Stainless cover on F85 pump. Galvanic Corrosion?

[bcboomer]

The bronze sea water pump on my W46 is worn so I want to rebuild the pump. I see a reasonably priced kit on ebait with a stainless steel cover.
Would there be a corrosion problem? If so, would Tefgel on the screws and hylomar on the cover prevent a problem?

[Bycrick]

I was a real fan of the aftermarket SpeedSeal pump covers. Among other things, the kit included replacement stainless steel cover screws that had big knurled knobs rather than requiring a screwdriver or wrench for removal. As of last week, the third one has broken off right at the head, leaving a difficult to remove screw shank in the pump.

That’s in spite of careful use of Tefgel on the threads. As a guess, and only a guess, I’d think that the SS would be OK where the impeller is, because that water is always changing. But where thin layers of water can collect around the screws or between the cover and the body, you might have an issue.

[bcboomer]

Thanks for the info. I had tried to buy a SpeedSeal but he didn't have one to fit. Perhaps if I use the bronze screws there won't be a problem.

[billknny]

Bronze and stainless steel live happily together, no worries.

Just as an example, most sailboat rigs have bronze turnbuckles on stainless studs. My saltwater cooling pump is all bronze with stainless screws. Give me ten minutes to think about it and I'll come up with ten more examples.

[bcboomer]

Thanks Bill, but I wonder why Bycrick has had the stainless screws fail.
Come to think of it, my bronze pump has stainless washers and lock washers under the heads of the bronze screws. No visible problem, but they don't contact water.

[Jim Cate]

Thanks Bill, but I wonder why Bycrick has had the stainless screws fail.

I dunno why his failed, but mine failed from over torquing on my ham-handed part. The screws on my pump are tiny: I was able to drill out and re-tap for 6-32 replacements, and 6-32 is damn small! Very easy to exert too much force on the fairly large thumb screw heads.

If you visualize the setup, no entrapped salt water should be in a place to bother the screws, unless there is a drip from an external source, and if one uses some lanolin or other grease when installing, there should be no issues. S/s and bronze are quite similar in the electromotive series as others have shown.

I'd be happy with a 316 cover plate. I'd inspect for any corrosion when doing normal servicing and rethink if pitting began to show. I doubt if it would.

Jim

[Bycrick]

The failed screws were all 4mm on a Westerbeke Genset. My guess is that salt water could get trapped under the knurled knob, between the knob and the cover plate. Even with Tefgel, if the water sits in this area, it will eventually corrode. The screws broke within 1/16” of the knob itself, in the area where the screw passed through the cover plate. The SS stub that was left in the pump body was just fine.

[tkeithlu]

I think there's a perception problem on stainless steel. It seems so strong because it's shiny and does not corrode (mostly, watch the type!). It's really not up to the shear of a graded steel bolt; kind of mushy, in fact.

[Mithril Bham]

I love my SpeedSeal.
Now I'm worried.

[oleman]

McMaster.com has bronze screws in various sizes. I would not use anything else in a bronze pump body unless it was being sold immediately!.

[Bycrick]

I didn’t find any knurled head screws that small at McMaster. I’m sure you can buy small bronze screws in boxes of 100. At the same time, the Speedseal screws that Alex sent me for the Yanmar pump are still fine. This time I had to replace the Westerbeke pump because it needed shaft, bearings, seals and to fix the broken screws/holes for the cover. The screws were the least of the problem.

[Compass790]

Had experience with a few bronze pumps over decades with ss screws no worries

[Compass790]

Forgot to add the shafts are stainless so don't sweat it.

[Disailor]

For those needing to replace bearings: There are very few mfgrs of bearings so the various sizes often do double duty. The smaller of the two sealed bearings on the raw water pump (Jabsco or Johnson?) that came with my Yanmar 3ym30 is also the bearing for the clutch shaft on a Chevrolet std tranny. $1.99 at the auto parts store! All they need to find you a replacement is the outer & inner bore diam as well as the thickness - they lookit up by size.

[billknny]

Originally Posted by oleman

McMaster.com has bronze screws in various sizes. I would not use anything else in a bronze pump body unless it was being sold immediately!.

You know not of what you speak.

Bronze and stainless are fine. Even UNDERWATER. For example, my MaxProp (bronze body) is held together by stainless screws and has been for 25 years.

Millions of bronze props sit on stainless shafts.

Most sailboat rigs have bronze and stainless parts threaded together, and that is WAY better than stainless on stainless.

Many bronze prop struts have stainless bodied cutlass bearing installed in them.

Etc, etc, etc.

What EXACTLY do you expect to happen?