We have a 1987 hunter 34 with a yanmar 3gm diesel. I have owned this model for three sailing seasons and just put our boat in for number 4. At the end of last yr, on the hard the raw water system would not take my antifreeze without some persuasion. When the boat was dropped in on friday I had more problems with this. The exhaust sounds hollow and like a muffler blown out vs the typical muffled sound and water coming out the back. Our exhaust water has never been all that powerful but adequate and the motor has never overheated. Anyway this needed to be looked at and I was going to fix it. This is for the novice, copy this off and leave it on your 34 hunter because it may happen to you away from the marina and this simple guide will help you thru the process. 1 set the hook if you can, turn off the power and shut the raw water intake by the stuffing box. 2 you should have probably two extra impellers and gaskets on board. 3 you will need sockets and a screw driver. not too sure on the socket size so IN ADVANCE make sure you have the proper size. a cresent wrench will work. 4 as you are kneeling looking at the engine look on the left side at the small belt. the pully it attaches too is where the impeller is. it is behind the pully. 5 remove the two hose clamps that attach to this pully.make sure you have a container below as a cup or two of water will come out. no big pressure thing though. take the hoses off and let them drain into the container. after a minute or two dump the container out to avoid a mess. inspect the two clamps and replace if necessary. one of mine was pretty rusty so i replaced it. 6 remove two long bolts and the entire pully and impeller system will come off. 7 on the back, there are six scews. some of mine, the head from the phillips screw driver were stripped so i replaced all of them.they are metric size. remove the screws,and gently remove the cover. a regular screw driver may be required to help loosen the cover . inside you will see your six vane impeller. three of my vanes were gone and the others were cracked. i used a screw drive to gently pry the impeller out. there was no special clip holding it in. you do have to line up the slot to put back in and note which way the vanes are bent. if you are not sure, just touch your ignition to see which way the engine turns then insert so the vanes drag behind. our engine turns clockwise. i put alittle vasoline in the impeller holder to help lubricate. i then cleaned the cover of the old gasket with a razor blade and reinstalled everything. 8 remember to open the raw water intake. start the engine, look for leaks and that should be about it. this whole process should take about one half hour once you have done it. along with replacing filters, this is a very important item we, not the marina should know how to fix. good luck. craig 4
Great Write-Up!
I would just add that the impeller blades that broke off had to go somewhere. Yours apparently flushed through the system and out the wet exhaust. I've had to replace the impeller on my 4JHE just once. After replacement, I still had cooling problems until I found the broken material in the SW exhaust line nipple to the Mixing Elbow. When I'm running the engine, I find the best source of knowing that the engine cooling system is working is just to place my hands on the SW pipes into and out of the Sea Strainer. They should be as cool as the sea water. If they're too hot too touch, you've got an overheated engine. If you haven't yet read "TRIMMING THE "IRON GENOA", you might find it useful. It's at the related link. Thanks Sam
I would just add that the impeller blades that broke off had to go somewhere. Yours apparently flushed through the system and out the wet exhaust. I've had to replace the impeller on my 4JHE just once. After replacement, I still had cooling problems until I found the broken material in the SW exhaust line nipple to the Mixing Elbow. When I'm running the engine, I find the best source of knowing that the engine cooling system is working is just to place my hands on the SW pipes into and out of the Sea Strainer. They should be as cool as the sea water. If they're too hot too touch, you've got an overheated engine. If you haven't yet read "TRIMMING THE "IRON GENOA", you might find it useful. It's at the related link. Thanks Sam
Thanks
Thanks for your experience Craig. I have changed my impeller once before but will keep a copy of your note aboard. Your non-experienced novice step-by-step direction was perfect. The directions for some of these simple procedures are not very helpful for a non-mechanic first-timer.
Thanks for your experience Craig. I have changed my impeller once before but will keep a copy of your note aboard. Your non-experienced novice step-by-step direction was perfect. The directions for some of these simple procedures are not very helpful for a non-mechanic first-timer.
One Suggestion
Good explanation. That's how I do it. but to be honest, I have an entire spare raw water pump all set to go. If your at sea and rocking and rolling around, its not as easy as it looks to change the impeller . .I always ended up loosing some of the [6]little screws. Forget about trying to salvage the paper gasket . But if your are going to replace the impeller. I have two suggestions: silicon sealant is needed for the brass cover plate to the pump. It can replace the gasket . . Also reverse the impeller cover plate . .the old one may have a circular groove etched in it from the old impeller. Reversing it gives you a fresh surface to work with. Second, I always pour a litte water down into the hoses before I reconnect them, just to make sure the pump doesn't run dry . .it also helps prime it. As far as silicone sealant, what I use is DOW Aquarium Sealant . that's right what they use to fix fish tanks. It sets up quickly and is extremely waterproof . .obviously. Fred Miller S/V M Squared
Good explanation. That's how I do it. but to be honest, I have an entire spare raw water pump all set to go. If your at sea and rocking and rolling around, its not as easy as it looks to change the impeller . .I always ended up loosing some of the [6]little screws. Forget about trying to salvage the paper gasket . But if your are going to replace the impeller. I have two suggestions: silicon sealant is needed for the brass cover plate to the pump. It can replace the gasket . . Also reverse the impeller cover plate . .the old one may have a circular groove etched in it from the old impeller. Reversing it gives you a fresh surface to work with. Second, I always pour a litte water down into the hoses before I reconnect them, just to make sure the pump doesn't run dry . .it also helps prime it. As far as silicone sealant, what I use is DOW Aquarium Sealant . that's right what they use to fix fish tanks. It sets up quickly and is extremely waterproof . .obviously. Fred Miller S/V M Squared
Is the aquarium sealant highly adhesive?
Fred - If the aquarium sealant is highly adhesive, as I suspect it is, you might have real problems getting it off again. Have you checked this? Just a thought.
Fred - If the aquarium sealant is highly adhesive, as I suspect it is, you might have real problems getting it off again. Have you checked this? Just a thought.
Don't think it is any more adhesive?
Larry: I do not think that it is really any more adhesive than regular silicone. The real difference is that it will not kill your fish. I just used this stuff on our water tank because I figured "if it's OK for the fish, it's okay for Steve". When you try to remove silicone you usually need to use a razor or such to clean the surfaces before you recaulk. I think that have a sheet of gasket material aboard may not be a bad idea. Depending on a tube of any type of sealant when you need it is usually not very prudent. They are always dried up when you really need them the most.
Larry: I do not think that it is really any more adhesive than regular silicone. The real difference is that it will not kill your fish. I just used this stuff on our water tank because I figured "if it's OK for the fish, it's okay for Steve". When you try to remove silicone you usually need to use a razor or such to clean the surfaces before you recaulk. I think that have a sheet of gasket material aboard may not be a bad idea. Depending on a tube of any type of sealant when you need it is usually not very prudent. They are always dried up when you really need them the most.
gasket required for design clearance
Replacing the gasket with silicone not a good idea, unless as some kind of at sea emergency operation where no gasket is available. Even there would be better to repair a torn gasket with a sealant and put it back on till a new one can be obtained. The silicone can extrude into the pump itself, not a good situation, especially if it sets before the pump rotates and second, tightening the screws down will reduce the clearance to zero. The 1gm, 2gm, and 3gm pumps are designed with the thickness of the gasket providing the design clearance between impeller and pump body. Figure from gm manual attached shows that without the gasket, an interference situation will result since pump housing width is less than width of impeller.
Replacing the gasket with silicone not a good idea, unless as some kind of at sea emergency operation where no gasket is available. Even there would be better to repair a torn gasket with a sealant and put it back on till a new one can be obtained. The silicone can extrude into the pump itself, not a good situation, especially if it sets before the pump rotates and second, tightening the screws down will reduce the clearance to zero. The 1gm, 2gm, and 3gm pumps are designed with the thickness of the gasket providing the design clearance between impeller and pump body. Figure from gm manual attached shows that without the gasket, an interference situation will result since pump housing width is less than width of impeller.
Attachments
Also something else to check......
I just replaced mine ...The old one was in good condition but I changed it anyway...The engine would over head if the rpms were 2800 or higher.. So when I winterized the motor last year I noticed the raw water seemed to be pulling out just fine..I then checked under the boat and the hole for the raw water was half the size it should have been because of all the bottom paint jobs...I enlarged the hole to it's orginal size and all is well.. Replaced all the hoses,belts,fuel filters and oil....She now runs like a top.. Good Sailing to you
I just replaced mine ...The old one was in good condition but I changed it anyway...The engine would over head if the rpms were 2800 or higher.. So when I winterized the motor last year I noticed the raw water seemed to be pulling out just fine..I then checked under the boat and the hole for the raw water was half the size it should have been because of all the bottom paint jobs...I enlarged the hole to it's orginal size and all is well.. Replaced all the hoses,belts,fuel filters and oil....She now runs like a top.. Good Sailing to you
Quick Change Impeller cover
I replaced my impeller cover with a quick change cover which came from a manufacturer in England. I'm sure you have seen the ads in the cruising magazines. I got it because the brass screws always used to break off when taking off the cover. It uses an o ring to make the seal and knurled knobs which are hand tight. Easy to change. Also, you might want to check for those broken vanes are. They might be in your heat exchanger.
I replaced my impeller cover with a quick change cover which came from a manufacturer in England. I'm sure you have seen the ads in the cruising magazines. I got it because the brass screws always used to break off when taking off the cover. It uses an o ring to make the seal and knurled knobs which are hand tight. Easy to change. Also, you might want to check for those broken vanes are. They might be in your heat exchanger.
Thanks, Craig
Craig....we know each other @ Lake city. Mn. You have probably just helped me figure out how to change the impeller system on my 1980 33' boat. Thanks. Bob Gielow
Craig....we know each other @ Lake city. Mn. You have probably just helped me figure out how to change the impeller system on my 1980 33' boat. Thanks. Bob Gielow
Great post. I'll agree with Sam's comments. Make sure to flush your system before intalling the new impeller. Short story: I bought my current boat from an owner on another lake. He brought it from his dock to the marina that was going to put it on my trailer. When I went to move it the next day, no peeing. New impeller installed, no problem. I trailered the boat to its current location where it stayed in its cradle through the winter while they did the bottom job. First warm spring day my marina put it in the water, I'm behind the wheel, excited to take her to her new slip, a short 200yrd away, I start the engine, float off the trailer and make my way across the cove. Over heat alarm, no water pumping. I coasted into my slip somehow. The new impeller was shot. I'd never flushed the lines and pieces of the old one fouled the new one. Lesson learned.
I can't believe I just read that....I wrote that 16yrs ago......since then I have owned a cape dory 22, two typhoons, two J22's and my current sailboat a 1994 35.5 legend....life goes on....
I have the same boat and engine. When I change the impeller it is necessary to loosen and remove the alternator belt first. Loss of prime resulting in no water flow can also occur due to an air leak at the raw water strainer. Twice when reassembling I have had the water pump belt jump off the drive pulley which also resulted in no water flow.