Water seals

[oldone]

What is the expansion rate of copper to ally and steel ? Once copper is formed that is it ?...............interested in the concept,but \'devils advocate\' as well :guinness

[ianelvar]

What is the expansion rate of copper to ally and steel ? Once copper is formed that is it ?...............interested in the concept,but \'devils advocate\' as well :guinness

Expansion coefficients:

ali 22.5

cast iron (grey) 10.8

copper 16.5

rubber (hard) 77

Steel 13

Bolts are made of steel, plates are made of iron, housings made of ali, seals made of rubber. But what kind of rubber?

Now, a bit of dead reckoning...

Assumptions:

The ali housings make up 60-70% of the length between the bolt thread where it enters the front plate, and the bolt head clamping down on the back plate. We are left with two housings, and the middle and rear plates sandwiched between the front plate and bolt heads.

We can largely discount thermal expansion of the front plate, as it does so mostly outside the bolts ability to control its expansion. IE it should expand forward of the front housing.

We have three expansion coeffiecients londitudinally - bolts, housings and plates.

So, some more dead reckoning. Ali and iron in a 70/30 mix down the length of the motor should yield an expansion coeffiecient of around 17

Steel is 13, so in theory, the bits the bolts clamp together expand a little bit more than they do, thus creating more stretch in the bolts and greater clamping force. Great so far.

We\'re also smack on target for coppers expansion rate of 16.5. BUT, as the housings and plates are held tightly by the bolts and their own thermal expansion as we have already established, they can\'t be forced apart by the expansion of the copper, and it ought to make a better seal.

However, if the rubber seals normally used do have an expansion coefficient of 77, then we\'re far short of that with copper.

The biting question is; is this a problem? Or will the small amount of thermal expansion in copper be enough to make the seal, coupled with its relatively high strength and ability to be pressed into and stay in shape

Regarding reation between copper and ali, This crossed my mind too.

There are copper rings that seal things like fuel lines, sensors etc. all over most engines, so i\'m tempted to say that it shouldn\'t be an issue.

Sorry for the long post. Really interested to hear a few more opionions.
And thanks for making me think, Oldone!

[kev-yorks]

One more thing guys to throw into the mix is the fact using dissimilar metals in a water based environment you may well get electrolysis. It could be quite embarrassing if the copper became a sacrificial anode. Its too many years since chemistry lessons and too early in the morning for working this one out so over to you guys.
Kevin

[FD3UK]

I thought that water seal failure was because of corrosion of the plates between the waterways and seal grooves, Rather than the seal failing?

Also when rebuilding my engine I used the the Rotary aviation seals which have a lot less give than Mazda seals(but more than copper). I was warned by a reputable engine builder that he\'d seen these seals break the land between seal groove and waterway.

[nikp]

I thought that water seal failure was because of corrosion of the plates between the waterways and seal grooves, Rather than the seal failing?

No, it\'s usually because the rubber becomes brittle and breaks down and flass into bits. I had a 3cm long piece of water seals missing from mine when we tore the engine down!

[ianelvar]

One more thing guys to throw into the mix is the fact using dissimilar metals in a water based environment you may well get electrolysis. It could be quite embarrassing if the copper became a sacrificial anode. Its too many years since chemistry lessons and too early in the morning for working this one out so over to you guys.
Kevin

Good point.
You can get copper head gaskets for a lot of engines which have an iron block and ali head, so I can\'t see this being a problem though.

[yamaster]

how would you join each side of the copper togeter when they meet? so there would be no leeks? after putting it into the grove?

[Martiny]

I thought that water seal failure was because of corrosion of the plates between the waterways and seal grooves, Rather than the seal failing?

This is true, but I would still expect the copper to last langer even if the plates have corroded?

[ianelvar]

how would you join each side of the copper togeter when they meet? so there would be no leeks? after putting it into the grove?

The tried and tested way of doing this is to use a kind of lap joint in the copper.

The (poor) illustration shows a section looking through the groove, with the plate on the bottom, and the housing on the top - pre torquing down. The copper is proud of the goove, ready to be squashed. The white line represents the lap joint which will get pressed together to form a tight seal once the bolts are tightened. This can be initially cut with a hacksaw, then finished with a file before the seal is inserted into the groove.
It should easily be possible to supply them in pre-cut, pre-jointed lengths with a former for bending each size around to make the correct shape, should we ever get that far!

[ianelvar]

This is true, but I would still expect the copper to last langer even if the plates have corroded?

This I\'m not too sure about, and it would be a difficult one to test. Copper should withstand an awful lot of punishment, and problems like nikp\'s where section are totally destroyed would be almost impossible. But, it\'s not as elastic as rubber, and doesn\'t expand so much, so it might not be able to fill a large hole left by a piece of plate that corrodes away.

However, how many engines fail through corroded plates rather than seals breaking? Is it a common occurance, and how many fail in this way with the proper mix of coolant in the system?