Gearbox Replacement

Yanmar KBW-20 Gearbox

Note:- To view any image in a higher resolution just click on that image.
Also, there are many other photographs on this subject held on file

  On our return “motor” to Portsmouth Harbour after a quick Partners Day-sail we slowed near Gosport Fuel birth to top up our fuel tank but their price was so close to Wicormarine’s we decided to continue our passage and use the services of Wicormarine as it was so convenient.   Engaging forward gear again we noticed a noise emanating from the gearbox like a long scraping/crunching sound and after what seemed a long pause (just a second or two) there was a quiet “clunk” and forward gear started to actually drive.  OK this must have been a glitch or so we thought and hoped.  We motored onwards another 20 minutes to our mooring slowing down and eventually entering neutral and reverse.  Then, when we required forwards again there was no drive at all. By then we had our lines ashore and were safe and started investigating our problem.   It was rather obvious that we had Reverse gear but lost Forward gear and so our gearbox had to be removed for repair.  Were we lucky?  Well, a big yes for the weather, a safe mooring on our return and a no for the 33 years old gearbox.

Gearbox removed (with Aquadrive removed)
resting on Engine

Engine Bilge with Gearbox and Aqua Drive removed

   Access to the gearbox was as good as you can get (over and all around) and the gearbox to engine nuts were easily removed although the Aquadrive had to be removed to allow the gearbox to be separated from the engine.  It’s a very heavy gearbox of rugged construction and required several hands to make life easier including the use of a rope but it was rather straight forward with access being the main advantage.   As we were on our mooring, as a safety measure the deep sea propellor shaft seal was blocked with timbers to ensure little (if any) sea water passed into the bilge.  Once the gearbox was removed it was taken to the Engineers workshop for dismantling and repair.

Aqua Drive removed

   It was later found that the Friction plates (I can only assume just the Forward set) were worn smooth and had to be replaced.  Chasing the engineer’s company for an update I found that nothing was forthcoming as unfortunately their Yanmar contacts for spares were furloughed due to the Coronavirus and as the expected cost of replacing both Forward & Reverse sets was considerably high (it is a Yanmar gearbox with Yanmar prices after all) we were also investigating fitting a newer design replacement gearbox with the more modern Cone clutches which may well be cheaper in the long run.   Our gearbox is a Yanmar KBW-20 actually made by Kanzaki in partnership with Yanmar and although rugged felt as it was designed to fit in a armoured Tank.  Its looking like an outage of several weeks.  And all at a time when we are now almost available for a sail.  First week in June and we can stay overnight.  Well, without a gearbox. Many days had gone by without our engineer’s company making contact and after I started calling them they let slip that they were only contacting suppliers for a new gearbox in the Barrus group. I immediately started calling my own contacts and those of my Partners.  Unfortunately they also came up with nothing to report however one suggested a refurbished box instead of a repair.  Frustratingly with our sailing season seemingly slipping by we still await a call.   Then by chance one of my contacts suggested a PRM120 replacement gearbox although not sure whether it would fit.   Would you believe that my engineer’s company also had been told of a supplier who had the necessary Friction plates however had lost the details.   So much for reliability!   I contacted the owner of PRM Newage Ltd who was extremely helpful and explained that the PRM120 had been replaced by the PRM125 that if it would fit it would be perfect and that I should contact Lancing Marine in Brighton for more details of adaptor plates etc.   This I did and they too were extremely helpful leaving me with some homework to ensure it would fit.   There are problems with the gearbox’s I/O shafts “drop” dimension that I have to investigate. Days later, after taking some detailed measurements on board I found that the PRM125 gearbox would not fit.  I also checked the other suitable and smaller gearbox in PRM Newage’s range but they wouldn’t fit either.   Back to Marine Power and more contacts had arisen.  With the possibility of waiting for many weeks for Yanmar spares at a vast cost I now had the option of a Replacement KBW-20 gearbox at a very much reduced cost but the contact was not answering the phone.  He did however return my call and to my amazement he was a fountain of knowledge.   I just wished I had made his contact weeks ago.

Dismantled Yanmar-Kanzaki KBW-20 Gearbox, Bell Housing

Remaining gears in box (after Clutch plates removed)

Forwards gear friction (clutch) plates found worn smooth

All other gears & bearings shown in good condition

  Unfortunately without the ability of raising or lowering the engine or prop shaft I am left with just a few options.  Have our current gearbox repaired via our engineers at vast cost and a guess at whether the necessary spares & tools would  still be available. Continue researching for a refurbished KBW-20 gearbox within the UK, a cheaper option. Lastly extend my investigations to other countries, say France where most of the Kelt 39 yachts reside.   My Partners have opted to the former and wait.   A call from our engineers mid July to say they may have a replacement gearbox from “ZF Marine”, type “ZF 30 M”.   This is almost the same design as our KBW-20 but being new will come with a guarantee at a similar cost and of course be much more reliable.  Initial investigations show there will have to be some alterations for the installation but so far looking at the engineering drawings it looks promising.  Only problem so far is the ordering lead time in excess of 6 weeks to 2 months.   Meanwhile we are still investigating the possibility of obtaining another KBW-20 second-hand box as a direct replacement. This will of course give us much more time to source spares to repair the old box (should we feel it necessary).

Reverse gear Friction plates showing slight wear

  We have a plan. Its now late July and one of our Partners visiting family in Cornwall was given a name to contact. It turned out to be the successor to manage Cellar Marine who after several unsuccessful telephone calls I was informed had ceased trading.  How wrong I was.   I have had dealings with this company in the past and found them to be very helpful so I was looking forward to at least discussing our problem.  They actually had in stock a very old probably second hand KBW-20 gearbox and it was first thought to be a direct replacement for ours.  Unfortunately it had the wrong gear Ratio resulting in a much slower propellor speed so it would have to be modified.   This was not possible at Marine Power as they had no spares at all and limited tools nor did Cellar Marine have the necessary gears however they thought they might be able to repair our gearbox from stock spares.

   After a few calls & texts explaining exactly what was wrong with out gearbox they found they had almost a set of the Friction plates we required and they were prepared to cannibalise their own gearbox for any additional parts they did not have in stock.   My Partner even offered to drive from London to Cornwall to deliver (and hopefully collect) our now dismantled gearbox.  Unfortunately he had to cancel however another Partner volunteered and we made the arrangements.
   Our gearbox was boxed and collected for delivery to Cellar Marine for what could be a 4 hour repair, in reality the next day Fishermen in trouble would get priority. Collection and delivery by one of my Partners (car) was planned for very early August so we could be ready for sea at the end of the first week of August (one hoped).  There are many advantages of repairing our own gearbox, one being speed of a repair and the most important, a straight forward reinstallation on board.   We looked after our gearbox with rigid annual servicing and an inspection when it was stripped on the bench showed the gears and bearings were in very good condition so hopefully there would be many more years of life in her yet.   It was delivered to Cellar Marine very early on the Tuesday 4th (August) whereby the engineer first pointed out that a most important part was missing.  Worried telephone calls were made and the missing part located on the bench back at Marine Power, Bursleden.  To say the least when assured that ALL the parts were boxed, we were not amused!   Fortunately that part could be “borrowed” from the spare gearbox with Cellar Marine.  Marine Power did offer to post the item first class but that would have meant staying in Cornwall for at least another 2 days.   Work was completed late that Tuesday evening  and was collected and transported the following day back to another of my Partners in Hartley Wintney.   This made it ready for me to collect 2 days later on route to Marine Power for them to complete the assembly and install it on ADAT.  This was duly undertaken and the gearbox was installed.

Refurbished gearbox installation complete with
Deep Sea seal, Bilge Sentry and MG Duff Electro Eliminator

  Alignment of the Aqua drive became a time consuming problem but was successfully undertaken just leaving a very leaky Deep Sea Seal.   After checking its alignment it was found to be severely worn and the exact mating position could not be found therefore I decided to gain as much sailing time for the remainder of this season and with much more alignment put up with the now minor leaks, monitoring on a regular basis.   We do have 330 Ah of domestic batteries and a 20 Ah (at 20 knots wind) wind generator so I felt it should easily cope.  The gearbox had been tested on the bench at Cellar Marine as part of the assembly and drained of any oil in preparation for carriage back to home, the Marine Power engineer part filled the gearbox with the wrong oil (SAE-30). Without any means of extraction and unable to attach a socket to the sump drain plug we had to wait for the engineer to obtain an extractor.  Once this was completed he used the correct oil (our oil) and filled the gearbox to its correct capacity (1.2L of ATF-G). As a matter of course to ensure all had been aligned correctly (gearbox/Aqua Drive/Prop Shaft) I wanted to run tests on ADAT’s mooring at Wicormarine.  We started the engine and tentatively engaged forward gear when immediately the whole assembly (engine, gearbox and Aquadrive violently shook.   We thought we stopped the engine but the Morse operator called to say the engine had stopped on its own accord and we then found the gearbox locked in forward gear. Urgent discussions took place between myself, our Marine Power engineer and Cellar Marine in Cornwall and by agreement it was decided to yet again remove the gearbox and return it to Cornwall.   Cellar Marine offered to arrange carriage from Marine Power.   So we were back to as it was so many weeks ago. What was expected to be no more than a week’s outage had turned out to be nearly 8 weeks (and counting).  The carriage to Cellar Marine was ordered as 2 day but due to a suicide on route it actually took just over 6 days. When it arrived it was immediately repaired, just an errant bearing that was easily replaced. Then a 2 day carriage was arranged by Cellar Marine back to Marine Power at Bursleden which took 3 days and was “lost” on delivery.  Since there were high tides and the area was flooded it was delivered (a usual arrangement) to another office and was soon located.   After receiving Marine Power’s account we opted to install the gearbox ourselves and arranged to collect it and pay our account however the gearbox was not to be found. It seems Marine Power had carried it to another branch assuming that they were to install it on the boat in spite that they had been informed otherwise.

Final full installation of refurbished gearbox

  I am happy to report that on the same day (26th August) it was installed by all of the Partnership under my direction.  Once the gearbox alone was installed (8 bolts, 4 nuts and no alignment) it was tested successfully.  Then all alignments of the Aquadrive and Deep Sea seal followed with a final and full test. Starting the following day ADAT was successfully trialled at sea for for the next 4 days by 2 separate Skippers.   Celebrations of completion of this 10 week outage (and my recent birthday) were made in the “Salt Cafe” at Wicormarine.