LQ9 deck surface
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TECH Apprentice
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From: Sedro Woolley, WA
LQ9 deck surface I am cleaning the deck surface on my heads. I got the block back from being hot tanked, bored/ honed and new cam bearings installed. I might take it to another machine shop for a light mill on the deck.
The surface had a good bit of old gasket material. I used a combination of carb cleaner, scotch bright and razor blades. The surface is flat, and none of the fine scratches on the surface catch a finger nail. I am using L92 heads and want opinions if you think the surface is clean enought to seal with MLS head gaskets. The engine will be N/A no boost or nos.
Here are some surface pics. The flash is kind of deceiving as there are no real dark spots on the surface.
The surface had a good bit of old gasket material. I used a combination of carb cleaner, scotch bright and razor blades. The surface is flat, and none of the fine scratches on the surface catch a finger nail. I am using L92 heads and want opinions if you think the surface is clean enought to seal with MLS head gaskets. The engine will be N/A no boost or nos.
Here are some surface pics. The flash is kind of deceiving as there are no real dark spots on the surface.
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Joined: Aug 2010
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From: Harford Co. Maryland
Gaskets rely on a certain minimum RMS for proper sealing and even if you "scotch brite" by hand you "could have" removed this RMS or created a low spot.
I would at least have it looked at and maybe have just a skim cut to make sure it's true.
I would at least have it looked at and maybe have just a skim cut to make sure it's true.
Looks good from the little you can tell in the pictures. Most of the time the shops cut ends up being a little more course than the stock deck. They need to run the cutting head at the slowest speed to produce the best finish, but they seldom do. You could hand lap the surface with a stright block starting with 400 grit and penetrating oil and go higher grit if you want. I've always had better results hand finishing the surface over what the machine shop leaves you with.
Gaskets require a certain R.A. to be able to seal. True, going slow will give you the lowest RA, but that surface would leak because the surface is to smooth for the gasket.
Take for instance Cometic gaskets, a lot of people have problems with them leaking. It's because Cometic has a specified RA finish required for their gaskets.
They have calculations on how fast the machine needs to go to get the RA desired.
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Teching In
Joined: Sep 2010
Posts: 29
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From: North Georgia
You should have it decked if you are going to an MLS gasket.
I have seen guys bring in blocks and heads that have been cleaned the way yours has been and it will scare you to death when you start surfacing them. It is almost impossable to keep from rounding the edges and around the tops of the cylinders with a scotch brite wheel.
If you have it done then you need to ask the shop what type of bit they use in there surfacing machine, It should be done with a CBN cutter.
Andy
I have seen guys bring in blocks and heads that have been cleaned the way yours has been and it will scare you to death when you start surfacing them. It is almost impossable to keep from rounding the edges and around the tops of the cylinders with a scotch brite wheel.
If you have it done then you need to ask the shop what type of bit they use in there surfacing machine, It should be done with a CBN cutter.
Andy
Yes they do and if you call them up and ask them they want it as smooth as possible, but give a number to shoot for as most people are not going to polish the deck, etc. The surface imperfections give a place for combustion to leak around the fire ring starting a HG failure. They don't state the finish needs to be this number than this number only, just that it has to be at least as smooth as the number provided.
I've had high power turbo imports in the past. If anyone knows how to seal things up it's those guys. Hand lapping is more common than you would think in some of these apps. It will almost always end up smoother than any shop is going to get it on the machine and seal better.
I've had high power turbo imports in the past. If anyone knows how to seal things up it's those guys. Hand lapping is more common than you would think in some of these apps. It will almost always end up smoother than any shop is going to get it on the machine and seal better.
It's all about R.A. (Roughness Average)
Gaskets require a certain R.A. to be able to seal. True, going slow will give you the lowest RA, but that surface would leak because the surface is to smooth for the gasket.
Take for instance Cometic gaskets, a lot of people have problems with them leaking. It's because Cometic has a specified RA finish required for their gaskets.
They have calculations on how fast the machine needs to go to get the RA desired.
Gaskets require a certain R.A. to be able to seal. True, going slow will give you the lowest RA, but that surface would leak because the surface is to smooth for the gasket.
Take for instance Cometic gaskets, a lot of people have problems with them leaking. It's because Cometic has a specified RA finish required for their gaskets.
They have calculations on how fast the machine needs to go to get the RA desired.
Thread Starter
TECH Apprentice
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From: Sedro Woolley, WA
Again, thanks for all the input. I talked to a shop today about getting it done. I also took a straight edge and did not find any low spots. At one area it seemed like the .0015 feeler would start to go under the edge, but I think it was the way I was holding it. Does anyone know if the stock gm or felpro gaskets better?
From my original post "The surface is flat, and none of the fine scratches on the surface catch a finger nail",
you can feel the roughness on the surfaces, just no sharp edges from damage and the surface is not polished.
From my original post "The surface is flat, and none of the fine scratches on the surface catch a finger nail",
you can feel the roughness on the surfaces, just no sharp edges from damage and the surface is not polished.
Last edited by mcdonald77; Dec 27, 2011 at 06:14 PM.
I really think you are ok with what it looks like above. Your NA build will not tax the gaskets so I'd probably just use stock GM MLS ones unless you are trying to tighten quench with a thinner aftermarket gasket. GM gaskets tend to seal very well without much effort. Stock GM MLS gaskets are around .053"-.054" compressed and what I run my 383 NA engine.
