Yanmar Rear Main Seal?

[TommmD]

I have a '95 Hunter 35.5 w/ a Yanmar 3GM30F, no hour meter. Owned her for three years, runs very nice. Use Rotella T6 5-40. This summer I've developed a drip, coming between the tranny & engine. Its more than few drops & needs to be addressed when the boat comes out for the winter, in the next month or so.

First thought is its a rear main seal, looking to see who's been thru this & how common it is. I'm not looking to repower the boat.

After running an A-4 for ten years, this engine is a joy, largely because diesel is so much more forgiving than gas.

[Lepke]

Rear main seal failure is common in most engines. Usually with age. The rope type get compressed and the rubber seal type gets brittle with age. Worn engines with lots of blowby and not enough venting will force air and oil out the seals.

[TommmD]

Hmm .. need to learn how to do a compression check on a diesel. Don't just pull the plug as on the A4. If rings are gone the equation changes.

[sailorchic34]

The issues with using full synthetic oil is it cleans very well. Which is why it should not be used on engines run some time with dino oil. Invariably seals start leaking pretty much every time too.

Luckily it's a pretty quick job for the gm series, once the tranny is unbolted and removed, remove damper plate and flywheel. The rear seal is mounted on the rear bearing holder. Easiest to remove by unbolting and removing the bearing holder and then prying it out with a screw driver and installing the new seal.

You might need to change the seal behind the front crank pulley too. But after that you can run the T6 leak free.

[Matsubob]

You're in luck! If that is all that is leaking, simply splitting the transmission and engine. The flexplate and flywheel will then need to be removed, and this will expose the rear seal and rear main bearing holder. It is a round "holder", held onto the block with bolts. Remove the seal holder by prying it out of the block, change the seal out and reinstall. Then come back up with flywheel and flexplate and Presto! the oil seal leak is solved!

[dcapn88]

Similar situation: I have Universal M50 that I am pretty sure is leaking oil , big-time, out the rear main seal. I can (and have done previously) move the engine forward, remove the trans/bellhousing/flywheel. My question is: can I then replace the rear main seal, (i.e. in the boat)?

[TommmD]

So I had it looked at when I had it hailed last fall, &; was told the external hard piped oil lines were the problem, loosened by vibration & we're dripping down the rear of the engine. Had them replaced & it absoltuely did the trick. Engine mounts too, for the vibration.
Good luck,

[lockie]

Originally Posted by TommmD

So I had it looked at when I had it hailed last fall, &; was told the external hard piped oil lines were the problem, loosened by vibration & we're dripping down the rear of the engine. Had them replaced & it absoltuely did the trick. Engine mounts too, for the vibration.
Good luck,

The external oil lines are known to rust out on GM's. This happened to my 2GM. I was incredibly lucky as I had just berthed in a safe harbour through pretty wild weather, when I noticed black bilge. Oil had been pumped out through a small rusted hole, down to just above safe sump level! A bit longer and I'd have had a seized engine and no way to get to shelter under sail!

Cheers, Graeme