Sudden development of loud knock in Cummins 8.3

#4 cylinder. Same exact thing that happened to my buddy two weeks ago. Mechanic called either #6 or #4 before he even pulled the valve cover. Sure enough it was #4 that dropped, and once the head was off he found that #6 was cracked and not far from the same fate as #4 suffered.
He got lucky that it was all contained in the cylinder and they had enough room in the 420 Sundancer to get the pan out of the way to get to everything. No damage to his turbo either.
Hopefully you're friend has the same luck.
The good news is that once the job was done the motor runs flawlessly.
If he gets a certified Cummins guy to do the job they might be able to point him in the right direction for info about getting some money out of Cummins.
My friend is hoping they at least make good for the price of the head.
 
JVM225 said:
#4 cylinder. Same exact thing that happened to my buddy two weeks ago. Mechanic called either #6 or #4 before he even pulled the valve cover. Sure enough it was #4 that dropped, and once the head was off he found that #6 was cracked and not far from the same fate as #4 suffered.
He got lucky that it was all contained in the cylinder and they had enough room in the 420 Sundancer to get the pan out of the way to get to everything. No damage to his turbo either.
Hopefully you're friend has the same luck.
The good news is that once the job was done the motor runs flawlessly.
If he gets a certified Cummins guy to do the job they might be able to point him in the right direction for info about getting some money out of Cummins.
My friend is hoping they at least make good for the price of the head.
Click to expand...


Did your friend have them pop the head off the other motor to check for cracking there as well?
 
Not yet at least. Unfortunately there is not enough room to do the repair in the engine room. The engine will have to come out. For now he just wants to get this one fixed. I wonder if the cracks could be detected by bore scoping the engine thru the injector bores? Did your Freire have any pictures of the cracks?
 
Sorry my question was directed to JVM225. I can certainly see why Carpe's friend wouldn't want to pull an engine just to check.
 
Actually it's my apology that's in order, need to pay closer attention to the thread quotes. No harm done I suppose, the price is right for this form of entertainment;)
 
From what I have read here and boatdiesel.com the main cause for 480CEs dropping valves is over-propping causing EGTs that are too high. If this boat is still running the props fitted by Sea Ray it will almost certainly need 1-2" of pitch taken out to bring the loads back to Cummins specs. It might be worth your friend considering a new head for the other engine while everything is apart in case it is close to the same fate.

https://www.sbmar.com/articles/propping-cummins-6cta-8-3-480ce-vs-430450-diamond-engine/
 
PH321, wow, that's good intel. He does have the original props and his boat cruises faster than mine at lower RPM. I've got 2inch smaller diameter props with the same 27 inch pitch. I'm definitely under loading my engines while burning more fuel trying to keep up. I've been struggling with whether or not to replace mine with the larger props. I'm thinking now I'll spend a little more in fuel and save my Powerplants!
Thanks for the heads up and the link.
Rusty
 
Hi Rusty,

I did notice your other thread about the props. My understanding with modern diesels is they use x amount of diesel to produce a given amount of horsepower whether that horsepower is produced at 2200rpm or 2400rpm. In other words you should use the same amount of diesel to cruise at 20knots regardless of what props are on. Just that your engines will be much happier under-propped than propped at their limit.

There's plenty of reading on the topic at www.sbmar.com . Tony there has experience with these engines in fishing boats with 10,000+hrs so definitely knows what's involved in keeping them reliable. If you're happy with your speeds in the 2200-2400rpm range then I would just leave the props.

Paul
 
copb8tx said:
Did your friend have them pop the head off the other motor to check for cracking there as well?
Click to expand...
No need. The other engine was replaced last season, as a result of an unrelated problem, and that new motor has the latest design head on it.
 
Carpediem44DB said:
Engine is Cummins 8.3 480CE. By most accounts the engines are solid and reliable power plants for these boats. They are man made machines though and anomolies do occur. Just a tough break. This just reinforces the reality that you should not own any vessle of this caliber unless you are financially and mentally prepared to make serious investments in repairs and maintenance. The term "break out another Thousand' won't quite cover this though!
Click to expand...

I have a sympathy gut-ache for you - that really sucks.

I posted the opinion about financially preparedness as they relate to marine diesels in another thread about my neighbor who just doesn't strike me as wealthy enough to absorb huge repair bills. Update: maybe I'm not as smart as I think I am. His engine has been repaired to the tune of $38,000, but insurance covered it because his impeller was intact! Apparently the logic was that the intact impeller suggested reasonable maintenance, so the overheat was considered a covered incident. It wouldn't have occurred to me to call my insurance company, but again, maybe I'm not so smart.
 
Carpediem44DB said:
PH321, wow, that's good intel. He does have the original props and his boat cruises faster than mine at lower RPM. I've got 2inch smaller diameter props with the same 27 inch pitch. I'm definitely under loading my engines while burning more fuel trying to keep up. I've been struggling with whether or not to replace mine with the larger props. I'm thinking now I'll spend a little more in fuel and save my Powerplants!
Thanks for the heads up and the link.
Rusty
Click to expand...

Its stories like this that remind me to back down a bit and be happy I lost some speed when I reduced pitch this winter.
 
A little update on the engine issue, still waiting for engine to be removed due to back up in yard. Scheduled for Tuesday.
Actual prop pitch is 26 x 23.77. Since he did not have a chance to do a WOT run to determine max RPM between the time he bought it and the time it dropped the valve seat he has no idea whether or not the boat was over propped and overloading his engines. You guys that operate 420 sedan bridges with the 480 CE engines, what props and pitch are you running? Love to know your numbers.
 
I'm going to chime in a little bit of knowledge I learned from Tony at Sbmar.com. This boat/engine should be propped to match the 450 diamond engines. You need to achieve 2650 wot but the safe bet is 2700-2750 wot. My engine was achieving 2500 so I adjusted both sets of my props and had a valve lash adjustment performed. It cost me 3.5knts but hey the fact is the boat was previously overpropped. One positive is my boat has so much more spunk now, literally instant throttle response and jumps up on plane easily.
 
Did they not do a WOT run during sea trial? That would at least be a starting point. Dropping 1" of pitch should roughly get you an increase of 100 rpm at WOT

I will echo the advice above, Tony at sbmar.com (and previously boatdeisel) strongly recommends to prop the 480CE using the 450C curves.
 
Update on Sea Renity's 480CE with the dropped seat. Engine came out on Thursday and delivered to Cummins service center in Sacramento on Friday. Opened today and this was found. Looks like a piston, rod, new head and probably a turbo as pieces of seat were found in exhaust elbow after the turbo.
He's going to replace the head on the port engine while it's hauled.
Gonna be an expensive Sumer!
 

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Going back together this week, having entire bottom end rebuilt since it is out if the boat and new heads on both engines. $42000 by the time he's back in the water and then probably 3 days of deep cleaning after being in the boat yard in the middle of Delta farm land during harvest season!
Ouch!
 
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