Yanmar 4JH3 versus 4JH4

[duncan_ellison]

Does anyone with eyes-on knowledge know the physical differences between the Yanmar 4JH3 and the 4JH4

The changes were driven solely by the European RCDII requirement, so I'm guessing that the main differences would be emissions control.

[StuM]

Here's a comparison

[Vasco]

Originally Posted by duncan_ellison

Does anyone with eyes-on knowledge know the physical differences between the Yanmar 4JH3 and the 4JH4

The changes were driven solely by the European RCDII requirement, so I'm guessing that the main differences would be emissions control.

From a cruiser's viewpoint the major difference is you can get at the impeller in the 4JH4 without being a contortionist or magician. Replacing the impeller in the 4JH3 was not easy.

[GreenWave]

Originally Posted by Vasco

From a cruiser's viewpoint the major difference is you can get at the impeller in the 4JH4 without being a contortionist or magician. Replacing the impeller in the 4JH3 was not easy.

I have a 4jH3 and will second that the impeller access sucks. Must have the small bolt-like puller and a right angle needle nose.

[chrisr]

we have a pair of 4JH2s' and got the same problem with the water pump impeller. in fact worse in our case as it's a cat and you can really only get at the top of the engines...

what engineer thought that was a good place to put the pump !

cheers,

[kcj]

The 4jh4 is rated at 3000rpm. The 4jh3 is at 3800… any idea what they did to make the change?

And I think the water pump">raw water pump can be flipped so it’s in front of the engine…if that makes it any easier….

[GreenWave]

Originally Posted by kcj

The 4jh4 is rated at 3000rpm. The 4jh3 is at 3800… any idea what they did to make the change?

And I think the raw water pump can be flipped so it’s in front of the engine…if that makes it any easier….

Flipping the water pump on a 4Jh3 is possible if you have the room in the engine bay. On mine the Alternator and starter would pose problems for starters (pun intended).

[skipperpete]

Originally Posted by duncan_ellison

Does anyone with eyes-on knowledge know the physical differences between the Yanmar 4JH3 and the 4JH4



The changes were driven solely by the European RCDII requirement, so I'm guessing that the main differences would be emissions control.

One of the most obvious differences is the head and injectors. The injectors are under the valve cover and a new level of care is required to remove that cover to adjust the valves and crossheads. The injector stem seals are quite fragile and its best to carefully remove them before attempting to lift off the cover. The injector leakoff line is also under there and it’s another potential source of lube oil contamination if the washers or connections leak. Oh, 16 valve head too.
Pete.

[skipperpete]

Here’s the JH progression