Dipping block in citric acid: bad idea?

[Luis A.]

Hi guys,

First time poster, long time lurker. I have a BMW 6 cylinder block that I had dipped at the machine shop to get rid of all the gunk but it still has surface rust. Cylinders have been honed and it's ready to be primed and painted after I de-rust it. My plan is to dip it in a citric acid bath but I'm wondering if the citric acid will attack the cylinder walls and other machined surfaces and thus ruin them? What concentration would you advice, in terms of pounds of acid powder per gallon of water?

Any thoughts?

Thanks in advance!

Luis

 

[SGKent]

I would suggest that if the cylinders are honed already you do nothing other than get some WD-40 on them now. Brush off the surface rust on the block with a hand brass or wire brush and paint it. If you mess up the honed surface you will have to have it honed again and they will probably hot wash it when they are done and mess up your paint again. If they over-hone it the ring gap will grow and let compression out. For every .0003 - .0005 they take off the cylinder the ring gap will grow by 3.1416 X that .0003 - .0005.

 

[Zeke]

Protect the cylinders and start with distilled white vinegar to convert the rust. If you wanna hurry it up a bit, use some phosphoric acid solution. But, that has to be washed off and really should be neutralized with baking soda.

I don't know anything about citric acid. I've been restoring cars for years and have always used vinegar or PA. You might use a thin coat of self etching primer. I don't think a thin coat will fail with the heat.

 

[Luis A.]

Thanks guys. Citric acid is successfully used, just like vinegar or pa to remove rust, oftentimes by adding it to the cooling system and letting it circulate. I just don't know what it would do to the honing and other machined surfaces. Maybe instead of dipping it I should brush it off since it's not that bad. I was just looking to save work...

 

[brownbagg]

we use citric acid to remove concrete from concrete trucks, it wont even hurt the paint under it

 

[bad_idea]

you called?