Prop Re pitching

Port Credit 390

New Member
Jan 1, 2024
5
Lake Ontario
Boat Info
Sea Ray 2004 390 Motor Yacht
Engines
Cummins 480 CE
Good Day to all
New member,and first post.

Recently bought a 2004 390 Motoryacht with what i am being told now are the dreaded Cummins 6CTA8.3 480hp CE engines.

I,ve been told by many that these are bullet prove engines except for one issue they seem to be known for, the valves and or seats dropping.
I did read about this issue before buying the boat and thought if i addressed a few things i would be ok.
Seems im hearing more and more that this is defiantly a when it will happen issue. Not a if it will happen.

So to be on the safe side I have ordered new upgraded heads from Cummins. Cheaper than a whole rebuild when the valve does lets go.
The main issue however is that these heads run to hot due to the engines being over propped from factory. And to eliminate that problem pitch has to be taken out.

Has anyone else run into this issue? I have the factory 24 x 28 in props on the boat at the moment.
I want to sent them out and take 2 inches out of the pitch. There is alot of posts on Seaboard marine,s site and Boatdiesel about the issue of overloading these particular engines and the consequences if they are not corrected.

Has anyone else had any experience with these engines and re pitched?

Thanks in advance for any comments

Martin
 
Hi I have a 400 db same engine i bought this boat with 450hrs had the wheels turned down too 22.5 no problems it will cruise @23 mph at 2100
 
Good Day to all
New member,and first post.

Recently bought a 2004 390 Motoryacht with what i am being told now are the dreaded Cummins 6CTA8.3 480hp CE engines.

I,ve been told by many that these are bullet prove engines except for one issue they seem to be known for, the valves and or seats dropping.
I did read about this issue before buying the boat and thought if i addressed a few things i would be ok.
Seems im hearing more and more that this is defiantly a when it will happen issue. Not a if it will happen.

So to be on the safe side I have ordered new upgraded heads from Cummins. Cheaper than a whole rebuild when the valve does lets go.
The main issue however is that these heads run to hot due to the engines being over propped from factory. And to eliminate that problem pitch has to be taken out.

Has anyone else run into this issue? I have the factory 24 x 28 in props on the boat at the moment.
I want to sent them out and take 2 inches out of the pitch. There is alot of posts on Seaboard marine,s site and Boatdiesel about the issue of overloading these particular engines and the consequences if they are not corrected.

Has anyone else had any experience with these engines and re pitched?

Thanks in advance for any comments

Martin
I havent personally. I have the predecessor, the 450 Diamond. But looks like you’ve done thorough research. Follow Tony’s guidance to treat them as if they are 450 Diamonds. Prop to the 450 Diamond fuel consumption curve. Cummins basically took the stock 450 Diamond, did some voodoo magic to the fuel delivery and such, and declared it now a 480 hp motor. But didn’t change any parts or materials to accommodate that extra power. The new heads they invented were an after the fact necessary solution to appease the owners.
 
Thanks for the reply
How do you find these engines to be otherwise. Have you replaced the heads or do you plan on doing so. Don’t know if you are familiar with Tony at Seaboard marine but after speaking with him about the heads he seems to think for peace of mind change them out now to the upgraded version , repitch the props and your good for 10 000 hour engines. Just bought this boat in September and is on the hard till April. Other than that for the short time i ran them they seem great
 
Im waiting for 1 of the heads. Back ordered for who knows how long. But i did manage to get one. And what does it say stamped on the casting. MADE IN BRAZIL. That makes me feel good.
 
I havent personally. I have the predecessor, the 450 Diamond. But looks like you’ve done thorough research. Follow Tony’s guidance to treat them as if they are 450 Diamonds. Prop to the 450 Diamond fuel consumption curve. Cummins basically took the stock 450 Diamond, did some voodoo magic to the fuel delivery and such, and declared it now a 480 hp motor. But didn’t change any parts or materials to accommodate that extra power. The new heads they invented were an after the fact necessary solution to appease the owners.
Interesting that you say that. I asked Tony about having my existing heads rebuilt with new valves and seats. He said its not the same as the new designed heads. So what is the difference. Who knows.
 
Thanks for the reply
How do you find these engines to be otherwise. Have you replaced the heads or do you plan on doing so. Don’t know if you are familiar with Tony at Seaboard marine but after speaking with him about the heads he seems to think for peace of mind change them out now to the upgraded version , repitch the props and your good for 10 000 hour engines. Just bought this boat in September and is on the hard till April. Other than that for the short time i ran them they seem great
They are great engines. Love mine. But gotta pull and take apart and clean the aftercoolers every two years. Make sure you do that as another immediate thing then start the two year cycle. I would definitely change the heads if I were you. That’s the only replacement head they sell for the 6CTA now, including the 450 Diamonds.
 
Interesting that you say that. I asked Tony about having my existing heads rebuilt with new valves and seats. He said its not the same as the new designed heads. So what is the difference. Who knows.
I’ve never been able to find out the difference in the old and new heads. I’ve asked around a bunch but no one knew.
 
Just a good way to sell new i guess. This boat has always been in freshwater. But has probably never had the coolers serviced. So i hear what you’re saying. Will definitely pull them anyway and go over them before the new season. Thanks
 

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