Engine Mount

[Troy Scott]

I'm in the process of fitting new equipment and cosmetically upgrading my CD36. While I'm at it, I plan to have the engine removed because the mount is very rusty. I'm thinking I might want to have the original mount duplicated in stainless steel or bronze. Thoughts?

[Parfait's Provider]

The metalurgists need to pipe up here, but I suspect stainless will be a problem because it needs air to keep from rusting and the bed has to be buried in glass to be secure to the hull. Mild steel, as many of us have discovered, rusts too. How about Corten steel?

There must be a reason we don't see bronze beds, but I am not sure what it is. Maybe the incompatibility with the steel bolts in the engine mounts? Can you get custom mounts with steel on the engine side and bronze on the other?

I am not sure what is in the new bed that Robinhood makes for their 36, but it has plenty of surface area to spread the load to the hull. It could be glass over white oak for all I know. It provides a nice pan under the engine so you don't have oil dripping into the bilge proper. Of course,if you don't have a Perkins 4-108, it may not drip much into the bilge. If you are going to redo the bed, a pan would help bring the engine installation up to current standards.

[Russell]

I had the same problem, rusting engine bed, to the point the glass which encased the metal pipes which made up the bed had cracked due to the rust.

What I did was remove the engine, with plans to remove the old engine bed and redo it somewhere. When the glass was all cut off of the old pipes I was able to clean them up and found plenty of metal left on them. I considered replacing them with stainless, but as already pointed out, stainless would not be happy without oxygen if it was glassed in. So I stayed with the current setup, cleaning them up and reglassing them.

[Tom Blanchard]

last winter I repowered my CD 36 with a Yanmar 3JH4 and planned to remove the old rusty mounts. when the old 4-108 was removed and the beds examined and cleaned, there was plenty of metal there, so rear brackets were made adapting the Yanamr to the old beds. after a redesign of the new brackets, it seems to have worked ok. using the old beds avoided a lot of glass grinding dust.

[Troy Scott]

Thanks Ken, Russell and Tom,

The input so far is helpful. As Ken suggested, a metallurgist needs to join in the discussion.

I understand that SS needs air to maintain it's qualities, but doesn't the the corrosion problem happen when moisture is next to the SS with air excluded.... as in vinyl-covered lifelines? If I use epoxy to glass the SS mounts into the hull, wouldn't the question of water be eliminated? And BTW, I would seal the SS before installation first with epoxy primer and then with catalyzed polyurethane paint. Wouldn't the combination of the paint prep and epoxy resin with the fiberglass pretty much eliminate the corrosion problem?

[Parfait's Provider]

As I understand it, even waxing SS stanchions will cause them to rust. Not sure whether any other coating would be a hinderance or not.

[Matt Cawthorne]

The issue with stainless is the fact that salt water can get in at the edges of where you glass it and in the case of an almost perfectly tight joint set up a galvanic cell. The galvanic cell happens between the oxidized coating on the stainless and the non-oxidized core material. It takes a while to start, but once started, it is extremely aggressive. A new oxidized layer does not form to shut the process down in a crevice. Chlorides disolve away the material and then carry the iron to the edge of the crevice where the iron can be taken by the oxygen (lower energy state). The chloride is now free to migrate back to the source and grab some more iron. Very .

I have a CD-36 and feel that in a few years it will be due for an engine bed. I am considering either making one up from fiberglass or using mild steel and having it hot galvanized. If a part is galvanized, the cell works in reverse of stainless and the electrical potential coats zinc onto the exposed metal.

If I do fiberglass, I will build up supports in glass that the engine mount/isolator will bolt to directly.

Matt

[fenixrises]

Hi Troy,

Multiple options, with caution.
Caution: Grinding fiberglass in confined spaces is a very large pain in the a**. If you do not have experience working with FG materials it can be a nightmare.

Replacing engine beds is no easy project, no matter how it is done or the material chosen.

If the original beds and fiberglass are sound but cosmetically nasty you could remove the engine and clean the steel with a compound that replaces the iron oxide(rust) with iron phosphate. This is a commonly available liquid used by metal workers. It is called something like "Phosfo". It will leave a surface that is good for repainting. Afterwards use a high content cold zinc primer and finish with a two part epoxy.

OR if the steel is too far gone make new parts from mild steel.
Stainless is not good for this. It is much more difficult to work and is subject crevice corrosion and becoming brittle from vibration. Gauling is also a problem when drilling and tapping for fasteners.

If you use mild steel(original parts or new) you could have the part(s) hot dip galvanized. This is easy to do but difficult to find someone who will do such a small job. Most galvanizers will only do 500 lbs of steel as the smallest job.

BUT it is possible to find someone who will sandblast the steel and flame spray it with either molten aluminum or zinc. This is a very common process. Years ago I had a small LPG tank flame sprayed for a nominal charge. With the proper primer the coated steel can then be painted with epoxy.

OR you might think about replacing the the beds with a buildup of fiberglass. Someone else mentioned the possibility of getting a molded FG pan from Robinhood. This might be an ideal solution IF it fits without a lot of trouble.

Making new beds of FG is not hard BUT it is messy. Epoxy sounds ideal BUT most FG materials are difficult to work with when using epoxy because there is no styrene in the resin. The styrene breaks down the binder used when making FG fabrics. It helps hold the fabric together, especially FG mat which is totally held together by binder. Vinylester resin would be the resin of choice for this project. Needless to say there will be the need to do a LOT of grinding.

An easy way to make the beds is to use polyurethane sheet foam. It is usually available from home building stores. It is used for home insulation. This is not the common white styrofoam, which dissolves when exposed to polyester or vinylester resins. It comes in one inch thick sheets, often with aluminum foil on one side. One sheet should be plenty to do the job. It cuts easily with a trim knife or hand saw.

Build up layers of the foam, shaping it to the hull with a coarse sanding block. Attach the foam to the hull with "Bondo". Bondo can also be used to fill minor gaps and irregularities. On the top layer of foam cut a flat groove to hold a piece of 2" wide 3/8" thick mild steel flat bar. The steel plate should be as long as possible and positioned correctly for the engine mounts. Care must be taken to insure the finished height and width will allow the engine to fit properly.

FG over one whole side at a time. You will find it is easier to do this if you make full size patterns for the FG material from some kind of heavy weight paper. I would recommend 3-4 layers of FG material.
Bi-axial FG material made on a 45 degree bias would be best. If possible each layer should overlap the preceeding layer by 3".
After this is done you can use the sheet foam to make a drip pan. Then FG over the foam. After all FG work is done mix industrial talc with resin to a putty like consistency. Use this mixture to fill in the weave of the FG fabric, sand smooth and paint.

Kinda makes you think if it is all really necessary!!!

Happy grinding,
Fred B.

[Tom Blanchard]

Troy, after removing my engine, I had two engineers/sailers, one who built his own steel boat, look at my engine bed. They agreed that; 1) the mild steel is not in a hostile environment on the CD 36 if properly coated, and 2) with recoating the existing bed had plenty of strength for a repower.

[Troy Scott]

Gentlemen,

Thanks for all the input! This is a great forum.

I guess I'll be able to judge the situation better after we pull the engine. It's certainly possible that a rework of the existing mount would be satisfactory. I'll be happy with cleaning and recoating the old mount if that's a reasonable option. I think I can get it hot galvanized if I can get it out. If the exposed parts of the mount are rusty, I have to wonder what the parts of the mount inside the glass are like. What have you guys found WRT the encased parts of the mount? Are they protected and not rusty? What about rust from the inside of the tubing? My previous experience with welded engine mounts is on airplanes. The tubing on those mounts is hollow, and is sometimes filled with linseed oil to prevent corrosion. Is the mount hollow or solid?

[Troy Scott]

Tom Blanchard,

Did you have the mount recoated in place, or did you remove it for recoating? What coating process did you use?

[Troy Scott]

Fred B.,

Could this be the steel treatment/paint prep you wrote about?:

http://www.epi.com/metal-finishes/zinc- ... s.html#662

[Al Levesque]

We had the mount removed from our CD33. It was a three point mount and we needed four. The interior was not really encased since the ends were open. The mount had plenty of metal left and would have lasted as long as the new engine. It was a major grinding job to remove it and it was cut up in the process. If we had had a CD36 we would have pursued the Robinhood mount. They do not have a similar mount for the CD33. We now have encased wood stringers glassed in place and this looks like it would be much more adaptable to any future engine change.

[Parfait's Provider]

If the mount is already rusting to the point that the glass is fracturing around it, then there isn't much choice but to remove the mild steel. When the expansive flaking has started, I think you are in for the whole dollar. Parfait's mount was open-ended; I don't know whether closing it off and filling with an inert gas is worth the trouble; after all, the original mounts last for a couple of decades, so a bit more protection, like galvanizing or coating, ought to do the trick even longer.

[fenixrises]

Hi Troy,

That site you posted looks like the stuff.

BTW if you use steel tubing and weld caps on the end of the tubes it is not necessary to fill the tube with anything. In a short period of time the oxygen available inside the tube will be used up and corrosion will stop.

Take care,
Fred