Quick Double Nickel

iTrader: (5)

I want to mill my block to get the pistons to sit .020 out of the hole. I will be using the stock GM MLS gaskets so the quench area should be about .035, I believe. Is it safe to run the stock pistons .020 out of the hole?

brad8266

iTrader: (23)

Thats very far out of the hole. The piston ring may come out of the hole which you dont want. If you want .035 quench why not just run a .040 gasket and call it a day, the hell with milling the block

GuitsBoy

iTrader: (4)

You would have to have top ringlands .010 - .013 thick to have a ring come out the top! I call shenanigans.

JPH

iTrader: (2)

take the average man, check both sides of the piston.

hammertime

iTrader: (1)

It's much easier to remove the thickness from the gasket than the block. I'd imagine the only reason you are asking is because you must have the engine completely torn apart.

Do you want to run the MLS gaskets that bad, or is there another reason?

Quick Double Nickel

iTrader: (5)

Yes, the engine is completely torn down. And yes I want to run the MLS gaskets, over say the Cometics, becasue 1) I can get them pretty damn cheap, and 2) I've heard (through this board) that they are a lot easier to install and deal with not-so-perfect deck surfaces a lot better than the Cometics. The engine is going in a daily driver and I don't want to run into the problems with the Cometics.

The top part of the first ringland is at least .125" away from the top of the stock piston, so I don't think that will be a problem. I more wanted to know if sticking the piston that far out of the hole will cause an instability problem.

hammertime

iTrader: (1)

The piston skirt should control stability, so I don't see how that would be an issue. A couple of minimal complications that could arise:

1) Deck surface on the block should be plenty thick, but you could run short on room if another rebuild requires decking later.
2) If you are running boost or N20, the .025 thicker deck may give marginally more strength for gasket retention
3) You will be creating a larger 'crevice volume' around the head of the piston, basically inside the gasket surface. I would think it should still be so marginally small as not to matter, but there is a possibliity of increased emissions and increased sensativity to detonation.

Personally, I would opt to have the deck surface honed smooth for better gasket sealing, run the .040 or .045 Cometic as required with the amount of material removed, and save room for resurfacing later if needed.

Quick Double Nickel

iTrader: (5)

I thought I read somewhere that the Cometics require a certain level of "smoothness" that's measured in some sort of industry standard, just like the hardness scale of heat treatment. Does anybody know what that is?

brad8266

iTrader: (23)

yeah you have to clean the deck surfaces with the cometics. You should be cleaning the deck good anyway. Use a green scratch pad to clean the decks, that is plenty enough. The idea is not to have any dirt or old gasket stuck to the deck. If you want to you can also spray the gasket with 2 coats of permatex copper gasket spray to ensure good seal.

I have cometics sprayed weith 2 coats and they havent had a single leak. The cleaning was easy to do.