I just took the cover off the salt water pump on our engine to find a blade missing off the impeller, despite the pump only having about 100 hours on it.
Annoying, but here’s where things really went down hill:
The Offshore Voyaging Reference Site
The Offshore Voyaging Reference Site
I just took the cover off the salt water pump on our engine to find a blade missing off the impeller, despite the pump only having about 100 hours on it.
Annoying, but here’s where things really went down hill:
At least your pump is in a good location to get to. Mine’s facing the back of the engine so when I have to change the impeller it’s done completely by touch.
Talk about a motivation killer to do the right thing!
Hi John,
Ouch, that’s horrible.
There is a special place in hell for boatbuilders who don’t think of that kind of thing and provide access to frequent service points on the engine.
It’s something that mechanical engineers are increasingly being trained to pay attention to.
Granted, not all of them actually listen in class, hence the tremendous variety of curses levelled at the likes of Audi on r/JustRolledIntoTheShop, but if you buy a good modern marine diesel from Beta or Yanmar you will generally find that considerable thought has been given to the service points.
Whether you can actually get to the engine while it’s in the boat is an equally important matter. At the last Annapolis show I was amazed by the differences in builder philosophies here. All the Beneteaus had full easy access to all sides of the engine even while holding a large wrench and I could have replaced the engine mounts by hand in an hour. On the Catalinas, you could get to the dipstick, front belt, and oil fill; the impeller was “difficult” and anything else involved disassembling carpentry.
Sounds like an Atomic 4 to me!
It’s actually a circa 1997 Yanmar 4JH2E.
This brings up the subject, why did the impeller fail in the first place since it’s likely that this impeller came with the boat, you may not know whether it’s an OEM or otherwise I have found that genuine OEM’s on my Johnson seawater pump are the best I have heard bearing comments as to the reliability of some substitutes, including globe. Thanks, Neil.
Hi Neil,
Good point, but in this case I replaced the whole pump when I bought the boat so I’m pretty sure the impeller was a genuine part.
i put a strainer in the hose from my pump to the heat exchanger, just like the one between the thru hull and the raw water pump for this very reason- i can easily see if i have lost a blade with out taking anything apart and if i have it is not going anywhere.
Hi Matthew,
Probably a good idea, although I always worry about changing stuff like that because it adds restriction to the flow, particularly as the strainer gets dirty. Which strainer did you use?
Hi John, what is your maintenance interval engine hours for an impeller change? Just curious..
Hi Ee Kiat,
What ever the engine manufacture calls for in the manual. That seems to vary. Now I think about it, this is the first time I have ever had an impeller fail on me, so following the manual seems to work. Back in the day on the M&R 56 I used to replace the pump every 2000 hours (if memory serves) to avoid wear issues and leaks.
I went through a similar scenario last year with 1 1/2 blades MIA. I located some debris in the heat exchanger but wasn’t convinced it was enough material. I then separated the gearbox supply cooling line at the gearbox (Isuzu) and found the missing blade jammed into the supply side fitting at the casing. I expect the flow was restricted to at least half. I’ve had the boat for 10 years and it came with a dozen impellers. I change them annually so the last impeller I installed was at best 10 years old. It was just prior to setting off for the Philippines in June, an approx. 1400 nm passage, so I ordered 6 new impellers. I have kept the 2 remaining old stock impellers for now but I’m not sure why. Because they look new I suppose. I doubt I’ll use them.
Hi Austin,
Good point that we have to diligently look for all the pieces when this happens.
Hi all, i just noticed from John’s photo above that there is an O-ring on the impeller cover plate. That is a very sensible design. I have a Jabsco impeller cover without the O-ring. The replacement impeller comes with a wafer thin paper gasket which serves little use in preventing water leaks. Being not so good a hands on mechanic, I did managed to rip the fine threads on the impeller housing while attempting to tighten the plate. From then on, I have an adverse apprehension in changing impellers. I was thinking of using silicon and the wafer thin gasket but not sure if the small bits of silicon will cause blockages downstream. I would appreciate any advice on preventing water leaks please? Thank you.
Hi Ee,
My Yanmar has an o-ring seal and it always popped out when putting the cover on until I tried a couple of dabs of grease in strategic spots. The grease held it in place till I secured the cap.
On an older engine with a thin paper gasket such as you described, I also had trouble always getting and keeping a good seal. I ended up using Permatex, “2 Form a Gasket” non-hardening by applying a very thin layer on the paper gasket both sides. Messy, unless more careful that I, but it did the job. In a pinch after I destroyed a paper gasket inadvertently, I cut out the gasket form in chart paper: worked just fine.
My best, Dick Stevenson, s/v Alchemy
Hi Dick,
Good ideas, thanks.
Thank you very much Dick. I will try your suggestion soon as my impeller is 2 years old but has about 70 hours. Sealant takes hours to cure and I suppose the engine would be out of action for many hours (including installation time) out at sea for an impeller change on my boat. Not ideal but perhaps one has to put up with a bit of leaks until a proper job can be done. I wonder if there is a aftermarket O ring sealing kit for a Jabsco raw water pump. That would dramatically cut the time to replace impellers.
Hi Ee,
The sealant I mentioned does not need curing: think more like tar (with all its messy connotations).
John made a good point about checking the surface for scratches and/or an errant piece of grit. The Permatex might need some cleaning up when changing impellors and you might be tempted to use a razor blade, but I can be a bit heavy-handed and do much less damage to the work or myself if I use a plastic razor. I find them sometimes hard to find, so I buy a handful and keep finding uses for them
My best, Dick
Hi Ee,
Yes, there are covers which use an o-ring that you can buy after-market. I have used Speed Seal covers (https://www.practical-sailor.com/systems-propulsion/diesel-engines/a-speedseal-and-a-jabsco-puller) for my raw water cover for years and 2 engines. The o-ring is certainly an advantage and it is designed in ways that seem to allow for less friction and wear on the impellor. The design also uses knurled nuts of a diameter that fingers can use and slick ways of positioning the cover so that the cover lines up easily to the holes: far less fumbling.
I have never had any trouble with this product, but I have never seen reviews until I just saw this PS article.
Let me know what you think and I would appreciate feedback from any other users.
My best, Dick Stevenson, s/v Alchemy
Hi Dick, Wow, that Speedseal cover plate was what I have in mind to do away with paper gasket and messy sealant. However, they are not available just yet (relaunching soon). I shall check on them again. Thank you very much Dick for the fine recommendation!
Hi Ee Kiat,
Yes, those paper gaskets are a pain. That said it should not leak as long as the mating surfaces are clean and free of imperfections. And yes, those screws are very easy to strip. Might be worth getting a torque screwdriver: https://www.morganscloud.com/jhhtips/why-we-need-a-torque-screw-driver/
Hi John, yes, a torque screwdrive is a good idea! Hmm.. I dont think my raw water pump provide specs for screw torque though.. May I know what torque do you use for your impeller screws?
Hi Ee Kiat,
You can look up screw torque in a number of places. Here’s just one: https://crafter.fastenal.com/static-assets/pdfs/Torque_of_Stainless_Steel,Non_ferrous_Torque.pdf
Thank you John. Sorry to trouble you on this as I didnt know it is a universally available data! I always thought that it involved 2 materials ie the bolt and the threaded part and every assembly ie stainless steel into bronze thread. But it is a good guide if lack of manufacturer’s data. Always learning something new everyday..
Hi Ee Kiat,
You are right that material plays a role in torque spec. Most torque tables are based on getting a tension in the bolt that results in ~75% of yield stress for the shank. Weaker bolts obviously require lower tension and therefore lower torque. You also need to look at the other factors including bolt thread strength, mating part thread strength, head strength and drive strength. Probably the easiest thing to do is to use a calculator like this one: https://www.futek.com/bolttorque/metric . That one looks at all but the last 2 factors I mentioned and they do not limit for hex head and socket head cap screws, just things like button head, flat head, etc. I have actually replaced the water pump screws on several engines with socket head cap screws as I find them easier to use in confined spaces.
Regarding sealing, the paper gasket may seem weird but you would be amazed at what can be sealed with no gasket at all if the parts are flat enough and have enough fasteners. A few things that are likely to cause leaks:
Eric