Same here - good o-ring grease does the job.

Check the case for proper chamfer. The lube ("goop") provided with the Supertec case sealing kit is actually Dow 55 o-ring lubricant. It's hard to find an o-ring lube with better properties for this application.

Thanks for the comments Henry. I sent you an Email.

Andrew - The beer cups are a nice touch :-)

Which flavor? I use Krytox 226 on bearings. It is expensive $150+ for a cartridge, but it does work well in certain applications. It is Fluorinated grease.

It is good for around 500°F, but I prefer o-ring grease for o-rings.

I believe in using whatever works for you.

GPL 207 is the preferred flavor. I also use this on the oil return tube, distributor, oil cooler and other rubber ring seals. There are many forms of Krytox out there with various properties... this one is suitable.

Timely thread for me. I haven't really started assembly yet on my '84 3.2l but I checked the case last night and I only have chamfers on one half of the case as well. I ordered the tool from McMasterCarr and will take care of that before I assemble.

We use the Dow 55 for two main reasons.
First, the Dow is a Phenyl-methyl silicone grease formulated for O-rings with properties that add a slight seal swell for increased sealing of rubber (including synthetic rubbers) to metal surfaces.
Second, silicone based products like Dow 55 resists the capillary action or wicking that can occur when white grease is used to seal petroleum based oil products.

Henry,

Are you using this Dow Corning 55 Molykote?

http://www.dowcorning.com/applications/search/default.aspx?R=392EN

I know they have different flavors but see this carries a relatively low temp rating. Would like to compare to the Krytox specs.

Dow 55 in a 5.3 oz. tube is on sale at Grainger for $6 on clearance. And then newgrainger.com opens and it's gone.............

No, we aren't using commercially available Dow 55 Molycote. We're using a mil spec product directly from military suppliers.

As to your question: what specs do you believe Krytox has that are important to this application? I'm wondering what function you think a lubricant in this application (o-ring that seal engine oil) performs?
That question was awkward so put another way: why are we (engine builders) putting anything on an o-ring?

I was going to put the spec sheets side by side. Not commercially available you say but yet you sell it making it... commercially available. Is that right?

My answer to "why are we (engine builders) putting anything on an o-ring?" is:

To keep the o-ring from becoming compromised during installation. This would include ripping, tearing, or pinching the o-ring when assembling the parts. The lubricant allows the o-ring to move instead of stick on the surgically clean dry surfaces that we have prepared prior to assembly. Without lube, it would be all too easy to damage the o-rings and prevent them from functioning in their intended purpose (to seal oil in and dirt out).

just my $0.02 (like I said before, use what works best for you. The opinions here are just that, opinions, and your mileage may vary.)

Why so combative?
The truth is, I don't sell it. I buy it in large quantity container that makes selling it impracticable. Much like most of the products I make, I made them because I needed them for my projects.
I needed a high quality o-ring lubricant so I sourced the best I could find for the shop. It works well so a add a small amount (literally a little baggie) to my sealing kit as a favor.

Johnman: You are absolutely correct "To keep the o-ring from becoming compromised during installation". After the o-ring has seated, the lubricant has done it's job and any product that can cause a capillary action or wicking is counter productive. That is why we avoid white grease and petroleum products in these applications.

I'm not combative, but I would like to compare the materials by the data sheets. Why aren't you forthcoming? Just curious.

I used Dow Corning Molycote 111 (because it was the o-ring grease I had) on my ongoing rebuild for the o-rings. That wasn't a mistake I hope?

No worries Magnus, Dow 111 is primarily a Silicone-based compound that resists wicking and has been used by many people on this forum with success.

Thanks, good to hear!
They did go in quite smooth.

I used the sealing kit from Henry with the green viton O-rings and the Dow 55. Unfortunately I had the through bolts on the wrong side, and decided to reinstall them on the oher side, for purely cosmetic reasons. Some got damaged in the process, and I can see one that did excatly what the OP shows in the picture.

Now I still have the blue O-rings that came with the case sealing kit. Can I use those with the Dow 55 or are they going to be worse than the green ones?

The issue is the same with my SC case: the bores are not chamfered. So does this mean that the blue rings are similar to OEM (harder?) and will work better in my case?

The blue o-rings were designed for a different sealing/washer system. They are very soft and under similar conditions will show even more damage (less chance for good sealing) than Viton o-rings. You're always taking a chance if the case holes are not properly chamfered.

Or you could just lather on some more lube, that ought to do it.

;)http://forums.pelicanparts.com/uploa...1376092374.jpghttp://forums.pelicanparts.com/uploa...1376092445.jpghttp://forums.pelicanparts.com/uploa...1376092550.jpg

Just thought our O-ring guru would like to see what a properly cleaned engine looks like before reassembly...

Metal masturbation.

So the Dow 55 Silicone grease:

1) Weakens rubber tensile strength tremendously.

2) Causes rubber to swell greater than 10%; Viton actually will shrink. Common application is for temporary relief of gearbox leaks.

Keep slapping it on there though. I sure as heck wouldn't.


See for yourselves:
http://www.cibsupply.com/pdf/dc55.pdf

Henry, would you have a nice pic of a "properly chamfered" case hole?