Yanmar Raw Water Exhaust Manifold

[Blitz]

Looking for suggestions and advice. I removed my exhaust manifold which is on a raw water cooled 3GMD Yanmar engine. I removed it more for preventative maintence to ensure that there wasn't too much carbon build up on the exhaust gas side. It was good. Think it was removed about 15 years ago for a good cleaning.

On the raw water side, it has some flakey rust that should clean up easily, might even sand blast it and check for cracks. I know if it fails it could mean major damage to the engine or being stranded without an auxiliary. The exhaust manifold is 29 years old but engine only has less than 2, 500 hours.

After cleaning up the manifold and painting the outside I was hoping that someone might have a suggestion for a treatment or coating I could put on the inside of the raw water part of the manifold. Would a rusty metal primer, paint or copperless ablative bottom help or hurt to lesson the internal rusting of this part?

Or is this just one of those parts that I need to periodically need to replace overtime before it fails as preventative maintenance? ($550-$650) Has anyone been told this by there mechanic?

Thanks for your help,

Neal

 

[Blitz]

 

[kloudie1]

Neal, we used to have a rule of thumb that the rust-to-metal conversion is about 8:1.. meaning that if the rust layer is 1/16" thick, the metal loss is about 1/8 of that.. or 1/128" usually this looks a lot worse than it really is.. Use some calipers to find the thinnest place and if that spot is less than 1/16" or so, then you can have it brazed over with bronze. There is almost no pressure in the water jacket, so it does not have to be very strong, only water tight. The place I'd suspect as being the thinnest would be where the exhaust gas impinges on the inside of the box, opposite the water jacket.. Make sure that the zincs are always good and clean and it should last another many years.. If you want to keep it cleaner, there is a process called Electroless Nickel Plating that would lay down a thin nickel coat that would stop corrosion and not hurt the heat transfer as a paint would. An industrial coating place may let ya piggy-back on another job and not charge too much. Another cheaper way might be to flame spray or plasma spray a layer of aluminum-bronze onto the inner surface.

 

[Ron20324]

.... An industrial coating place may let ya piggy-back on another job and not charge too much. Another cheaper way might be to flame spray or plasma spray a layer of aluminum-bronze onto the inner surface.

Just yesterday I recived a mail-ordered (from Parts Express) product call "TINNIT", made by Datak. There are two crystals you mix with water of 131 degreesF. With some other steps- including "cooking" it, you can coat metal with a tin coating. I have no idea if it works. I got it to try to plate brass bars for hi-amperage busses bars. Anyone else used this stuff?

 

[Rob19574]

I believe some shops can apply a coating of ceramic over the cleaned metal interior. I think risers on Mercruiser gas inboards do this on the exhaust risers. That may be overkill and it could be a cheaper alternative to just carry a spare riser if you plan on doing any extensive cruising.

 

[Blitz]

Neal, we used to have a rule of thumb that the rust-to-metal conversion is about 8:1.. meaning that if the rust layer is 1/16" thick, the metal loss is about 1/8 of that.. or 1/128" usually this looks a lot worse than it really is.. Use some calipers to find the thinnest place and if that spot is less than 1/16" or so, then you can have it brazed over with bronze. There is almost no pressure in the water jacket, so it does not have to be very strong, only water tight. The place I'd suspect as being the thinnest would be where the exhaust gas impinges on the inside of the box, opposite the water jacket.. Make sure that the zincs are always good and clean and it should last another many years..

Good information. Makes me think it's not so bad, don't see any thin spots. Thanks