MLS Gasket-Advice and experience please for prep
 

Hey everyone. I just had my block’s surface cleaned up. The machine shop took .003 of the Block. It is nice and shiny I don’t see high or low spots. I have never installed a MLS head gasket before. How do I know if my freshly decked block is actually an acceptable sealing surface? The deck is flat but I have no clue about the RA of the finish. Some people speak like the RA is the most critical thing ever and others get away with using wire brushes on an undecked Block. What is the real deal here?

Also, why no copper? It was not only a common practice on MLS gaskets in the racing scene, it was also used by manufacturers, specifically, Dodge, that released a TSB many years ago that instructed users to use copper during the MLS installation.

There seems to be be so many contradictions of what needs to be done. I understand there are textbook perfect answers, but I would like to know what is more real world. Realistically is my freshly milled Block good enough or do I need to get someone with a RA Meter to check it? I used composite gaskets on my old cars and it was easy. CLean old gasket off, lay new gasket on, done.

I have read read the threads here and watched the prep videos linked. I also noted that the machinest who made the videos stated that you could prep a “good” Block by hand for MLS (assuming deck was straight and overall condition was good not pitted to hell and back)

thanks yall

RA matters in that it needs to be smooth. If there are machining marks, your HG will be displeased. The surfaces should be smooth if you run a fingernail along them.

Flat, machined deck
Flat, machined head
Clean and dry
OEM head dowels
OEM gasket, straight out of the bag, don't touch the surface, straight onto the motor

[/thred]

The deck of block was cut .003. The head was shaved by Jim Drago .008 (2015 spec miata head). So total combined is .011. Do you still reccomend OEM or is the .040 Cometic a better choice with that much total removed?

Also, does the OEM MLS gasket have any type of sealant applied to it at the factory? Something along the lines of what gel-pro applies? I know my block is straight and flat but it’s the RA I’m worried about. I feel like a few minutes with some 220 grit would assure the proper finish but I’ve never messed with mls prior to now. On composite a friggin wire wheel was good enough for head swaps.

Your pro engine builder or a dial indicator can answer that question for you. I would not touch your freshly machined deck surface with sandpaper.

Is the Cometic considered inferior to the OEM or is it simply more expensive? Tomorrow night when I get back home I will snap some pictures of the block’s deck.

I just went through this with a engine I have. I took a machinist edge with 600 grit and then I did 1000 grit.... it's now disassembled and waiting to go to the machine shop. It would've been fine to slap some copper and run it for a while, if I was a willing to do it all over again right. I did it cause I wanted quick and easy, which it wouldn't have been and I was just being impatient.

Like it was said before CLEAN surface on block and head to where you can't feel anything with your nail and a clean gasket. The emphasis on OEM is cause it's good to go, cometic isn't needed and a big reason the Mazda gasket is cheaper has much to do with scale of manufacturing.
I did get arp studs though.

Alright guys, sounds good. I’m home now. I just checked the block. The machining is better than I thought. No finger nail dragging anywhere, no light under straight edge. It’s nice and shiny. There was one small spot where some surface rust popped up over the last three days but I wiped it off and doused it in oil. Other than the stain from the surface rust spot it looks perfect.

here are a couple pics. There is dust and lint on the surface as it hasn’t been cleaned yet. I am now thinking that maybe I will take it back to the shop and have it decked another .001 after I bore/hone. Rationale is as follows. I decked it .003 to clean it and make it flat. That makes the bore/hone that much more accurate. An additional .001 after will make sure everything is perfect prior to assembly. I will immediately have block cleaned after final deck. Does this sound like a solid plan? The deck job is $67 so it’s not crazy price wise.

https://cimg8.ibsrv.net/gimg/www.mia...3cd291bd51.jpg

​​​​​​​Can't feel anything on them though right?

No it feels smooth to the touch and much less than your picture.

Go for it. I would run it as is. But if you really want this to be your life motor, pay 67 more bucks. Looks fine to me as is.

Thanks man. I called the shop today and they said their finish is used daily for MLS gaskets. They did not have a RA number handy but oh well. I described the small surface rust as well to them and told them my plan to redeck...like you they said clean it off and use it, it will be fine. So I guess that’s that. Next up is to have the head checked. Crank is being finished this week. Bore and hone with torque plate from FM will be done end of next week hopefully. Then cleaning... and assembly. I am building this one myself. Fun times.