Technical What is this white powder stuff?

G' day guys,

Im hoping that someone can tell me what this white powder is. I pulled the heads (Ebelbrock aluminium) off my flathead today and some of the bolts have this white powder on them.

When I put the heads back on should I coat the length of them with a light grease?

Any advice would be appreciated.

Thanks...RodSports.

 

I believe that some of the head bolts enter the water jackets. To prevent leaks bypassing the head bolts a sealant is applied to the threads . It may be the residue from the sealant . Although withdrawing the bolts would clear the threads so the other cause may be electrolysis a reaction between the steel bolt and the ali head, there would be corrosion damage to the head around the bolt holes if that were the case . If the bolts were reluctant to come out the head , the residue would catch in the threads as the bolts were pulled through..

Given that the threads are clogged it might be the latter .. but looking closely the clogged threads are toward the top of the thread so there is a chance that is sealant residue that hasnt entered the tapped hole in the block ..

What condition are the heads in around the bolt holes ?

 

G'day Redoxide,

They're fairly clean and the bolts came out easily. When I built the motor I used a thread sealer (a GM dealer product). The heads are clean as well.
Your electrolysis theory makes sense, would a cause be from a poorly grounded block?

 

You usually find that the head sacrifices some of its material in and around the area the dissimilar metals come into contact. If the heads are clean with no sign of electroysis damage, it might just be the sealant residue .. ?

Im not any expert in this stuff , a wee bit research might answer the question of earthing. Its something to go on though.

 

What’s the hole that passes through look like cause that looks like alloy corrosion.

 

I use stuff called Indian head. It's a shellac gasket compound. I have been using it for years and never had a coolant leak around any bolt. But like everything else. Clean clean clean prior to applying

 

It looks like liquid Teflon residue?
I think GM head bolts are coated with a similar product .
At least that is what a few sets of aftermarket GM head bolts I have purchased had on them .

Tommy

 

Some flathead head bolts pass into the water jackets. That's thread sealant. Get some permatex thread sealant before reinstalling them or you'll have a water leak.

Sent from my SM-G977U using The H.A.M.B. mobile app

 

and/or
https://en.wikipedia.org/wiki/Galvanic_corrosion

 

caused by aluminum reacting to dissimilar metal in water - common - to help prevent that need to run a sacrificial anode - some for use where normally drain petcock installs - some special radiator caps have anode attached - search on summitracing.com, etc

 

Cocaine for a thousand Alex

 

Aluminum oxide.

 

It's the stuff that kept that bolt from breaking off way down in the block!

 

Not corrosion or galvanic. Galvanic would be between the alum head and what it touches, the block or bolt. Not the steel bolt in the cast iron block. It's thread sealant. Clean the bolts and use new sealant when putting back together.

Sent from dumb operator on a smart phone

 

^^^ agreed. & run a tap down block holes

 

I was always told to not use a tap to chase threads. I was told it will cut new metal every time it goes in the hole. They make thread chasers that do not cut metal. They look similar to a bolt with a line cut straight down the bolt across the threads. At least that is what a machinist friend showed me.

 

Another vote for using a thread chaser instead of a tap.

 

Kudos to the members of the Hamb. When I read the title asking about white powder, I was expecting this to go down hill fast. It didn't, guess I'm the only member with a warped mind.

 

Thread chaser is the right thing to use, not a tap!

 

I took an extra bolt, used the Dremel to cut two vertical slots thru the threads opposite each other. Ran it up and down each hole a couple of times with acetone atf mix then used a brass spiral brush to clean up. Worked well.

 

Yes I was young and dumb when I did mine , all my studs seep because of it

 

Thanks guys, Ive been away with work for a few days so havent been able to respond. Back at it this weekend so will provide an update - really appreciate your help.