Head bolt question.

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M

macawman

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Preparing to reinstall the head on my 56 Johnson 10 horse and noticed something odd about the original bolts. Initially, I thought they had been painted aluminum color but even acetone wouldn't dissolve it. They are steel bolts, but it appears to be some form of aluminumized plating. That's just a wild speculation, but I'm wondering if the bolts might have been coated due to a dissimilar metals corrosion issue?
 
Yes, and those coatings prevail today through many different manufacturers. The coating is similar to a galvanize (zinc) coating and is done through electroplating.
It was done for two main reasons.
First was as a corrosion block.
Second was as a thread lubricant. In areas like engine mount bolts where stainless fasteners go on stainless bolts the two would gall and the bolt would have to be cut or twisted off to remove.
For those who work with stainless on a daily basis the answer is common and that is to add a lubricant. Unfortunately for those not in the know this did not happen often enough hence the manufacturers stepping in and coating the fasteners.
 
Thanks for the insight, Pappy. When speaking of lubricants, I assume you are referring to dry or semi-dry lubricants like molyb or graphite ?
 
The zinc coating itself acts as a lubricant.
When you have a stainless bolt going into a stainless housing or a stainless nut going onto a stainless bolt with any kind of torque you almost always have to have a lubricant. Stainless is soft and will gall easily in these applications. A good grease or a coating like above will protect against this galling.
Stainless "cold" works. Hit with a hammer....it hardens. Drill it....it hardens as you drill and will kill ordinary bits. Bend it......hardens. You get the idea.
 

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