2GM20 Engine Mount sizes incorrect

[Channel Sailor]

Today I discovered the engine mounts on my 1995 Jeanneau yacht are incorrectly installed. The front mounts are 75 starboard and 100 Port. Should be both 100 on the front. This means I have a softer mount on the starboard front. Similarly the rear mounts were, until today, 75 and 100 which was also incorrect as they should be both 75. The engine does suffer from a strange resonance though most of the mid range speeds, a small amount of shaft wobble and it does wobble somewhat at tick over enough to rattle the mast and a few interior fittings. Hence why I swapped the aft two for new ones (matching 75s) to see if it would solve the problem.

Unfortunately due to tides and Christmas I cannot get out for a sea trial for a couple of weeks, so I am wondering if this was an error in the factory by the installers or they have been set like this solve a boat specific resonance problem. Has anyone had reason to have non standard or non matching mounts Port and and Starboard and why?

 

[Ammonite]

Someone more knowledgeable than me will be here in a moment but here's an extract relating to yanmar mounts. Personally I'm more familiar with differences front to back due to the weight but sounds like you need to do some further research ;-)

Yanmar mounts are manufactured specifically for each side of the engine. That is, either the starter side or the oil filter side, as engine torque will change the effective loading on either side of the engine. Make sure that you get the mounts positioned on the correct side of the engine.

Also, a word of warning if you do end up changing them (you are probably aware they are stupidly expensive) that just because someone advertises a mount as being a direct replacement my experience suggests this is not the case at least when it comes to the 1GM10. I flagged it with R&D at the time but their "direct" replacement is a completely different height that would have meant changing the engine beds. This was on a Jeanneau Fantasia 27. Happy to stand corrected but I'm pretty sure it wasn't me who had it wrong. Rant over ;-)

 

[Channel Sailor]

I should clarify that I have had changed the rear two mounts today. Yes the parts are expensive. The question I have posed is because I want to understand if a previous owner perhaps discovered that stronger/firmer mounts are required on the Port side aft and weaker on the Starboard side Fwd, both to reduce vibration. Even though this is contrary to Yanmar instructions.

Perhaps contributing to a resonance problem is because the engine is not actually mounted on “Beds” forming part of the hull, it is mounted onto a raised galvanised steel frame that in turn is bolted to two of the aft cross beams. I think this is unusual, but not sure.

 

[Plum]

Today I discovered the engine mounts on my 1995 Jeanneau yacht are incorrectly installed. The front mounts are 75 starboard and 100 Port. Should be both 100 on the front. This means I have a softer mount on the starboard front. Similarly the rear mounts were, until today, 75 and 100 which was also incorrect as they should be both 75. The engine does suffer from a strange resonance though most of the mid range speeds, a small amount of shaft wobble and it does wobble somewhat at tick over enough to rattle the mast and a few interior fittings. Hence why I swapped the aft two for new ones (matching 75s) to see if it would solve the problem.

Unfortunately due to tides and Christmas I cannot get out for a sea trial for a couple of weeks, so I am wondering if this was an error in the factory by the installers or they have been set like this solve a boat specific resonance problem. Has anyone had reason to have non standard or non matching mounts Port and and Starboard and why?

Hi. Engine manufacturers go to great lenths to determine the correct design and elastomer properties and that each mount takes its designed share of the load. I recommend you ensure all mounts are of the correct type/specification for each corner as per the manufacturers/mariners spec (without assuming what you had wss correct) and then ensure you adjust them so all four are equally compressed. It is all to easy to align an engine correctly with the shaft but end up with a diaginal pair taking a disproportionate loading often causing vibration problems. Don't worry if your engine rocks/rolls excessively as certain revs, this is not always a problem and the manufacturer should have ensured the roll axis passes somewhere near to the axis of the shaft coupling.

Www.solocoastalsailing.co.uk

 

[Daverw]

I understood from my 2GM20 manual that the mounts are 100 front and 75 rear, I did change mine two years ago for R&D mounts that were 150 and 100, the extra stiffness has made so much difference both quieter and less vibration. They were just about a straight swap

 

[vyv_cox]

When my 3GM was installed it produced unusual vibrations. I forget the actual values but each fore and aft pair were the same. The aft pair were changed for a harder compound that did improve things.