The main thing is finish. The lower the RA number, the better. For a metal head gasket you want the finish to be near polished. If you've got a good, flat surface to start with you can hand lap it. I hand lap my blocks and heads, even if I take them to a machine shop, when I'm using a mls gasket.

dsm_racing said:

The main thing is finish. The lower the RA number, the better. For a metal head gasket you want the finish to be near polished. If you've got a good, flat surface to start with you can hand lap it. I hand lap my blocks and heads, even if I take them to a machine shop, when I'm using a mls gasket.

Click to expand...

Hey, what do you use to 'hand lap' your head and block?

I have a machined steel block that I had made just the right size to wrap a piece of sandpaper around. I use progressively finer sandpaper and WD40. It's mindless and time consuming, but your arm gets a good workout.

Excellent! what number grit did you start and end with?

Could not lapping the surfaces be the reason why so many guys have MLS problems even after resurfacing?

Most MLS gasket failures are due to the surface being damaged, or not being smooth enough. The block and head need to be 50 Ra or lower, find a machinist that has the correct equipment to measure Ra or it's just a waste of time.

You have to treat the machined surface of the head like it's made of glass. Don't let it touch anything from the time it's machined to the time it's installed on the block. The smallest imperfection can cause a failure, and this is where most people have issues. They wonder why they're pushing coolant at high boost, well it's most likely because the surface of the head got scratched up before, or during, installation.

You have to remember that the MLS gasket isn't going to conform to imperfections in the head, like a composite gasket would, thats why it needs to be perfect. Copper spray seems top be somewhat popular, but in my opinion, it's a bandaid for a half-assed job.

Hand lapping isn't necessary if the machinist has the right equipment and does his job correctly, but it sure won't hurt anything if done correctly.

what is the correct way?

dsm-onster said:

what is the correct way?

Click to expand...

If you're doing the block a lot of people would argue that it's safe to do it with the engine still in the vehicle, I don't agree with that, but it's up the owner of the engine.

Here's an article that might give you an idea of what it's all about, notice he mentions it's a bandaid for bad machine work, like I mentioned in my previous post.

http://www.mail-archive.com/[email protected]/msg03409.html

You'll have to scroll down through the bs to get to the article.