I am having to rebuild my BUKH DV20 chain case (water pump / hand-crank unit). It seems for a long period there has been a small water leak from the back of the water pump into the case which has caused complete breakdown of smaller components and bad corrosion on anything larger.
I am keen to understand how the components are lubricated, there seems to be a small diameter passage (~8mm) through into the engine block near to the spline drive from engine - is this some form of passive oil flow ?
In disassembling the case it seems that previous maintainer of the engine has used a liquid gasket between the engine block and the chain case which appears to have blocked this passage so I am assuming no engine oil in and no path out for any moisture.
Other than parts diagram I cant find details of how this is lubricated online so any insights would be great. Thanks.
The pump bearings are lubricated by engine oil. There should be a lip seal on the outside of the ball bearings to stop the oil from leaking out on the waterpump shaft and a lip seal on the water side to keep the water from entering the bearings. You may find that at some time in the past a marine mechanic rebuilt the water pump and placed a lip seal on the wrong side of the ball bearings and they have failed. The parts diagram does not always get it right either and you have to make sure the parts diagram is meant for your engine.
I had this problem recently and I rebuilt the pump using sealed ball bearings. I did put a lip seal in behind the bearings but just as a spacer really. Use Youtube to find out how to rebuild the unit but just think logically as you do the work.
My recent experience for a raw water pump is; if the lip seal on the water side has been leaking for a while, the shaft could be corroded and scored. A new lip seal might not completely seal. Sounds like you will be replacing both lip seals and the bearings, so you might want to get a new shaft as well if any damage. Depending on the cost of a rebuild kit and the condition of the pump housing (eg any scoring, corrosion where the impeller goes etc) you could think about a new pump. Whatever the situation, just make sure the hole in the housing between the raw water seal and the oil seal is not blocked and raw water can drip out if the lip seal is bad. Last thing you want is raw water making its way into the engine.
Thanks @ramona and @john24 very helpful and I will probably replace the pump shaft just to be sure. So is the engine oil lubrication just the hole at the bottom of chamber, do you know if this is pumped from the oil pump or passive based on sump pressure ?
Select to expand quotedeancs said..
Thanks @ramona and @john24 very helpful and I will probably replace the pump shaft just to be sure. So is the engine oil lubrication just the hole at the bottom of chamber, do you know if this is pumped from the oil pump or passive based on sump pressure ?
Just pull it off and take it into your workshop and pull it down. Watch a video first to see if it has a C clip hidden between the two bearings. These Johnson pumps just use off the shelf bearings and lips seals. two lip seals and two ball bearings will cost about $35. The shaft will probably be fine but if required will be about $100, new pump will vary from $460 to $600 depending where you shop! When first assembled these would have had some grease in the bearings but in operation are just splash lubricated.
The Johnson water pump seals have stainless steel components, they are not just the run of the mill standard lip seal.
Select to expand quoteJolene said..
The Johnson water pump seals have stainless steel components, they are not just the run of the mill standard lip seal.
Engineering shops sell lip seals with the SS ring. Johnson just use off the shelf items like everybody else. Use the part numbers off the exploded diagrams. Boat trailer grease in the lip seal with the standard ring on the water side would probably last long enough anyway.
The best guide I have found for rebuilding a raw water pump is at pbase.com/mainecruising/raw_water_pump&page=all
Very clear pictures.
Some bearing stores stock lengths of stainless steel garter springs for lip seals.
If you can accurately measure, you can replace a steel garter with a stainless steel one
Select to expand quoteJolene said..
Some bearing stores stock lengths of stainless steel garter springs for lip seals.
If you can accurately measure, you can replace a steel garter with a stainless steel one
Or buy an appropriate seal and pop out the garter spring and replace it with an identically sized o'ring for the seal facing the water. This is what I have done and the bearing and seal vendor had a minimum charge of $10, explained this and offered me another as a spare, still within the minimum charge. 
Thanks everyone for the advice and guidance, I have stripped down the water pump and can now see what people have been suggesting. I have ordered the bearings, sleeves, chain, lip-seals, o-rings and circlips etc from Bukh. Someone on one of the FB groups seems to have a chain-case, just waiting on confirmation.
