Hi Magnus,

What material are your rings/seals that you are using the 111 on? There is a warning from DOW about using this on silicone rubbers. The use is not recommended by manufacturer due to weakening. If you're using it on a silicone rubber then I would recommend replacing the rings, cleaning all remnants thoroughly away and using an alternative grease before continuing with the rebuild.

Cheers,

^^^ Ya', using silicone "rubbers" probably isn't a good idea! :p

True enough but required.

She is guaranteed to hate it.

For those of you who have concerns, Viton is resistant to silicone grease and as I've stated many times in the past, the Wrightwood Racing gaskets sets we use come with Viton o-rings and seals.
Quality overhauls start with quality parts.

Looking at the materials sheet from Dow that I posted above, Viton loses approximately 40% of original tensile strength in contact with Dow 55. Not good.

A shame to have done all that work, present it as proper in a snide, underhanded suggestion that the photo examples I provided are not proper... when you used Henry's suggestion of Dow 55 on it and now know it's eating your seals when at operating temperature. Shame. Good luck to you and your seals sir.

Oh and Lindy - problem in one of your pictures you might want to fix.

Your tin is upside down (I've highlighted it in red to make it easy for you to understand). To be proper, you'll need to swap this with the one on the other side as that will also be upside down. SmileWavy

http://i458.photobucket.com/albums/q...ps6b589050.jpg

Viton is a fluorocarbon and compatible with silicones.

Fluorocarbon (Viton®, FKM)

Since it’s introduction in the mid 1950’s, Fluorocarbon elastomers (most commonly known as it’s Trademarked Viton name) are the most significant development in recent history. Due to it’s excellent mechanical and physical properties, and outstanding resistance to a wide spectrum of chemicals, Fluorocarbon compounds have grown to be a major importance in the seal industry. Fluorocarbon o-ring compounds exhibit excellent high temperature resistance and low compression set. The normal operating range of Fluorocarbon is -20°F to +400/450°F with certain compounds formulated to operate outside this range.
Recommended For: Non-Compatible:
Petroleum Oils Skydrol
Silicone Fluids Amines
Diester Fluids Ketones
Halogenated Hydrocarbons Hot Water/Steam
Chemical Service Brake Fluid

Viton is unquestionably a great o ring material for engine seals. It's approximately 60% as good strength wise when used with Dow 55 according to Dow at 158° Fahrenheit (I strongly encourage anyone interested in this topic to open the link I posted above to the Dow spec sheet. It's in laymans terms and very easy to understand. You don't need anyone to interpret it for you). Silicone is only a small part of the Dow 55 recipe and it's the other ingredients in the recipe that are likely decaying the Viton at operating temperatures.

Upside down tin or an engine full of dirt...

You present yourself as an expert here but your work, based on the photos you posted, looks like ****. Hope you don't charge anyone for that level of craftsmanship.

I don't claim to be an expert but I do my own homework (and share it) instead of believing what someone else writes on the internet. That's the only way we'll continue to improve these old rigs instead of just repeating what the last guy did whether it's correct or not. Don't like that approach then I don't know if there's much helping you.

I must be missing the obvious but It appears that according to the chart you posted, the viton shrinks less with the DOW 55.

http://www.cibsupply.com/pdf/dc55.pdf

Am I reading the chart correctly?

You're interpreting it correctly. Nice that they include a control set in their graphs. Makes the information easy to put into context. The viton shrinks but less with the DC 55.

The tensile strength graph is very telling. That's what should be concerning for everyone using this on viton. If the decay over time is linear then rough math in my head says approximately 175hrs at 158°F. I doubt it is linear... possibly to be accelerated.

The original poster asked if he had a problem and the consensus is yes.
Many of the early SC cases were shipped with errant machine work.
The case through bolt o-ring chamfer was missing.
Here is what the case should look like.
The chamfer is about .035" deep and 45degrees.
When the o-ring is installed on the stud and slid into the case the crush should be .035 to .045".


http://forums.pelicanparts.com/uploa...1376244553.jpg
http://forums.pelicanparts.com/uploa...1376244568.jpg
http://forums.pelicanparts.com/uploa...1376244578.jpg

So let's get this straight; Henry recommends Dow 55 on Viton O-rings and has been building his engines this way for a very long time. I wonder if any of his clients (thousands) have any more than 175 hours on their cars. In my estimation that's about 8,750 miles. My guess is actual use in a build with history trumps a chart every time.

It's not as if they will poof and disappear into thin air. I would just choose (and I already did and shared) a non-reactive grease that doesn't weaken the seal over time.

Just because Henry jumps off a bridge doesn't mean you should follow.

Thanks Henry for the clear and concise reference info.
I can tell you even before I take my bolts out, my case has no such chamfer.
Regards

Mike: Although I do appreciate the vote of confidence, I don't use Dow Molycote.
Although I see no evidence that Dow 55m causes any problem, there are many products listed under the Dow 55 name and 55M or Mylocote is only one. The product we use is a milspec o-ring lubricant composed of 98% silicone. Viton is impervious to silicone.


Back to the important part of this discussion:

To enhance or repair the case chamfer we use a combination of tools. A custom tooled facing tool and a counter bore.

95% of all the magnesium cases we see need the case through holes repaired. Anyone building a new engine or replacing case o-rings on a 2.0-2.7 mag case without refacing the case is doing the job poorly.

http://forums.pelicanparts.com/uploa...1376247138.jpg
http://forums.pelicanparts.com/uploa...1376247152.jpg
http://forums.pelicanparts.com/uploa...1376247242.jpg
http://forums.pelicanparts.com/uploa...1376247397.jpg

When you cut a case in this manner, are you using flat-faced washers where the ring contacts or are you running a beveled washer as well? Looks flat-faced in the middle picture and would be something for folks to consider as needed if they're going to DIY bevel the case holes.