Fo8 Sealing

[RogerH]

Hi Folks,

a thread is running at present regarding a wobbly liner. Mention has been made to sealant on the Fo8 seal.

 

Along with many people I use Welseal. But, is there a better product.?

 

How about many of the silicon sealants.?

The area is attacked from one side with water and anti-feeze. The temperature is not the great. The pressure is only 7 PSI at most.

 

A decent coating of a silicon sealant may reduce the long term corrosion of the Fo8 seal from the coolant etc.

 

Roger

 

 

[Z320]

I used finaly only the Fo8, proof since 8 (?) years,

with additional seal the liners have been too high, that was not proof on the head

[Geko]

To add to this: The Fo8s that came with my 89 mm kit (Powertune) are made of steel whereas those of the Moss kit are made of copper. Surely the corrosion will operate differently on either. So what would be the sealing treatment to apply depending on the Fo8 material?

[Z320]

mine have been made of aluminium

[Geko]

mine have been made of aluminium

 

I think i lied, perfectly possible that the powertune Fo8 is made of aluminum

[Charlie D]

The Fo8 seals are a bit of a mystery to me.

 

The three different materials (copper, steel and ali) seem to be different thicknesses. I don’t think that the dia of the pistons has anything to do with it as the OD of the liner spigot is going to be same, no matter what pistons are used.

 

The Fo8 gasket makers could have made the thickness of them whatever they wanted, the type of material should not really matter. Unless it is to do with "Standard" thickness of the different metal sheets.

 

I believe that the differences in thickness may help getting the liner protrusion perfect, but why the different materials (unless it’s a cost thing.)

 

And as has been mentioned, the steel ones will probably corrode quicker than the copper ones. (But then again does the manufacturer really care about what happens 5 –10 years down the road.)

 

As I say, a bit of a mystery as to why certain materials and certain thicknesses were made.

 

 

 

Charlie

[RogerH]

The steel and Ali look very similar - use a magnet.

 

My steel Fo8's lasted 20 years and would have had more years if I hadn't pulled the engine apart.

 

Why different materials !! - haven't a clue

In theory the steel gaskets are best suited for the structure of the block - steel on steel.

Ali and Copper could break down with Galvanic corrosion.

 

Roger

[Z320]

when I bought my car the drain tap was proken away, realised that 1 year later,

the remainig nipple was proof to water and preasure anyway by the mud sediment around the 4th cylinder

[Z320]

Hi Roger,

I remembered two Fo8 stored in my workshop, found and tested them.

Its absolute amaizing: they are made of MAGNETIC aluminium

Sorry me, you are right

 

 

Please be anyone so kind and explain me what Fo8 is written complete?

Looks some like the german "Fuß" = "foot"

[Motorsport Mickey]

"Please be anyone so kind and explain me what Fo8 is written complete?"

Fo8 = Figure of 8 gasket.

So called because the twinning of the gaskets together makes them look like a figure 8 (on it's side)

eg … OO

The gaskets can be cut out of whatever material you want to whatever thickness you require. Just buy a few sheets in whatever material and clamp together with wood and tripan out on a machine and finish with hand snips. Seem to remember somebody showing it on a website.

Mick Richards

PS: I don't have much any trouble with the Fo8 gaskets and their seal or getting their heights correct, you just need to apply yourself to it without trying any "one measure" machine everything and put it back together it will be right work...it won't.

 

After fitting the Fo8 dry, fit liners and fit the head and torque down to 80 lbs ft, measure liner heights dry, disassemble (secure liners with overlapping large washers torqued down to about 40 lb ft) and machine block or liners to use whatever thickness Fo8 you want to use, reassemble DRY with the Fo8 gaskets and measure again (with depth micrometre) at 4 points around the liners make sure the height is between 3 and 5 thou high on the block, and that means the same height for each liner anywhere between 3 and 5 thou (I've taken them up to 6 thou when trying really hard). If any liner is different lower ie 5.5.3.5 then disassemble the engine and machine the + 5 liners down 2 thou to equal the 3 thou low liner to make a set of +3 thou liners. Then reassemble with Wellseal (my choice) on the Fo8 gaskets, fit the head with old gasket and torque down to 80 lbs then remove the head and recheck the liner heights, if all is well fit a new headgasket (my choice again with Wellseal) and final fit head and torque down to 105 lb ft...done.

 

Mick Richards

Edited July 6, 2018 by Motorsport Mickey

[Charlie D]

Actually, a “Figure of 8” on it’s side looks more like the “Infinity” symbol.

 

I wonder why they were not called “Infinity seals” ?

 

Charlie.

[Motorsport Mickey]

Actually, a “Figure of 8” on it’s side looks more like the “Infinity” symbol.

 

I wonder why they were not called “Infinity seals” ?

 

Charlie.

Cos they don't last that long lol.

 

Mick Richards

[Z320]

Fo8 = Figure of 8

 

Thanks

[Waldi]

I have no knowledge about 4 cylinder engines (at all).

Below is just at thought:

In the oil industry we use several types of gaskets: soft, full metal, composites etc.

Reading about the Fo8, which is a metallic gasket, I think the hardness of the Fo8 gasket is important. If too hard, it will not deform, resulting in leakage., too soft is no good either, it cannot withstand the loads.

For soft metal gaskets we often use pure iron, like Armco, with a maximum hardness of 95-100 HB (Brinell).

This is notablicy softer than the mating flange material, and ensures the gasket is plastically deformed, not the flanges.

Maybe this helps,

Waldi