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Old 23-09-2012, 12:54   #1
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Perkins 4-108 Oil Leak

I need some advice about my leaky Perkins.

Ran about 9 hours yesterday before the wind finally filled in for a great 4-hours sailing to finish the trip, 15-20 kts, jib & jigger. Terrific! . But, I needed to add oil.

I installed my motor is '86, about 1100 hrs now, and I'm leaking oil from front and rear seals. About 3/4 qt was needed at the end of the day. I assume the condition will likely get worse and I'll need to pull her out, no easy task. Otherwise she runs perfectly. I hear on the Forum that these engines always leak and, even after an overhaul, she'll still leak. Any advice would be very welcome.

Thx

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Old 23-09-2012, 13:40   #2
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Re: Perkins 4-108 Oil Leak

If the gaskets and the seals are installed properly, they don't leak. any four stroke needs maintaince, fix those leaks when ya first see em !! if ya wait it will end up costing you more ! other then the lack of room to fix them in most boats, it's really not all that bad to fix gasket and seal leaks. Seals can be changed in place if ya get resourceful with a small jack and a few blocks of wood ! If ya can't do it yourself well the cost go's up ! When ya hire a mech. to do it for ya, hang around and watch what he do and what type of gsaket sealer he use's! and maybe next time ya can do it yourself ! just a thought
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Old 23-09-2012, 13:52   #3
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Re: Perkins 4-108 Oil Leak

That's what they do when they get old. I was lucky and replaced all the seals last year before I installed the engine, on an engine stand in a comfortable shop with any necessary tools and equipment. I used Volvo anaerobic sealant on all the flat parts, it's the same as Loctite 574 but cheaper, and I used Dow RTV on the joints. I wouldn't try the job in the boat, the rear main and the oil pan gaskets are just too finicky. 4 piece pan gasket and a 2 piece rear main seal, there are too many chances to screw it up even in a nice shop, not to mention upside-down in a bilge. Don't over tighten the front cover bolts, follow the manual, they're really loose. The gasket there is really thick and the metal is really thin and it's really easy to deform the cover and the gasket.
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Old 23-09-2012, 14:30   #4
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Re: Perkins 4-108 Oil Leak

We have a 4108 with just over 1000 hrs now since the rebuild. It leaks, although not as much as yours seems to be. We tend to be down 100 to 200 ml (.1 to .2 of a quart according to my trusty converter) after that kind of motoring day.

Three-quarters of a quart sounds like a lot for a 9 hour run. As a comparison, we went through just over 1 litre (~1 quart) in 48 hours of motoring. Could your engine have been low before you began the trip?
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Old 24-09-2013, 00:14   #5
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Spent the morning building a bladder under the engine out of thin rubber sheeting (looks like pond liner) my engine leaks a small amount consistently. If I can keep it out of my bilge water I will continue as-is if not will work to re-seal or possibly repower. I can't stomach rainbows in the water from my bilge. I have diverted the small and lower bilge pump into a five gallon bucket that I have been dumping in the oil recycling.
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Old 24-09-2013, 00:14   #6
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Originally Posted by sww914 View Post
That's what they do when they get old. I was lucky and replaced all the seals last year before I installed the engine, on an engine stand in a comfortable shop with any necessary tools and equipment. I used Volvo anaerobic sealant on all the flat parts, it's the same as Loctite 574 but cheaper, and I used Dow RTV on the joints. I wouldn't try the job in the boat, the rear main and the oil pan gaskets are just too finicky. 4 piece pan gasket and a 2 piece rear main seal, there are too many chances to screw it up even in a nice shop, not to mention upside-down in a bilge. Don't over tighten the front cover bolts, follow the manual, they're really loose. The gasket there is really thick and the metal is really thin and it's really easy to deform the cover and the gasket.
Still no leaks?
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Old 24-09-2013, 11:47   #7
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Re: Perkins 4-108 Oil Leak

I'm with Bobconnie on this one. Oil leaks don't fix themselves and only get worse. Not to be a smartass but there is a technical reason for the leaks, and a technical solution to repair them. It's not normal for any engine to leak oil let alone Perkins.. Much much better to do the repair at a time of your convenience and choosing than continue to live with the possibility of a breakdown when you least need, or expect it.
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Old 24-09-2013, 11:58   #8
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Re: Perkins 4-108 Oil Leak

Bill Trayfors has posted that he installed a Walker Air Sep and it keeps his engine room much cleaner than it was. I'm not sure if it has solved all leaks from his Perkins but it seemed to have helped a great deal.
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Old 24-09-2013, 18:31   #9
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Re: Perkins 4-108 Oil Leak

A much simpler solution for a cleaner engine room is to change the wire gauze air filter on the air inlet manifold for a paper element type. You need to fabricate a piece of alloy pipe to slide onto the inlet and be clamped in place with a small oil breather pipe welded in. Connect them both onto to the air inlet, find a suitable position in the engine room as far from the pilot station as practically possible, then use some semi flexi rubber hose that will not delaminate and connect it to a paper element filter(you can get second hand filter case from a scrap yard). any oil mist from the engine is recirculated and the paper element filter will reduce noise from the air intake by 50% making your cruising more pleasant, you will be surprised how much dirt it catches too.
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Old 25-09-2013, 18:49   #10
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Re: Perkins 4-108 Oil Leak

If you replace the front (easy) and rear (harder) seals, plan on replacing the oil pan gasket too--its cork and it degrades with time. I've done all of them in the boat, but I had pretty good access.
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Old 25-09-2013, 23:19   #11
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Originally Posted by donradcliffe View Post
If you replace the front (easy) and rear (harder) seals, plan on replacing the oil pan gasket too--its cork and it degrades with time. I've done all of them in the boat, but I had pretty good access.
Thx everyone. I really appreciate your thoughts on the matter.

Don, can you give me a sense in how much time it took you to replace the different seals? Thx,

Dave
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Old 28-09-2013, 08:31   #12
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Re: Perkins 4-108 Oil Leak

As a professional mechanic I can say there are basically four reasons front and rear seals leak. Old dry rotted or failed spring etc., excessive end travel end in crankshaft this is back and forth movement, manuel will tell specs seldom over .005 of an inch, groove cut in crank by rubber seal it happens, rings bypassing allowing air fuel mixture in bottom end of engine therefore a burping condition, anykind of pvc where applicable positive crankcase venilation valve. Just my experience Rich
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Old 28-09-2013, 08:33   #13
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Re: Perkins 4-108 Oil Leak

You might just remove oil add cap and see if gases are coming out, simple blow by check
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