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Old 09-26-2017, 10:47 AM   #1
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Lehman Damper Plate Replacement - My Experience

Recently, I had the damper plates replaced on my two Lehman 120s. The engines have 5,500 hours and there is no indication in the maintenance records (some blank spots) that the plates were ever replaced. There is only one reference to the plate having been “inspected” at 2,500 hours when one of the Velvet Drives was serviced. The service life on Lehman damper plates is generally estimated at 2,500 hours. We are leaving to do The Loop next may and I did not want to worry about a damper plate failing.

I had a yard do the work. I know how to do it and also have a brother who is an experienced Lehman mechanic. However, we are both in our later sixties and this kind of work is no longer in our best interests. Two boat units, all in. Well worth the money (to me).

Instead of “standard” plates, I used R&D Marine plates sourced from PYI of Lynnwood, WA. The plates are three (3) times the cost. Many folks might not choose this option because of the cost but once I had seen the plates that had been removed compared to the construction of the PYI plates, I was quite happy with the choice I had made. The old plates where, I think, rather flimsy sheet metal. The PYI plate is machined from solid steel about 3/8 inch thick.

Here’s what the website says about the plates:

R&D Marine Damper Drive Plates are designed to prevent gearbox rattle at low engine speeds, which allows an engine to operate through its entire RPM range. Today's marine diesels are designed with lightweight flywheels which do not create the inertia of an older heavy flywheel. The lighter flywheels result in gear chatter or rattle at low RPM's. This rattle translates into gear wear and damage to the drive-train. Our damper plates eliminate this problem.

Three types of damper plates are available for different applications:

1. A "Linear" damper plate is designed for general applications. This damper provides a linear dampening of the torque applied to the system.
2. A "Hammer Head" damper plate is designed for general use where motoring at low Rpm's is common. This damper provides a two stage dampening of the torque with 10 degrees deflection of the element.
3. A "High Deflection" damper plate is designed for use in vessels where low RPM engine use is the norm as in work boats or where gear noise is being experienced. The "HD" damper gives three distinct stages of dampening with 33 degrees deflection of the element, virtually eliminating gearbox rattle for extended use even at idle speeds.

All styles of these damper plates use a molded polyurethane element to absorb the engine torque. The fail-safe design of the plate makes sure that even in the unlikely event of a flexible element failure (from severe shock load), the drivetrain system would remain functional. The back plates for the R&D Marine damper plates are punched and ready to install. They can be installed within the existing space of a metal damper.


Operating result: the new plates are as advertised. At idle speed the engines run noticeably smoother. Gone is the harmonic vibrations that, with Lehmans, only disappear when the RPM is increased. Yesterday, I had to idle outside our fairway while the marina folks cleared our berth that was occupied in our absence. The owner had not moved his boat timely as agreed. The Lehmans purred quietly the entire time. Plus, although it may be my imagination, it seems that engagement with the transmissions is smoother as well. These plates do not employ springs that can break and literally stop a running engine if lodged in the bell housing just right.
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Old 09-26-2017, 11:13 AM   #2
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Thanks for the report. Interesting review.

The easiest way to get your damper plates to last is to always go to idle before you shift gears. Sometimes, in the heat of battle, that can't always happen.

I applaud your decision to pay someone to do it, I wish more of my older friends would do that too. I have one friend that paints his own 55' bottom, then complains about the sore back for weeks after. Not logical.
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Old 09-28-2017, 06:23 AM   #3
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"The easiest way to get your damper plates to last is to always go to idle before you shift gears. Sometimes, in the heat of battle, that can't always happen."

Which is why they invented the single lever control.
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Old 09-29-2017, 10:13 PM   #4
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I applaud your decision to pay someone to do it, I wish more of my older friends would do that too. I have one friend that paints his own 55' bottom, then complains about the sore back for weeks after. Not logical.
Some old folks need their cars, the rest of us need our physical prowess to prove we are still "non-dependent".

Yes I still turn wrenches like they are window cranks, and yes I complain all the time. I just bought my son a chrysler crossfire (cause it was a grab it now deal) and i have spent the last 4 days complaining about how my lower back hurts as I rip the rubber of those rims.
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Old 09-30-2017, 02:08 PM   #5
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Damper

Thanks for the information about the dampers. I've got 7k hours on mine and in a few weeks will pull it apart to inspect. Sounds like you really recommend the new type. Any surprises during the installation?
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Old 09-30-2017, 02:21 PM   #6
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I asked about the newer type plates and the old school spring type....

Just about universally, the pros said the spring type on a Lehman only asking 50 hp or so was the choice.

Granted corrosion leans towards the composite plates, but overall failures dont support the newer style plates.

Now I have no real idea, but American Diesel, Bomac and several mechanics with Lehman experience all concurred.
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Old 09-30-2017, 02:50 PM   #7
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Thanks for the information about the dampers. I've got 7k hours on mine and in a few weeks will pull it apart to inspect. Sounds like you really recommend the new type. Any surprises during the installation?
If you're going to the trouble of inspecting the damper plate, I'd replace it given the age and the cost of a new one. I was on a delivery this past June when a damper plate failed going 16 knots. There was no warning just no forward or reverse. We replaced ours on our FL SP135. Start to finish, with two guys, about 4 hours.
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Old 09-30-2017, 03:37 PM   #8
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If you're going to the trouble of inspecting the damper plate, I'd replace it given the age and the cost of a new one. I was on a delivery this past June when a damper plate failed going 16 knots. There was no warning just no forward or reverse. We replaced ours on our FL SP135. Start to finish, with two guys, about 4 hours.
So, purely out of academic interest (Bruce), whats the process to inspect and or replace?
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Old 09-30-2017, 04:33 PM   #9
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I replaced my Centa (springless) damper plate a few months ago. It was still under warranty but I changed it myself.
Inspection or replacement is fairly straightforward. Just remove your gearbox and bellhousing, then unbolt the damperplate.

The Centa damper plates also use 2 stages of rubber bumpers instead of spring to control noise and vibration. They are smooth when in good condition, but may fail early if shaft alignment is poor or if engine mounts aren't adjusted properly.
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Old 10-02-2017, 06:30 PM   #10
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I asked about the newer type plates and the old school spring type....

Just about universally, the pros said the spring type on a Lehman only asking 50 hp or so was the choice.

Granted corrosion leans towards the composite plates, but overall failures dont support the newer style plates.

Now I have no real idea, but American Diesel, Bomac and several mechanics with Lehman experience all concurred.
Not surprised that all of the "standard guys" stick with the tried and true even though they may never have tried the different. I don't know which was the better choice although I am confident I did not make a bad choice. What I do know is that those old Lehman engines clearly run more smoothly at dead idle with the new and different.
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Old 10-02-2017, 07:20 PM   #11
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Who says the pros I talked to were tried and true standard guys?

Tbese were guys actively repairing Lehmans day in and day out including the recommendation from American Diesel to stick with the old style spring type.

The vibes I notice near idlek are engine related, not dampner plate so how would I know either way?

Not saying the composite plates dont run smoother, but there must be more to it based on the 5 or 6 recommendations I got to stay with the spring type.
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Old 10-02-2017, 07:59 PM   #12
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As you, I value highly the advice of the good folks at American Diesel. My point was that folks who have done things the same way for a long time, decades even, tend to be risk averse when it comes to alternative solutions. Think about this. Bob Smith always recommeded using Marvel Mystery Oil in diesel fuel, an incredibly bad idea. (It REDUCES lubricity.) I'm not saying the choice I made was definitely the better choice. What I am saying is the acknowledged experts have never tested the alternative and have no way of knowing whether the other product is not a better choice. Hence, the safe advice is to use what always has been used. I will be dead by the time what I installed craps out so I will have to "eat crow" or not from heaven.
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Old 10-02-2017, 08:43 PM   #13
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I also recently replaced my drive plate as part of gearbox overhaul. Attached is some pictures of old and new. New unit is silicon based. Evidence of separation was shown on the old rubber block style. The old unit had done over 5000h mostly in commercial services in the vessels previous role as a crab boat.
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Old 10-02-2017, 08:59 PM   #14
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Larger engines were recommended to use the composites, smaller engines the spring type...

From various engine shops, some very familiar with the new technology plates.

Not my recommendations, but just plain old fashion, 6 month old research.
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Old 10-09-2017, 10:32 AM   #15
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damper inspection and engine support

On my GB 36 the rear engine mounts are attached to the transmission. How do you support the rear of the engine in order to slide the transmission back for inspection?

Dan
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Old 10-09-2017, 10:37 AM   #16
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On my GB 36 the rear engine mounts are attached to the transmission. How do you support the rear of the engine in order to slide the transmission back for inspection?

Dan
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Can't help Dan. I paid a guy to do the work.
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Old 04-07-2019, 09:41 PM   #17
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On my GB 36 the rear engine mounts are attached to the transmission. How do you support the rear of the engine in order to slide the transmission back for inspection?

Dan
'
Drive wooden blocks under it (thats what I did) or chain it from above.
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Old 04-08-2019, 06:01 AM   #18
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I think one day you will get a return on your investment when you can demonstrate to a prospective buyer how your boat does not rattle and vibrate at slow speed; and in the interim enjoy those benefits yourself. I cannot count the number of times I have explained that racket to the uninitiated. Good job:-)

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As you, I value highly the advice of the good folks at American Diesel. My point was that folks who have done things the same way for a long time, decades even, tend to be risk averse when it comes to alternative solutions. Think about this. Bob Smith always recommeded using Marvel Mystery Oil in diesel fuel, an incredibly bad idea. (It REDUCES lubricity.) I'm not saying the choice I made was definitely the better choice. What I am saying is the acknowledged experts have never tested the alternative and have no way of knowing whether the other product is not a better choice. Hence, the safe advice is to use what always has been used. I will be dead by the time what I installed craps out so I will have to "eat crow" or not from heaven.
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Old 04-08-2019, 06:36 AM   #19
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replacing damper plate

I am 73 years old and and am just finishing up replacing the damper plate on a velvet drive matched to a 4-108 in a sailboat. If you trawler guys think it s tough, try it in a sailboat. The tight work space is the problem-other wise just a routine job-keeps me flexible. Bob
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Old 04-08-2019, 09:37 AM   #20
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Lehman’s need a touch of fuel to find the “sweet spot” near their idle speed so they don’t rattle themselves off their mounts. Try adjusting the power lever to avoid this. Not a damper issue, they probably need a bigger flywheel. Letting it rattle can damage the plate though.
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