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Old 04-26-2018, 04:07 PM   #1
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Different HP Diesels?

I'm interested in "group think" on this one. We are looking at an '83 Defever 44. It has twins - one is a Lehman 120, the other is a Lehman 135. I've never seen or heard of a configuration like that but the present owner explained that it was built with two 120's, one of which failed while under warranty. The explanation is that there were no 120's available at the time, but there was a 135 - so they used it. As far as I know it's been that way for 3,000 hours. What kind of issues might crop up - difficulty synchronizing? Unequal acceleration curve? More wear on the 120 than the 135? Obviously it means two different sets of spares but I could live with that. Thought?
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Old 04-26-2018, 04:31 PM   #2
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No problems with any of the issues you mention. You probably won't notice any difference between the two engines.

David
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Old 04-26-2018, 05:04 PM   #3
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There should be zero sync issues as the tachs will tell the controls what RPM to set. You may see a slight difference in the RPMs, but heck even with the same engines you will get different readings. My Luggers are ~50 off!
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Old 04-26-2018, 07:40 PM   #4
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Even perfectly matched engines can run a few rpm different on each side. Often the transmission ratio is a little different on the counter rotating engine. Or the prop pitch is slightly different.

But remember props move boats, engines only turn them. So with the same ratio and the same prop on both sides, the engines should run at the same rpm no mater if one is huge and the other is small.

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Old 04-26-2018, 10:47 PM   #5
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I'd say the only concern is that future buyers may be concerned, which could affect the resale value in the future.
If a slight discount is built into the price now, then that takes care of the problem.
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Old 04-26-2018, 11:31 PM   #6
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Itís not a big deal with those engines. Now if one was a 375 cat and the other was a 120 Lehman, that would be an issue. Buy it. I have a friend here that Has the same setup in his marine trader.
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Old 04-26-2018, 11:48 PM   #7
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If there is a problem, it`s that it doesn`t have 2 x 135s, rather than 2 x 120s.
But, I don`t think there is a problem. Both good engines, sufficiently matched. The 135 will be a tad easier to service as regards fuel injection.
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Old 04-27-2018, 12:10 AM   #8
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Not an operational issue, we have the same configuration for the same reason. They both drive the same size and pitch prop, there is no discernible difference in throttle movement and synching is easy. If it is a good boat don’t let that stop you.
American Diesel and Bomac Marine support both engines.
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Old 04-27-2018, 12:13 AM   #9
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I have replaced both my engines. One with a Cummins reman of 330hp and the other with a new long block and the best peripherals (most of them rebuilt) from the original 2 engines which were 315 hp. I have no issues as I never operate at the top end except to do a WOT run several times a year to check that I can reach 2800 rpm on both. Having a 21 year old boat with two engines under 300 hours, even if they vary slightly in design is a huge comfort.
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Old 04-27-2018, 08:59 AM   #10
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Diferent HP Diesels

Thanks for the feedback on this. We look at the boat tomorrow and I'll report back.
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Old 04-27-2018, 09:54 AM   #11
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Yep, no issues expected using a FL 120 and FL 135.

Even seen a charter boat with a Cat on one side and a Cummins on the other. He had no issues either, other than getting guff from the peanut gallery.
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