O-rings

[John Hofstetter <hofs@domain.elided>]

>Subject: Coating o-rings with brake fluid?
>
>	I'm about to install new water pipes on my 345 (between the heads and
>the water pump), and the book says, "Coat seals (rubber o-rings) with
>hydraulic brake fluid and install ...".  Has anyone coated new o-rings
>with brake fluid before installation?  I'm tempted to coat the o-rings
>with aviation form-a-gasket or copper sealer before the install.  With
>brand new pipes and o-rings, the fit is fairly tight, but coating with
>brake fluid?  I don't understand the reason for doing this.  Will the
>brake fluid cause the o-rings to expand, improving the seal?  Sharing any
>ideas or experience with this would be appreciated.
>
>Thanks for your inputs,
>Mike Ryan

Mike,
The brake fluid lubricates the o-rings without causing any deterioration 
of the rubber. No help in sealing would be gained by using the brake 
fluid, but the lubrication might help prevent damage to the o-rings as 
you push them in. 

One of the new silicone lubricants such as the K-2 that I use a lot would 
do the same thing. I had to use a sealant on my installation because one 
of the mating surfaces in the head was corroded, but if you don't have 
the corrosion, I'd use the brake fluid or silicone.
John