Yanmar engine mounts keep failing 3JH4E

[flyingfishUK]

We have a beneteau 40.7 with a Yanmar 3HJ4E engine. Since November last year we have had 3 sets of engine mounts fail with no obvious cause. We replace the mounts then about a month later they snap again! A local marine engineering company have removed the engine and gearbox, checked alignment then refitted. We have just had another set of mounts fail again! We have contacted Yanmar but they have never heard of this fault... emm

The engine runs perfectly in neutral, forward and reverse

The engine mounts are the standard set fitted to all engines of this type

Has anybody had this problem before?

Regards

Andy

[pedcab]

Originally Posted by flyingfishUK

We have a beneteau 40.7 with a Yanmar 3HJ4E engine. Since November last year we have had 3 sets of engine mounts fail with no obvious cause. We replace the mounts then about a month later they snap again! A local marine engineering company have removed the engine and gearbox, checked alignment then refitted. We have just had another set of mounts fail again! We have contacted Yanmar but they have never heard of this fault... emm

The engine runs perfectly in neutral, forward and reverse

The engine mounts are the standard set fitted to all engines of this type

Has anybody had this problem before?

Regards

Andy

I've heard about that problem a few times and the causes were found to be one or more of the following:

1- Shaft alignment issues
2- Shaft length issues (too long shafts)
3- Outside shaft support alignment/ sturdyness
3- Propeller balance

[St Anna]

Having a 4jh engine and having replaced 2 of the mounts, I can concur with the above comments.
Alignment is the key. I have a hydra-drive (a kind of flywheel principle) which allows the shaft to be a little offline without upsetting the engine mounts.

[sea_hunter]

Shaft alignment.

[luck66]

I do not know if the Benateau has a strut bearing, but that is one thing that is seldom checked that can cause problems.

[noelex77]

Welcome to the forum
I have not had any problems with my Yanmar engine mounts, but I have met a few boats that have.
There is an Australian company that makes very good replacement engine mounts, that seem much better made for less money than the originals.
They are called Polyflex or something similar if you go to Google Australia you will find them.
If you have problems I will try a search , but my internet is very slow from the boat.
There was a article in PBO a few years back about a Yanmar owner that made the switch to these mounts ,successfully, after experiencing a short life with the originals.

[jreyn1944]

How are your mounts failing? Did the stud break? Or, was it a rubber failure?

We have twin Yanmar 4Jh4E motors. All four mounts failed on the port engine last weekend. The studs sheared off just inside the bottom thread on the lower adjusting nut. We were underway, and with the motor free to move since all four mounts were broke, lots of water came into the engine room real fast through the so-called drip-less shaft seal- thank God for twin pumps and a good crew with buckets. The front outboard mount on the starboard engine is also broken; the other three are not. The nut on the engine mount is resting on top of of the broken-off stud in the mount, off-set by about the diameter of the stud. If I continued to operate the engine, I'm sure the other three mounts would fail, in a cascading-type failure, since the remaining mounts would be overloaded.

I agree with the previous post concerning the mounts being aligned with each other. Some basic measurements should provide insight into the relative mount alignment. On a 4Jh4E, the stud-to stud center line athwart-ship distance is 470 mm (18.5"); the fore-aft distance is 506 mm (19.9"). I plan to make some measurements this weekend