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I recently opened up my machined block I got back from the shop I’m pretty sure everything is okay, then again I’ve never rebuilt an engine. Before I put the MLS head gasket on i cleaned the block surface with brake clean and a rag which left white stains. It’s an aluminum block not sure if these stains are an issue. I also noticed a gouge in the block surface.

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  • Welcome to Motor Vehicle Maintenance & Repair!
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Sep 9 at 13:15

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This should not cause you issue, but there are several things you should do prior to assembly.

First, check the block in the area of the stains by running a fingernail across it. If your fingernail drags across these where you can feel it, then there's an issue. I'd give you a 99.9% probability you won't feel anything, as it looks fine in the images (but you never know).

NOTE: I just noticed in the 3rd pic machine marks in the deck of the block. You'll probably feel these when running your finger nail across them. This is not what I'm talking about above. I'm talking about where you are finding the white splotches.

Next, clean the block faces with acetone. This will clean off any of the residue left behind by the brake cleaner. I'd suspect the cleaner you used was chlorinated, which is not good for aluminum, but isn't going to kill it. Next time try using non-chlorinated versions and you won't (shouldn't) have this issue. Use paper towels as the "rag" to get it clean. The paper fiber from the towel which gets left behind will breakdown over time, so will not be an issue. The fibers left behind by cloth towels won't break down as easily and will help to clog up the works inside the block.

And I don't know if you were going to, but I'd tape everything off after getting the block clean and paint it. This does a couple of things, like makes the block easier to keep clean (a clean engine on the outside allows it to run more efficiently), as well as help you to be able to detect any leaks if you use a lighter colored pain. I typically use a high-temp ceramic type engine paint which will withstand a higher heat than typical house paint. I will clean, prep, primer, and paint. This method makes it a little more durable. Just a suggestion.

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  • Thank you, I ran my finger nail across and don’t feel anything on the stains. It’s weird I thought that to but the cleaner I used is non chlorinated and yes I was gonna paint it with POR15, I’ll clean it up with acetone and paper towel thank you for the tips. Does that gouge look like an issue? In the first photo. It’s definitely feel able with a nail.
    – Muhammad Durrani
    Commented Sep 9 at 13:57
  • Since the block is aluminum, you can take a sharp razor blade and take down the gouge if it is sticking up. Usually, something very small like that isn't going to cause an issue. The gasket and sealer (if used) will usually take up any difference in height. If the gouge were running across the entire surface or if it was sticking up high enough, it might cause an issue. That doesn't look too bad to me, though.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Sep 9 at 14:00
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    @MuhammadDurrani Just a note: I've used POR15 and it's great stuff. If by chance this is going to be a "show car" that will sit with the hood open in direct sunlight for many days in its lifetime, POR15 is not the best choice. Direct sunlight degrades it, so it's usually recommended to paint over POR15 in direct sun exposure to protect it from sunlight. For any other use where the hood is closed most of the time, POR15 has no problem with occasional sunlight.
    – MTA
    Commented Sep 9 at 16:39
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    @MTA - Also good to note that POR15 gets EVERYWHERE. Sticky stuff. If you get it on your clothing, it'll not come out. Cannot re-use paint brushes, so get the el-cheapo ones from Harbor Freight. Once a can is opened, you pretty much use what you can, because when you put the lid back on, it will bond the lid to the can and you'll not get it open again. Great stuff, yes: caveats abound with it though.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Sep 9 at 18:11
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    @MuhammadDurrani As long as it's open season on POR15 tips, I'll mention that if you intend to apply two coats as recommended, it's absolutely essential to follow the directions on the can and do the second coat while the first coat is still tacky. If you wait until the first coat dries hard, the second coat will just bead up into ugly drops and it won't spread. You would have to scuff-sand the entire block if the first coat dries hard before you re-coat, so don't let that happen!
    – MTA
    Commented Sep 9 at 19:08

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