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ramseybuckeye July 29th 06 02:10 PM

Gasket Maker Question
 

I am replacing an O Ring on a Honda engine oil cooler and with Permatex
Sensor-Safe High-Temp RTV Silicone Gasket (red). The TDS for the
product states 24 hour cure. I assume I need to wait 24 hours, or will
it acually seal faster?


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Al Bundy July 29th 06 02:30 PM

Gasket Maker Question
 

ramseybuckeye wrote:
> I am replacing an O Ring on a Honda engine oil cooler and with Permatex
> Sensor-Safe High-Temp RTV Silicone Gasket (red). The TDS for the
> product states 24 hour cure. I assume I need to wait 24 hours, or will
> it acually seal faster?
>
>
> --

When they say 24 hours for full-cure, that's what they mean. They made
the product and silicone is still silicone. The cure rate has been
about the same for years. However, I have found some that sets up very
quickly and you could assemble in a few minutes and wait for the full
cure. But when you block the air, you retard the curing. It is possible
to have silicone that almost never cures, just like when it's in the
tube.

I have doubts as to whether this is a good application for the product
anyway. If it had an O-ring, I would always replace it with an O-ring.
If this doesn't leak right away on you, it certainly will degrade over
time and leak-in my opinion.


Don[_1_] July 29th 06 03:07 PM

Gasket Maker Question
 
On Sat, 29 Jul 2006 06:10:06 -0700, ramseybuckeye
> wrote:

>
>I am replacing an O Ring on a Honda engine oil cooler and with Permatex
>Sensor-Safe High-Temp RTV Silicone Gasket (red). The TDS for the
>product states 24 hour cure. I assume I need to wait 24 hours, or will
>it acually seal faster?


What you are doing is quite dangerous. If a little string of silicone
breaks off and blocks an oil metering hole it could be disasterous for
the engine.

Don
www.donsautomotive.com


jim July 29th 06 03:21 PM

Gasket Maker Question
 


ramseybuckeye wrote:
>
> I am replacing an O Ring on a Honda engine oil cooler and with Permatex
> Sensor-Safe High-Temp RTV Silicone Gasket (red). The TDS for the
> product states 24 hour cure. I assume I need to wait 24 hours, or will
> it acually seal faster?


Most of the silicone adhesives sold for automotive application are
moisture-cure silicones, so moisture in the air is the usual agent for
curing and the rate of cure depends on the humidity. This can be
accelerated with the direct application of water or steam. The problem
is that if you get the outer skin to cure too fast that creates a
moisture barrier that prevents the inner part from curing. That's more
of a problem if the application is thick or pushed deep into a crack.
A thin film of soapy water on the surface is considered by some to be
the best method to get a rapid cure and a smooth blended surface (like
when you are caulking a bathtub). Others claim a little spit on the tip
of your finger is the best method of shaping the surface and getting a
rapid cure.

-jim

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Scott Buchanan July 29th 06 09:18 PM

Gasket Maker Question
 
The others are right about this not being a good way to go.

Your real question is about the RTV. RTV cures when it is exposed to the
moisture in the air. The cure time varies with the amount of moisture in the
air. The instructions probably says 24 hours for "full" cure. The cure rate
is exponential. That is it will reach 1/2 cure in a couple of hours 3/4 cure
in about 8 hours and so on until full cure is achieved.

In your application, I would roughen it up some with 220 grit and solvent
clean the surface. Then apply a thin layer to each side making sure to keep
it away from the oil passage. Since it needs moisture from the air to cure,
wait 5-10 minutes before assembling.

My experience is that RTV doesn't like hot oil under pressure.




"Don" > wrote in message
...
> On Sat, 29 Jul 2006 06:10:06 -0700, ramseybuckeye
> > wrote:
>
> >
> >I am replacing an O Ring on a Honda engine oil cooler and with Permatex
> >Sensor-Safe High-Temp RTV Silicone Gasket (red). The TDS for the
> >product states 24 hour cure. I assume I need to wait 24 hours, or will
> >it acually seal faster?

>
> What you are doing is quite dangerous. If a little string of silicone
> breaks off and blocks an oil metering hole it could be disasterous for
> the engine.
>
> Don
> www.donsautomotive.com
>




July 29th 06 09:21 PM

Gasket Maker Question
 

"Scott Buchanan" > wrote in message
...
> The others are right about this not being a good way to go.
>
> Your real question is about the RTV. RTV cures when it is exposed to the
> moisture in the air. The cure time varies with the amount of moisture in

the
> air. The instructions probably says 24 hours for "full" cure. The cure

rate
> is exponential. That is it will reach 1/2 cure in a couple of hours 3/4

cure
> in about 8 hours and so on until full cure is achieved.
>
> In your application, I would roughen it up some with 220 grit and solvent
> clean the surface. Then apply a thin layer to each side making sure to

keep
> it away from the oil passage. Since it needs moisture from the air to

cure,
> wait 5-10 minutes before assembling.
>
> My experience is that RTV doesn't like hot oil under pressure.


I don't fully agree with your chemistry, but the facts are that if you dont
do it
correctly, you can get in trouble. If you do the work properly, and have
the
appropriate silicone compound, they work well.

You ABSOLUTELY MUST let this material 'vulcanize' completely before
putting it into service. This may take a number of hours. ( On the blue
RTV, I found I got best results when letting it cure 12-24 hours. I got a
lot of leaks until I developed patience in the curing process.)

Some people on here used to recommend letting it wait a few minutes until
it 'skins over', and then assembling it ready to use. NOT SO.

It should stand undisturbed, dry, until the curing process is complete.

As Don said, if you get an engine full of silicone strands or flakes, you
have
bought into trouble.



July 29th 06 09:34 PM

Gasket Maker Question
 

> wrote in message
...

>
> I don't fully agree with your chemistry, but the facts are that if you

dont
> do it
> correctly, you can get in trouble.


I guess I should have gone a little further, if I were going to say anything
about curing.
Common types are acetoxy/acetic acid/anhydride based, where moisture
initiates the cure with
release of small amounts of acetic acid.

These are the cheaper and more ordinary variants.

There are others, better and more expensive, which depend upon other
reactions.

A catalytic amount of moisture will start this type of crosslinking
reaction. Too much water
is not a good thing.

And that is enough about chemistry.

Read the instructions, err on the conservative side. Better still, use the
O-ring that was designed
for the application.



shiden_kai[_1_] July 30th 06 05:17 PM

Gasket Maker Question
 
wrote:

> Read the instructions, err on the conservative side. Better still,
> use the O-ring that was designed
> for the application.


Now...."there" is the proper answer!

Ian



shiden_kai[_1_] July 30th 06 05:24 PM

Gasket Maker Question
 
wrote:

> You ABSOLUTELY MUST let this material 'vulcanize' completely before
> putting it into service. This may take a number of hours. ( On
> the blue RTV, I found I got best results when letting it cure 12-24
> hours. I got a lot of leaks until I developed patience in the curing
> process.)


This is not possible in the environment that I work in. I've found,
(and I've used it every day since GM first started using it) that the
most important thing is that the surfaces are absolutely clean and
dry. There can be no oil on the surfaces...etc. I don't notice any
problems with jobs that I've done, and I often see the same cars
back in my bay up to 5 years after I've performed a repair.

Every now and then, the timing of the job happens to be right
at the end of the day, and I'm able to leave the RTV untouched
overnight after assembling. Pretty rare tho, and I've noticed no
problems with quality when simply putting the components together
and starting the engine right up.

For you hobby mechanics, you have the time to let these things
"set up". It's not possible for a flat rate dealer tech to do it this way
unless I had 3 bays (which I don't).

Ian



ray July 30th 06 09:19 PM

Gasket Maker Question
 
shiden_kai wrote:
>
> For you hobby mechanics, you have the time to let these things
> "set up". It's not possible for a flat rate dealer tech to do it this way
> unless I had 3 bays (which I don't).
>
> Ian
>


I'm a diy-er, and I'll admit to not waiting for the silicone... once the
parts are reinstalled, it's time to test-fire it. Not been a problem.

of course, I'm not reinstalling an oil pan and immediately driving 500
miles... usually just around the block and then leaving it overnight, so
I guess it has a chance to cure.

My best/worst silicone jobs are the end seals on a "classic" SBC. Every
third time we do it it leaks and I have to redo it. Always in the same
spot, back by the oil sending unit. But I'm getting better.
(don't ask why the intake is coming off so often... but if you wanna
know, I've gone through a couple of engines... and swapped cams and
intakes for more power... and the odd blowed up engine...)

Ray


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