Metal Head Gasket - Surface Machining Requirements

[88AW11SC]

Hi Guys,

1988 AW11 SC (Big Port)

About to do a head reco on my GZ, leaving the block in. I plan to use a TRD metal gasket from Castle Hill Toyota.

Two questions:

1) Have been told when using a metal gasket the surfaces have to be almost mirror finish. I dont plan to remove the block so I cant have it machined. If I hit it with some steel wool and 2000 grit wet and dry will I be OK? Dunno what the factory finish is like though...

2) Stock gasket is apparently 1.2mm thick. TRD supply both a 0.5mm or 0.8mm gasket. Any ideas on where the comp ratio will be with either gasket? Wouldn't want to go over 9:1 from the 8:1 stock ratio.

Thanks Guys,
Matt.

[CrUZida]

I personally wouldn't use an MHG unless I decked the block and machined the head.

Unfortunately decking the block requires removing it, and stripping it. So you may as well do a full bottom end rebuild...

[andrew_mx83]

i beleive 40thou (1mm) is around 1 point of compression extra

and dont use a MHG unless u deck the block

[CLG]

I would also exercise extreme caution with your plans to clean the block surface as you've mentioned - any contaminants making their way down the bore will have negative effects on service life, you'd be surprised how quickly wear takes place.

[88AW11SC]

Hmmm you have all seconded my concerns!

Thats a bugger! I was looking for an easy way to gain a few KW.

Anyone know of plain composite head gaskets that are thinner? Or the material wont support a thinner gasket?

OK then, where can I get some cams for her here in Australia?

[neal]

I tried the steel wool and sandpaper method on a flat piec of wood, but clearly could not get any sort of smoothness and flatness where i could install a 250$ MHG.

You could always use a brand new sharpening stone (80 x 300 mm) and stone it for hours.
Then use some 2000 grit paper or diamond paste on a float glass about the size of your block and has to be wider than the block. This is what i did. Constantly check the deck with a straight edge and filler gauge as you go along. Also use kero on your stone and block. making sure you put rags in your bores, you dont want any material getting to you rings, you stone then clean is the process you want to repeat. once done and happy use metho to clean every thing.

Do not focus on one spot for too long with the stone or the float glass , you have to do a nice circular motion without the dowells in the block.

9.1 ratio souds like fun

P.S it took me 26hrs to prep my 7mgte block to a stage i was happy with. You dont have to spend stupid hours iam abit anal.

Neal

[neal]

i beleive 40thou (1mm) is around 1 point of compression extra

and dont use a MHG unless u deck the block

Is this for the 4age only or your just a generalisation, i would love to see your calculation.
and what thichness would the head gasket be.

[Joshstix]

If you're only after the gasket for more compression to boost power slightly rather than for the reliability benefits of metal gaskets why not just get the head shaved when it's getting reconditioned?

[88AW11SC]

Joshstix shaving the head is also an option.

The whole reason Im looking at the MHG is for power first, reliability second. The MHG was simply because its thinner.

Im not an engineer by any stretch of the imagination and thought it would be a better option to get a thinner gasket.

In either case (MGH or shaved head) will the valve reliefs on the pistons be large enough? Am I gonna have pistons hitting head components?

[neal]

Well dude its fairlly simple, when building for POWER, if you are concerned about all that you should be measuring clearances yourself on your motor. not based on here say.
remember power isn't cheap.

[88AW11SC]

remember power isn't cheap

Aint that the truth! Especially with the exchange rate down the toilet like it is right now.

There is nothing wrong with her right now, shes just a little tired - makes me second guess the 'need' to freshen it up.

[andrew_mx83]

Is this for the 4age only or your just a generalisation, i would love to see your calculation.
and what thichness would the head gasket be.

very much just a generalisation.

hg's are normally anywhere from 0.8 - 1.2mm unless u go for a larger, de-comping one (ie HKS 2mm etc)