Transmission rattle

On my Mainship 34 trawler twin 4lhastp one transmission is making a rattling( what I call death noise) when in gear at idle once I give it a few hundred rpm’s more it goes away and is quiet. Mechanic believes there is a sacrificial plate between engine and transmission that could be failing. Is anyone familiar with this ?

Greetings,
Mr. RL. Damper plate, perhaps? If so, a maintenance item.

My experience says it is not the dampener plate. My guess is we are talking about a velvet drive transmission. I have seen this issue in velvet drive transmissions. Maybe some one can confirm transmissions type.

tiltrider1 said:

My experience says it is not the dampener plate. My guess is we are talking about a velvet drive transmission. I have seen this issue in velvet drive transmissions. Maybe some one can confirm transmissions type.

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Yes, it's the damper plate springs becoming worn and loose in their mounts. When RPM is increased the springs compress and the rattling stops. Eventually one or more of those springs will break and drop down to the bottom of the bell housing where they have been known to stop an engine dead. Replace the damper plate soon. By the way, there is no such thing as a "sacrificial" plate. The damper plate is not part of the transmission. It is bolted to the engine flywheel and is synonomous with a pressure plate on vehicles with manual clutches.

A failed damper plate is extremely common and produces precisely these symptoms. I’m not familiar with other issues with Velvet Drive, though I’ve owned a few, but even so those issues would be far less common than a failing damper plate.

Start there.

tiltrider1 said:

My experience says it is not the dampener plate. My guess is we are talking about a velvet drive transmission. I have seen this issue in velvet drive transmissions. Maybe some one can confirm transmissions type.

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Yanmar 4LH engines are probably matched with ZF transmissions. Very unlikely to have older velvet drives. Yanmar damper plate goes for about $500 ea. I believe they are polyurethane so may not have springs. Investigation of noise location should be done with mechanics stethoscope.

Our Mainship has ZF transmissions. In order to make the props counter rotating one transmission is in forward and the other is in reverse when moving forward. At idle speed and moving forward the transmission in reverse rattles. Goes away with a slight load. At idle speed and moving in reverse the other transmission rattles, as it is now in reverse. After some research I've decided it is the design of the transmission causing the noise. It has been rattling since we bought the boat 7 years and 1400 hours ago so I think if it was a damper plate it would have broken a long time ago. As an aside, I just found out that the Z in ZF stands for Zeppelin, the company that made dirigibles.

You can buy a bushing kit for the polyurethane type damper plates for about $50. Easy to replace on the Centa brand damper plates.

Pulling the transmission can be a pain in the butt. Before you start, pick up a couple 4" long bolts the same diameter & thread as the bolts holding the gearbox onto the bellhousing. Cut off the heads and screw them in by hand. Use them to guide the gearbox shaft into the damper plate splines.

I agree w RT.
Edit, and AusCan

But once I had a very noisy (rattle like) gearbox .. (Kanzaki). It was aluminum and seemed to amplify the noise.
I installed a pricy gear oil pump and plumbed it (in and out) to the gearbox. I then mixed motorcycle synthetic racing oil w 85/140 automotive gear oil and one other thing I can’t remember. All to get the viscosity up.
That fixed the noisy gearbox noise and no other changes were noticed.

I’m quite sure the gear teeth in the trans were whack’in back and forth from the three cylinder engine’s torsional vibration (Yanmar).

AusCan said:

Pulling the transmission can be a pain in the butt. Before you start, pick up a couple 4" long bolts the same diameter & thread as the bolts holding the gearbox onto the bellhousing. Cut off the heads and screw them in by hand. Use them to guide the gearbox shaft into the damper plate splines.

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McMaster sells double ended studs. I leave them in.

Change the oil . I had ZF’s do this. I ran them on #46 hydraulic oil and 30# motor oil 50/50. Solved the problem .

Nomad Willy said:

I agree w RT.
Edit, and AusCan

But once I had a very noisy (rattle like) gearbox .. (Kanzaki). It was aluminum and seemed to amplify the noise.
I installed a pricy gear oil pump and plumbed it (in and out) to the gearbox. I then mixed motorcycle synthetic racing oil w 85/140 automotive gear oil and one other thing I can’t remember. All to get the viscosity up.
That fixed the noisy gearbox noise and no other changes were noticed.

I’m quite sure the gear teeth in the trans were whack’in back and forth from the three cylinder engine’s torsional vibration (Yanmar).

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The noise often is from the gearbox, but but a good damper plate can reduce or eliminate the rattle. Mine does until the bushes wear out. I'm still searching for the the root cause of the problem.

If it’s a straight cut gear transmission they can rattle. A lot has to do with the prop. At low speed the hull can make the blades cavitation. This causes what would be normal Load to disappear for a split second . This lets the prop speed up . When that happens the gear flips from one side to the other causing a rattle. Think of a harmonic wave. The minute you speed up the engine load overcomes any slippage and the rattle goes away. This is also very common with twin engine boats that run a transmission in reverse . The ratios are often slightly different and it unloads one prop. Usually just a few hundred RPM makes it go away.

AusCan said:

The noise often is from the gearbox, but but a good damper plate can reduce or eliminate the rattle. Mine does until the bushes wear out. I'm still searching for the the root cause of the problem.

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AusCan,
Looks like my damper plate was OK since the increased lube oil viscosity solved the problem completely.
Did’nt think of the damper plate then. But I can see how it likely would have solved the problem also.

FYI the syn oil I used was two stroke racing oil that wouldn’t work in two stroke oil injected engines .. not recommended by the manufacturer. Viscosity too high. Very high viscosity retention at high temperatures. Hard to mix and doesn't stay mixed for long periods.

I think the semi-transparent multi-colored damper elements used in place of the usual springs or plastic wedges have the best dampening absorption rates and should be the most effective. But since they don’t seem to be the most widely used there may be a downside like don’t last as long …. but I don’t know.

I’d like others to follow up on this and deliver better and more recent information. Springs in damper plates probably are susceptible to variations in dynamic rotational mass and rpm in addition to other things that are involved. In short it appears to me that most damper plates ideally should be designed for only one engine. Food for thought .. or/and conversation.

Roger L said:

On my Mainship 34 trawler twin 4lhastp one transmission is making a rattling( what I call death noise) when in gear at idle once I give it a few hundred rpm’s more it goes away and is quiet. Mechanic believes there is a sacrificial plate between engine and transmission that could be failing. Is anyone familiar with this ?

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You didn’t say what type of transmission you have. 4LH Yanmars can have a Kanzaki transmission that is a gear driven (vs hydraulic) transmission. A rattle at low idle is somewhat normal. If it is a Kanzaki change the gear oil every year. Use same oil as in engine.

Thanks for the counter rotating info but the port transmission is quiet in forward and reverse.

I’m hoping this is the correct diagnosis as the mechanic suspects, not a major repair.

Greetings,
Mr. RL. I've never done it but I understand changing a damper plate is NOT considered a major repair.



I could be way off here but...I'm not sure about your "mechanic". "Mechanic believes there is a sacrificial plate..." Perhaps you should hire someone more familiar with the technology of marine machinery.

RT Firefly said:

Greetings,
Mr. RL. I've never done it but I understand changing a damper plate is NOT considered a major repair.



I could be way off here but...I'm not sure about your "mechanic". "Mechanic believes there is a sacrificial plate..." Perhaps you should hire someone more familiar with the technology of marine machinery.

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Yes, removing the damper plate, eight bolts more or less, and replacing it with new is not a big deal. Plates cost less than $200 or so. It is a big deal to remove the transmission or even just sliding it back on threaded bolts. It requires decoupling the prop shaft and sliding it backwards through the stuffing box which sometimes can be difficult in itself. So, not a major repair?

I replaced the damper plates in our last boat. It was easy BUT I had the engines and transmissions out of the engine room at the time so it was easy to slide the transmission back from the engine. If the engine and transmission are installed in the boat it may range from easy to a real PITA depending on how the boat is configured.

Greetings,
Mr. c. Forgive me for trivializing damper plate replacement but I was thinking in the context of OUR boat where there is oodles of room to work in the ER. I defer to Mr. C's statement of "... it may range from easy to a real PITA...".

RT Firefly said:

Greetings,
Mr. c. Forgive me for trivializing damper plate replacement but I was thinking in the context of OUR boat where there is oodles of room to work in the ER. I defer to Mr. C's statement of "... it may range from easy to a real PITA...".

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No problem. I will note that my boat has great access as well but removing a transmission or even sIiding it back on bolts is more than a bit of work to this guy. I just wanted to let newbies know that this is not simple task in any setup. I am a very good boat mechanic, plumber, electrician, and carpenter and rarely pay to have anything done on my boat but when it came time to replace the dampers I paid a guy.

I would consider it a job that is simple in skills, but depending on equipment and accessibility ranging from easy to difficult in time and physical work.

It is just unbolting things and replacing a part.

The only sorta tricky part is sliding the tranny back and some have enough play
so they dont even uncouple the shaft....so total work does depend greatly.

The new [FONT=&quot]Hurth ZF45A transmissions on my boat rattle at idle. The mechanic, who installed the transmissions, told me this is normal for this model transmission. The damper plates were replaced when the transmissions were replaced, so it's unlikely loose damper plate springs are the cause.
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In most cases a rattling damper plate, where the rattle stops with a slight increase in rpm, is not an emergency repair situation. You might consider doing the repair as part of your next haul out and have the props and shafts checked at the same time. Depending on how your engines are mounted determines some of the level of pita. It’s less if the rear engine mounts aren’t connected to or with the bell housing, more if it is.
I have a legacy product similar to the suredrive coupler https://www.suredrivemarine.com/ They are attached between Hino EH700 engines and ZF Hurth When the rubber bumpers wear to the point of a significant idle rattle,

A mechanic once told me that many cases of damper plate rattle that he's seen are actually the engine running rough at idle. Something causing a misfire and often fixed by changing plugs or wires or sometimes an injector issue. Don't know if that's right or not, but he said that he'd always check the engine before servicing the transmission.

Pcpete said:

In most cases a rattling damper plate, where the rattle stops with a slight increase in rpm, is not an emergency repair situation. You might consider doing the repair as part of your next haul out and have the props and shafts checked at the same time. Depending on how your engines are mounted determines some of the level of pita. It’s less if the rear engine mounts aren’t connected to or with the bell housing, more if it is.

I have a legacy product similar to the suredrive coupler https://www.suredrivemarine.com/ They are attached between Hino EH700 engines and ZF Hurth When the rubber bumpers wear to the point of a significant idle rattle,

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Whoa, that Suredrive sure looks like a fantastic coupler.

Make sure idle speed is not set low on the one that rattles. Four bangers run rough at idle, and more so if idle rpm is low. That can absolutely cause gear rattle.

Frank60 said:

A mechanic once told me that many cases of damper plate rattle that he's seen are actually the engine running rough at idle. Something causing a misfire and often fixed by changing plugs or wires or sometimes an injector issue. Don't know if that's right or not, but he said that he'd always check the engine before servicing the transmission.

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I had this issue, and read about the same cause. Low and behold I found a BROKEN spark plug, when replaced fixed my idle rattle.

Roger L said:

Thanks for the counter rotating info but the port transmission is quiet in forward and reverse.

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I was just reading this thread. I have the same power plants in my Pilot 34. I have exactly the same issue ZF/Hurth reverse gears. Port is quiet Starboard is noisy only when at idle. Pick the rpm up to 1000 quiet. What was your findings ? What resolved the issue. I tend to agree that this is a common issue. I have researched many other forums including Boat diesel and it is known as ZF rattle. There are a few service bulletins out there that recommend changing fro ATF to 10W-30 motor oil to help reduce the noise.