Plastic Classic Forum

Hi All,


I'm getting ready to do the oil seal work on my 1979 Yanmar 3QM30 (H) in my C&C 40 sailboat. It occured to me while researching this project that one of the things that can cause an oil seal to fail is the breakdown of an engine mount(s).

The old style yanmar engine mounts currently on the boat have always been pretty stiff and the engine has always maintained good alignment.
It is possible, however, that the mounts are breaking down and that is what helped cause the oil seal to start leaking. ( note - the seal only leaks when the engine is under full load and the boat is underway - and then only a very tiny amount )

My question is... Is it a good idea to replace the mounts as a matter of course since the engine will be off the bed anyway? Is there a certain type of mount I should be looking for?


Thanks,

George Jones
C&C 40 "Delphinus"

Frankly I can't see how the rear main seal would be affected by a misalignment of the prop shaft. I can see where the rear seal for the transmission could be, but why would a misalignment cause the transmission to shift and thus move the front splined shaft out of alignment to the flywheel--and thus the rear main?

I have a 3GM30F and it came with very tall and very flexible Yanmar engine mounts. I used Vetus #75 mounts instead because the Yanmar engine installation manual specifically warned that the Yanmar-supplied mounts needed to be replaced on a regular basis or they could break. The broader flexing of the soft mounts also meant that I would have more wear on the cutlass bearing and packing gland as well.

I'll stay away from theories or comments on the suitability of one mount type versus another, but regardless I would opine that it would be wise and efficient to replace your mounts as a matter of course now, if you're going to remove the engine anyway.

All flexible mounts lose their capabilities over time, and there's no better time to replace than when you remove the engine for some other purpose.

Hi Guys,


Thanks for the notes. David, I think you are right, maybe a transmission seal but not the main engine seal -- thanks for the tip on Vetus mounts. Tim, I think I will replace them just to be on the safe side -- they've got to be very old at this point.

That big old cast iron block engine doesn't seem to vibrate or move at all when underway and I never see any wear on the cutlass bearing. I'll stick with some short very firm mounts like what's on there now.


Thanks guys,

George Jones
C&C 40 "Delphinus"

a good quality shop that sells mounts should be able to spec out correct mounts by weight hp number of cylinders and a few other parameters. if you have had the boat since new and you like the way the mounts you have had worked then just order a replacement set otherwise you can look into other mounts. the mounting holes may not line up and being you have a yanmar you most likely have metric studs on the mounts. I forget the name of the company we use but they sell fail safe mounts and the guy answering the phone is very knowledgeable.

George,

The exact info on the Vetus mounts: they are Type K 75's

http://viewer.zmags.com/showmag.php?mid ... #/page126/


David

Hi Guys,

Thanks for all the good information. I'll take some pictures when it's all done.

George

C&C 40 "Delphinus"

Hi All,


Quick update. I've ordered 4 new motor mounts. In doing the work I found that one of the mounts was broken -- good thing I pulled the engine. The mounts I went with are exact replacements for what's already on there. This was the easiest way to go as all 4 mounts have matching shim plates underneath them to raise the engine to the correct level. These are the mounts...

http://shop.torresen.com/ships_store/in ... 07-1&frm=g


George Jones
C&C 40 "Delphinus"