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Beneteau 361
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Discussion Starter · #1 ·
Last year towards the end of the season I started noticing some oil drops in the bilge. Mirror inspection showed possible leak around the rear end of the oil pan, between the oil pan and back plate.
After hauling for the season I removed/cleaned/inspected/re-painted/re-installed the oil pan and put some oil in the engine for the winter, around 1 liter or less. The bilge was clean all winter.
Two weeks ago I topped up the oil to normal level, and the leak is back. I did not yet run the engine, and the oil pan can now be ruled out, so what else can be leaking? I hope not the dreaded rear seal...but I don't see how the oil would even reach there without running the engine.
Any ideas would be appreciated!
 

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Mechsmith
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Two possibilities, and I've seen them both.

Fatigue crack in pan. It will look like a hairline crack and can be very hard to see.

Rust pit through the pan. Again very hard to see. Clean things with an appropriate solvent and plenty of light.
 

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Beneteau 361
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Discussion Starter · #3 ·
Thanks for the suggestion. I cleaned everything with solvent and a few days later had a good look with mirror and lights. The pan was clean and the oil was found on the bottom of flywheel housing. That means most likely rear main seal.
Wondering if this can be replaced in water without removing the engine? My transmission is BW-7 and I have PSS seal with plenty of room aft of the tranny.
 

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Mechsmith
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Probably if you have plenty of room. The seal is a one piece type. You will probably find it easier to remove the plate that it is mounted into and then remove the seal from the plate.
The flywheel has to come off and this involves some very tight bolts. You will need some way to lock the flywheel or use an impact wrench on the flywheel to crankshaft bolts.

If you decide not to remove the plate you must be very careful not to damage the crankshaft or the plate.

I have pulled similar seals out by drilling the metal part of the seal with a small drill bit and using some sheet metal screws and a claw hammer pull it out. The plate is aluminum and will score, warp or dent easily.

It's preferable to pull the plate off and replace the gasket under it also.
 

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Beneteau 361
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Discussion Starter · #5 ·
Thanks for the tips, much appreciated. How about removing the tranny? I guess the main problem is access to the bolts, or is there more to that? Also is there any tricks for moving the shaft back while keeping the PSS compressed?
 

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This is an old thread but worth a shot..


I also have a B361 with the same engine and oil leak. I suspected it was the rear main seal and went in there and changed it, transmission off, flywheel etc. but also put a Speedi sleeve on the end of the crank shaft that the seal rides on.
After reassembly the leak was still there.
Now I assume (hoping) it’s just the oil pan or maybe the speedi sleeve didn’t work/seal. I don’t really want to go back in there again for what is a pretty small oil leak.

Did you ever get to the bottom of your leak ?

Were you able to change the oil pan seal with the engine in place ? How hard was getting the old gasket material scraped off ? Seems like a super akward place to reach up and scrape the bottom of the block. Have any pics ? Tips ? etc

Getting the seal off the block that holds the rear main seal was very challenging and with much better access/view
cheers
- James
 

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Beneteau 361
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Discussion Starter · #7 ·
I ended up removing/re-bedding the oil pan. There were a few awkward bolts but overall not too bad. Inspection mirror helps. There is enough clearance to do it with the engine in place. Once the pan is off you have more room to work with and removing the old gasket is not difficult. I used high quality liquid gasket maker instead of new $$$ gasket from Westerbeke. I also sanded and re-painted the pan. This excercise hovewer did nothing to the leak! I decided to not bother with the main seal replacement as the leak is quite minor and is not getting worse. I put in a fresh bilge pad every spring and get probably around 100ml of oil by the end of the season (~120 engine hours). Otherwise it is a great engine and still running fine after 20 years and 2100 hours with all original parts (in fresh water though).
 

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thanks for the response! Wasn’t sure you would see this.

All the older guys at the club just tell me to leave it alone and put a pad under it.
It’s only a tiny amount of oil after a whole summer of motoring 100+ hours I should probably listen to them……
Seems like a small oil leak on a 20 year old diesel is pretty standard

Knowing the gasket wasn’t that hard makes me want to do it, the rear main was an absolute nightmare, days and days of soaking it in gasket removal goo, lots of brake cleaner and a dremel with a brass wheel around the holes and orientation pin.

The access is not ideal for those rear pan bolts but doesn’t seem too bad.


I went in chasing that oil leak and ended up with the new rear main seal, new Transmission (Prm125) and engine mounts, a rebuilt high pressure fuel pump and injectors, glow plugs, rod’d out the heat exchanger, removed and welded gussets on the front engine mounting brackets, all new hoses on the cooling system, repainted a bunch of parts and replaced a few other small things.
I was trying hard not to open the Westerbeke can of worms again this winter but it keeps nagging at me
I even have the over priced westerbeke gasket.

On an unrelated note does yours idle rough below 1000rpm ? Smooths out as soon as you give it some throttle ?
 

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Beneteau 361
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Discussion Starter · #9 ·
The idle is supposed to be set to 1000-1200 rpm according to the manual. Mine does get rough when in idle forward with some load and it gets below 1000, especially when cold. I give it a bit of throttle then. I suspect the tach may not be accurate enough and the solution is to get the laser tach and set the idle properly at 1200.
 

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Seems like they are all a bit rough at lower rpm

I checked my tach with an optical tach and it’s very close +\- 25rpm
I have a kiwi folding prop so when I set the idle up to recommend RPM up at 1000/1100 and put it into reverse it slams the transmission pretty hard and stalls or almost stalls the motor. (My understanding is the kiwis have a very aggressive pitch in reverse and as the blades flop over to the other direction it allows the shaft to momentarily build a bit of speed with no resistance and then the blades hit their stops and the sudden increase in load bogs it down)
(The new transmission has the same ratios as the old one)

Considering going back to my fixed blade anyway which would hopefully solve that issue.

cheers
 
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