T&T: zinc scum

[Bruce Adornato via Trawlers-and-Trawlering]

It's been three months since I installed new zincs on my new to me 180 hour
old Yanmar 4LHA-STP in my mainship 30 and I checked them today or at least
4 of the 5.
.
They are about 25% or less gone but what is unusual to me is the amount of
yellow-white scum on all the zincs.
It is semi hard and required wire brushing to clear back to hard metal. I
run Yanmar coolant on specs. I have seen a little of this before on
previous boats but this seems excessive.

It seems the scum insulates the zincs from galvanic action. What is this
stuff? Is there a chemical engineer out there?

Second problem, the ridiculous 7/8 socket size, an atyptical size, (I dont
have one yet.. waiting by the door for the Amazon guy) for the one large
zinc refused to budge with my old Toyota crescent wrench and looks like it
has a lot of corrosion between the engine block and the bronze of the zinc
cap. I put some Liquid Wrench on it and plan to try again with a proper
socket set and breaker bar. If I heat the head of the bronze with a pencil
propane torch, does the bronze get tighter or looser? I suspect the
coefficient of expansion is greater for bronze than the engine block, so
maybe I should use my freon type freeze bottle to "shrink" the bronze. I do
not want to break anything other than the bond.

Should i have gone to metallurgy school rather than college?






--
bruce adornato
mainship 30
san francisco
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[Steve Sipe via Trawlers-and-Trawlering]

A 7/8" socket is hardly unusual. A trip to any hardware store or big box
should find one. Leave the crescent wrench in the toolbag.
I'm not sure I'd use a torch. Instead of trying to back it out, give it
a nudge tighter, just enough to get it to move. Then back it out. If the
zinc is threaded into a casting, you can do the breaker bar and correct
socket and strong arm it. If the zinc is in a copper or cupro-nickel
exchanger, be gentle. If the tapping has a hex head, use a box end
backup wrench to avoid torquing the body of the exchanger. torque wrench
to wrench. Again, no adjustable wrench on non-ferrous hex bodies, you'll
distort the tapping. Use a hex wrench. If the zincs are funky, just
replace them. If cost is a concern, save some bucks by replacing just
the zinc portion. Compared to what they protect, zincs are cheap,
they're called sacrificial for a reason. 3 months might not be excessive
for 25% erosion.  Coolant should have nothing to do with the zincs,
they're in the seawater circuit.

-------
Steve Sipe
Solo 4303 /Maerin/

On 3/14/2019 9:13 PM, Bruce Adornato via Trawlers-and-Trawlering wrote:
> It's been three months since I installed new zincs on my new to me 180 hour
> old Yanmar 4LHA-STP in my mainship 30 and I checked them today or at least
> 4 of the 5.
> .
> They are about 25% or less gone but what is unusual to me is the amount of
> yellow-white scum on all the zincs.
> It is semi hard and required wire brushing to clear back to hard metal. I
> run Yanmar coolant on specs. I have seen a little of this before on
> previous boats but this seems excessive.
>
> It seems the scum insulates the zincs from galvanic action. What is this
> stuff? Is there a chemical engineer out there?
>
> Second problem, the ridiculous 7/8 socket size, an atyptical size, (I dont
> have one yet.. waiting by the door for the Amazon guy) for the one large
> zinc refused to budge with my old Toyota crescent wrench and looks like it
> has a lot of corrosion between the engine block and the bronze of the zinc
> cap. I put some Liquid Wrench on it and plan to try again with a proper
> socket set and breaker bar. If I heat the head of the bronze with a pencil
> propane torch, does the bronze get tighter or looser? I suspect the
> coefficient of expansion is greater for bronze than the engine block, so
> maybe I should use my freon type freeze bottle to "shrink" the bronze. I do
> not want to break anything other than the bond.
>
> Should i have gone to metallurgy school rather than college?
>
>
>
>
>
>

_______________________________________________

[Rudy Sechez via Trawlers-and-Trawlering]

Bruce, a recent neighbor rebuilt a similar Yanmar engine. On his engine
those large anodes were in the coolant passages,as the engine was designed
that it could be raw water cooled. His anodes were screwed into steel caps,
the caps, by the time he was trying to remove them, were "fixed tight" in
the block. If your engine is similar and heat can be applied, try heating
the caps with a propane torch, then using the correct size socket, torque
the cap clockwise to loosen the threads, then back the cap out. If they
don't budge using a ratchet, try an impact wrench or a breaker bar. I'm not
a big fan of cheater bars on ratchets unless the added force required is
not to high as I've seen ratchet break from the added leverage. Breaker
bars are longer by design and usually built strong enough to handle the
load imparted by their length. 7/8 sockets are not an unusual size. Try
automotive parts stores, even Sears, places that sell sockets individually;
maybe even look in pawn shops.

*RUDY & JILL SECHEZ*
*BRINEY BUG*-a 34' Sail-Assisted Trawler
850-832-7748
Vero FL
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