"Crevice Corrosion" of Stainless Steel bolts

[fairdeal]

I was reinstalling the tilt/trim unit yesterday
on the 2005 F225 -
there are 8 M10 bolts that hold it to the brackets.
They are doubtless original to the engine.

I had previously chased the threaded holes with a tap
to make sure they were in good condition,
and wirebrushed the bolts,
and then applied teflon pipe sealant to the bolts before insertion.

As I was snugging the bolts -
not final torque, but starting to tighten -
the head of a bolt popped off !
and then another.

Classic example of 'crevice corrosion' -
the outside of the bolts looked fine,
nothing to suspect that they were compromised.

I'm just lucky that it happened at installation,
not when removing them after a long period
when they might be reluctant to be backed out

[

[99yam40]

what is going on with the white worms?
and that one bolt shaft looks hollow

[robert graham]

I've never seen or heard of a hollow bolt.....can't be a very good idea...

[boscoe99]

I don't know what it is about Yamaha bolts. Never experienced any that break so easily. New, old, does not matter.

[fairdeal]

LOL - they are hollow now,
because I drilled them for the "EZE-OUT"
the drilling itself wasn't easy, but fortunately I was prepared with cobalt bits

I can't recall any other Yamaha bolt shear on me..

interestingly, these bolts are the same part number
as used on the F225 to attach the lower unit to the midsection -
I've certainly had them on & off plenty of times.

But my engine has spent much of its life moored in Florida seawater;
although the lower unit was tilted up, for all but a few thousand hours,
those bolts on the bracket have been submerged
for a good part of ~16 years.

Hence the white worms...

[99yam40]

ok, that explains a lot.

I have had bolt heads sheer off before and they are better than the ones that sheer off down into the threaded area itself.
fighting some of both on a 77 FJ40 exhaust and intake.
I was suprized most came out

[DennisG01]

You're right - you are AMAZINGLY lucky that they snapped when they did. It's hard to believe, actually, that they DIDN'T snap on removal - certainly a lot more torque was needed to get them out.

[robert graham]

Why would Yamaha choose a hollow bolt design, especially since a hollow bolt must be weaker and bolts on marine/outboard applications tend to break off upon removal???

[DennisG01]

Why would Yamaha choose a hollow bolt design, especially since a hollow bolt must be weaker and bolts on marine/outboard applications tend to break off upon removal???

They're not hollow. Read post #5.

[robert graham]

They're not hollow. Read post #5.

O.K., I got it now!...

[Sheff 69]

Those failures don't look like crevice corrosion, they like fatigue failures (or corrosion fatigue failures).
If you've had the bolts out numerous times, that could explain why.
If you could get me a larger magnified view of the failure face (and in focus) I might be able to confirm.

John