Got the generator running

[All U Get]

Hi all,

It’s taken a while to finally get the right gauges and senders for our diesel generator (most places wouldn’t help for numerous reasons) and I fired it up. Well it ran for two minutes then quit and the engine compartment was full of exhaust. I aired it out and got the fire/CO detector quieted then started to investigate. There was a scattering of carbon leading back to the Hx/mixer elbow.

I got busy draining the antifreeze coolant and PB blaster on the flange bolts. After some effort I got the elbow off, it looked fine. The flange on the Hx however had eroded just beside the flange gasket. This Hx was new 2014 but shows the same erosion of metal that had happened to the previous one. Only exhaust gases run through this section with water injected further along in the elbow. What would cause this type of erosion and how can I fix it?

Here’s the picture. The arrow points behind the paper gasket where the metal is thin.

 

[SycloneDriver]

I'm guessing here.
1. Poor quality casting.
2. Needs zincs replaced more often. It's aluminum correct?

Sure looks like a lot of damage.

 

[jssailem]

Sure looks like a lot of damage.

Yes but that is what happens when a boat is used a lot cruising.

How was the HE zinc? I know mine was gone after a couple of years. Got lucky that the HE passed the pressure test. Now it’s on the 6 month check list.

 

[capta]

What genset is this? Color looks to be Onan, but I don't recognize the model.
I should think corrosion like that would require some liquid from time to time. You said it was a dry section of the system? Could your vented loop be allowing water to drip into this junction on shut down, just to have the heat boil it away leaving little or no indication it was there.

 

[All U Get]

The red arrow is the plug with raw water from the Hx above, no zinc. The yellow is coolant drain for Hx, no zinc. The green shows exhaust flow towards the mixer before any liquids are introduced, no zinc. Kohler genset powered by a Perkins 4.108.

 

[dLj]

I'm trying to understand. I've edited your last image - is this correct? Also, you wouldn't use zinc to protect aluminum, you'd have to go to a magnesium/zinc alloy, zinc is too close to aluminum on the EMF scale. Secondly, this is a dry area of the system, a sacrificial anode wouldn't work anyway as you need the part you are protecting and the anode to be in the same electrolyte (water/soil/that sort). But this is a dry section of the system. High temperature corrosion can occur without liquid being present. @All U Get - I'm heading off on a work trip in a couple hours so won't be able to monitor this thread for awhile. But if you can please look at the image below and clarify for me that this is correct, that would be useful. Also, and I know this is difficult, if you can take better photos of where the corrosion is taking place and post them, that would help a lot. You will have to figure out how to get lighting into that area with the corrosion to be able to see it better. I'll try to get back to you when I've time.

dj

 

[RitSim]

In addition to other suggestions above, it looks like a gasket failure. There should be no flow path across the gasket surface. Could be the flange has pits or the flanges are not flat and parallel. The gasket must be evenly loaded.

 

[All U Get]

In addition to other suggestions above, it looks like a gasket failure. There should be no flow path across the gasket surface. Could be the flange has pits or the flanges are not flat and parallel. The gasket must be evenly loaded.

After looking closer, the gasket was intact with the leak just behind the flange. The skinny arrow is pointing to where the corrosion let out the gasses.

Is there a way to rebuild this area or get it machined?

 

[JamesG161]

no zinc. The yellow is coolant drain for Hx, no zinc. The green shows exhaust flow towards the mixer before any liquids are introduced, no zinc. Kohler genset powered by a Perkins 4.108.

The Perkins engine should be protected by a Zinc.

My Kohler genset is powered by a 16hp Yanmar. The Yanmar has a pencil Zinc that has to be changed every 500 hour on the genset.
Jim...

 

[All U Get]

I’m curious as to where a zinc should be, in the coolant or raw water. My problem is in the dry area of the exhaust. I just talked with a cruise who said he didn’t have a zinc on his Yanmar engine.

The Hx is a Bowman PE 180.

 

[JamesG161]

I’m curious as to where a zinc should be

It should be on or near the heat exchanger [HE] on the raw water pump. On the sea side of course.

A few people with that Perkins engine my have a better idea.

How was the HE zinc?

@jssailem has that size Perkins, if I remember right.

Jim...

 

[jssailem]

I have not found a zinc on the engine block, but now you will have me looking... my zinc was in the Heat Exchanger. Or it was supposed to be. By the time I found it and got the Heat Exchanger off so I could remove the zinc the zinc was no more.

Now I have a new maintenance item on the schedule.

 

[JamesG161]

I just talked with a cruise who said he didn’t have a zinc on his Yanmar engine.

He better look!
The Previous Owner had 1200 hrs on the Genset Yanmar. The Zinc was totally gone and he never changed it.

The Yanmar Zinc is tough to find and change. One of those "stand on your head" spots. Mine had the original White paint on it.
I got lucky for sure.
Jim...

 

[JamesG161]

I have not found a zinc on the engine block

Nor will you find one.
The raw water Zinc does the protection.
Jim...

PS: My Volvo Penta [by Perkins] is protected by my shaft Zinc.

 

[Captain Larry-DH]

Nor will you find one.
The raw water Zinc does the protection.
Jim...

PS: My Volvo Penta [by Perkins] is protected by my shaft Zinc.

The 2 Volvo Pentas that I’ve owned have been isolated electrically from the the boat‘s 12v system. The momentary connections are made by relay for starter and stop solenoid, and are otherwise disconnected.

 

[kloudie1]

All U Get.. if ya take the part to a good machine shop, they should be able to repair the part .. They can thicken it up where it failed.. There is a process, "electroless nickel plating" that is not too expensive that may stop this future failure after the repair..

 

[JamesG161]

The momentary connections are made by relay for starter and stop solenoid, and are otherwise disconnected.

I have said that a few times in SBO, and they all didn't believe me. No stray currents allowed to my Volvo Penta.
Jim...

 

[All U Get]

Perkins 4.108 Bowman Heat Exchanger

Combined exhaust manifold and heat exchanger that fits Perkins 4.108. This is a high quality original equipment part as supplied by Perkins in their later factory marinised versions and known as the 'Bowman' heat exchanger

www.parts4engines.com

Here’s a new one! I’m going to check locally to see if I can get mine rebuilt, otherwise my silver bullet is going to have more toothmarks.

 

[JamesG161]

If you look at the rear view picture of your Bowman link, my bet is that "plug" is the pencil Zinc.

You might check your exchanger for that plug.
Jim...

 

[Captain Larry-DH]

I have said that a few times in SBO, and they all didn't believe me. No stray currents allowed to my Volvo Penta.
Jim...

Yes, and V-P also isolates the drive shaft (or leg) components from the engine block. The only connection is through the cooling water, and that's a closed system that's disconnected by the antisiphon loop when the engine isn't running (but it has no 12v connection while running except the moments when you start or stop it).