Cummins 250(39)s smoking-gctid812903

[capn_mark67]

Hi folks, I've searched around on he forums and got some info, but a bit more input would be appreciated.

Here's the scenario:

We are looking at a 4087 with the Cummins 250's. She has higher hours at about 2300, but has been well maintained. There is one new turbo, and all the injectors have been recently rebuilt. She reached 2650 RPM at WOT when the mechanic took her out. She runs smooth, but she is smoky, like really smoky. The solonoids on the pre heaters are not working - the surveyors' initial thought is this could be the reason. They had the boat running for 20-30 min so she wouldn't have reached full operating temp. We took oil samples but don't have the results yet.

Otherwise, she's a good boat, but I don't want a smoker. Any thoughts would be greatly appreciated!!

Thank you,

Mark

[TenMile]

When you say Cummins 250s do you mean the 4BTA 250Hp engines? I suspect the engines are the 6 cyl B-series which I believe are 270 or 330 HP?

Anyhow if they are smoky here are some possible causes:

1. As mentioned, if preheaters aren't operating, engines will smoke on start, but should clear up after a few moments when engines warm (about 5 or so minutes)

2. Aftercoolers (if present) have not been cleaned. This one can be a major so get the PO to have them cleaned and pressure tested.

3. Valves may need adjustment (simple job)

4. Dirty air filters

PS: I would think that if they had the boat out 20-30 mins and up to WOT -- those engines should have run up to operating temps so I wouldn't think that temperature would impact the smoking.

[Centerline2]

"TenMile" post=812912 wrote:
When you say Cummins 250s do you mean the 4BTA 250Hp engines? I suspect the engines are the 6 cyl B-series which I believe are 270 or 330 HP?

Anyhow if they are smoky here are some possible causes:

1. As mentioned, if preheaters aren't operating, engines will smoke on start, but should clear up after a few moments when engines warm (about 5 or so minutes)

2. Aftercoolers (if present) have not been cleaned. This one can be a major so get the PO to have them cleaned and pressure tested.

3. Valves may need adjustment (simple job)

4. Dirty air filters

PS: I would think that if they had the boat out 20-30 mins and up to WOT -- those engines should have run up to operating temps so I wouldn't think that temperature would impact the smoking.

I work on a LOT of the B series Cummins engines and the additional things that can cause a smoke from a seemingly perfect running engine is a cracked head, a cracked piston, (low compression in one or more cylinders), a bad or dirty injector, or pump timing... troubleshooting is difficult, but a compression test will point you in the right direction....

a cracked piston is the most difficult to repair as you need to pull the pan for access to the journals... all other things mentioned here can be repaired from the top, and is not difficult at all... with the exception of access to the engine as it sets in the boat.

[smitty477]

"We are looking at a 4087 with the Cummins 250's. She has higher hours at about 2300, but has been well maintained. There is one new turbo, and all the injectors have been recently rebuilt. She reached 2650 RPM at WOT when the mechanic took her out"

Deleted bad information thanks to p91473 - thanks.

[Norton_Rider]

"TenMile" post=812912 wrote:
When you say Cummins 250s do you mean the 4BTA 250Hp engines? I suspect the engines are the 6 cyl B-series which I believe are 270 or 330 HP?

Marine B-series were available in 180 through 370 Hp. I've seen a few 250 Hp 6BTA-6cyl engines.

[p91473]

I have the 6bta 250s. 2600 RPM is WOT as per Name plate on engines. My smoke issue was on the port side. Cause was turbo. Re-built the turbo, no smoke. Are both sides Smokey? Do not rule out old diesel fuel if both are putting out the same amount of smoke.

[capn_mark67]

Thanks everyone. Yes, 6 cyl 250 hp. I will find out if the side with the new turbo smokes less than the other. After running for say 10 min, does everyone pretty much rule out the non functioning pre heaters as a cause, or is this still a possibility?

Thank you,

Mark.

[boatworkfl]

I good diesel mechanic should be hired, prefer a Cummins mechanic from a Cummins marine dealer, diesel engines are expensive to work on.

[smitty477]

It is not the preheaters after 10 minutes.

What color smoke? White or blue?

With these many hours a blowby test would be a good idea.

Last time injectors tested/adjusted?

Do you have maintenance records on the engines?

[capn_mark67]

Thanks for the responses on this. I was looking through the old posts and thought I would mention this is not the boat we ended up buying. We have the 270's, and she is smoky on startup, but it clears fine after a few minutes. The problem all the major items have been checked, and it looks like the preheaters are the issue. I am looking at one of the pad type oil pan heaters, so we'll see if that helps.

[Redwngr]

Seems to be a bunch of Cummins marine info, parts, service, recons etc at this website.

https://www.sbmar.com/technical-information/

[yoeman]

My 250s smoked black and I spent months on it going over all engine issues with no improvement

Finally pulled it and re pitched the props down 2 reg

It's like a new boat