EZ30 Block flatness tolerance?

[Panda]

Hey all, 2004 BP 3.0 Outback.

 

I'm rebuilding this engine from the short block up, Had a teeny tiny external coolant drip from the head gasket above the oil cooler.....any sane person wouldn't worry about it but i saw it as an excuse to tear an EZ down and build my library of Subaru knowledge. I've had the heads hardness and crack tested and tidied up at the machine shop. I was wonder what the tolerances for flatness of the block are? obviously i'm limited to DIY methods for prepping the block. I've done the entire disassembly strictly to the FSM so far, however i can't seem to find the allowable tolerances for the block, it states the heads but not the block specs. Heads have been milled so they should be perfect, however the block.....i've used an old bathroom tile left over from a renovation with 600grit sandpaper and a lot of wd40 to clean up the block surfaces. With my feeler gauge I'm finding a gap about 0.003 or 0.004in across the block, light can also be seen from a torch. Just wondering if i should be worried about this? does anyone know what the specs should be? Will the "perfect head" surface clamp down and pull the block into a good seal? I'm using 100% OEM parts including the head gaskets. I'm also re using my head bolts but that might be a argument for another day.

 

Any opinions appreciated. Cheers

[Gripless]

Won’t it be the same as the heads, warped is warped so 0.002” or 0.05mm?

What’s the removed material limit in the service manual old one was something like 0.012" or 0.30 mm. So. You need to check how much the heads have been cut.

 

Shouldn’t you torque the case halves to spec before any measurement or machining work?
 

A mirror or glass sheet is about the flattest thing I’ve found for flat polishing. Don’t forget to rotate the part often so any uneven force you apply isn’t the same angle the whole time. Just because it is flat doesn’t mean it’s square.
 

Lol at AI summary, searched  “skim subaru block flatness” and got a summary of your post as the answer.

Quote

To skim the flatness of a Subaru block, you can use a flat porcelain tile with sandpaper sheets soaked in WD40. This method is effective for high mileage or beater engines. The process involves:

• Using a flat porcelain tile as a flat surface.
• Applying sandpaper sheets to the tile to create a flat surface.
• Soaking the sandpaper sheets in WD40 to prevent damage to the tile.
• Checking flatness using a machinist straight edge and feeler gauge.This method is a worthwhile approach for restoring the flatness of the engine block, ensuring a perfect seal between the cylinder head and the engine block. Proper skimming prevents common engine problems such as gasket failure, coolant leaks, and compression loss. It is a precision machining process that removes a thin layer of material from the cylinder head’s sealing surface, restoring flatness and smoothness.