Prepping a Engine Block

I thought I'd put this out to the whole group rather than just keeping it in the Queso thread. 

I've gotten the advice, from a highly trusted source, that I should sand down the mating surface on the block to properly prep it before replacing the HG on the Mini. 320 on an aluminum block, then flush out as much of the milkshake I can with cheapo oil, fill with new oil, run it briefly and then change the oil again.

 I really do trust the advice given to me as this person is very experienced and has never lead me wrong but, frankly, it completely wigs me out. 

WWGRMD? Fill as many holes as possible with paper towels and sand away? Definitely never run the risk of abrasive material getting into the engine?

Do not sand anything.

Scrape any debris off with a plastic scraper and you're good. If it's really stuck, get a can of aerosol gasket remover.  Stuff the bores with rags to catch any of the gasket bits

Never, ever, ever sand gasket mating surfaces. There is no way for you to be sure that it will come out flat in any way.

Not sure exactly what your friends experience is but I do this for a living.

I have heard of people sanding old school iron blocks and iron heads with cork gaskets.  I have been told the modern aluminum stuff with MLS gaskets requires a much better surface flatness than you can achieve this way and if it's not good enough as-is then it needs a machine shop.

So I've used a giant emery stone to clean off a deck but it was desperate times, the gasket sealed but I'm sure some abrasive material went through the engine. When I disassembled the engine (race engine) it looked like a motor that had ingested some level of grit.

If I'm not getting the deck skimmed I just clean it up with a scraper as Shawn G specified.

GM actually had a tsb out regarding NOT using the Roloc Scotchbrite cookies to clean gasket surfaces because the abrasive was wiping out bearings.

In reply to ShawnG :

The motor in question was nearing time for a rebuild, it had a minor head gasket issue and I was simply tying to get a few more weekends out of it. The bores and rod bearings weren't pretty but I knew I was going to replace all of the bearings and bore the block when I "hand" milled the deck. 

In reply to Tom1200 :

I think we've all been there. My reply wasn't specifically to your engine, just a general "don't do it" example.

That said, I've lapped a head and block flat with a sheet of glass and emery paper. Not something I would do again but I was racing on a starving apprentice budget.

I wouldn't try that in the car-not even on a Challenge car. You're risking abrasives in the engine as well as not being able to actually make the surface flat because you're working in an engine bay.

However, I do think you can prep a block by pulling the engine, stripping everything down and progressing through various grits of sandpaper on top of plate glass (the kind that sit on cheap coffee tables) that sits on top of a thick carpet. Turn the block upside down after marking the deck with magic marker.  Push/pull it across the glass until all the marker is gone, then repeat with progressively finer grits.  I've seen it described a couple of places but haven't given it a shot.

Will this be a bare block or an assembled shortblock? I've cleaned up the deck on a bare block with an electric grinder before and ended up just fine haha. I would put a bit more thought into it before adding grit into an assembled short block though.

Yeah, don't sand.

I continue to use the scotch-brite cookies on iron blocks.  I've never had any issues.  Anything that gets in the bores isn't going to kill anything before it is burned or escorted out the exhuast valve.  Seeing how long it takes to remove gasket material from the deck, I don't have any qualms about a bit of the abrasive in the bores.  Cavalier attitude?  Maybe, but it's never hurt anything on my blocks.

I just recently put incredibly expensive heads on a low-mileage LQ9 shortblock.  Prep consisted of  scotchbrite cookies, a long, flat file, and then a rag soaked in brake cleaner on the deck and in the bores.

In reply to Curtis73 (Forum Supporter) :

I continue to use abrasives to clean the block. But then I get crazy about air pressure washing everything out. Followed by high pressure hot water blasting. Then A hand scrubbing with warm soapy water followed by a rinse.  
  I let air dry followed with at least 4 cans of brake parts washing on white butcher paper.  If any stain dirt or grit is left. I re- soap and rinse. Air dry  and fresh white butcher paper and a Re-wash with brake parts cleaner.   I would continue but to date Ive never had to.  

I did the head of a Fiat X-1/9 once, port & polish, the whole deal.  Head was resurfaced by water cooled surface grinder, looked like a mirror.  My friend that who a foreign car repair shop said "Rough it up, there's no tooth for the gasket to bite on".  A quick mill job later, now it's got tooth and wicked more compression.

In reply to Curtis73 (Forum Supporter) :

I think the issue with scotch bright discs was the fibers getting into the oil and damaging the crank bearings. GM doesn't do TSB's based on internet wives tales so I believe them. Also I once damaged an aluminum head by being too aggressive with one of those causing a coolant leak. The alternative I use now is these

90% as effective and less likely to damage the metal. Plus they dont plug up with crud and last a lot longer than the fiber discs.

Curtis73 (Forum Supporter) said:

Yeah, don't sand.

I continue to use the scotch-brite cookies on iron blocks.  I've never had any issues.

You're lucky, then.  I killed a 3.8 Sable AND the 429 in my first car.  The 429 was knocking before I made it home from work.

It's the abrasive wearing off of the cookie that is the problem, not the material being cleaned.

If it was an MLS gasket car, I've never needed to do anything more crazy than wiping with a carb cleaner soaked paper towel.  (Not a rag, rags leave lint)  Maaaaybe scrape with a credit card.  If it's a composition style gasket, I have a nice flat carbide scraper that makes quick work of anything, including high spots in the metal around the head bolt holes.

Somewhat anecdotal, but here goes:

The mechanic I worked for in the 90's prescribed to the give it some tooth ideology. We had a piece of 40 grit we'd use, by hand. We never had a car come back. I hand sanded the head and block on my Miata (out of car, totally disassembled, sandpaper on flattest piece of plywood I could find. I have heard of using shaving cream to keep debris out. Basically, rotate the engine til all pistons are halfway up and down in the bore, fill, sand, scoop out and clean.

YRMV, and I don't mean to contradict everyone else, but I have done and seen it done with good results quite a bit.

Thanks all, I really appreciate the feedback. My friend is an extremely experienced mechanic who, as I said, has never led me wrong but responses here have confirmed that I can't get good with the sanding method. 

This is an assembled short block still in the car - there's no meaningful washing/rinsing/etc. that can happen. If this was a disassembled block, I don't think I'd have any reservations.