Premature Velvet Drive Failure
or How I Learned More About Damper Plates Than I Ever Intended
In early 2008 Sarah was re-powered with a Yanmar 4JH4-AE engine and Velvet Drive transmission to replace the original Westerbecke 60 engine and Paragon transmission.  In November, 2010, as I was approaching a dock in Jacksonville, FL I discovered that I had lost reverse gear in the transmission.
Cass' Transmission in Jacksonville removed the transmission and discovered that the forward and reverse ring gears were all but chewed away.  The ATF fluid in the transmission was chocked with metal filings.  Fortunately the main planetary gear was not damaged and the transmission could be re-built with new ring gears and a new oil cooler (among other parts).
Rather than have the re-built transmisson re-installed on the engine, I wanted to get an answer for why this less than 3-year old transmission failed.
On  the right is a picture of the engine with the transmission removed.

Cass offered two possible causes of the failure.

  1. Shifting between forward and reverse gear without bringing the engine to idle RPMs and pausing in neutral for a second or two before shifting into gear.
  2. A Damper Plate malfunction that caused the engine pulses at low RPM to be transmitted to the transmission like hammer blows on the gears.

I have certainly performed the improper shifting as described in the first cause.  When maneuvering in tight quarters, I have at times not let the engine go to completely idle and more commonly have shifted directly from one gear to the other without pausing in neutral.  However those actions have not happened often and the shifting gears without at least reducing RPMs to idle has been a rare ocurrence.  If those few errors caused the transmission failure, the Velvet Drive is a very unforgiving transmission and should probably be replaced.

The second potential cause of the failure was a lot more promising and less alarming than the first.  One thing that had bothered me from the first day back in 2008 when we fired up the engine and put it into gear was the very loud gear backlash noise coming from the Walter V-Drive.  My mechanic was equally concerned and contacted Walter about the issue.   He contacted Walter because the sound was coming from the V-Drive.  Walter said this would not be a problem for the V-Drive.  However, we never asked Velvet Drive about the issue.  Of course gear backlash at low RPMs is not uncommon, so there was no reason for alarm.  The noise disappeared once the RPMs were raised above 1,000.  The Westerbecke idle had been set to around 950 before I purchased the boat, and there was no loud backlash noise with that engine.  I reasoned that it would have produced a similar noise if the idle RPMs had been reduced to less that 800.

While having the transmission serviced I surveyed other P424 owners to determine their idle settings and whether or not they experienced the loud gear backlash noise as I have.  Only one other boat experienced the loud noise and that one clearly had a defective damper plate.  The others experienced a slight to no gear noise with idle RPMs in the 800 ranged.  So my reasoning that the Westerbecke/Paragon configuration would have produced the same backlash noise was erroneous.  I should have done that survey before accepting the repower.

On the left is a picture of the original Damper Plate after the transmission was removed.  I had a mechanic from the local Yanmar service rep inspect this plate and he noted that several of the springs were loose and most showed some degree of corrosion.
I requested he order a replacement Damper Plate.  So far I was unsusre that this plate was really defective, but I decided replacing the plate was something that should be done before the transmission is re-installed. 
A week so later the new Damper Plate arrived and the mechanic removed the old plate in preparation to install the new one.
The first thing we both noticed is the substantial difference between the two plates.  In the picture on the right the old plate is in the mechanic's left hand, the new one in the right.
First it was clear the plates are of two different designs.  The old one used springs to dampen the engine pulses.  The new one uses rubber bearings for this purpose.  This appears to be similar to the plates supplied by R&D (a PYI) company.  Browsing the Mack Boring website, it appears they are specifying R&D damper plates and couplings for many of the transmissions they offer.  I don't know if this a recent change.  Later I learned that the new plate was from Centra and was most likely ordered through Mastry, which is the Yanmar distributor for Florida.
The picture on the left is a side view of the two plates.  The new plate is clearly more substantial  than the old one, or at least it is a lot thicker.
The manager of the yard that performed the re-power has reviewed these pictures and from appearances he believes the old damper plate is indeed the normal one used with Velvet Drive transmissions.  That yard did not specify or install the damper plate, that was done by Mack Boring (Yanmar distibutor for Maryland) before delivery of the engine. 
The picture on the right shows the new plate installed on the engine.  You  can see the rubber bearings in the slot between the plate hub and the outer portion.
Until I have the transmission re-installed I will not have an indication that the plate difference is significant.  If the gear backlash noise is reduced when the engine drive is back in place, I will have some indication that the new plate is a positive change.  I did have the local yard evaluate the old plate for me.  See below.
On the left is the front side (toward the transmission) of the old damper plate.  Other than some mild corrosion and three slightly loose springs I can see no problems with this plate.
The only identification on the plate are the letters AISIN stamped on this side.  Using WikiPedia I have learned that AISIN is the world's largest manufacturer of automatic transmissions.  Thank you, once again, WikiPedia.
The photo on the right shows the side view of the old damper plate.  The back plate, which bolts to the engine fly wheel, is about 1/8" thick.
My understanding of how a damper plate is supposed to work is there are two plates, front and back, that are connected by the five springs.  The back plate transmits the engine rotation to the front plate via the springs, which absorb some of the engine pulses.  The front plate transmits the engine rotation to the transmission via the splined socket in the center.
The picture on the left is the back of the old damper plate.  This is secured to the engine fly wheel by six hex-head machine screws.
I'm having some trouble reconciling how this plate is constructed with my understanding of how one is supposed to work.  I thought the two plates should be able to rotate to some degree independently of each other with the springs providing the connection between the two.  However, on the front and back pictures you can see, between each of the springs, the heads of what appear to be five rivet-like fasteners that secure the two plates together.  In the side view picture, in the gap between the plates, you can see one of the rivets goes through both plates.  Possibly the holes in the plates for these rivets are somewhat larger than the rivet diameter allowing some play between the two plates, which is absorbed by the springs.  The new plate does not appear to have the same fastener arrangement between the two plates.
I took the old damper plate back to the yard for an evaluation.  One of the technicians declared the plate definitely defective.  Nearly all of the springs are loose to some degree or another, and they all should be under tension.  None of the springs are under tension.  When I asked how this plate works (see my questions above) the technician admitted he has never seen the internal structure of any Damper Plate.  That suggests both that these plates do not fail often, and when they do fail they exhibit easily recognized problems.  There is seldom a reason to test a plate to see if it meets specs or has failed internally.  Many mechanics recommend  replacing the damper plate anytime the transmission is removed (that was one of Cass' recommendations).
Re-Installing the Transmission
On  January 4, 2011 the mechanics re-installed the re-built transmission.
This included the new oil cooler and oil lines to/from the transmission.
After opening the water valve for the engine, I started the engine and put it in forward gear.  There was no gear backlash noise.  In reverse there was significant noise, but nothing compared to the previous operation.  The mechanics tightened a couple of machine screws on the V-Drive end of the jack shaft and the noise was reduced somewhat.
It  appears the new damper plate removed the severe gear backlash noise in  forward gear.  Some noise is still there in reverse and I will probably have another look at that before I depart on another cruise.
Cause of the Failure
I guess I'll never know for sure.  I believe the evidence points to the damper plate, if not as the cause, certainly a major contributing factor.  I also believe the damper plate was either DOA from Mack Boring or failed when the engine was intially put in gear.  The fact that there was a very loud low RPM gear backlash from the start, and then the noise went away when the new damper plate was installed makes me believe the original damper plate was DOA.  While it is normal have some gear backlash, especially with the Walter V-Drive,  this backlash noise was very loud.
I had hoped Mack Boring would consider the evidence that the damper plate failed at the start of the warranty period and provide some level of coverage for the premature transmission failure.  At a minimum cover the cost of replacing the damper plate.

No joy on that.  The engine and transmission  were nearly two years out of warranty, and Mack Boring would not even consider that the damper plate failure occurred during the warranty period.  I received no compensation from Mack Boring to help offset the cost of the failure.  My engine installer, Zahniser's Yacht Center, was much more forthcoming with financial consideration, although they clearly had no responsibility for the failure.  I have been a satisfied customer of Zahniser's for more than 35 years, and I will continue to be their customer in the future.  Mack Boring is another matter.
I was much too quick to accept the re-installation of the transmission.  I went with a local yard because they are a Yanmar dealer.  I was still self-deluded into thinking Mack Boring might feel some responsibility for the situation so I kept Yanmar service reps involved.  Dumb and Dumber.
The picture above shows that the Velvet Drive oil cooler was installed improperly.  The ports for the oil lines to and from the transmission must be on top, not on the side.  If oil cooler is not aligned with the ports on top the oil will drain back into the transmission sump giving a false indication of the oil level.  When I picked up the transmission from Cass, this was the most important thing he impressed on me for the re-installation.  I made sure the mechanics were aware of this requirement.  I even showed them pictures of the original installation as delivered from Mack Boring.  With all that they still got it wrong.  Of course I didn't check their work, I was so thrilled to have the backlash reduced to background noise I just closed up the engine box and went on to the next project. 
It wasn't until a few weeks later that I was reviewing the pictures on this page when I noticed the installation screw-up.  It wasn't a big deal to fix the problem as shown on the right.
I guess the mechanics had difficulty getting the oil hoses to reach and line-up with the cooler ports so they just did what they thought would work.  I was less than 20' away and they could easily have advised me of the problem they were having.  Instead they just threw it together.
The solution to getting the hoses aligned with the ports was to re-route them as shown on the left.
Now I'm a little concerned that the mechanics may have screwed something else up that isn't so visible. 
A Really Big Oops!
The replacement damper plate seemed to work really well, and I thought the severe gear backlash was a thing of the past.  I motored nearly all the way from Jacksonville, Fl to Patuxent River, MD and spent the summer cruising the Chesapeake Bay (mostly under power).  At the end of October I started south for another winter in Jacksonville.  On the way I stopped in Oriental, NC to have a few items with the engine checked by Deaton Yacht Services.  During that checkout the new damper plate failed.  I discovered that it had been installed incorrectly.
The new saga of the damper plate is described on my web page covering the trip south in 2011.