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Old 16-11-2021, 17:05   #1
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Engine vibration

I have a Power Cat with 2 Yanmar 4LHA engines. The vibration at idle is pretty awful. As part of normal maintenance we just had new shafts, cutlass bearings and Dripless seals installed. I also installed new motor mounts but did not go with OEM because they didnít seem to last long enough. I had metal in metal with the Yanmar mounts (2Xís). Engine alignment is dead on. There are 2,500 hours on the engines and I never had the injections cleaned. Is that the likely culprit? Anxious to hear from someone more knowledgeable than I. Appreciate and grateful for responses.
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Old 16-11-2021, 17:57   #2
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Re: Engine vibration

I had a pair of 4LHA-STE on a previous boat, and I felt they vibrated a lot at idle. However, kick the throttles up just a bit, and they smoothed out. Likewise, there was a certain mid-throttle RPM I’d get a noticeable vibration (harmonics?). I’d have to bump RPM’s up or down a 100 to get out of that rough spot. I’ve noticed that before on other 4 cylinder in-line diesels, and older gas 4’s. I’ve always thought it was just the nature of in-line 4’s. Are yours running well at other RPM’s? Without hearing/feeling yours I of course can’t say whether yours are “normal” or if they are the same or worse than mine were. Others may have more brilliant answers than mine!

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Old 16-11-2021, 18:28   #3
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Re: Engine vibration

I appreciate your quick response. Iíve had the boat for 13 years and it is far worse and continues to do so. With 2500 hours on the engines Iím wondering if cleaning the injectors is long overdue?
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Old 16-11-2021, 20:59   #4
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Re: Engine vibration

I’m not a diesel mechanic and do not claim to be an expert. It is my understanding that, yes, dirty or worn injectors can create rough running which equals vibration. I would have a mechanic assess the entire fuel system - both injectors and pump timing. Worn engine mounts on an already vibration prone engine can exacerbate the issue. You mentioned that you went aftermarket with your replacement mounts. Because quality OEM mounts are (or should be!) designed very specifically to the weight, torque, vibration frequencies, etc.of a motor and its installation, one must be careful when choosing aftermarket. Don’t get me wrong, there are better-than-new aftermarket mounts in the automotive and trucking industry… and I assume the marine industry. But a too soft or too hard of a mount can cause issues as well. Overall, I’d have the engine (specifically fuel/intake system) gone over, and have a second look to ensure your mounts are appropriate. That’s my nickel’s worth!
Best of luck!
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Old 17-11-2021, 06:21   #5
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Re: Engine vibration

I think that Phyrcooler has done a good job of analyzing the problem.

If I understand you, both engines are vibrating. That's a bit of a coincidence. If true, then I favor the engine mount or harmonics argument over the injector argument. My bet is that the engines have a harmonic at your idle speed, and squishy mounts are letting it take over. If that hypothesis is correct, changing the engine speed by a few hundered RPM should stop it.
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Old 17-11-2021, 11:21   #6
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Re: Engine vibration

I realize I didnít adequately define the problem. The port engine has significantly more vibration. It gets every cabinet door juggling and if I even put my eyeglasses on the countertop they begin to vibrate. All this at neutral, bad at low rpms and lessens significantly as throttles advance. The motor mounts are next to new. I chose IsoFlex mounts because the Yanmar mounts havenít held up very well and I had metal on metal. I am leaning towards having the fuel injectors cleaned. Is 2500 hours on injectors a lot without a cleaning?
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Old 17-11-2021, 14:11   #7
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Re: Engine vibration

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Originally Posted by vanderd View Post
I realize I didnít adequately define the problem. The port engine has significantly more vibration. It gets every cabinet door juggling and if I even put my eyeglasses on the countertop they begin to vibrate. All this at neutral, bad at low rpms and lessens significantly as throttles advance. The motor mounts are next to new. I chose IsoFlex mounts because the Yanmar mounts havenít held up very well and I had metal on metal. I am leaning towards having the fuel injectors cleaned. Is 2500 hours on injectors a lot without a cleaning?
If theyíve never been doneÖ then definitely. Per your operating manual, they should be checked at 250 hrs and every 1,000 hr or 4 years. Likewise your valves. Injector timing at 2500 hrs. If you havenít been doing all thisÖ then definitely time!
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Old 18-11-2021, 10:33   #8
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Re: Engine vibration

A lot of those smaller Yanmars vibrate like an SOB. That's why they use those super soft mounts. Otherwise the engine would jerk the lags right out of the bed. The mounts are so soft that Yanmar recommends that you replace them every 1000 hours or 4 years. Whatever comes first.

I've seen it impossible to use a dripless shaft seal with a Yanmar due to the excessive engine movement on those soft mounts.

IF the engine is not smoking, the injectors are probably fine. About all you can do is adjust the valves, turn up the idle and make sure alignment is spot on with each mount holding up an equal portion of the engine weight. If the mounts are sagging, replace all four mounts.
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Old 18-11-2021, 15:01   #9
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Re: Engine vibration

Our engine wasnít smoking, but was running extremely rough at lower power settings. I had pushed the injectors about 300 hours past the recommended service interval. I finally pulled them and took them in, all three had atrocious spray patterns and none of the cracking pressures were the same.

World of difference after putting the refurbed injectors back in.
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Old 18-11-2021, 16:43   #10
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Re: Engine vibration

This past season I made a concerted effort to get caught up on those Yanmar service intervals - injector service, valve adjustment, secondary fuel filters (still had the gray painted FF ). In researching the parts availability, it became apparent that Yanmar has had difficulty with Tier 2 and Tier 3 compliance. Injector part no. Updates abounded and in some cases no updates and no availability of a Yanmar OEM injector. All four injectors had no atomization. As the service provider was only dealing with the injectors, he was not bound with the applicable emission standard, they replaced the tips attempting to match the original. The engine definitely smoothed out and piston slap eased at low power settings. At high power settings, there is a noticeable lack of turbo contribution, hence rated power available. As the OP's engine is similar in age and hours, I would recommend dealing with a testing/service center with experience with 4 LHA's. Ours is missing about a liter of displacement compared to the 4LHA, 4JH3-TE 75 hp, 2400 hours, DOM - 2006. We overpropped for fuel efficiency, thereby throwing about 10 hp away, not what you want in a power cat, either by overpropping or shorting fuel load by improper injector rebuild. As there is a variation in performance from port to starboard, a couple of other things should be checked- compression/ head gasket, tight to nil valve clearance, vented loop performance.
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