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RickBowman 02-24-2007 09:00 AM

3JH2 Yanmar Impeller
1997 hull #20 PS32PH with a 3JH2 series Yanmar 3 cylinder diesel.

How do you get access to change the impeller on this model engine? It appears that the alternator will have to be removed and it has been reported that the wiring to the alternator does not allow it to be moved any great distance. The impeller cover faces aft with 4 screws that need to be removed to allow impeller inspection "with a mirror, or maybe a digital camera", or for replacement. I like the direct drive feature of the impeller pump but it appears that maintenance is going to be rather difficult. Has anyone else maintained this with this model Yanmar engine?

Rick #20

SailorMitch 02-24-2007 09:49 AM


I am not familiar with that particular model, but on my 2GM20F you have to take the pump off in order to inspect/replace the impeller. There is no room behind the pump to remove anything, although the front is very accessible making removal not that tough.

It at least sounds like you can get to the back of the pump. Still, removing those small screws won't be fun. What I suggest to make removing the back cover plate at least possible is a Speed Seal. Made in Britain. It replaces the cover plate with a milled stainless piece that then uses 4 large knurled knobs to hold it in place. Unscrewing the knobs is a breeze compared to messing with those small screws. The Speed Seal also uses an O ring for a seal, doing away with that idiotic paper seal on most raw water pumps. You still have the issue of using a mirror or whatever to get to the impeller itself of course, but at least you can get the cover plate off without losing your religion.

RickBowman 03-09-2007 06:10 PM


I got the impeller out by gingerly persuading it with a very small screw driver "the size that is used to adjust carb settings on a small engine" and lightly prying off of the pump housing. I could only pry on about 90 degrees of the housing as that is all that is reachable. I did have to completely remove the alternator, and discovered that when the top arm bracket bolt that secures the bracket to the motor is removed, will drip coolant from the engine head. A slow drip, but a drip none the less, so the alternator bracket had to be reinstalled, adding another restriction to an already limited access. The alternator was removed and disconnected from all wiring harnesses. It was such a delightful experience, that I wish I could convey my deep appreciaition to the Yanmar engineering staff on a fine job well done. My little sister could have done as good.
Next, replace the impeller. Arrg. I greased up the splines on the drive shaft of the impeller pump and the inside of the impeller housing by feeling my way through it. No big deal there. Next, I needed to orientate the impeller vanes in the correct direction and at the same time line up the splines between the impeller drive shaft and the internal splines on the impeller, without being able to see much at all is this is facing the rear of the engine. Arrg. I ended up using a plastic wire tie to secure the vanes in the correct orientation compressing them and making the OD of the impeller quite a bit smaller. Then by usuing the tail of the plastic wire tie as a handle I was able to hold it in one hand whilst rotating the impeller with the other hand to try and line up the splines, all the while using my chin as a balance point to rest the upper part of my body on. Arrg. It sucked in, the bastard actually went in part way!Then I cut the wire tie off and pushed the impeller the rest of the way into the pump housing. I am waiting on the speedseal to arrive, which I thought was a good suggestion, which I had already considered early on, but blinked on the idea.
The 3JH2 already uses an o-ring for the impeller cover seal. To remove the impeller pump housing I would have to remove the front port engine mount bracket. Arrg. I really did not want to leverage off of the impeller housing but as I studied the limitied access environment, it became increasingly clear that to use an impeller puller would necessitate removing the engine starter motor. Arrg. This task is not meant to be accomplished in a seaway, nor is it a fast fix like some impeller changes are.

The job is finally completed awaiting it's test when the boat is launched this spring. The speed seal install went well of course. The alternator reinstall went ok, but like this entire task it sure was close quarters. This Yanmar is beginning to remind me of a Triumph 500cc trophy motorbike that was previously owned. Wouldn't you think that engineering could have gleaned something after 30 years?

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