Detroit Diesels - Anyone see this before?

[Captain Ralph]

My engine zincs only show wear when the engine has done a trip
When docked for a year the shaft zincs deteriorate but never the engine ones
It appears that the shaft zincs are protecting the engine
I think the photo shows salt crystals

When your engine sits, the water drains away from the engine zincs. Dry zincs don't wear away.

 

[ian w]

But are the shaft zincs protecting the engine
Should be as the shafts connect to the engines

 

[Captain Ralph]

But are the shaft zincs protecting the engine
Should be as the shafts connect to the engines

Shaft zincs, rudder, tabs and hull protect from stray currents between them selves, the environment and that ^&* boat tied next to you.
Sadly, Micro galvanic currents may happen internal to your engine. The raw water path thru your heat ex-changer contacts many different levels of bronze, copper, Stainless and silver solder, may be more. These zincs usually turn to mush before they are eroded away but a zinc may still be required.
Internal engine galvanic currents can not be protected from the shaft zinc.

 

[Salty lady]

My mechanic highly recommend not put a zink in the water pump as it’s on the intake side.
As the zink deteriorates pieces come off and go trough the impeller. Makes sense.

Salty Lady. 53MY #555
Ft Pierce. Chester Ct

 

[motoryacht lover]

Help me get this straight. Is teflon tape a no no in zincs? Does it interfere with the bonding by separating the 2 metals?

 

[Captain Ralph]

My mechanic highly recommend not put a zink in the water pump as it’s on the intake side.
As the zink deteriorates pieces come off and go trough the impeller. Makes sense.

Salty Lady. 53MY #555
Ft Pierce. Chester Ct

On lots of Detroit/Jabsco pumps, you have a plug on both sides of the pump.
I can agree with your techs comments partly, as long periods of no inspections occur of the intake zinc, it could chunk off and damage the pump impeller.
However, some feel this is an important location for a zinc protecting the pump shaft vs all around. This would be a protective plan up to you.

 

[Captain Ralph]

Help me get this straight. Is teflon tape a no no in zincs? Does it interfere with the bonding by separating the 2 metals?

Sadly some sealant will be required. IMO, even after the tapes or sealants are used, there is still plenty of metal to metal contact made from the zinc plug to the case it screws in to. Ohm it out your self, yep; zero resistance.

I remember trying to remove zinc plugs that wet in dry till they did not leak,, Pull bar near pulling the whole engine over till it (or something) came loose.

A lil tape or sealant and snug it in. The threads will cut thru and make metal to metal contact.
Sleep well on this.

 

[motoryacht lover]

Thanks for answering that for me.

 

[Briankinley2004]

Help me get this straight. Is teflon tape a no no in zincs? Does it interfere with the bonding by separating the 2 metals?

I have looked and looked for the write up but some guy that was a boat surveyor or mechanic did an actual study on this using ohm meters, etc and proved that Teflon tape or other sealants did very little, if anything, to interfere with the bonding and effectiveness of the zinc. If I ever find it again I will book mark. I don't think it was David Pascoe but some similar type page.

 

[cww]

I always use some kind of thread treatment on anything that touches saltwater, otherwise good luck ever getting it off.

 

[Pls]

Re: Detroit Diesels - Anyone see this befo

Copper conductive grease applied to the threads of the zinc and the zinc plug works well. Second the comment about not installing a zinc on the Jabsco pump, I had one break off and ruin the impeller. I have not noticed any additional corrosion on the pumps or their components without the zincs.

 

[zigzag930]

For an update. I pulled the two zincs caps from both engines. Two left the zincs in the housing, which I had to slowly jiggle out, but they came out fine. The other two were still screwed into the caps. One unscrewed nicely, the other broke off.

After "screwing" around (drilling, etc) trying to get the broken zinc out of the cap, I've decided to buy a new cap. I feel like a failure after watching that guy on you-tube rebuild that engine that was underwater, but I'm thinking he has more time on his hands than I do.

The zincs where in pretty decent shape, with about 70% left on all of them - but since they're all out, they are getting replaced. I have new gaskets for the housing and sprayed them down with CRC the other day, so hopefully they will come off easily.

Planning to bring my flat file to smooth down the flanges, install the new parts and hopefully not see any more white flowering on either side of the heat exchangers

 

[whoover]

Put the cap in a cup of muratic acid. That will eat the zinc out of the cap.

Walt Hoover

 

[ty1on73]

Quick poll- How many paint their zincs? whether interior or exterior... Me personally I don't- 1. believe they work best metal to metal 2. they are not permanent 3. seeing that they are not painted, it is a reminder that they are not permanent..

 

[jim rosenthal]

They should not be painted. It interferes with their function of protecting other metals.

 

[Captain Ralph]

They should not be painted. It interferes with their function of protecting other metals.

I am sure he meant the cap, not the alloy zinc.

 

[Avenger]

I am sure he meant the cap, not the alloy zinc.

If that's the case, then this doesn't apply, but most of them say "Do not paint" right on them.

 

[JD5652]

Painting the cap has no effect on functionality. I do not intentionally paint mine, but if it's within the spray zone when I'm doing some touch up painting, I do not tape it off either.

 

[DCMY #92]

When you disassemble the flanges look carefully at the mating surface of the the cast iron heat exchanger casing. I just spent several days removing iron oxide around a few bolt holes and on the mating surface, then filling with JB Weld Marine and sanding smooth. The bronze mating surfaces were fine. Full disclosure - my engines are 59 years old and were laid up for 10 years.

 

[zigzag930]

Everything is back together and no drips/leaks.

Now for the hard part...

Trying to find the paint to match. Did DD use tan paint on their engines? Did Hatteras paint them tan? Anyone know of a paint that matches (see 1st post for pictures)? I'm off to Homedepot to get some paint chip samples.