Best way to get surface rust off mating surfaces of an engine block?

[noahwins]

I have an very desireable engine block (to me, at least) that was neglected and sitting for a long time without Cosmoline or Fluid Film. It's developed a fine layer of surface rust on the head gasket mating surface and the oil pan gasket mating surface.

I asked a machinist what to do and he said use 800 grit sandpaper and a true, flat, level metal sanding block and carefully sand the whole length of the surface surface down.

I asked an engine builder for a second opinion and he said try using 3M white rolocs and a die grinder.

Who is right? Or is there another technique?

I'm trying to avoid the cost of getting it machined and taken down however many thou.

After the rust issue is resolved, I am going to coat the bare metal surfaces on the block in Fluid Film and wrap it in packing saran wrap because it's going back in storage in a dry, climate contolled storage unit with all of my other car parts. Anything wrong with this?

 

[bored350]

Method 1 is acceptable if performed with extreme patience, method 2 will not leave the flatness you describe. If this engine uses or will use an MLS style gasket, the flatter and finer the finish the better. If an "old style felt" type gasket is used, this is less of a concern.

Good example of proper sanding in this video:

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[noahwins]

Thank you. I was planning on using an MLS gasket because it's going to be boosted lightly, 7-10 psi using a blow through setup.

It's an iron block. I wonder why he suggested 800 grit? He was looking at the block when he told me his suggestion.

 

[Mr onetwo]

take it to a machine shop and have the surfaces trued up. You don't want to skimp on a motor thats going to be blown.

 

[sberry]

Spray it with some stuff, fix it when ready to use it.

 

[OccupantRJ]

Scuff manually with burgundy scotchbrite while using WD40 as a flushing lubricant. This how I bring back machined surfaces on machinery such as lathes, mills, table saws and drill press tables. The liquid produced will stain clothes and wood, so work on old cardboard that can be tossed.

 

[sqznby]

Good example of proper sanding in this video:

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Great video. That's exactly what I was going to suggest.

That's how I straightened some edges on a few tanks I made, they were aluminum. Worked great.

 

[Bellaireroad]

take it to a machine shop and have the surfaces trued up. You don't want to skimp on a motor thats going to be blown.

This



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[bored350]

The key to long life with an MLS gasket is surface finish (20 micro inches or better) and you likely didn't have that kind of finish to begin with. Based upon that and the low boost you plan to run, expect to have a competent machine shop square the deck and give you the finish those gaskets require so at this point, stabilize the rust and put the engine away until you're ready to use it. A few thou won't hurt anything on an iron block.

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[NUTTSGT]

The key to long life with an MLS gasket is surface finish (20 micro inches or better) and you likely didn't have that kind of finish to begin with. Based upon that and the low boost you plan to run, expect to have a competent machine shop square the deck and give you the finish those gaskets require so at this point, stabilize the rust and put the engine away until you're ready to use it. A few thou won't hurt anything on an iron block.

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Normally, I would have said a roloc and still would for the oil pan rails. However, since you are using a MLS gasket, I'd follow this advice above. MLS gaskets are getting more prevalent than what they used to be.

Your machine shop should know how to finish the surface. If he doesn't, you might consider finding another place.

 

[noahwins]

The key to long life with an MLS gasket is surface finish (20 micro inches or better) and you likely didn't have that kind of finish to begin with. B

Thanks for the spec.

You guys are right, I'll take it to the machine shop. I want to get this build 100% right.

 

[ilovevocs]

Post pics before spending money.

 

[toplessHO]

rolocs and oiled parts are iffy
the abrasive in the roloc is scattered thruout ,and some wont come out until its assembled and mixed with engine oil.
Use caution and make sure all of the abrasive is cleaned out.
800 grit wet or dry sandpaper isnt near as bad,and doesnt leave near as much abrasive everywhere like a roloc does.

 

[Bretny]

I have used a fine grit sharpening stone on engine decks with good success. Method 1 is basicly the same thing.

 

[ATC]

Scuff manually with burgundy scotchbrite while using WD40 as a flushing lubricant. This how I bring back machined surfaces on machinery such as lathes, mills, table saws and drill press tables. The liquid produced will stain clothes and wood, so work on old cardboard that can be tossed.

I agree. I just did this with my 460's intake mating surfaces, though, they weren't rusted.

 

[Hagatronics]

Thanks for the spec.

You guys are right, I'll take it to the machine shop. I want to get this build 100% right.

I'd have it decked at the time of build, not now. Engine builders are finicky. I had a brand new block that had a new closed deck freshly installed and decked. Engine builder wouldn't warranty it unless he re-decked it himself. Also if it's in storage who knows what other rust, nicks or scratches may occur over time.

 

[TimeWarpF100]

I have an very desireable engine block (to me, at least) that was neglected and sitting for a long time without Cosmoline or Fluid Film. It's developed a fine layer of surface rust on the head gasket mating surface and the oil pan gasket mating surface.

I asked a machinist what to do and he said use 800 grit sandpaper and a true, flat, level metal sanding block and carefully sand the whole length of the surface surface down.

I asked an engine builder for a second opinion and he said try using 3M white rolocs and a die grinder.

Who is right? Or is there another technique?

I'm trying to avoid the cost of getting it machined and taken down however many thou.

After the rust issue is resolved, I am going to coat the bare metal surfaces on the block in Fluid Film and wrap it in packing saran wrap because it's going back in storage in a dry, climate contolled storage unit with all of my other car parts. Anything wrong with this?

Pick up some PPG DX 579 metal cleaner & I will
Make that surface rust disappear in short order!
You will be shocked at how well and how fast it dissolves the rust.
Use with medium scotch brite

 

[Darkbreeze]

I know this is a fairly old thread, well, kind of. Three years isn't the worst necro ever, but I felt like addressing some of the misinformation here was necessary.

Having rebuilt over 500 engines, from start to finish, and probably some level of partial overhaul for at least another 500, I can without reservation say that while most of the advice here is good IF you have the availability of a machine shop or engine specialist, not everybody does and it isn't necessary in every case anyhow.

I'm not going to address the recommendations because for the most part they are good advice, however I will say that for SOME situations, especially if you have a known flat surface because it's been machined some time in the last few years without any occurrences of overheating or any known warpage as is common with aluminum blocks and heads, there is absolutely no reason why some very light sanding using a piece of double strength glass or perfectly flat machined steel, with a piece of 800 grit sandpaper, would be unacceptable for light cleanup of a slightly rusted block or cylinder head surface.

Even for "just" cleanup of those surfaces if no machine work is possible, could be possible and even acceptable, in a pinch. I've done such surfacing on more than 100 engines due to the closest machine shop being more than 80 miles away and wait times being over two months, with good effect. Obviously, it is not the perfect solution and we'd prefer to have the proper RA, but I have never had an engine come back with an early failure due to doing this UNLESS it was an engine with high mileage that had never been resurfaced at any prior time. Use a machinists level and glass with 800 grit, and you CAN do a passable job.

Further, it is also helpful to use a piece of glass large enough for the entire surface and the right goop, and you can easily see if there are any areas that are low or high so they can be addressed before final dressing. I am not disagreeing with methods here, but they are somewhat narrow in scope.

 

[MBfreak]

Darkbreeze, best advise !
I use 10 mm, most shops will give you a large piece from a replaced window free.
Take two pieces with blue and hold together so you see they ar actually totaly true.
Further, it is also helpful to use a piece of glass large enough for the entire surface and the right goop, and you can easily see if there are any areas that are low or high so they can be addressed before final dressing. I am not disagreeing with methods here, but they are somewhat narrow in scope.

Ola

 

[trs71]

The OP never mentioned WHAT the block was, did he? I mean if it's a 600 HP Hemi vs a 1936 John deere tractor?

It would make quite a difference IMHO....

 

[Shiftless]

The OP never mentioned WHAT the block was, did he? I mean if it's a 600 HP Hemi vs a 1936 John deere tractor?

It would make quite a difference IMHO....

OP hasn’t been seen in the past 9 months so maybe we will never know, but if it is anything like a 1936 JD engine, that would be very cool. OP said he is planning to supercharge with a 7-10 pound boost!