Repair report: Saildrive SD50 clutch refit (clutch slips).

- Lapping and calibrating the clutch is the be-all and end-all for a long service interval -

Published in the German technical sailing magazine Palstek 2-2021 (March 2021)


If the engine is running in the first or second position of the shift lever at the helm station, but hardly any water is being moved, a slipping clutch is often the cause. If this suddenly happens during port maneuvers, quick, prudent decisions are necessary.

Most of the time, the clutch grips after all, and the situation is saved. But then the cone clutch of the SD 50 needs to be serviced. You study the manual and service manual of the SD50 and read that the clutch should be lapped every 500 hours and that a new clutch is due every 2000 hours.
If you contact the Yanmar Service, you get offers of 500€ - 3000€ for the "lapping" and possibly exchange the cone, often with the instruction "ship out of the water". The internet is full of bad experiences with slipping Yanmar cone clutches and garages that are as incompetent as they are greedy. Really positive experiences can only be read occasionally. Most information describes "lapping" but not calibrating the cone clutch.





Repairs according to these instructions do not require taking the boat out of the water, just a little time and a few spare parts, some from the Yanmar parts service. These repair instructions describe "lapping" as well as checking and, if necessary, replacing wearing parts.

 Possibly not all spare parts are required. This depends on the wear condition of the clutch. If you go on a long journey, the spare parts marked below (*1) are the minimum equipment. A service kit is now ready. You can find that at the end of this post.

No. Count Designation Yanmar designation Part No. Info
1 1 M16x1.5 special nut, left-hand thread Top Nut 196324-04380 I had it turned/milled in a CNC workshop.(*1)(*2)
2 1 Support washer Trust Wascher 196322-04410 (*1))(*2)
3 1 Support bearing Collar Thrust 196320-04361 (*1)
4 1 Rings (2 pieces) Circlib 196322-04370 (*1)
5 1 Support washers, different thickness Collar set 196320-04400 (*1)(*2)
6 1 Fitting rings (T5, T1) Shim Set 75/85 196322-02320  Only if damaged
7 1 Fitting ring (T2) Shim 196320-02230  Only if damaged
8   Set of spring steel/stainless steel fitting rings0.1mm, 0.2mm, 0.25mm --- ---  (*2)
9 5 Stainless steel fitting rings 5x0,2mm Shim 196322-06630 

Only if damaged (*2)

10 10gr

Mix 60µ grinding powder with gear oil SAE30 to a paste or valve grinding paste (only use the fine regrinding paste)

--- ---  (*2)
  4 Needle bearing  Bearing 196322-04781  Only when needles fall out or are missing or every 1000h (*2)

(*2) Service Kit at the end of the repair report.

The problem with this clutch is:

1. That the collar set, which are support washers made of copper, are only available in 0.5mm increments. The solution here are adapter rings made of spring steel/stainless steel, which are available in 0.1mm, 0.2mm and 0.25mm increments. They make work a lot easier and significantly increase the service life until the next repair.

2. The bearing (also copper washers) is held on the underside of the clutch by circlips. Unfortunately, the rings also rotate and wear out very quickly. This creates further free play in the clutch.

3. The coupling is held in place by a lock nut, the lock ring of which is destroyed when removed. And according to the service manual after 500 hours. How sustainable is that?

Contrary to what is stated in the service manual, the clutch is not adjusted to a free play of 0.05mm - 0.5mm, but to approx. 0.2mm using the aforementioned fitting rings.

The free play on the forward and reverse shift lever must be adjusted exactly as specified in this manual. More on that later.

If all repair steps have been carried out correctly, downtimes until the next maintenance/repair of 1000 hours and more are possible, if not, then correspondingly less.

Required tools and spare parts:



feeler gauge; Paint brush; cleaning spirit; Set ring / open-end wrench; M8 eyebolt; callipers; triangular key file, small, narrow saw blade; old spatula with a continuous metal core and wooden handle; flat screwdriver small-medium-large; plastic mallet; metal hammer; massive vise; aluminum jaws; small chisel; stable impact screwdriver (with continuous metal core); torque wrench (150Nm); 27 socket, oil suction pump; Loctide superfest or other manufacturers with these properties (called screw tightener in the report); 2mm allen key;

Spare Parts: (see table above) and Service Kit at the end of this report.



Remove clutch:



Either you do an oil change, then you suck the oil out of the saildrive as described in the manual.
Otherwise it is sufficient to suck out the oil from the area below the oil dipstick.

Unscrew the 4 screws from the top cover. Pay attention to the O-rings (part no.: 024311-000090), (part no.: 24321-000950) and the fitting ring T5 (part no.: 196322-02320), they will continue to be used.

There are fitting rings above (T5) and below the coupling (T1) so that the coupling is at the correct height and sits firmly in the housing. Both will continue to be used.













Detach the gear cable from the clutch lever and loosen the two screws (red arrow).












Then drive the spatula between the flange and the clutch housing and further enlarge the gap with the small screwdriver. Pull the flanged clutch lever out of the clutch housing with small back and forth movements by hand.












Then loosen the 4 nuts on either side of the SD50 flange and turn back as shown. Important!! Leave the nuts on the studs.
Then drive back the screws (crosswise) and nut in the direction of the engine with a mounting iron or a plastic hammer.

This really works (most of the time).












If the 4 connecting screws between the motor and the Saildrive cannot be pushed back, a different procedure is necessary.

First remove all screws of the bell housing (red arrows).

Leave the nuts on the studs of the SD50 flange. (green arrows)
















Now the engine is unscrewed from the engine mount (4 screws). The motor is now moved away from the Saildrive by the length of the screw (red arrow) using an assembly iron or pulley block.

Therefore, the nuts must remain on the studs. (green arrows)



















Now screw an 8mm ring bolt into the coupling axle and use it to pull the coupling out of the Saildrive housing. A long M8 screw will also do.

Advantage of this procedure: The ship does not have to be out of the water

Possibly the adapter ring T1 is still hanging at the bottom of the coupling. Put this back into the clutch housing.


Disassembling the clutch:











Left: Then use a small chisel to chisel off the deformed portion of the original Yanmar nut (nut lock) so the nut can be twisted off. (Caution, the nut has a left-hand thread, i.e. loosen the nut clockwise). When the nut lock has been chiseled off, the nut is loosened and unscrewed with the 27 socket. This step is not necessary when using the nut from the service kit.

Center: The clutch is now firmly clamped in the vise using aluminum jaws or the spline tool from the SD50 service kit.

Right: On the way, without a vice, the clutch nut is loosened on a firm surface with the spline tool and a large wrench.

TIP: I hate chiseling on the clutch. (hard hits on the axle, metal chips, etc.)
However, if you use the nut from the SD50 service kit, it is secured well with 2 x M4 grub screws and some screw tightener on the thread of the grub screws and the nut. (The nut, thread on the clutch axle and the threaded pin must be well degreased (brake cleaner) so that the screw tightener works properly)

For the next maintenance, simply heat the nut to over 80°C with a hot air gun (it hurts a bit when touched), unscrew the threaded pins and unscrew the nut clockwise. The nut can then be reused.









Further disassemble the clutch:
















Check the lower support disc:




New on the left, old on the right. If the rings (part number: 196322-04370 and the support washer (part number: 196320-04361) show scoring, they must be replaced in any case.

This construction of support disk and circlips contributes massively to the increasing clutch play. The circlips move in the support washer and wear as they do so. The compensating movement should take place on the other side of the support disc on the copper disc.

 Note: another, more permanent solution without the parts shown on the left is in development.





Lapping the clutch:

"Lapping" means restoring the basic roughness of the clutch.                                                                 


The clutch is fully immersed in transmission oil. It penetrates first into the large and from there further into the narrow channels. Slow running of the machine with a slipping clutch is poison for this type of clutch. The cone clutch heats up and the oil burns in the narrow passages, which then clog. The burned oil acts like a polishing agent and grinds the running surface in the clutch bell. This shortens the time until the next maintenance. If the clutch is heavily soiled with carbon, the oil must also be changed. Many small pieces of carbon swim in the oil and tend to clog the narrow channels, since there is no oil filter in the SD50.

With a small triangular key file, the narrow blade of a utility knife or a very narrow saw, first open the wide and then the small oil channels again. Untreated in the photo above left, treated on the right.


Tip: Now it is clear why Yanmar prescribes the gear idling (neutral) when sailing. The water creates vibrations as it flows around the fixed propeller. These vibrations are transferred to the clutch and grind the clutch bell bare.

Another tip: Always switch quickly (quickly) from neutral to the first level forwards or 1st level reverse so that the clutch has engaged before the engine develops any real power. Always shift from forward to reverse slowly, pausing in neutral. If it bangs in the gearbox, it was definitely too fast.



On the inside of the clutch bell you can see brown deposits (left arrow) with a nice reflection of the brightly polished surface (right arrow)












Remove the needle bearings from the bell before lapping!


Now the entire running surface of the bell is wetted with the grinding paste and the clutch cone (with the correct side (*)) is inserted into the clutch bell. The coupling cone is pressed into the bell and moved back and forth by hand about 10 times, then the cone in the bell is turned a little further. Repeat this process 5 times. This brings you to 50 grinding processes and the clutch cone was turned completely in the bell.

 (*) The marked side (e.g. in my case: 4CA) of the coupling cone points downwards when installed in the Saildrive, or on the right in the upper picture "Further disassembling the coupling".







Now wash the bell and cone thoroughly in petroleum ether.











The lapped tread on the left, the untreated surface on the right.
If the running surface shows color changes after lapping, these can be caused by overheating, parts or even the entire clutch must be replaced.
When the parts have been cleaned again, you put the cone (both sides and pay attention to the correct allocation cone / bell) in the counterpart (bell) and check the minimum size with the caliper. The standard size is 29.4mm to 30mm. The minimum size is 29.1mm.








If it falls below, a new clutch is required (GEAR SET 196322-04152)









Calculation of the fitting ring T1 (fitting ring in the bottom of the gearbox):


The formula for the fitting ring T1: T1= (A - L1 - 10)
(+/- 0.025mm)

The height of the lower part of the coupling is L1. The default value is 68.2mm.

A=78.5mm. A number for the deviation is stamped on the SD50 below the nameplate. 3 means ==> 0.03mm.

Then A= 78.5mm + 0.03mm = 78.53mm.

(self-measured L1 = 68.25mm ==> T1=0.3mm)










Check needle bearing:



The needle bearings must be checked to ensure that the needles in the cage are complete.

If they fall out easily, all 4 bearings must be replaced. Yanmar requires replacement every 1000 hours.

(Part number: 196322-04781 or industrial type from the service kit)








Assemble the clutch:

When assembling, make sure that the labeled part of the cone is pointing to the right, as shown in the picture below.


















 When assembling, make sure that the fitting ring T2 (196320-02230) is in the correct position. T5 (196322-02320) is positioned when the cover is unscrewed. T1 should still be in the bottom of the clutch housing.

Then clamp the clutch firmly in a vise. Don't forget the aluminum jaws or use the spline tool from the service kit!


Measure free clutch play:




















Tighten the nut only slightly so that the free play can be measured.

Using the Yanmar Collar Set (copper back-up washers) (part number: 196320-0440) select the appropriate copper back-up washer or select a used one leaving 0.1mm - 0.5mm of free play. Then set the remaining play to approx. 0.2mm with the spring steel fitting rings and the feeler gauge.
Clean nut and thread oil-free (brake cleaner). Then apply screw lock and tighten to 150Nm with a torque wrench. Check the free game again.
Then tighten the two setscrews with the 2mm Allen key. Let the screw lock dry according to the manufacturer's instructions.


Lap the clutch along the way:




In order to disassemble the clutch on the go without a vice, at least a pipe wrench or wrench is required. The spline tool is placed on the splined shaft of the coupling and held with the pipe wrench. The nut can then be screwed on or off with the torque wrench and the 27 socket.











Insert clutch:

Screw the 8mm ring bolt back into the coupling. Apply a thin layer of oil to the clutch (engine oil) and ensure that the fitting ring T2 does not protrude. (see arrow in left picture). You can also pull a wide plastic cable tie over the fitting rings.

If the coupling does not sink completely into the housing of the SD50, simply turn the eyebolt slightly until the coupling sinks completely into the housing.













The round opening of the clutch housing must not cover the opening for the shift lever on the SD50 housing. Align evenly. You can feel it with your fingers. (See picture on the right)

Install clutch lever with shifter:







Insert the shift lever with the wide part to the rear (see arrow) towards the rear.

Then fix the clutch lever with the two screws.









Adjust shifter:

















When the clutch lever is screwed back on, the M8 Allen screw (red arrow) is removed. Be careful not to lose the fitting rings (green arrow). Set the clutch lever about 10°-15° off neutral. The shift lever is then retracted into the clutch at the lowest point.






The cone clutch is never centered. In order to determine the smallest depth L, the coupling axis must be turned using the ring screw until the depth gauge of the caliper protrudes furthest out of the hole. Now leave the coupling axle in this position.

The axis of the shift lever has a recess in the middle. Be careful, don't even measure with and without the indentation.
















Then use the depth gauge of the caliper to measure the depth L at the position of the Allen screw (see below). Be careful, the shifter has a depression in the middle (see next picture). The deepening must not be measured.









The thickness of the adapter ring is calculated:

T= (H - L + C) (+/-0.1mm)
L = depth of shifter (standard approx. 16.35mm)
H = screw length (standard approx. 17mm)
T = thickness of fitting ring (standard approx. 0.95mm)
C = distance between screw and shifter (standard = 0.3mm +/- 0.1mm)




Example: screw measured 17.1mm; depth of the shift lever measured 16.3mm; C should be 0.3mm.

==> T = 17.1mm - 16.3mm + 0.3mm = 0.5mm (+/- 0.1mm) ==> Choose a fitting ring thickness of 3x0.2mm = 0.6mm and screw on with the M8 Allen screw.

Use your hand to shift the clutch lever back and forth and check for free movement. In the forward, neutral and reverse end positions, the clutch lever sinks slightly into the transmission housing. That must be clear to see.

In the later, final test, this behavior of the clutch lever is checked again. Therefore, look closely at the behavior and remember it.


Calculate fitting ring T5:

















Calculation of T5 = (H6-L6) deviation +0 to 0.05mm

Measurement of H6 as shown above left. Measured H6 = 16.5mm.
Measurement L6 as shown above right. Measured L6 = 16.1mm.

T5 = (16.5mm - 16.1mm) = 0.4mm. Check the fitting ring and adjust if necessary.


Screw the transmission flange back together:












Retighten the 4 screws (green arrow) of the SD50 gearbox flange crosswise.

Turn the eyebolt slightly so that the pinion wheel slips slightly into the clutch.


Install transmission cover:




Now insert the two O-rings and the fitting ring T5.

Then insert the clutch cover and tighten the 4 screws crosswise.

Now screw the shift cable back on. The shifter cable sheath has a notch, the mounting bracket has a lug. The shifter cable is attached with the lug in the notch. The gear cable core is attached to the clutch lever with a cotter pin. There are no other setting options here.







Screw the gearbox and motor back together:

If the transmission bell screws had to be loosened:

Move the motor closer to the bell housing using the assembly iron or pulley block so that the screws grip again.


Then tighten the screws of the gearbox bell crosswise so that the engine is pulled towards the bell.

Then align the engine to match the engine mount and tighten the engine mount screws.






Fill up the oil again and check the oil level (see below "A word about the oil level in the SD50").

Now fill up the gear oil according to the instructions in the manual. For information on the oil level in the SD 50, please read the next chapter first.


A word about the oil level in the SD50:
Have you ever noticed traces of gear oil on the sail drive sealing flange? This could indicate an incorrect oil level in the SD50.

Do you change the oil yourself as part of the annual maintenance and follow the instructions in your operating manual?

Do you have the oil changed at a Yanmar service workshop? But even the service workshops do not all read the Yanmar Technical Bulletin.

The oil level in the SD50 is redefined in the Yanmar Technical Bulletin MSA 09-017 (dated 16.9.2009).
So check whether your SD50 has a long or short dipstick and only fill the SD50 up to the low mark on the short dipstick or up to the full mark on the long dipstick.

A new dipstick can be ordered from Yanmar Service using part number 196450-02350.




Another note: the new long dipstick has a black dot on the cap.






Reason from Yanmar: Due to the heating up during operation of the SD50, pressure builds up in the transmission. This pressure could escape through the drive shaft seal (to the engine). Oil can escape with it. During the subsequent cooling, a negative pressure could arise in the SD50, which could suck in water at the propeller sealing ring.

By increasing the ratio of air to oil level in the SD50, the pressure conditions are more favorable and the risk of water leakage is lower.

 Update January 2022: There is a new solution for this problem. Rebuild the SD50 Saildrive without pressure. The instructions can be found here.


"A word on gear oil"

The SD50 operating instructions refer to Mercury Quicksilver High Performance Gear Oil. As far as is known, this oil is not only attributed an exorbitant price, but also very good water-binding properties. I can confirm both.

If you always change the Simmerrings on the propeller of the Saildrive together with the underwater paint, so every 2-3 years, you can do without these properties and use SAE 90 GL3 or GL4 gear oil instead. This costs only 10% - 15% of the Quicksilver oil price and is perfectly adequate for the loads in the sail drive.

Never use GL4+ or GL5 or even higher alloyed oils. Not only are these more expensive, but they are definitely not good for the cone clutch.

And now for the technicians among the sailors:

An API GL4 lubricant contains additives specifically for manual transmissions. Manual transmissions contain non-ferrous metal (synchronizer rings). The friction of a GL4 oil must not be too low, otherwise the synchronizer ring will slip and shifting will become impossible. If the friction is too high, the shifting becomes notchy and scratches. The cone in the SD50 clutch is made of non-ferrous metal. Too little friction would cause the clutch to slip easily.

Also do not use GL4+ or GL4/5. This is thin like GL5 and doesn't contain as harsh additives.

An API GL5 lubricant contains special additives for highly stressed gears, such as E.g. hypoid gear. These gears have curved teeth. In addition to some advantages, this type of gearing has the disadvantage that the surfaces not only roll off each other, but also slide a little. This places increased demands on the material and requires the oil to have high lubricity. The additives contain sulphur, which in turn attacks non-ferrous metals.


Final test:

As in the chapter "Adjusting the shift lever", the transmission of the states forward, neutral and reverse is now checked on the clutch lever of the SD50.

1st test: Without running machine:
At the helm, an assistant adjusts neutral forward and back to neutral, and neutral to reverse and back to neutral. In the forward, neutral and reverse end positions, the clutch lever sinks slightly into the transmission housing. That must be clearly recognizable.

2nd test: With the machine running:
At the helm, an assistant adjusts neutral forward and back to neutral, and neutral to reverse and back to neutral. Even in the first stage, if there is one, it must be possible to clearly see and feel the propeller water in the corresponding direction (movement from the boat). In the forward, neutral and reverse end positions, the clutch lever sinks slightly into the transmission housing. Even now this must be clearly recognizable.

If the clutch lever does not completely follow the settings from the helm station, the installation of the shift cable on the Saildrive should be checked. The gear shift cable must then be checked at the control stand and, if necessary, adjusted so that the clutch lever moves as described in the "Adjusting the shift lever" chapter. The clutch lever was moved to the end positions by hand and wandered a little into the gearbox housing.



In gear or in neutral when sailing?

The wildest reasons why the gear should be engaged or the gearbox should run in neutral are circulating on the internet. In certain cases I agree to the Yanmar instruction. In the case of a fixed-pitch propeller, the gear must run in neutral. With a folding propeller, it is necessary to check whether a folded propeller transmits vibrations to the gear coupling.

Reason: If the gear is engaged while sailing, the water flows around the ship's propeller in a turbulent manner and generates vibrations. The vibrations are transmitted to the clutch cone, which sits in the clutch bell. These vibrations create small movements that polish the clutch bell and cause the clutch to lose engagement. The result is a slipping clutch.

Fake argument: "Not properly lubricated". It is claimed on the internet that the sail drive would not be properly lubricated if it were to run in the neutral position while sailing. In the user manual of the Saildrive SD50 in chapter 2 "Technical specification" under lubrication system "Oil bath type" is mentioned. With this type, all moving parts are always surrounded by oil. A pump is not necessary. So this argument is wrong.

Fake argument: "High wear". What is meant to wear out when the water flow drives the propeller and gear up to the clutch? The force is far too low to cause wear.


When sailing, only the axle with the nut rotates clockwise. The large bearing, here the upper one in the picture, only rotates when the machine is running. The axle with nut lies with its own weight of approx. 500gr. on the copper disc that rests on the stationary bearing. This is the explanation for the fact that the upper copper disk wears out, but the lower one hardly at all. I've never changed the bottom one.

If the upper copper disc has become too worn, the clutch will slip or not engage at all.

Here I am working on a solution with storage, but it will not be available until summer 2022.



SD50 service kit:

The service kit makes disassembling and assembling the clutch much easier. The M16 nut, the spline tool are made in a CNC workshop and the parts, including the 0.1/0.2/0.25 bearing washers, can be used over and over again.





1: Spline Tool (aluminum hard) = 100€

2: Nut M16x1.5 left (tool steel, reusable) = 55€

3: 0.1mm-0.2mm-0.25mm bearing washers (spring steel, reusable) = 10€

4: 0.5mm-1.0mm-1.5mm-2mm copper washers = 45€

5: Needle bearing 4 pieces = 40€

Simply load the order list, tick the parts you want and send me the file. (Info: The file can be edited directly in Acrobat Reader, but not in Windows Edge.)

Or write me an email






Not included in the service kit as it is easy to get.

Feeler gauge: Available in car accessory shops

27 socket from the ratchet box

M8 ring screw galvanized or V2A is available in hardware stores



 Owners who dare to use the clutch should, in addition to some technical experience, also have a feeling for technical components. Reading a calliper shouldn't cause any difficulties, but neither should working with grinding paste and a torque wrench. Anyone who does not have these skills should contact a service workshop. Through these work instructions, the owner knows the necessary work steps and how to recognize unnecessary (and expensive) steps by the mechanic and, if necessary, prevent them.

For example, installing a new clutch cone, while not undersized, will bring more money to the service shop. Some sailors have already told me about it.

Have a good trip and fair winds


These instructions were carried out and written to the best of my knowledge and belief based on a repair/maintenance I carried out myself.
The instructions were carefully created and checked by me. No liability is assumed for the use of these instructions or for damage caused by these instructions.


Jochen Brickwede in December 2021