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Old 11-29-2018, 05:52 PM   #1
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Knocking

Got a knocking in my port Ford Lehman 120. Injector? Any thoughts or advice. Just finished 800 mile trip.
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Old 11-29-2018, 06:30 PM   #2
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Greetings,
Welcome aboard. Sorry, I'm not a mechanic although we do have 120 Lehmans. I wouldn't recognize knocking if it bit me on the foot. Best wishes.
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Old 11-29-2018, 06:38 PM   #3
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Any smoke?

You can determine which cylinder causes the knock by loosening injector fuel lines one at a time. If the knock goes away when you loosen a particular fuel line, you have identified the cylinder. Knocks can be caused by injectors, bearings, pistons, valves, etc.
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Old 11-29-2018, 06:55 PM   #4
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Or a infrared gun to the exhaust manifold to determine which is colder if you are having a dead cylinder.
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Old 11-29-2018, 09:55 PM   #5
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A knock can also be caused by a faulty injector which feeds too much fuel or at the wrong time due to the pressure spec. being off spec.

Should be able to find the injector by doing as described in post #3 by gsholz
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Old 11-29-2018, 10:20 PM   #6
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You might be able to narrow down the source with a mechanics stethoscope. if knock is high on the engine you might have an injector problem or timing issue. If knock is low then it might be connecting rod wrist pin bearings that could fail due to high mileage, high load, blocked oil passage.

Might be a good idea to pay for an hour of diagnostic time from your local diesel expert. Knocks aren't good.
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Old 11-29-2018, 10:31 PM   #7
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Anyone know if Lehman 4cyl 80s engines have the same cooling passage silting issue as the 6cyl 120s do,at the last cylinder, gearbox end? Can you pinpoint the knock source?
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Old 11-30-2018, 05:21 AM   #8
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As far as the cooling issue...may want to call Brian at AD.

When I was redoing my damp er plate and asked about it....unless I was mistaken..... he said not to worry about it as it was more myth than reality.

Again, I could be mistaken but it might be an internet myth that keeps going.
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Old 11-30-2018, 06:14 AM   #9
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Post a video (or audio) of the engine making the noise.
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Old 11-30-2018, 06:41 AM   #10
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Pulling the injectors is no big deal, and most shops will check them for free or $5.00 each , if they get to rebuild the bad ones.
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Old 11-30-2018, 09:33 AM   #11
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Use a stethoscope or even a length of hose to locate the source of the sound.
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Old 11-30-2018, 10:33 AM   #12
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Unless you have a background in diesel engine service, your interpretation of a sound could be all over the spectrum. Even if you're somewhat of a gearhead, familiarity with the particular engine you're looking at goes a long way in qualifying a sound you're hearing.



Go ahead and learn as much as you can, but I'd still call in a pro. Let them have a look-see/listen without you offering up any conclusions or diagnosis. Then see if their observations have any parallel to your own. Don't get ahead of yourself.
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Old 11-30-2018, 10:45 AM   #13
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does the knock go away with increased rPM or in and out of gear?
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Old 11-30-2018, 01:25 PM   #14
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One thing to keep in mind is that a failing damper plate can also cause a knocking that can sometimes sound like it's coming from the engine.

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Old 12-07-2018, 01:49 PM   #15
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Test as gsholz recommended then check for white smoke in the exhaust which my go away when the engine warms up, as may the knocking sound. If you have white smoke, stick your bare hand into the exhaust smoke then see if your hand feels oily. If so this is most likely is unburned fuel in the exhaust which is indicative of a bad injector. Dark smoke could mean lub oil in the exhaust, which probably won't go away when warmed up and could be much worse that a stuck injector.
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Old 12-07-2018, 02:07 PM   #16
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Quote:
Originally Posted by ProMaritime View Post
Test as gsholz recommended then check for white smoke in the exhaust which my go away when the engine warms up, as may the knocking sound. If you have white smoke, stick your bare hand into the exhaust smoke then see if your hand feels oily. If so this is most likely is unburned fuel in the exhaust which is indicative of a bad injector. Dark smoke could mean lub oil in the exhaust, which probably won't go away when warmed up and could be much worse that a stuck injector.
It is white smoke and is clearly leaving a sheen of diesel on the water.
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Old 12-07-2018, 02:08 PM   #17
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Couple of issues - all diesels will put out "white smoke" this time of year. Every Fall there are posts about people freaking out over white smoke.

The only way to tell if it is the dreaded number 6 cylinder fail is to disconnect the injector and see if the sound gets lesser. It may, however, not silence the clunk if there is physical damage. A shortcut to determine if it IS number 6 is to remove the injector and use a camera to peer inside the cylinder. If it is number 6, you will see signs of cylinder scoring and a rebuild is necessary.

This is a reminder to all owners to read their manuals and "burp" the cooling jacket as per instructions. These engines were designed for horizontal installations in generators and combines etc and the fact that we tip them backwards when we stick them in a boat causes problems, as well as the proper oil level.
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Old 12-07-2018, 06:17 PM   #18
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While anchored in B.C. this past summer, I started my engine and an immmediate loud knocking sound emerged from the engine room. I limped into Canoe Cove Marina for a diagnosis by Raven Marine. What I thought was a bad injector turned out to be much worse. A camera scope in the #6 cylinder revealed scored lining and a damaged piston.

After removing the cylinder head, it was found that a valve seat dropped out which caused the valve to drop down and ride up and down on the piston, thus the loud knocking sound. The head was badly dimpled and damaged beyond repair.

Fortunately, my insurance company accepted my claim as an “accident” and covered the cost of my $36,000us repair bill, minus my deductible. My engine is a 14 year old Cummins 450c with 1673 hours that has been meticulously maintained and all service protocols have been followed since new by Cummins professionals.
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Old 12-07-2018, 07:02 PM   #19
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Greetings,
Welcome aboard.
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Old 12-07-2018, 08:03 PM   #20
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Another FL 120 horror story:

Loud clanking started on day while running down San Diego harbor. Heard clearly on the flying bridge. Turned out to be number six cylinder on port engine. Water had seeped down from one of those stupid over-the-engine muffler installations where the inner steel tube in the muffler can had rotted and into the cylinder where the damage was done before I bought the boat and before I had changed the exhaust to a down angle exit.

The engine had to be pulled, bored and all new pistons installed for $6,500 in 1987.
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