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Old 09-22-2016, 08:43 AM   #1
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Injectors, new OR rebuild ?

On our twin Cummins 6BT5.9M ( 1988 @ 3300 hrs. ) there some whitish smoke ( looks almost water vapour ) and some fuel smell when engines are cold, one maybe two cylinders are running a bit cooler than the rest. It was suggested that I need to look at servicing all the injectors in very near future.
Question: Buy new OR rebuild the old ones ? can anyone eyeball the cost ? also what brand if they are to be new ?

Thanks in advance as I know nothing about diesel engines .... FB

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Old 09-22-2016, 09:19 AM   #2
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I have two 1989 6BTs. I purchased one Cummins OEM injector for $125 as a spare. My engines have 4500 hrs. I see that whitish vapor/smoke at RPMs over 2000. I believe it is vapor/steam. The cooling on these engines is marginal at higher RPMs. I also have the fuel film out the exhaust when the engines are cold, It goes away when they warm up. Its not significant. The engine consume less than a pint of oil every 250 hours. The PO had the injectors cleaned and set at 1800 hours, reason unknown. I will wait until I see something worse before I work the injectors.
I am no mechanic, this is just mt 2 cents on my engines. Boatdiesel.com will give you answers from experts.

Dave Frye
Fryedaze, Monk 42' 1989 Overseas Co
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Old 09-22-2016, 09:28 AM   #3
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Every city has diesel injection shop that can rebuild them and test them first to let you know how they are performing. Ask if there are any newer design tips for better fuel spray.
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Old 09-22-2016, 09:59 AM   #4
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How does it run when its warm? Does it smoke then? They all smoke when cold. Don't do anything until it smokes when warm.
"...Tongue tied and twisted, just an earthbound misfit..."
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Old 09-22-2016, 10:44 AM   #5
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If you are stating this because its noticeably worse then before it would be worth bringing into a good shop to get tested, rebuild is necessary.
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Old 09-22-2016, 01:14 PM   #6
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Those older Cummins 6B engines have a different size injector body than the more modern ones. I believe 1991 (or so) was when they changed.
So yours are probably the 9mm diameter ones (newer are 7 mm).
That means the older ones are rarer. If it were me and I would go rebuild.

However, the reason Cummins changed was to put more material into the head in areas that has thin cross section. Those thin areas had a tendancy to crack.

Not trying to scare you about the cracking as I don't know how common that really is but running cooler might mean you should investigate.

Hopefully Ski will chime in here. If he doesn't you should send him a private message to read this thread.

BTW I had a pickup truck with a 9mm injector engine. I hopped it up and ran it pretty hard and the head was not cracked when I sold it with almost 200K miles.

Jay Leonard
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40 Albin
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