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Corrosion Resistance Of Plated Bolts

I am having a corrosion problem with cylinder head bolts on an inboard engine. Where the threaded end of the bolt protrudes into the water jacket (salt water cooled), it corrodes away in short order. A bolt supplier suggested I try "Yellow Zinc" plated bolts. Is this a wise move? Stainless head bolts are WAY out of my price range. Any suggestions would be greatly appreciated.

Thanks,

Paul Noetzel
- Garden City Park, New York
2003

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It will help but not nearly as much as you'd probably like. Almost all plated bolts like this are zinc plated with a chromate conversion coating. When the chromate conversion coating is heavier and more corrosion resistant it is yellow instead of clear or bluish. But that thin zinc plating on a few bolts comprises a 'sacrificial anode' inside the engine, so it will probably last no time at all regardless of the conversion coating.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

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2003

Paul,

I find it a bit weird that your bolts PROTRUDE into the water jacket.

l. If they protrude by too much, why not use a shorter bolt?

2. Then you have two options

a. Run teflon tape all over the bolt threads AND especially over the end of the bolt. Any plumbing supply house should keep this teflon tape.
b) use molyslip or a similar grease on the bolt.

As mentioned, I find it rather unusual that the bolt heads extend into the salt water. Cap them, so-to-speak, as above and surely you'll no longer have any problems.

Food for thought, anyhow.

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).

Thanks Ted:

You confirmed what I was thinking that the zinc would act as a sacrificial anode. I was just wondering if the conversion coating would help. Oh well, I guess I have to bite the bullet and buy the stainless head bolts.$OUCH$!

Thanks again,

Paul Noetzel
- Garden City Park, New York
2003