Surface Finishes ...

[powerdoctor]

I have heard alot of mixed views from all kinds of people and I want to hear some of your views here.

As I was always told, by books and GM specs for fininshes ....

The head gasket surfaces should have a minimum 400 grit tooth to them, as well as any gasket surface for gasket retention.

I have always built them like and never experienced any problems to date.

I have even seen in print also, that GM recomends polishing the crank with 400 emery, even if its new.

Any thoughts or links here guys?

[ForcedFirebird]

I make the heads almost to a mirror shine for aluminum. ~5-8 microns is the stock finish, but you want more if you are using MLS gaskets. You can use a fly cutter and mill, but make ABSOLUTELY sure the head is square to the table. Muliblade cutters are supposed to be the best.

GM says that the AL heads need to be within .005" within 6", after milling them, I can get .0025" across the entire surface O.O

Iron is more forgiving, I have just scraped them clean and re-installed them without problems.

I might have it saved on the home PC, but here's a littl info...

http://www.aa1car.com/library/ar396.htm

Found that just by surfing Google

[IsaacHayes]

I keep the surfaces like the head to LIM smooth as possible. Those seal with a rubber gasket and you don't want a porous or rough surface for that.

[Superdave]

I usually clean all the gasket surfaces with 800 grit just before installing..

[powerdoctor]

" Will too smooth of a surface with paper gaskets cause issues? "

I feel it may lead to seepage or gasket walk ... any thoughts?

[ForcedFirebird]

" Will too smooth of a surface with paper gaskets cause issues? "

I feel it may lead to seepage or gasket walk ... any thoughts?

What gaskets? Paper, I'm guessing intake manifold?

[powerdoctor]

yes on iron head engines, or ford small blocks or sbc's ect..

Not to meantion the water pump, thermostat, throttle body ect...

[IsaacHayes]

I've never had a problem with smooth surfaces and paper gaskets. Even re-using paper gaskets that are flattened and hard. (re-used my old upper intake gasket a few times).

[powerdoctor]

But what is your definition of smooth?

To me 400 is smooth.... to others 5 microns is smooth, lol.

[ForcedFirebird]

I've never had a problem with smooth surfaces and paper gaskets. Even re-using paper gaskets that are flattened and hard. (re-used my old upper intake gasket a few times).

As many times as I take my motor apart, I actaully glue the gasket to the removable surface and put light coat of oil on the other side and they are re-usable several times. I usually end up removing them before they ever leak.

Another reason to like the 3500 top end - rubber UIM gaskets

[ForcedFirebird]

But what is your definition of smooth?

To me 400 is smooth.... to others 5 microns is smooth, lol.

I wish I had pics after these were cleaned, but you get the idea...

http://s158.photobucket.com/albums/t87/forcedfirebird/Hybrid%20Build/?action=view&current=100_3359.jpg

http://i158.photobucket.com/albums/t87/forcedfirebird/Paul%20in%20VA%20mods/100_3601.jpg

http://i158.photobucket.com/albums/t87/forcedfirebird/Paul%20in%20VA%20mods/100_3601.jpg

http://s158.photobucket.com/albums/t87/forcedfirebird/Paul%20in%20VA%20mods/?action=view&current=100_3608.jpg

http://s158.photobucket.com/albums/t87/forcedfirebird/Paul%20in%20VA%20mods/?action=view&current=100_3608.jpg

http://s158.photobucket.com/albums/t87/forcedfirebird/Paul%20in%20VA%20mods/?action=view&current=100_3608.jpg

[IsaacHayes]

I've put oil on both sides so it doesn't stick and tear. Even dry I've learned out to unstick it without tearing it. My custom cut TB gasket is soaked in oil anyways cause of the PCV pools oil there since the 3500 TB neck goes so low. I need to get some gasket paper and cut a real gasket. Heh. Well, hopefully soon I'll have a 3.5l TB on there and can use it's own oem gasket.

[ForcedFirebird]

We also have a surface table, guarenteed to be within millionths (.00001"). I use a big sheet of 500 grit wet paper, and lay it on the table, then sand the object in figure 8's for a final finish after milling.

Isaac, that works als, but I like to make sure that the piece that is in my hand after removing it from the motor is the part the gasket is stuck to, lol.

[IsaacHayes]

Yeah but I oil it on both sides so it doesn't stick to either!

[3400-95-Modified]

eh, 150 grit sand paper will do it all... LOL

Actually this was what my heads looked like after they were surfaced.

Buffed the CC too, could have smoothed it out but I didnt feel that comfortable with the dremel.


All done