Cylinder head surface turned black

[JohnsXr400]

So I made huge rookie mistake yesterday. I'm rebuilding my xr400 after engine failure (blown piston). I got my top end all disassembled. I figured it was time to get the parts all cleaned up. Here's where I made the stupid mistake. I had some purple power laying around in the garage and figured it would be a good cleaner for my parts. I took a wash bucket and filled it with some purple power and diluted it with water. I took my top end parts and placed them in the bucket and let them sit overnight. I now know that was a huge mistake. I pulled the parts out and they actually didn't look half bad but when I pulled my cylinder head out the smooth aluminum surfaces all turned a matte black color. SOAB! The surface is now rough to the touch. I'm so upset and I just don't know what to do from here. So my questions is, is there anything I can do to combat this? I figured I can machine surface the bottom side, which I have to do anyways, but what about the top? Is there any way to clean/machine the cam journals and the valve spring seats? Or is this thing toasted? I don't know what to do, any help is appreciated, thanks.

Edited May 20, 2017 by JohnsXr400

[brianbenson]

evidently, purple power etches aluminum. 

i'd put it back together and run it.  it won't be as tight as before, but it will run.

 

[jaguar57]

just clean the black rough stuff off with fine sandpaper

[turbo dan]

Corrosion.  Steel rusts orange, aluminum white or gray.  The bad news is the journals.  That surface corrosion already increased the clearance, removing it will increase them even more.  I don't know if that is usable or not.

[JohnsXr400]

5 hours ago, brianbenson said:

evidently, purple power etches aluminum. 

i'd put it back together and run it.  it won't be as tight as before, but it will run.

 

 

3 hours ago, jaguar57 said:

just clean the black rough stuff off with fine sandpaper

 

3 hours ago, turbo dan said:

Corrosion.  Steel rusts orange, aluminum white or gray.  The bad news is the journals.  That surface corrosion already increased the clearance, removing it will increase them even more.  I don't know if that is usable or not.

Thanks for the advice guys. I was afraid this was the case. I probably would just use some sand paper and call it good, but I'm OCD and I would like to avoid putting a bad part with new/good parts. The biggest thing I'm nervous about is the journals as turbo dan mentioned. I bought a new cam for this thing and it just seems silly to me to put it on this head. Thinking about getting a new head now. I really don't want to spend extra money but like I said I don't to question this thing when it gets put back together. Anyone have any advice on where to get a good reliable Head? Thanks. 

[jaguar57]

can't you just see if there is any noticeable play with head parts caused by the removal of that corroded layer?

[JohnsXr400]

1 hour ago, jaguar57 said:

can't you just see if there is any noticeable play with head parts caused by the removal of that corroded layer?

Thats what I'm going to do first. Hopefully its still within tolerance. I'm just planning for worse case scenario. 

[jsantapau]

take the head and the camshaft to a machine shop  and see if line boring the cam journals can bring it back to spec.   then some emery paper laying flat on a piece of glass and polish the head gasket surface area.  if the valve guides and valve seats did not etch you will be fine  if they did etch well new guides/oversized valve stems and the seats cut /replaced  may be in order.   any good automotive style machine shop can answer your questions

[highmarker]

Hopefully you rinsed everything really good with hot water , might want to seal the external surfaces with high temp clearcoat or your gonna be fighting corrosion from here on out.

Edited May 23, 2017 by highmarker

[bikedude987]

IF the valve guides and seats are good, then you can use the head.  Deck the head surface to restore flatness/remove oxidation, and gently (soda blast?) the journals to remove oxidation.  Check clearances with pastigauge and the result will determine your next step.  Worst case is you'll have to have the journals welded up and re-machined...

[JohnsXr400]

On 5/21/2017 at 0:29 PM, jsantapau said:

...if the valve guides and valve seats did not etch you will be fine  if they did etch well new guides/oversized valve stems and the seats cut /replaced  may be in order.   any good automotive style machine shop can answer your questions

 

40 minutes ago, bikedude987 said:

IF the valve guides and seats are good, then you can use the head. 

It looks like the acid got to all the seats. Is there a way to clean those up? I just can't think of anything that will get into those tight spaces. From what I can tell it looks like it started to eat into the seat surface but not by much and only in a few spots as you can see in the pictures. How can I check to see if they are still good? I realize that these are all good questions for a machine shop but I would just like to know what I'm getting into. Thanks guys.

 

 

[grayracer513]

Don't run the engine with the gray coating on any wear surface like the cam saddles.  Aluminum oxide is a hard abrasive.  Clean it off to the extent possible and check the camshaft clearance with PlastiGage.

[ossagp]

On 5/22/2017 at 4:01 PM, JohnsXr400 said:

 

It looks like the acid got to all the seats. Is there a way to clean those up? I just can't think of anything that will get into those tight spaces. From what I can tell it looks like it started to eat into the seat surface but not by much and only in a few spots as you can see in the pictures. How can I check to see if they are still good? I realize that these are all good questions for a machine shop but I would just like to know what I'm getting into. Thanks guys.

 

 

I think when you are referring to seats you,  you mean the place where the spring seats rest.   Those aren't going to be hurt by the pitting that I am seeing.  The steel SEATS that go over them will make that a non issue if that is what you were referring too.  the actual ferrous valve seats look like you need to surface them and by now the guides need some help. 

[skorpan777]

There are pretty cheap used  head on ebay 

Edited May 31, 2017 by skorpan777