Hints and Tips - Silicon Gaskets

From: Donald Rowley
To: British-Cars-Pre-war
Subject: Silicon Gaskets
Date: Thu, 25 Mar 1999

Has anyone used silicon gasket?

I thought I ought to try and do something about the oil leaks on my Alvis 12/50 engine while I am reassembling it. The three places I had thought of using silicon gaskets are: between block and aluminium crankcase to replace a paper gasket, and on the metal-to-metal joints between oil pump and sump and between a cover plate and sump (aluminium).

It seems that there are two types of silicon gasket, blue and red, for different applications, but the packaging is not very explicit.

What happens when having spread the silicon on the face and the nuts are tightened? The packaging says that any excess on the outside can be trimmed off with a knife or wiped off with a suitable solvent. I am not too fussed about the outside, what happens inside? How do you stop it squeezing into water/oil ways?

Once again I dip into the vast pool of experience of the listers for suitable advice, please.

Don Rowley
1927 Alvis 12/50
Weymouth, Dorset


From: Maggie Shapland
To: Donald Rowley
Subject: Re: Silicon Gaskets
Date: Thu, 25 Mar 1999

> It seems that there are two types of silicon gasket, blue and red, for
> different applications, but the packaging is not very explicit.

I use hylomar very successfully (which is blue) and thin cork for any metal to metal joints.

>
> What happens when having spread the silicon on the face and the nuts are
> tightened? The packaging says that any excess on the outside can be trimmed
> off with a knife or wiped off with a suitable solvent. I am not too fussed
> about the outside, what happens inside? How do you stop it squeezing into
> water/oil ways?

dont put too much on the surfaces! I just use my finger and smear it on- it certainly doesnt ooze about very much and have never had any problems.

Maggie Shapland, Computing Service, University of Bristol,


Date: Thu, 25 Mar 1999
From: Rick Weid
To: Maggie Shapland
CC: Donald Rowley
Subject: Re: Silicon Gaskets

The Red is for High Temperatures. The blue for cooler. The problem is the O2 sensors. I don't think your car has one. RTV cures with moisture. Locked in the spots you spoke of it may never cure. The "rubber worms" that break off, if you do not clean up, plug holes everywhere except where you want them to.

It is good stuff if used properly.


From: Jim Runciman
To: Donald Rowley
Subject: RE: Silicon Gaskets
Date: Thu, 25 Mar 1999

From my experience I can only say beware. As you correctly anticipate you dont know what squeezes inside the engine and it will end up on the suction gause on the oil pump or other places where it can do a similar amount of damage. At the risk of stating the obvious the most common cause of oil leakage is surfaces which aren't flat. I generally use paper gaskets and Hylomar spray on gasket cement sealer with good results however if the mating surfaces have sufficient area to facilitate the machining of a groove then one can use O ring material which is almost invariably better than gaskets.

Hope this drivel is of some interest.

Jim Runciman


From: Will, Dale
Subject: RE: Silicon Gaskets
Date: Thu, 25 Mar 1999

I confess that I used silicon sealer in several locations on my Triumph Southern Cross recently, and all seems well. If there is any doubt about the mating surfaces, then you must make a thicker gasket. I echo the concern of others that a thin smear should do it. I also tend to favor the outside of the mating surface with the idea that the stuff will squeeze to the interior edge of the joint and stop there. The same principle as a good fireman who can spray just enough water into a burning house to put out the flame and leave the house as dry as possible afterward...

Dale Will


From:Joseph
Date: Thu, 25 Mar 1999
Subject: Re: Silicon Gaskets

Can anyone tell me why copper annealed gaskets would not work in these areas??

Joseph


Date: Thu, 25 Mar 1999
From: Rick Weid
To: Joseph
Subject: Re: Silicon Gaskets

> Can anyone tell me why copper annealed gaskets would not work in these areas??
>
> Joseph

They will work. Based on clamp force and area. You need more bolts the greater the area.


From: Dave Smith
Date: Thu, 25 Mar 1999
Subject: Re: Silicon Gaskets

I remember hearing about a motorcycle engine designer from Japan explaining to some bemused British engineers in the 70s how they made those amazing things: bike engines that didn't dump the oil on the floor/ tyres/ brakes/ exhaust/ rider.

First get the mating surfaces flat

Then make sure you have enough bolts holding the parts together

er.... that's it

Given that neither of those things is always possible in venerable engines, silicon goo seems to do a good job in a lot of cases in making up for poor clamping, slight variations in surface and perhaps casings flexing around as they harness the vast power of an A7 or MG TC. It's true that lumps rolling around inside the engine can be problematic, but if you can avoid that, then silicon is a lot easier to make into a gasket than copper and at reasonable temperatures and pressures, might it not be even more effective?


From: Maggie Shapland
To: Joseph
Subject: Re: Silicon Gaskets
Date: Thu, 25 Mar 1999

> Can anyone tell me why copper annealed gaskets would not work in these areas??

I have a copper annealed head gasket for my 1925 Talbot- which works better than copper asbestos for me. The last copper gasket lasted 20 years, the last copper asbestos 10 miles (and the head and block is flat) but it was an original one of indeterminate age. I think it was 1.5mm thick

----------------------
Maggie Shapland, Computing Service, University of Bristol


From: Graham Orme-Bannister
Date: Fri, 26 Mar 1999
Subject: SILICON(E) GASKETS !

I hate to be picky but SILICON is a metal, its the stuff they make computer chips out of.

SILICONES are a family of polymers based on various organo-silicon compounds with a range of interesting properties including chemical inertness, thermal stability, electrical resistance and water repellance. They are available in forms from thin liquids to hard rubbers and resins.

SILICONE RUBBERS are the materials used for jointing, gaskets and sealants, often supplied as air curing solutions. One of the earliest gasket applications was in the superchargers of war time B-29 bombers. They were not around pre-war.

SILICONES have all sorts of fascinating properties. They are physiologically inert and used for surgical implants. (you might think SILICON breast implants would be rather uncomfortable but they are frequently referred to in the press). Hard rubber inserts were around long before Viagra. They also have very strong foam busting properties and are the standard additive used in engine oil to prevent foaming.

Ticking off over. I am just an irritable old retired metallurgist, but I do hate terminological inexactitudes.

Graham Orme-Bannister
Alresford, Hampshire, UK


From: Neil Sherry
To: Maggie Shapland, Donald Rowley
Subject: Re: Silicon Gaskets
Date: Sat, 27 Mar 1999

I have also used this stuff and would just add that some joints rely on the thickness of a paper gasket to provide proper clearances (eg bearing retaining, end clearance in some oil pumps).

Neil Sherry
Herts, UK
'34 MGPA, '68 MGC, '71 Sprite, '71 Rover P5B


Date: Fri, 26 Mar 1999
From: David Whittle
Subject: Gaskets again!

Just to add my random thoughts to the pile:-

1. In general, IMHO anything like plastic gasket etc is a waste of time! The only time things like this work is where you have a good enough mating surfaces that it would have worked without it.

2. You should all remember that gluing components together is a very silly idea, as they have to come apart again one day, and it may be a lot sooner than you expect. It took three weeks to get the Head of our Humber because some silly person used a paper gasket and some Goo. The whole front end of the car was suspended 12 inches in the air by the head whilst vast amounts of penetrating oil soaked in to everything. Finally the gasket had to be sawn partially through with a home made brass blade.

3. Mating surfaces should be clean and flat, gaskets of the right sought used (paper/cork/copper etc) and a light coating of grease (possibly high temperature) applied to each side of the gasket, they should not be glued in place with all these awful coloured substances. When you take things apart you should be able to undo some bolts, take off the component, take off the gasket in one piece and possibly even reuse it.

Would you use a soft Rubber drain plug in your sump, no you would not for fear of it letting go and ruining your engine. Why then use it somewhere else for just an important a job.

As was said (and I have learned the hardway) there is no secret to a good seal, its just clean, flat,mating surfaces, with a good surface finish, the correct gasket material & thickness, a smear of grease on mating faces, the correct torque on the fasteners.

As an impoverished motorcyclist years ago I tried all bodges with sealers, its all a waste of time. Do the job properly take some time, it will save in the long run.

Happy Tinkering!

David Whittle
Wantage
Oxon
UK


From: Dave Wilcox
To: Donald Rowley
Date: Mon, 29 Mar 1999
Subject: Re: Silicon Gaskets

My ha'peth on this subject would be to state that from my experience it is a matter of common sense and judicious application. I have used Silicone gasket for a number of engine and other (axle, geartbox) rebuilds without any adverse affects on them. When I did my first rebuild I was advised by a knowledgeable peer to squeeze an even bead of the silicone onto one of the mating surfaces and lightly bolt up avoiding excess being squeezed out. The components are then left for a minimum of 24 hours to cure and only then bolted up fully. The advantage to be gained is where you have situations as with the block and crankcase of an Austin Seven, ie cast block, ally crankcase with different expansions rates, together with an A frame that twists in use, particularly when trialing, any marginal movement at the mating surfaces is compensated by this sqeezable gasket. The gain is an oil tight engine. You can usually tell nowadays whose using conventional gaskets and whose using Silicone by looking at the ground underneath any Seven!

Dave Wilcox
Stoney Stanton UK


Date: Tue, 30 Mar 1999
From: David Laver
To: Bill Hoskins
Subject: Re: Silicon Gaskets

Bill Hoskins wrote:
> Dear David:
>
> I must take umbrage with your remark that silicone is a bodgers'
> material. When I worked on the Trans-Am crew (SCCA's professional GT
> series), the only "real" gaskets that we used in the engines was a head
> gasket. These engines were, by the way, 8000RPM, 13:1 Chevrolet V-8s that
> put out close to 600 HP. They always stayed dry, and we never had any
> problems with silicone gasketing materials.
>
> Regards,
>
> Bill Hoskins
> '63 Sunbeam "Imp" (Vintage racer)
>

Bill,

An interesting story from the other end of the spectrum.

I suppose I class myself as a bodger and took the material down with me... I find it excellent and its all I use other than the head gasget. What was the procedure to apply it? Did you use all the different tubes of different spec materials or have a big tub of something generic? Were there spates of failures that drove you to silicone or is it accepted practice?

David


Date: Wed, 31 Mar 1999
From: David Laver
To: "Bill Hoskins"
Subject: Re: Silicon Gaskets

Bill Hoskins wrote:
> Hi Dave...
>
> The primary reason for the change-over to silicone in place of
> "real" gaskets was simply the cost. Racing engines are torn down with GREAT
> regularity (or should be!), and the cost of conventional gaskets starts to
> add up after awhile. :-)
> Nothing special in the way of materials...usually the Permatex 'Blue'
> silicone. You're right about the procedure; we would put the stuff on, let
> it set for about 30 minutes, put the mating part in place and run the nuts
> down until we had about .015 clearance between parts. Let set for a couple
> of hours, and then torque to requirements. We did use the orange stuff for
> exhaust manifolds, however.
>
> By the way, my Imp engines go together with the same materials, and
> they seem to remain quite dry.
>
> Regards,
>
> Bill

Bill,

I've never been brave enough to use it on exhaust manifolds... Another application!

David


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